Bell Ringer Which features do you have that match your

mother? Your father? Which of the following features do you have?

Widow’s Peak? Ability to roll your tongue? Attached earlobes?

Simple Genetics

Exploring How Traits are Passed On

Punnett Squares In order to determine the traits that a person

might inherit, we use a simple diagram called a Punnett Square! Punnett Squares give us the probability of an

offspring having particular traits

Pieces of the Puzzle Before completing a square, you must know the

components Allele-An allele is a variant form of a gene

Humans inherit one allele from each parent that determines a trait For example, alleles might determine if you have curly or straight

hair, are tall or short, etc. Dominant-A dominant allele show their effect even if there

is only one copy of the allele (think of them as being strong!) Dominate alleles are denoted by a capital letter (ex. A)

Recessive- A recessive allele will only show up if no dominant alleles are in place (think of them as being weak!) Recessive alleles are denoted by a lowercase letter (ex. a)

Dominant and Recessive alleles pair together to determine a trait

(ex. AA, Aa, aa)

Homozygous vs. Heterozygous So…alleles pair together (AA, aa, Aa) Homozygous-if both letters are identical (both

dominant (capital) or both recessive (lowercase)), the alleles are homozygous “Homo” means “same” Ex. Let’s say “A” represents the allele for a widow’s peak,

and “a” represents the allele for a straight hairline A person with “AA” would be called homozygous dominant A person with “aa” would be called homozygous recessive

Heterozygous-if both letters are different (one dominant (capital) and one recessive (lowercase)), the alleles are heterozygous “Hetero” means “different”

A person with “Aa” would be heterozygous Would they have a widow’s peak or a straight hairline?

Phenotype and Genotype All of these allele combinations tell us the

phenotype and genotype of a person

Genotype-The genetic, inheritable information of an organism Example: A person’s genotype is Aa

(heterozygous); they can pass on either a dominant allele or a recessive one to their children.

Phenotype-The outward, physical appearance of an organism Example: A person has a widow’s peak

Let’s Practice Dominant or Recessive?

A b B

Heterozygous or Homozygous? AA Bb cc

Phenotype or Genotype? She is homozygous recessive (rr) She has blue eyes

Building a Punnett Square Consider the following alleles for pea

plant color: AA (Yellow-homozygous dominant) Aa (Yellow-heterozygous) aa (Green-homozygous recessive)

Let’s say you had two pea plants, both heterozygous yellow (Aa), and you wanted to know what color plants would be produced. How would you find out? Set up and Punnett Square

Building a Punnett Square What we know: Both parent plants are Aa So, cross Aa x Aa will be carried out in the

Punnett Square below:Mother

Father

*Note: It doesn’t matter where you set up the mother/father, the results will be the same!

Building a Punnett Square So, how do you carry out a Punnett Square?

Father’s letters cross to the right Mother’s alleles cross down, filling in the squares

to complete the allele Mother

Father

AA Aa

Aa aa

*Notice each potential combination has one allele from mom and one from dad

Interpreting the Final Square Once the square is finished, always determine

the genotype and phenotype ratios of the possible offspring

Genotype: 1:2:1 -1 AA, 2 Aa, and 1aa

Phenotype: 3:1 -3 Yellow, 1 Green

Note: These ratios are equally probable for each offspring, meaning each offspring has the same chance of inheriting the traits!!

Practice Complete the Cross: Tt x tt

Genotype:

Phenotype:

Practice What is the probability of producing offspring

that have short whiskers from a cross of two long whiskered seals, one homozygous dominant and one heterozygous?

Genotype:

Phenotype:

W= long whiskers (dominant)w=short whiskers (recessive)

A Few Notes on Genetics… Some traits are controlled by more than one

pair of genes, and so present a wide range of phenotypes (ex. Skin, hair, eye color)

All traits depend on both genetic and environmental factors Heredity determines your traits, but the

environment may play a role in how they act

Bell Ringer

W= long whiskers (dominant) w=short whiskers (recessive)

What is the probability of producing offspring that have short whiskers from a cross of two seals, one homozygous recessive and one heterozygous? Draw the Punnett Square Determine the Genotype ratios Determine the Phenotype ratios Answer the above question

Bell Ringer

W= long whiskers (dominant) w=short whiskers (recessive)

What is the probability of producing offspring that have short whiskers from a cross of two seals, one homozygous dominant and one heterozygous? Draw the Punnett Square Determine the Genotype ratios Determine the Phenotype ratios Answer the above question

Genetic Diseases

How Diseases are Carried Through Generations

Dominant and Recessive If a disease is recessive, both parents have to

pass on a mutated allele to the offspring Those who are heterozygous (Aa) are carriers,

meaning they have the mutated allele and can pass it on, but are healthy themselves

If a disease is dominant, only one parent has to pass on the mutated allele for offspring to have it Can a person with a dominant disease be a

carrier?

Let’s take a look at some specific genetic diseases…

Cystic Fibrosis (cf)-Recessive This disease causes a

mucus buildup in the lungs and digestive system

Those affected have difficulty breathing and poor growth

Common in those with European Ancestry

Live expectancy up to 35 years thanks to gene therapy

Sickle Cell Anemia-Recessive This disease affects a

person’s red blood cells A mutation causes the cells

to be long and bent (“sickle” shaped)

The odd shape causes the cells to get stuck in blood vessels Cuts off blood flow and

circulation Common in those with

African ancestry Carriers are associated with

malaria resistance-we’ll discuss why later!

PKU-Recessive

PKU- Phenylketonuria A condition in which the body

is missing the enzyme that breaks down phenylalanine, an amino acid

This means it builds up in the body, which results in mental deterioration Memory loss/identity loss!

People affected have to keep a low protein diet and have the enzyme injected regularly This must be done for life!

Genetic Disease Punnett Squares A woman is concerned that she may develop

Huntington’s Disease because her father has it. What is the probability that she has Huntington’s?Note: The mother does not have Huntington’s Disease.

Huntington’s-Dominant This disease affects the

muscles of the body Those affected will slowly

have muscle function decline Painful, like a muscle cramp that

won’t go away Unfortunately, it often does

not show signs until the person reaches mid 30s-can take up to 20 years to kill! Shows up after the person has

already had children, meaning that they have already passed the allele

Affects all people!

Genetic Disease Punnett Squares A woman who is a carrier for Cystic Fibrosis

marries a man who is also a carrier. What is the probability that they will have a child with Cystic Fibrosis?

Bellringer-4/23/15 Complete the Genetic Diseases Review

Worksheet on your desk. We will work on this for 30 minutes.

Bellringer-4/24/15 We have a quiz today. You have 10 minutes to

study for your quiz. Be sure to review: Definitions How to complete Punnett Squares Genetic Disease patterns and symptoms

Bellringer-4/27/15 Complete the Punnett Square review sheet on

your desk!

Complex Genetics

Codominance, Incomplete Dominance, Sex-Linked Traits, and Blood Typing

Incomplete Dominance Sometimes, one allele is not completely

dominant over another allele In this case, the offspring are blends of both

parents! The heterozygote has a unique phenotype

because one gene does not dominate the other Example: Red Flower (RR) + White Flower (WW)=

Pink Flowers (RW)

Incomplete Dominance During incomplete dominance, organisms who

are heterozygous for a trait have the opportunity to pass either gene to the offspring

Therefore, a cross between two heterozygous organisms have the following results:

1 RR: 2 Rr: 1 rr1 Red: 2 Pink: 1 White

Incomplete Dominance Example A red carnation is crossed with a white

carnation and the resulting offspring are all pink (indicating incomplete dominance). What would be the result of a cross between a pink and a white carnation?

Codominance Sometimes, both alleles are equally dominant

Therefore, both alleles will be expressed in phenotype

In this case, the offspring display the traits of both parents! Example: White Cow (WW) + Brown Cow (BB)=

White and Brown Cow (BW)

Case Study: Sickle Cell Anemia Although we discussed Sickle-Cell Anemia’s

recessive inheritance pattern, the disease does display a certain codominance Those homozygous affected (aa) have misshapen

cells Those homozygous unaffected (AA) have normal

cells Those heterozygous (Aa) are unaffected carriers,

but can have some misshapen cells mixed in This unique feature means heterozygous individuals are

resistant to severe malaria!

Codominance Example A bird with white and blue feathers mates with

another white and blue bird (BW). What are the phenotypic ratios of the offspring?

Bellringer-4/28/15

Complete the bellringer sheet on your desk!

Blood-Typing Human blood types include a codominance

pattern Humans can have type A, B, AB, or O blood The alleles involved are two codominant alleles (IA

and IB), and one recessive allele (i)Genotype Blood Type

IAIA or IAi A

IBIB or IBi B

IAIB AB

ii O

Blood Type Practice Problem The father is type A homozygous, and the

mother is type O. What are the possible blood types of their children?

Is Parentage Possible? Ralph has type B blood and his wife Rachel

has type A blood. They are very shocked to hear that their baby has type O blood, and think that a switch might have been made at the hospital. Can this baby be theirs? Explain.

Bellringer-4/29/15 Write the possible genotypes for the following

blood types: Type A: __________ or ___________ Type B: __________ or ___________ Type AB: _________ Type O: _________

Solve: There is a mixup between babies at the hospital. The baby has type O blood. On set of parents have the genotypes IAIA and IAi. The other set of parents are a heterozygous Type A mother and a heterozygous Type B father. Make the crosses of both sets of parents. Which set does the baby belong to?

Sex-Linked Traits Genes located on the sex chromosomes are

called sex-linked genes

Usually found on the X Chromosome Because of this, males are much more likely to

express a trait than females, because males only have one X chromosome!

Sex-Linked Traits Let’s take a look at the possible alleles in a

recessive sex-linked disease: Female: XAXA, XAXa, XaXa

Notice that the female must inherit 2 recessive copies to display the trait. It is also possible for females to be carriers of sex-linked traits.

Male: XAY, XaY Notice the male does not have a second X to help mask

the trait. This means that if he inherits the recessive copy, he will display the trait!

Because of this, males are much more likely to inherit a sex-linked trait!!!

Common Sex-Linked Traits Hemophilia-A bleeding

disorder that slows the blood clotting process

Color-Blindness-The inability to see color, or perceive color differences

Because of its X-linked inheritance, both of these conditions are more common in men

Sex Linked Problems Cross a woman carrier for hemophilia to a

hemophiliac man. What percentage of the females could inherit the trait? Males?

Pedigrees

Inheritance Patterns Through Generations

What is a Pedigree? A pedigree is the recorded ancestry of a

family Pedigrees allow us to see the genotypes and

inheritance patterns through the generations of a family

What Does a Pedigree Tell Us? Pedigrees can give us insight into how

traits are passed through families. You can tell a lot through a pedigree. For example: The phenotypes and genotypes of individuals The inheritance pattern.

If more males are affected, it is likely sex linked

If there are no carriers and one of the parents must have it, the disorder is dominant

If carrier parents produce some affected children, the disease must be recessive

Pedigree Example Problems What type of inheritance pattern is shown

below? What would be the genotype of individual I-1?

Pedigree Example Problems What type of inheritance pattern is shown

below? What would the genotypes be of individuals II-

1 and III-5?

Bellringer-4/30/15

In guinea pigs, black coat color (B) is dominant to white coat color (b). What percentage of the offspring will be white when a homozygous black guinea pig is crossed with a homozygous white guinea pig?

a. 0% b. 25% c. 50% d. 100%

Sickle cell anemia is a genetic disease caused by an autosomal recessive gene. If each parent carries one sickle cell allele, what are the chances that their child will have sickle cell anemia?a. no chanceb. one in fourc. two in fourd. three in four

When Mendel was experimenting with pea plant crosses, one of the traits that he examined was seed texture. The two phenotypes are smooth and wrinkled. The totals for his F2 (small 2) generation was 5,474 smooth and 1,850 wrinkled, yielding a probability ratio of approximately

a) 2:1b) 3:1c) 4:1d) 5:1

A scientist crossed red roses with white roses (R'R'). The cross revealed a pattern of incomplete dominance in the heterozygous condition (Rr). What percent of offspring of the cross were red roses?

a) 0%b) 25%c) 50%d) 100%

26. A woman heterozygous for A blood marries a man heterozygous for B blood. What is the probability that they will produce offspring with AB blood?

a) 0%b) 25%c) 75%d) 100%

The inheritance of short wings in Drosophilia fruit flies is an x-linked, recessive trait. Which would most likely result if a short winged female mates with a long winged male?a) All offspring would be short wingedb) All females will be long winged, and all males

will be short wingedc) All females will be short winged, and all males

will be long wingedd) Half of the males and females will be short

winged, and half will be long winged

Color blindness is inherited as a sexlinked trait in humans. Use a Punnett Square to complete a cross of a colorblind male with a female with normal vision who is a carrier of the trait.