Heredity - Plainfield North High Schoolpnhs.psd202.org/documents/rkieft/1518541803.pdfNaturally...

HEREDITYHOW YOU BECAME YOU!

ESSENTIAL QUESTIONS• Why do individuals of the same species vary in how they

look, function and behave?

WHY DO INDIVIDUALS OF THE SAME SPECIES VARY IN HOW THEY LOOK, FUNCTION AND BEHAVE?

Answer: Genetic variation!

ESSENTIAL QUESTIONS

• How does sexual reproduction lead to genetic variation?

HOW DOES SEXUAL REPRODUCTION LEAD TO GENETIC VARIATION?

• You get half of your DNA from mother and half from father, so you end up being a new combination of all of their DNA!

ESSENTIAL QUESTIONS• Is there anything besides genetics that can influence

Genetic variation in a population?

IS THERE ANYTHING BESIDES GENETICS THAT CAN INFLUENCE GENETIC VARIATION IN A POPULATION?

Yes!Environmental Factors can also have an influence

If one trait is better at helping an organism survive than another, that trait will show up more over time

ESSENTIAL QUESTIONS

• How is probability used to predict the expression of traits?

HOW IS PROBABILITY USED TO PREDICT THE EXPRESSION OF TRAITS?

ESSENTIAL QUESTIONS

• How does genotype affect phenotype?

HOW DOES GENOTYPE AFFECT PHENOTYPE?

• Genotype: Actual genetic makeup (what copies of a gene you have)

• Phenotype: Traits that you actually get from your genotype

AN INVENTORY OF MY TRAITS

• Let’s take a look at some of your traits!!!!

• I’ll be showing pictures as we go through check whether you have each form of the trait discussed.

• After you will meet with your groups to pool all of your data together and graph it.

• Then we will meet back as a class to collect whole class data and graph it.

DETACHED EARLOBES ROLL MY TONGUE

HAVE DIMPLES CLEFT CHIN

COLOR BLIND HAND CLASPING

STRAIGHT HAIRLINE

CLASS TRAITS DATATrait Yes No

Detached Earlobes

Tongue Rolling

Dimples

Right-Handed

Freckles

Naturally Curly Hair

Cleft Chin

Allergies

Cross left thumb over right

See colors red and green

Have a straight hairline

DOMINANT OR RECESSIVE?Trait

Detached Earlobes Dominant

Tongue Rolling Dominant (70% of population)

Dimples Dominant

Right-Handed Dominant (93% of population)

Freckles Recessive

Naturally Curly Hair Recessive

Cleft Chin Recessive

Allergies Recessive

Cross left thumb over right Unsure (50/50)

See colors red and green X Linked (why colorblindness is more common in men)

Have a straight hairline Recessive

ANALYZE YOUR TRAITSOn the back of your sheet answer the following questions:

1.Which traits did you have that were most common?

2.Are dominant traits always the ones that the most people have?

3.What traits can you think of that you have that your parents DO have?

4.What traits can you think of that you have that your parents DO NOT have?

5.If you have traits that your parents DO NOT have, how could this have happened?

Introduction to

Genetics

Genetics and Heredity

• Heredity: the passing of traits from parent to offspring.

• Genetics: The scientific study of heredity

• Traits: specific characteristics (ex: hair color, height)

• Gregor Mendel 1822-1884

• Born to farmhands in Heinzendorf, Austria

• Despite family wishes, studied to be a monk.

• Once exhausted from his religious duties, he studied to be a teacher, and taught secondary school at the monastery

Genetics History: Gregor Mendel

Genetics History: Gregor Mendel

While teaching at the monastery, Mendel started some experiments growing garden peas.

Mendel’s Crossbreeding

• Mendel’s garden had an array of different types of peas

• Tall vs. short

• Round vs. wrinkled seeds

• Green vs. yellow seed color

• Pod shape & color

• Mendel cross-bred plants with different characteristics (crossed a tall plant with a short plant)

• Offspring of cross-bred plants are called hybrids.

Terminology

• Gene: characteristic(height)

• Allele: form of the characteristic(tall or short)

– You have spots for two alleles per gene. One from your mother and one from your father.

Gene

Allele

Dominant Allele

P: Parent Generation

F1: Offspring of parent generation (kids)

F2: Offspring of two F1’s reproduction. (grandkids)

Genotype:

What allele’s you actually have (BB)

Phenotype:

The trait you end up with (Black Hair)

Terminology

Mendel’s Findings

Principle of Independent Assortment

-Different genes are inherited independently of one another.

ex: How you inherit hair color does not affect how you inherit eye color.

Mendel’s FindingsPrinciple of Dominance: Some alleles are dominant over others

The appearance of different traits has to do with dominance (how strong one gene is over another)

• Dominant alleles (or characteristics) always show in the offspring if the allele is present.

• They are always symbolized by a capital letter.

• Recessive alleles (or characteristics) only show in the offspring when the dominant allele is NOT present.

• They are always symbolized by a lower-case letter.

Dominant & Recessive Alleles

• Which allele is dominant?

• How do you get blue eyes?

• Can you get blue eyes if both of your parents have brown eyes?

• How?

Baby Dragon Lab• Make sure you READ the DIRECTIONS!!!!

• If you do not follow the directions properly points will be taken off.

• You will be creating your own baby dragons.• You will work in pairs, but everyone turns in their own

paper!!!

• Take the alleles of the parent plants (TT and tt) and put them on the sides of the Punnett Square.

• Separate the gametes into the boxes.

• What do the F1 plants look like? Tall or short?

Punnett Squares

T

T

t t

Tt

Tt

Tt

Tt

Punnett Square Practice

Two F1 plants are crossbred (Gg x Gg). Make a punnett square showing their

offspring.

Two parental plants are crossbred (RR x rr). Show what the F1 generation looks like.

F1Cross Punnett Square Analysis

How many of the 4 F2 offspring will be tall?

What is the ratio of tall to short offspring?

What three genotypes are present?

What is the ratio of the genotypes?

What are the genotypes for two tall F1 plants?

Complete a Punnett Square to cross the two F1 plants:

Punnett Square Analysis

What are the parents genotypes?

What is the phenotypic ratio of the offspring?

What are the parents phenotypes?

What is the genotypic ratio of the offspring?

Long (L) is dominant over short (l). Cross a Heterozygous parent with a short parent.

Dihybrid CrossesCrossing TWO Traits at the same time!

So far, the punnett squares we have done in class have traced one gene, predicting the outcomes of genetic crossing. (ex: height)

• These would be considered mono-hybrid crosses.

Dihybrid crosses cross two individuals that differ in two traits.(ex: height and eye color)

The genes are located on separate chromosomes, so the traits themselves don’t effect each other.

Example: White fruit color (W) is dominant over yellow fruit color (w), and flat shaped fruit (D) is dominant over round shaped fruit (d).

Parents: White, flat fruit x Yellow, round fruitWWDD wwdd

F1 offspring: WwDd

F1 cross: WwDd x WwDd

F1 cross: WwDd x WwDd

First we need to figure out what possible gametes each parent could contribute.

These are what we are going to write on the sides of the square.

WwDd:

1. WD 2. Wd 3. wD 4. wd

(Since both parents have the same genotype, we can use this on BOTH sides of the square, if the parents have different genotypes we would have to do this process for the other parent as well)

F1 cross: WwDd x WwDdFill in the gametes for each parent on the sides of the Punnett square and fill in the boxes as normal

Possible Gametes:

WD Wd wD wd

WD

Wd

wD

wd

WWDD WWDd WwDD WwDd

WWDd WWdd WwDd Wwdd

WwDD WwDd wwDD wwDd

WwDd Wwdd wwDd wwdd

Analyze the Punnett SquareExample: White fruit color (W) is dominant over yellow fruit color (w), and flat shaped fruit (D) is dominant over round shaped fruit (d).

List the possible Genotypes of the offspring:

List the possible Phenotypes of the offspring:

What is the probability of have a yellow round fruit?

What is the genotypic ratio?

What is the phenotypic ratio?

For a Dihybrid Cross of two

heterozygous in BOTH traits parents, the PHENOTYPIC

RATIO is ALWAYS

9:3:3:1

Dihybrid PracticeSet up a punnett square using the following information:• Black fur (B) is dominant to white fur (b) in Guinea Pigs. Rough fur (R) is dominant to smooth fur (r)• Cross a heterozygous parent (BbRr) with a heterozygous parent (BbRr)

List the possible Genotypes of the offspring:

List the possible Phenotypes of the offspring:

What is the probability of have a yellow round fruit?

What is the genotypic ratio?

What is the phenotypic ratio?

Dihybrid PracticeSet up a punnett square using the following information:Black fur (B) is dominant to white fur (b) in Guinea Pigs. Rough fur (R) is dominant to smooth fur (r)

Cross a heterozygous parent (BbRr) with a homozygous parent (bbrr)

List the possible gametes for each parent:

Heterozygous:

Homozygous:

List the possible Genotypes of the offspring:

List the possible Phenotypes of the offspring:

What is the probability of have a yellow round fruit?

What is the genotypic ratio?

What is the phenotypic ratio?

Probability

Mendel realized that the principles of probability could be used to explain results of genetic crosses.

• Probability: the likelihood that a particular event will occur.

– Flipping a coin: heads up or tails up. (Equal probability).

– 50% chance it will be heads. 50% chance it will be tails.

Calculating Probability

• If you flip a coin 3 times, what is the chance it will land heads up all three times?

• Multiply the probability of each flip.

1st flip 2nd flip 3rd flip

• Each time your parents “flip a coin” and have a baby, they have a certain probability of passing on a trait.

• Since each gene is passed down independently, this leads to genetic variation in two offspring of the same parents.

• Don’t forget about crossing over! This increases genetic variation amongst offspring as well!

Probability and Genetic Variation

Crossing Over: Happens during Meiosis

Terminology

• Organisms that have two of the same alleles for a particular gene (TT) or (tt) are homozygous.

• Think: “homo” or “same”

• Organisms that have two different alleles for the same gene (Tt) are heterozygous.

• Think: “hetero” or “different”

• Phenotype: the physical traits (what it looks like)

• Genotype: the genetic makeup (the letters)

• If the parent plants are true-breeding, their alleles will look like this:

Tall: TT Short: tt

• Each offspring will inherit half of the parent’s alleles (or genes).

F1 (1): Tt F1 (2): Tt

Since the offspring in F1 were tall, what was the dominant allele?

• Both F1 plants have one “T” and one “t” (each inherited from the parents)

• How many different combinations of gametes can we put together from our parent F1 plants?

TT Tt Tt tt

The F1 Cross

Mendel’s Crossbreeding results

• Mendel found when he crossed a tall plant with a short plant, that the F1 offspring were all tall.

He reasoned that…

– Tallness must be the “stronger” gene

– Shortness must be the “weaker” gene

Then Mendel crossed two tall F1 offspring

-3 were tall, and 1 was short

How was one F2 offspring short if both F1 parents were tall?

Tt

t 1/2

Tt

T 1/2

T 1/2

t 1/2

Tt1/4

Tt1/4

TT 1/4

tt1/4

F1

F2

F1

Gametes

Types of Dominance

Complete Dominance

• Genetic crosses that result in the dominant phenotype being shown due to a dominant gene being present.

• Ex: Tallness is dominant. Crossing a homozygous dominant pea plant (TT) with a homozygous recessive pea plant (tt) results in F1 offspring all having a dominant gene (Tt)– These problems use the same letter (T)

T T

t

t

Tt Tt

Tt Tt

Incomplete Dominance• When some alleles are neither dominant nor recessive.

• One allele is not “stronger” than the other.

– Phenotypes are blended together.

• Uses TWO letters

• Crossing a red flower (RR) with a white flower (WW) creates pink flowers (RW).

R R

W

W

RW RW

RW RW

Co-dominance

• When both of the phenotypes are visibly seen.

– Phenotypes do NOT blend, they are both seen.

• Uses TWO letters

• Ex: In a breed of chickens, the allele for black feathers is co-dominant with the allele for white feathers.

B B

W

W

BW BW

BW BW

Black (BB) father and White (WW) mother produced Black AND white (speckled) baby chicks

Example 1

• In mice, the two most common colors seen are brown (BB) and white (WW). How would you cross a brown mouse with a white mouse to get a cream-colored mouse?

• What type of dominance is this?

• What is the probability of getting a cream colored mouse from this cross?

Example 2

• In certain breeds of salmon, there are fish with the “A” allele for scales (Aa) and without scales (aa). When you cross the two breeds, some fish end up with scales, some don’t.

What type of dominance?

What’s the probability of getting a fish with scales?

Example 3

You have identified a new species of grasshopper that come in two different colors: ones with red stripes (RR) and ones with yellow stripes (YY). When you cross them you get a grasshoppers with red and yellow stripes.

• What type of dominance is this?

• What will the offspring look like?

Example 4A species of chicken’s color is determined by CODOMINANT genes. A Heterozygous

(BW) chicken is crossed with a Homozygous (BB) chicken:Complete a Punnett Square for this cross

What color is the Heterozygous (BW) parent chicken?

What color is the Homozygous (BB) chicken?

What is the probability that a black chick will be born?

What is the probability that a white chick will be born?

What is the probability that a black AND white chick will be born?

What is the probability that a GREY chick will be born?

What is the genotypic ratio for this cross?

What is the phenotypic ratio for this cross?

Example 5A species of flower’s color is determined by INCOMPLETELY DOMINANT genes. R is

for Red and W is for White. A Heterozygous (RW) flower is crossed with a Homozygous (RR) flower:

Complete a Punnett Square for this cross

What color is the Heterozygous parent flower?

What color is the Homozygous (RR) parent flower?

What is the probability that a Red flower will be made?

What is the probability that a White flower will be made?

What is the probability that a Red AND White flower will be made?

What is the probability that a PINK flower will be made?

What is the genotypic ratio for this cross?

What is the phenotypic ratio for this cross?

Multiple Alleles

• A gene (characteristic) with more than two alleles is said to have multiple alleles.Ex: coat color in rabbits, blood types.

– Most characteristics we’ve dealt with so far have two alleles (R and r). Multiple Alleles have more than two (ex: A, B, O in blood types).

***There can be multiple alleles for a certain trait, but each individual STILL ONLY HAS 2 ONE FROM MOM, ONE FROM DAD.****

Polygenic Traits

A trait that is controlled by two or more genes (each with two alleles)

– Ex: AaBbCc

Polygenic inheritance usually shows up as a range of variation such has height, skin color or hair color.

Human Blood Types• There are 4 different blood phenotypes

• A

• B

• AB

• O

• 3 alleles are in the pool instead of just two (A, B, O)

• You still only get ONE from Mom and ONE from Dad.

Genotypes for blood type

ALLELE CODES FOR

IA Type A Blood

IB Type B Blood

i Type O Blood

Type O is the recessive blood type, which is why it gets a

lowercase (i).

Genotypes & Phenotypes of Blood

Genotype Phenotype

IAIA Type A - Homozygous

IAi Type A - Heterozygous

IAIB Type AB - Heterozygous

IBIB Type B - Homozygous

IBi Type B - Heterozygous

ii Type O – Homozygous recessive

Example Problem:Dad is homozygous for Type A blood. Mom is heterozygous for Type B blood.

Do a Punnett Square to find out the offspring.

IAIB IAi

IAIB IAi

IA

IA

IB i What are the new genotypes? Phenotypes?

• IAIB Type AB• IAi Type A• IAIB Type AB• IAi Type A

Blood Donors & Receivers

Sex – Linked Genes• We each have two sex chromosomes (one donated from mom, one

donated from dad.

– Females: X X– Males: X Y

• Genes on the first X chromosome are shared traits between the sexes, and is inherited from your mother.

• Genes on the Y chromosome contain very few instructions (primarily just for male development).

Sex-Linked Disorders

Two of the most common sex-linked disorders are

–Colorblindness

–Hemophilia

The genes that cause these disorders is located on the X chromosome (usually passed from mother to son)

• This makes it very rare for a colorblind father to pass the gene onto his son.

Sex-linked Genotypes

Genotype Codes for:

XRXR Female – Homozygous – Dominant

XRXr Female –Heterozygous – Dominant

XrXr Female – Homozygous – Recessive

XRY Male – Dominant

XrY Male – Recessive

Example Problem:

• Colorblindness is an X-linked recessive disorder. Show a cross between a heterozygous mother and a father who is colorblind.

XRXr XRY

XrXr XrY

XR

Xr

Xr Y• What are the new genotypes? Phenotypes?

• XRXr – (F) Not Colorblind• XRY – (M) Not Colorblind• XrXr – (F) Colorblind• XrY – (M) Colorblind

Using Karyotypes to Identify Disorders

Karyotypes can be used to identify certain genetic disorders.

Normal Karyotype Klienfelter’s Syndrome

What is a pedigree?

Pedigrees: a chart that shows how a certain trait is passed from generation to generation.

–Shows family relationships, including marriages and births.

–Pedigrees can show us the genotypes of family members.

What are they used for?

• Pedigrees are commonly used in families to find out the probability of a child having a disorder in a particular family.

• In the practice of breeding animals pedigree charts are used to plan animal breeding in order to enhance desirable traits.

When can we use pedigrees?

Pedigrees work best to demonstrate simple dominance inheritance.

–Not all genes can be traced through a pedigree because some genes are polygenic.

Pedigree Symbols

• Females:

• Males:

• Verticle lines: parent/child relationship

• Horizontal lines: marriage

• Shaded shape: infected family member

• Unshaded shape: not infected family member

• Half-shaded shape: carrier of the gene

Determining Genes on a Pedigree

You can determine the genes of family members on the pedigree in a few easy steps….

1. Fill in the genotypes of the infected people first.

2. Do a punnett square to find out the missing genotypes.

Example #1

Albinism is caused by a recessive allele (a). The following pedigree shows 3 generations.

Is individual #2 homozygous or heterozygous for normal skin color?

Heterozygous!

Why?

Because individual 2 had to have given their child a copy of the recessive allele

2aa

aaAa

Chromosomal Disorders

• Problems with large portions of genes (or entire chromosomes)

• Can be devastating

Nondisjunction

• The most common error happens in meiosis, where chromosomes fail to separate = nondisjunction

Down Syndrome

Down syndrome: Trisomy 21 if chromosomes fail to separate an individual might end up with 3 copies of that gene, called trisomy.

Phenylketonuria (PKU)

• Phenylketonuria (PKU) is a recessive genetic disorder in which a baby is born without the ability to properly break down the amino acid phenylalanine.

• Children who get this disorder inherit the recessive allele from both parents.