1. Incomplete Dominance, Codominance and Sex-Linked Traits

2. 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.

3. 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.

4. Interactive Journal Entry “Patterns of Inheritance SC.912.L.16.2”
Left Side
Right Side
Complex Patterns of Inheritance Notes (Note: when copying reduce size to 67% to fit in composition books; students can staple/tape it in landscape format)
“We Do” Complex Patterns of Inheritance Small Group Practice

5. Complex Patterns of Inheritance
Wait! This should have been RED, but incomplete dominance makes it pink
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

6. Incomplete Dominance Cross
RR: red
Rr: pink
Rr: white
R r
A heterozygous flower
(Rr) Is crossed with a homozygous dominant. What are the genotypes and phenotypes of F1?
R R RR Rr RR Rr
Genotypes: 50% RR; 50% Rr Phenotypes 50% red; 50% pink

7. 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.

8. 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
50% IA IB
50% IA IA
50% Type AB 50% Type A
IA IB
IA IB

9. Multiple Alleles There are 3 or more forms of a gene for a trait.
Blood type is an example.
Hair color is another example
Review that there are 3 or more forms of blood types. Review that 3 or more alleles control the color of a persons hair.

10. Polygenic Inheritance
A trait produced from 2 or more genes.
Examples: Skin color, fur color, hair color, height.
Emphasize the term “Poly” means many and genic is derived from the term “gene” – thus the definition a trait produced from two or more genes.

11. 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.

12. Sex-Linked Punnett Xh Y XH XH Xh XH Y Xh Xh Xh Xh Y
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
50% chance a male will get the disease; 50% chance a female will get the disease. XH Xh
XH Xh
XH Y
Xh Xh
Xh Y

13. We Do… Small Group Practice Problems – Left Side
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?

14. 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?

15. Exit Slip
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 flower b. red flower c. white flower d. red and white spotted flower

16. In fruit flies the trait of red eyes (R) is dominant to white eyes (r)
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.

17. 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.

18. situations which illustrate these exceptions.
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
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.

19. 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 flower b. red flower c. white flower d. red and white spotted flower

20. In fruit flies the trait of red eyes (R) is dominant to white eyes (r)
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.

21. 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.

22. situations which illustrate these exceptions.
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
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.