Incomplete Dominance, Codominance and Sex-Linked Traits

START: In fruit flies the trait of red eyes (R) is dominant to white eyes (r). The trait is carried on the X chromosome.

Based on the Punnett square above, which statement best describes the eye color of the fruit fly offspring?

a. There is a 50% probability that female offspring will have red eyes.b. There is a 75% probability that female offspring will have red eyes.c. There is a 50% probability that male offspring will have red eyes.d. There is a 75% probability that male offspring will have red eyes.

SC.912.L.16.2 Discuss observed inheritance patterns caused by various modes of inheritance, including dominant, recessive,

codominant, sex-linked, polygenic, and multiple alleles.

Complex Patterns of Inheritance

Incomplete Dominance: Neither allele is completely dominant or recessive. The heterozygous will be a blending of the two alleles.

RR: Red Rr: pink rr: white

Wait! This should have been RED, but

incomplete dominance makes

it pink

Incomplete Dominance CrossRR: redRr: pinkRr: white

A heterozygous flower(Rr) Is crossed with a homozygous dominant.What are the genotypesand phenotypes of F1?

R r

R

R

RR Rr

RR Rr

Genotypes:50% RR; 50% Rr

Phenotypes50% red; 50% pink

Codominance• This is when both alleles are expressed fully

and separately. – Examples: many organisms with spots

• Both the brown (black) and white are being expressed in the heterozygous

– This would be the same Punnett Square as before except for blending colors at heterozygous we would have spotted colors.

Codominance and Blood Types• Blood Types are an example of co-dominance also

– if the antigen(s) are there they are expressed.

A type A (IAIA) mates with a type AB. What is the predicted blood types of their children?

IA IA

IA

IB

IA IA IA IA

IA IB IA IB50% IA IB

50% IA IA

50% Type AB50% Type A

Multiple Alleles• There are 3 or more forms of a gene for a trait. • Blood type is an example. • Hair color is another example

Polygenic Inheritance

• A trait produced from 2 or more genes. – Examples: Skin color, fur color, hair color, height.

Sex-Linked Traits/ Disorders

• Female: XX Male: XY • Genetic disorders are typically on the X

chromosome. • Males only need one affected X to express the

disorder. • Females typically carry these disorders and

males tend to express them if they receive the affected “X” from their mother or father.

Sex-Linked Punnett

In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males will either have the disease or not (but they won’t ever be carriers –why?)

Set up a cross between a man who is a hemophiliac and a woman who is a carrier. Determine the probability of their children getting the disease.

Xh Y

XH

Xh

XH Xh

Xh Xh

XH Y

Xh Y

50% chance a malewill get the disease; 50% chance a femalewill get the disease.

We Do… Small Group Practice Problems – Left Side

1. A black (B) fish which is homozygous dominant mates with a white (b) fish which homozygous recessive. This trait shows incomplete dominance. What is the genotype and phenotype of the F1 generation?

Day 2 Small Group Practice Problems – Left Side

3. A black (B) fish which is homozygous dominant mates with a white (b) fish which homozygous recessive. This trait shows codominance. What is the genotype and phenotype of the F1 generation?

In certain species of pansies, white flowers and red flowers are codominant alleles. When a white pansy and a red pansy are crossed, what is the expected flower color?a. pink flowerb. red flowerc. white flowerd. red and white spotted flower

Exit Slip

In fruit flies the trait of red eyes (R) is dominant to white eyes (r). The trait is carried on the X chromosome.

Based on the Punnett square above, which statement best describes the eye color of the fruit fly offspring?

a. There is a 50% probability that female offspring will have red eyes.b. There is a 75% probability that female offspring will have red eyes.c. There is a 50% probability that male offspring will have red eyes.d. There is a 75% probability that male offspring will have red eyes.

It was suspected that two newborn babies had been exchanged in a hospital. Mr. and Ms. Jones received baby #1 and Mr. and Ms. Simms received baby #2. Blood typing on the parents and the babies are shown in the following table.

Based on these blood typing results, were baby #1 and baby#2 switched at birth?A. No; it is impossible for Mr. and Ms. Jones to have a baby with a Type O blood type.B. Yes; it is impossible for Mr. and Ms. Jones to have a baby with a Type A blood type.C. No; it is impossible for Mr. and Ms. Simms to have a baby with a Type A blood type.D. Yes; it is impossible for Mr. and Ms. Simms to have a baby with a Type O blood type.

Scenario A

In a rabbit where its brown colored coat is controlled by a single gene, which has four alleles.

Scenario B

In a human where its green eye color is controlled by three genes.

Scenario C

In a tan colored chick, whose mother is has brown feathers and father has white feathers.

Scenario D

In a black and white spotted chick, whose mother has black feathers and father has white feathers.

There are many exceptions to Mendelian inheritance rules. The table below shows four situations which illustrate these exceptions.

Using your knowledge of genetics, which scenario would demonstrate polygenic inheritance? a. Scenario A c. Scenario C b. Scenario B d. Scenario D

In certain species of pansies, white flowers and red flowers are codominant alleles. When a white pansy and a red pansy are crossed, what is the expected flower color?a. pink flowerb. red flowerc. white flowerd. red and white spotted flower

In fruit flies the trait of red eyes (R) is dominant to white eyes (r). The trait is carried on the X chromosome.

Based on the Punnett square above, which statement best describes the eye color of the fruit fly offspring?

a. There is a 50% probability that female offspring will have red eyes.b. There is a 75% probability that female offspring will have red eyes.c. There is a 50% probability that male offspring will have red eyes.d. There is a 75% probability that male offspring will have red eyes.

It was suspected that two newborn babies had been exchanged in a hospital. Mr. and Ms. Jones received baby #1 and Mr. and Ms. Simms received baby #2. Blood typing on the parents and the babies are shown in the following table.

Based on these blood typing results, were baby #1 and baby#2 switched at birth?A. No; it is impossible for Mr. and Ms. Jones to have a baby with a Type O blood type.B. Yes; it is impossible for Mr. and Ms. Jones to have a baby with a Type A blood type.C. No; it is impossible for Mr. and Ms. Simms to have a baby with a Type A blood type.D. Yes; it is impossible for Mr. and Ms. Simms to have a baby with a Type O blood type.

Scenario A

In a rabbit where its brown colored coat is controlled by a single gene, which has four alleles.

Scenario B

In a human where its green eye color is controlled by three genes.

Scenario C

In a tan colored chick, whose mother is has brown feathers and father has white feathers.

Scenario D

In a black and white spotted chick, whose mother has black feathers and father has white feathers.

There are many exceptions to Mendelian inheritance rules. The table below shows four situations which illustrate these exceptions.

Using your knowledge of genetics, which scenario would demonstrate polygenic inheritance? a. Scenario A c. Scenario C b. Scenario B d. Scenario D