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7th Grade PSI
Inheritance and Variation of Traits
20151102www.njctl.org
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Table of Contents: Inheritance andVariation of Traits
• Mendelian Genetics
• Using Punnett Squares
• Test Crosses
Click on the topic to go to that section
• Genetic Mutations
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Mendelian Genetics
Return to Tableof Contents
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Heredity
Did you ever notice how much children look like their parents and their siblings?
As you can see, it's not only something that happens in humans! This is true about all living things on Earth.
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Frequently Asked QuestionsI am sure that questions like these have crossed your mind before:
• Are children ever identical to their parents?
• Why do some people look more like their dad and some look more like their mom?
• How do I get traits from my parents?
• Why are some people born with birth defects or diseases?
These questions (and more) will be answered in this unit!
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Genetics & HeredityHere are two related terms that will show up quite a few times in this section. Try to define them with your table and then pull the tab for the definition:
Genetics
Heredity
Answer
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Review: CellsEarlier this year, we talked about the parts of the cell.
We also talked about mitosis and meiosis and how these processes help organisms live and reproduce.
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Review: MitosisMitosis is the process that helps individual cells reproduce.
In mitosis, one "parent cell" reproduces its DNA and then splits into two identical "daughter cells". The daughter cells are completely identical to the parent cell.
The Stages:
Permission Granted: Jeff Sale San Diego St Univ
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After meiosis, the pairs of chromosomes split.
This means that each sex cell ends up with 23 individual chromosomes (1/2 of what they started with)!
The human cell on the left has all 23 pairs of chromosomes (one pair is shown).
Click on the cell to see what happens after meiosis!
Review: MeiosisMeiosis occurs in all animals that reproduce sexually (2 parents).In meiosis, the cell splits in two individual sex cells without duplicating its DNA.This means that after meiosis, the sex cells have half of the DNA as a normal body cell.
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1 Where is all of the genetic information (DNA) found in the cell?
A nucleus
B cytoplasm
C cell membrane
D mitochondria
Answ
er
A
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2 The process of creating new cells from existing cells is called mitosis.
True
False
Answer
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3 The purpose of mitosis is _______________.
A growth of organisms
B repair of damaged tissue
C both A and B are true
D Neither A nor B are true
Answer
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4 Each cell in the human body has 23 pairs of chromosomes. How many chromosomes total will each daughter cell have after mitosis?
Answ
er
46 total
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5 Each cell in the human body has 23 pairs of chromosomes. How many chromosomes total will each sex cell have after mitosis?
Answ
er
23 total (1/2 of what was originally there!)
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6 Meiosis leads to:
A Four offspring cells
B Genetic Variation
C Cloning
D Both A and B are true
E A, B, and C are true
Answer
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7 After meiosis, the number of chromosomes is the same in the parent and offspring cells.
True
False
Answer
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Gregor Mendel
In the 1800s, an Austrian monk named Gregor Mendel conducted a series of experiments that were designed to uncover how traits are passed on from parent to offspring.
His experiments were aimed at addressing one of the most fundamental issues concerning heredity:
What are the basic patterns of heredity?
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1. The “blending” hypothesis : This idea stated that genetic materialfrom the two parents blends together
ex: a red flower and a white flower will produce a pink flower
Two Prevailing Original Hypotheses At Mendel's time, there were 2 popular (and incorrect) ideas to explain heredity:
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2. Inheritance of mutations: This idea stated that traits present in parents are modified as they are used or not used, and passed on to their offspring in the modified form.
Two Prevailing Original Hypotheses
ex: A giraffe has a long neck because her parents kept stretching their own necks out to reach the leaves in the trees, and the long neck trait was passed on.
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In order to complete his experiment, Mendel needed to choose an organism that had the following characteristics:
Mendel's Experiments
Usually small
Has a short life span Inexpensive to take care of
Produce many offspring in a relatively short period of time
Easy to experiment with
Why do you think these traits would be important to scientists?
Talk about each one at your table and be prepared to share your thoughts.
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Mendel's ExperimentsHow many living things can you think of that fulfill these guidelines? Make a list with the person sitting next to you.
Click below to see what Mendel chose to work with.
The garden pea
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Mendel chose pea plants for his experiment because:
• There are many varieties with distinct traits (such as color).
• He could easily control the matings through crosspollination.
• Each pea plant has both the male and female reproductive organs.
Mendel's Choice: The Pea Plant
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Mendel chose to track 7 traits (or "observable characteristics") that only came in one of two forms.
The Traits of Pea Plants
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8 Pea plants were particularly a good choice for use in Mendel's experiments for all of the following reasons except that...
A Peas show easily observed variations in a number of characters, such as pea shape and flower color.
B It is possible to completely control matings between different pea plants.
C It is possible to obtain large numbers of offspring from one cross.
D Peas live for an unusually long time.
Answ
er
D
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Experiment #1: Monohybrid Cross
For this experiment, he crossed a purple flower with a white one.
This is called a monohybrid cross because the parent plants differ in only one trait, their flower color.
Results:All of the offspring had purple flowers.
One of Mendel's experiments looked at flower color. A pea plant can either have purple or white flowers.
"mono" = one
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Monohybrid Cross
Mendel then mated two of the purple offspring plants. This cross produced 929 plants.
Results: 705 of the 929 plants had purple flowers and 224 had white flowers
Use a calculator What percentage of these flowers were purple?
_____________________%
Answ
er
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Monohybrid CrossCan you make any conclusions based on these results? Write any ideas below.
Think about the Blending Hypothesis. Does this experiment support or disprove this hypothesis. Why?
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Based on the results from this experiment, Mendel concluded that the trait for white flowers did not disappear in the purple plants, but instead that the purplecolor factor was controlling the flower color.
He also concluded that these plants must have carried two factors for the flowercolor character: one represented purple and one represented white.
Interpreting Mendel's Results
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9 A genetic cross in which the parents differ in only one trait is known as a ___ cross.
A monohybrid
B dihybrid
C self
D test
Answ
er
A
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Webquest: Mendel's Peas
This lab will have you try out some of Gregor Mendel's experiments on genetics and heredity.
By the end of this webquest, you will have an idea of the different patterns of inheritance he saw in his experiments.
Click on the picture above to access the website!
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From Mendel's experiments, he came up with a few ideas that reshaped the study of genetics. His first idea was that genes come in different forms. This causes organisms of the same species to still have some differences.
For example, the pictures above show that the human eye can look a variety of different ways, such as being blue or brown.
Alleles
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Alleles
There is a variation of the gene for flower color in pea plants that can cause it to be purple. Another variation makes it white.
The alternative forms of genes are called alleles.
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The Passing on of Alleles
Looking at his experiments, Mendel also concluded that an organism inherits two alleles (one from each parent) for each trait.
The two alleles may be the same or they may be different.
These alleles will pair up in the child and will determine what the child's physical traits are.
Mother Father
Represents an allele
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Each allele can be represented with either a capital or lowercase letter.
An organism that has two of the same alleles (i.e two identical letters)for a gene is homozygous for that gene.
Homozygous Organisms
Examples: Two capital letters (AA) Two lowercase letters (aa)
"homo" = the same
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An organism that has two different alleles (i.e two different letters)for a gene is heterozygous for that gene.
Heterozygous Organisms
Example: One capital and one lowercase letter (Aa)
"hetero" = different
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If the two alleles of a pair are different (heterozygous), one allele determines the physical appearance and is called the dominant allele.
The other allele has no noticeable effect on the appearance and is called the recessive allele.
Memory Tactic: The dominant allele dominates the recessive one.
Dominant and Recessive Alleles
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In other words, Mendel came up with the idea that one variation of the trait will be shown.
Dominant and Recessive Alleles
If one parent has blue eyes and one has brown eyes, the child would more than likely end up with one or the other, as opposed to something like this:
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This hypothesis also went against the "blending hypothesis" from before. How did that hypothesis work?
?
According to Mendel's hypothesis, if the two variations are red and white, then the offspring will either show the red or white trait only.
Dominant and Recessive Alleles
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Describing TraitsWe can describe a trait in terms of the physical appearance of that trait or the alleles present for a trait.
For example, suppose we are looking at the pea plant below. We can either say that it has purple flowers or that its alleles for the flower color trait are Pp.
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Phenotype vs GenotypeWhen you describe the physical appearance of a trait, you are describing its phenotype.
When you describe the alleles of a trait, you are describing its genotype.
Phenotype: purple flowers
Genotype: Pp
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Phenotype vs GenotypeIn humans, there is a gene for eye color.
The brown eye gene (B) is dominant to the blue eye gene (b).
Suppose that you meet someone who is homozygous dominant for this gene. What is their genotype and phenotype? Click in the boxes to check your answers.
Genotype Phenotype
BB brown eyes
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MotherFather
Law of SegregationA sex cell carries only one allele for each trait because allele pairs separate (or segregate) from each other during meiosis and go into separate cells. This is known as The Law of Segregation.
This means that the parent can't "accidentally" pass on two of the same chromosome.
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10 Alternate versions of a gene are called ___.
A chromatids
B heritable factors
C heterozygotes
D alleles Answ
er
D
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11 An organism that has two identical alleles for a gene is said to be ___ for that gene.
A dominant
B recessive
C homozygous
D heterozygous
Answ
er
C
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Using Punnett Squares
Return to Tableof Contents
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We just discussed Mendel's Law of Segregation. Use the space below to explain it in your own words.
The Law of Segregation
MotherFather
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The possible combinations of sperm and egg (the human sex cells) can be shown using a Punnett square.
A Punnett square is a diagram for predicting the results of a genetic cross between two individuals.
Punnett Square
?In order to understand how our Punnett Square will look, we need to figure out how many possible combinations of alleles there can be.
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12 According to Gregor Mendel, how many alleles did an organism have for each trait?
Answ
er
2
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Setting Up a Punnett Square
All organisms have two alleles for each characteristic and passes one of these on to the offspring (remember the Law of Segregation!).
The image on the right demonstratesthis as seen in humans. Fill in the blanks to note the number of chromosomes in the parent and sex cells.
MotherFatherParent's Cell
____chromosomes
Sex Cells
____ chromosomes
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CombinationsIn order to find out the possible number of combinations, let's picture it in a different situation: clothing.
Below, you see four pieces of clothing. Make as many different combinations of shirts and pants as you can!
BA
Place combinations here.Shirts Pants
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CombinationsOn the page before, we had 2 possible types of shirts (A and B) and 2 possible types of pants (purple and black).
We discovered from our activity that there are 4 possible combinations of these pieces of clothing.
Creating each possible combination is fine when the numbers are small, but what about when this would not be practical?
A A B B
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The Counting PrincipleIf there are A number of options for one object and there are B number of options for a second object, then the total number of combinations of the two is:
A x B
So in our example, there were 2 types of shirts and 2 types of pants. The total number of combinations of shirts and pants will be:
2 x 2 = 4
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13 Mindy is at the ice cream parlor. There are 6 different flavors of ice cream and 4 different types of cones. How many different types of ice cream cones can she make?
Answ
er
6 x 4 = 24
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14 Steven is making a sandwich. When he opens the refrigerator, he sees 2 different types of breads, 5 different types of meat and 2 different types of cheese.
How many different sandwiches could he make using one type of bread, one meat, and one cheese?
Answ
er
2 x 5 x 2 = 20
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Back to the Punnett Square...
Since the mother can pass on 2 alleles and the father can pass on 2 alleles, there are 4 potential combinations. (2 x 2 = 4)
Therefore, our Punnett Square is going to consist of 4 boxes:
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As Mendel said, alleles come in two different forms: dominant or recessive. Mendel represented these different traits with either a capital or a lowercase letter.
An uppercase letter represents a dominant allele, and a lowercase letter represents a recessive allele.
We will be using these letters in our Punnett Square.
A aDominant Recessive
Dominant and Recessive Traits
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Genotype
In order to set up our Punnett Square, we need to know what the parents' genotypes are.
The "genotype" is what the person's genes, or DNA, look like.A person's genotype determines what trait they have and what visible trait you will see!
For our sample Punnett Square, let's give the parents the following genotypes:MotherAa
FatherAA
Memory Tactic: The "genotype" tells you what the "genes" look like
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Setting Up a Punnett SquareA Punnett Square works like a data table; information will be put on the top of the table and on the left of the table.We will put one parent's genotype on the top (in this case, the mother's) and the genotype of the other parent (the father) will go on the left.
Mother's Genotype
Father's Genotype
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Setting Up a Punnett Square
Click on the boxes to uncover the components of the Punnett Square:
Mother's Genotype
Father's Genotype
A a
A
A
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Setting Up a Punnett Square
AA Aa
AA Aa
Click on the boxes to uncover the components of the Punnett Square:
Mother's Genotype
Father's Genotype
A a
A
AThe genotypes in the Punnett Square represent the possible combinations that the offspring could have.
The offspring can only be either be AA or Aa.
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15 Two of the four boxes contained "AA." Which term below accurately describes this genotype?
A Homozygous Dominant
B Homozygous Recessive
C Heterozygous
D Heterozygous Dominant
Answ
er
A
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16 The other two boxes contained "Aa." Which term below accurately describes this genotype?
A Homozygous Dominant
B Homozygous Recessive
C Heterozygous
D Heterozygous Dominant
Answ
er
C
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PhenotypeWe have already learned that "genotype" is what the genes look like.
The "phenotypes" of an organism are the observable characteristics, the organism's physical traits. The phenotypes are based on the genotypes and can be seen very easily.
What are some phenotypes of the man to the left? Make a list with your table.
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Dragon Crossing Activity
In this activity, you will be given the task of breeding a special dragon for the king. Use your knowledge of Punnett Squares, genotypes and phenotypes
to complete the process!
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Mendel's Experiments
A A
a
a
In his experiments, Mendel crossed a homozygous dominant purple flower with a homozygous recessive white flower.
Complete the cross:
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The dominant allele shows in the heterozygous flower, while the recessive allele has no effect on flower color. Therefore, a Aa flower has a purple phenotype (purple is dominant).
AA Aa
Phenotype
Genotype
Heterozygous Genotype
Even though the genotypes are different, What do you notice about the phenotypes?
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On the flip side, if an organism shows the recessive phenotype, there is only one way their genotype could look:
aa
Phenotype
Genotype
Homozygous Recessive Genotype
The organism HAS to have two recessive alleles. If it has even one dominant allele, what phenotype will it show?
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17 In Mendel's experiment three slides back, what colors were the offspring flowers?
A All purple
B All white
C All pink
D 1/2 purple, 1/2 white
Answ
er
A
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The Next GenerationIn the next step of Mendel's experiment, he took 2 of the offspring from his first cross and decided to cross them as well:
Aa x Aa
Set up and complete the cross below:
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18 How many flowers in the 2nd generation were purple?
Answ
er
3
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19 Three out of four flowers were purple. What percentage of the flowers were purple?
Answ
er
75%
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We can see that if both the mother and father pass on an A allele, the offspring will be AA and therefore have purple flowers.
In this type of cross, this particular genotype (homozygous dominant) will statistically occur in about 1/4 of the offspring.
F1 Generation
F2 Generation
A
a
A a
AA
Aa
Aa
aa
Looking at genotypeLooking at Genotypes
Mother's Genotype
Father's Genotype
AAHomozygous Dominant
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F1 Generation
F2 Generation
AA Aa
Aa aa
There are two ways in which a heterozygous organism can emerge:
Mom passes on A Dad passes on aMom passes on a Dad passes on A
What percent of offspring could have the Aa genotype?What color will their flowers be?
Looking at genotypeLooking at Genotypes
Mother's Genotype
Father's Genotype
AaHeterozygous
A
a
A a
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The remaining 1/4 of the plants will likely inherit an a from both the mother and the father.
These plants will have a aa genotype and will be what color?
Looking at genotypeLooking at Genotypes
Mother's Genotype
Father's Genotype
aaHomozygous Recessive
F1 Generation
F2 Generation
A
a
A a
AA
Aa
Aa
aa
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In this example, AA and Aa plants had the same phenotype but different genotypes.
Genotype vs. Phenotype
AA or Aa
Phenotype Genotype
We have already established that the genotype (what the genes look like) determines what the phenotype (the physical traits) will be.
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Genotype Phenotype
Purple
Purple
aa
Complete the chart below for the flowers we have discussed.
Genotype vs. Phenotype
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20 Red flowers (R) are dominant to white flowers. According to the chart below, Parent Plant A has what color flowers?
A Red
B White Parent Plant B RR
Parent Plant A Rr
Flower Genotype
Answ
er
A
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21 Red flowers (R) are dominant to white flowers. According to the chart below, Parent Plant B has what color flowers?
A Red
B White
Parent Plant B RR
Parent Plant A Rr
Flower Genotype
Answ
er
A
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22 The plants below can produce white flowers.
A True
B False
Parent Plant B RR
Parent Plant A Rr
Flower Genotype
F1 Generation
F2 Generation Answ
er
B
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23 The probability that the Parent Plants A and B will produce a plant with red flowers is ______%.
Parent Plant B RR
Parent Plant A Rr
Flower Genotype
Answ
er
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Jane and John ActivityHow are traits passed on from parent to offspring?
In this activity, you and a partner will be determining the traits of two individuals and will use a Punnett Square to look at the possible genotypes that their child can have!
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Test Crosses
Return to Tableof Contents
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How can we tell the genotype of an individual with the dominant phenotype? In Mendel's pea plants those with WW or Ww both appeared purple.
So if we have a pea plant with purple flowers, how do we determine which genotype the plant has?
Determining Genotype from Phenotype
AA ?
Aa ?
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Test CrossA test cross involves breeding the individual whose genotype we are trying to determine with a homozygous recessive individual.
In a test cross, you will always cross an organism that shows the dominant trait with one that shows the recessive trait.
Permission Granted:Penn State Dept of Biology
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Test Cross
In a test cross, the unknown genotype is either homozygous dominant or heterozygous.
What would the offspring look like if the unknown genotype is homozygous dominant? Complete a punnett square to determine your answer. Click below to check your answer.
F1 Generation
F2 Generation
p p
P
P
Pp Pp
Pp Pp
All offspring would show the dominant phenotype.
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Test Cross
What would the offspring look like if the unknown genotype is heterozygous? Complete a punnett square to determine your answer. Click below to check your answer.
F1 Generation
F2 Generation
p p
P
p
Pp Pp
pp pp
Half of the offspring will show the dominant phenotype and half will show the recessive phenotype.
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Test Cross Results
If any offspring displays the recessive phenotype, the parent must be heterozygous (Pp).
If all offspring display the dominant phenotype, the parent must be homozygous dominant (PP).
Permission Granted:Penn State Dept of Biology
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24 An organism's expressed, or physical, traits are known as its:
A genome
B genotype
C phenome
D phenotype
Answ
er
D
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25 Crossing an individual that is homozygous recessive with an organism of unknown genotype that exhibits a dominant phenotype is known as a ____________.
A hybrid cross.
B heterozygous cross.
C testcross.
D unknown cross.
Answ
er
C
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Setting up a Testcross
To complete a testcross, you must always cross one organism with the dominant phenotype with one that shows the recessive trait.
F1 Generation
F2 Generation
p pP = Purplep = white
In order for the one flower to be white,it must have one particular genotype.
This genotype has been added to the Punnett Square to the right.
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Setting up a Testcross
F1 Generation
F2 Generation
p p
P
P = Purplep = white
As for the other flower, we know it must have at least one dominant allele, which has been added to the Punnett Square on the right.
How do we know this must be true?
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Solving a Testcross
F1 Generation
F2 Generation
p p
P
The other letter is being represented by a "?" because we do not know if it is a "P" or a "p" yet.
We need to look at the offspring in order to know what the parent's genotype is. Because of this, we will do two different crosses to see how the offspring will differ.
?
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Solving a Testcross
F1 Generation
F2 Generation
p p
P
?
We can begin filling in the Punnett Square above with the information we have so far:
This will help us see what allele we must fill in for the question mark.
Pp Pp
?p ?p
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F1 Generation
F2 Generation
p p
P
P
F1 Generation
F2 Generation
p p
P
p
PP x pp Pp x pp
__________% purple flowers
__________% white flowers
_____/4 purple flowers
_____/4 white flowers
_____/4 purple flowers
_____/4 white flowers
__________% purple flowers
__________% white flowers
Pp Pp Pp Pp
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Testcross Trends
The percentages on the prior slide hold true for every testcross:
If every offspring shows the dominant trait (100%), the parent with the dominant traitis homozygous dominant (ex. PP).
If about half of the children show dominant and the other half show recessive (50% / 50%), the parent with the dominant trait is heterozygous(ex. Pp).
FYI: If even one child shows the recessive trait, the parent must be heterozygous. The percentages above only represent the probability.
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Testcross ActivityThis activity will allow you to practice setting up and solving testcrosses.
At each station will be a different situation.
Using the file folder and the sticky note papers, you will set up and solve the testcross.
You will then transfer the information to your student worksheet!
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Genetic Mutations
Return to Tableof Contents
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Review: DNADNA is the blueprint of life.
DNA contains ______________ that carries instructions for making proteins that control an organism's life functions.
DNA is shaped like a ____________.
Each rung of the ladder is made up of compounds. The order of these compounds determines what protein will be made in the cell.
100
Review: DNA
DNA can be found in the _____________ of the cell.
It plays a vital role in cellular reproduction (which is called _________) and helping the cell survive.
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Review: Base Pairs
DNA is made up of 4 bases: adenine , thymine , guanine , and cytosine .
We will refer to them as A T C and G.
_____ and _____ always bond together.
_____ and _____ always bond together.
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Review: Protein Synthesis
These bases play a role in protein synthesis .
During protein synthesis, information from DNA is carried to the ribosomes, where it is used to make proteins out of amino acids.
The sequence of genetic information found on the genes determines what kind of protein is made.
For example:
AAG or TCG
Each of the trios above will lead to the creation a different protein.
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The Role of ProteinsProteins have much more significance than we think! They do most of the work in our cells and are the basis for all of the organs and tissues in our bodies.
Proteins are made up of many different subparts known as amino acids . The
sequence of letters in our DNA determines what amino acids are
made.
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The Role of Proteins
The image to the right may look like a blob, but it is actually a protein knownas hemoglobin.
This protein is found in our blood and isresponsible for carrying oxygen from theblood to the rest of the body!
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Types of Proteins
Antibodies are responsible for getting rid of viruses and bacteria in the body.
Enzymes carry out all of the chemical reactions inside of cells. They also help form new molecules by reading the DNA.
Messenger proteins, such as hormones, send signals throughout the body to coordinate different things.
Some proteins are required for structure and support for cells. They also allow the body to move.
Finally, some are responsible for transport and storage of atoms and molecules in the body.
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MutationsEvery cell in your body contains a copy of the same exact DNA.Every so often though, a mutation will occur to alter your genetic blueprint.
A T
A
G
T
C
T
C
A
G
A
A
A
A
T
T
T
T
C G
A mutation is a change in the DNA sequence that can reshape your entire genetic code. It could happen as a result of an error in DNA duplication or by the insertion or deletion of genetic code inside the cell.
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Mutations
In the example above, the base pair of G and C was somehow eliminated. This may have happened accidentally through an error during DNA replication or the DNA could have been damaged in some way.
As a result, the genetic code changes. What used to read as AAG and TTC before now reads as AAT paired with TTA after.
This will result in different proteins being made.
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The Domino Effect of Genetic MutationsFor example, read the sentence below:
THE BAD DOG CAN NOT RUN
Now let's remove one piece of this sentence (the "A" in "BAD") and move all of the other letters up in its space:
THE BDD OGC ANN OTR UN
There is a chain effect throughout the rest of the sentence because one piece is missing!
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Environmental Causes of MutationsThere are a few different environmental causes of mutations in human DNA. Some of the most common causes are:
Radiation (such as UV radiation from the Sun)
Chemicals (such as coming in contact with radioactive waste)
Viruses (when viruses attack your cells, they can damage the DNA inside)
Although your body has ways of repairing most accidental changes to your DNA, some errors make their way past these checks and become permanent mutations.
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26 Mutations can happen as a result of exposure to _________.
A sunlight
B radioactive chemicals
C certain viruses
D all of the above
Answ
er
D
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27 Does your body repair all mutations?
Yes
No
Answ
er
No
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28 Changing one letter in the genetic code can cause a mutation.
True
False
Answ
er
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Types of Mutations
Genetic information can be altered through an error in DNA replication or from some sort of environmental damage after the baby is born.
These are called acquired mutations.
If the mutated DNA is present in the sperm or egg cells of an organism, it could then be passed on to the next generation.
A mutation that is acquired from one's parents is called a hereditary mutation. Every cell in this organism's body will have the mutated DNA.
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Are All Mutations Harmful?As was said before, a mutation in one's DNA will alter the proteins that are being coded for in the body. If one or more of these proteins is not functioning properly (or is missing entirely), it can disrupt normal development within the body or can cause a medical condition.
These illnesses are known as genetic disorders .
Progeria Tuberous Sclerosis
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Are All Mutations Harmful?
On the other hand, there are some genetic mutations that have no negative effect on the body at all and some that are even beneficial!
This section will look at a number of possible effects of genetic mutations.
5 ft6 ft 2 in
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Mutations Can be Helpful! Sometimes, DNA mutations can cause an organism to be able to survive better in his or her environment.
For example, imagine that there is an organism with a genetic mutation that makes it immune to cancer. What types of advantages would this creature have over other organisms in its same species?
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29 Mutations can occur in DNA _________.
A only before a baby is born
B anytime during an organisms life
C only when an organism is exposed to something bad
D only when the pregnant mother does something to cause them
Answ
er
B
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30 All mutations are bad.
True
False
Answ
er
False
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Mutations Can be Helpful!
There are people out there who have genetic mutations that help them live longer, healthier lives. One realworld example comes to us from a small village in Italy called "Limone sul Garda."
Some of the people in this community possess a mutation in a protein in their blood that helps their bodies clean out cholesterol from their veins.
Possessing this trait allows the people to eat whatever they want with little to no risk of heart disease.Out of about 1,000 people in the town, more than a dozen have lived past 100!
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Passing on Beneficial Mutations
Organisms who have a beneficial mutation will oftentimes lead longer, healthier lives. If this is the case, there is a strong possibility that these living things will give birth to many offspring who also possess this useful
trait.
If this is able to continue for many generations, the mutation will become more common and will be viewed as a normal variation of a trait.
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Beneficial Mutations and Natural Selection
Organisms with a beneficial genetic trait
are more likely to survive to pass that trait on to their
offspring.
Natural selection is a gradual process wherein some traits become more or less common in a population over time.
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Adaptation by Natural Selection
Adaptation by natural selection happens over long periods of time, through many generations. Usually these changes are in response to changes in the environment.
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Distribution of Traits
As the environment changes, organisms will also change. Those traits which help them to survive better and reproduce will become more common in the population.
The traits which hinder reproduction and success will become less common.
Over time, the whole population will change!
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Case Study: Peppered MothsThe peppered moth is a good example of how natural selection can cause different genes to be passed on.
The peppered moth varies in color from light light white/gray to black. The frequency of each color has changed drastically over the past 200 years.
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Case Study: Peppered MothsInitially, the peppered moth population was mostly light colored. The light colored moths were camouflaged against the light colored tree trunks on which they rested. The dark colored moths were not camouflaged and they were eaten by predators.
The light colored moths survived to reproduce and pass on the light colored gene to future generations.
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Case Study: Peppered MothsWith the Industrial Revolution, however, the amount of pollution dramatically increased. The air pollution caused the tree trunks to be stained a darker color.
How do you think this affected the peppered moths? Write your ideas below.
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Case Study: Peppered Moths
Since the tree trunks were now a dark color, the light moths were no longer well camouflaged. They were eaten by predators while the dark moths were able to hide on the tree trunks.
The dark colored moths survived to reproduce and pass on the dark colored gene to future generations.
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Artificial Selection
Humans have the ability to influence certain characteristics by selectively breeding specific traits in animals.
Both of the animals to the right are dogs. How did they become so different?
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Artificial Selection
By choosing which traits are preferred in plants and animals, humans can choose to breed organisms with those specific traits.
Those characteristics will then be passed on to offspring through the animal's genes.
Why is this called "artificial selection"?
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Artificial Selection
There
There are many ways humans can influence selection in organisms.
These days, it is easy to select traits using methods such as gene therapy, artificial husbandry (breeding), and even genetic modification.
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31 Animals reproducing on their own in the wild in response to changes to their environment is considered ___________ selection.
A natural
B artificial
Answ
er
A
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32 Natural selection happens very fast, often in one generation.
True
False
Answ
er
False
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33 Natural selection causes changes to traits in populations in response to changes in the ____________.
A animal's DNA
B environment
C mutations
D father's DNA only
Answ
er
B
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Some Mutations Are Neutral
There are some mutations that have no effect, either positive or negative, on our bodies.
Most mutations that occur as a result of a DNA replication error or exposure to radiation is corrected and repaired quickly by the body. Still, there are some that sneak by yet prove to not affect the organisms in a negative way.
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Harmless Mutations
Cats have a number of harmless body mutations that give variety to the species.
Some cats have a mutation that causes their ears to naturally curl.
Other mutations in DNA can cause cats to have a curly tail.
Each of these mutations has a neutral effect on the cat. It neither helps it survive nor hurts it.
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Harmful Genetic Mutations
Harmful genetic mutations can come from an error in DNA replication in the cell, exposure to radiation, or from an error in the passing on of
genetic information from parent to offspring.
Just one incorrect portion of the DNA can cause a change in the
entire chain.
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34 Is the body capable of correcting mutations on its own?
Yes
No
Answ
er
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Down SyndromeOne relatively common genetic disorder is Down Syndrome.
A normal human baby is born with 23 pairs of chromosomes one from the mother and one from the father.
What do you notice about the chromosomes to the right which came from a person with Down Syndrome?
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Down SyndromeThis genetic mutation causes significant problems for the child.
Some common characteristics of individuals with Down Syndrome include:
Shorter height Weaker muscles Irregularly shaped mouth, tongue, and teeth Lower IQ Heart defects
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Genetic DisordersIt is important to keep in mind that genetic disorders are never the
fault of the individual who must suffer with the ailments.
More often than not, a person who has a certain genetic disorder was born that way and could not help getting the disease. All living
things deserve our respect!
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Genetic Disorders Baby Project
In this wrapup activity, you will be practicing the skills obtained during this unit and you will also be researching a genetic disorder that you will then teach to the class.
F1 Generation
F2 Generation
A a
A
a
AA Aa
Aa aa
