Study Guide 5 Pedigrees

Question 1

The pedigree below shows the passing on of straight
thumbs (recessive) and Hitchhiker’s thumb (dominant).
Shaded shapes mean the person has a straight
thumb. Hitchhiker’s thumb is NOT an X-linked trait

a. Is individual IV-2 heterozygous or homozygous
for this trait? Explain your answer.

Answer 1

We cannot be certain, they could be either. Given that the parents are both heterozygous, and IV-2 does have hitchhiker’s thumb, they have a 33% chance of being HH and a 66% chance of being Hh

Question 2

The pedigree below shows the passing on of straight
thumbs (recessive) and Hitchhiker’s thumb (dominant).
Shaded shapes mean the person has a straight
thumb. Hitchhiker’s thumb is NOT an X-linked trait

b. Why is there a double line (as opposed to a single line) between individuals III-1 and III-2? (Hint: what is different about this pairing than the other matings shown on the pedigree, represented by a single line)

Answer 2

The double line represents inbreeding. Persons III-1 and III-2 are first cousins

Question 3

The pedigree below shows the passing on of straight
thumbs (recessive) and Hitchhiker’s thumb (dominant).
Shaded shapes mean the person has a straight thumb. Hitchhiker’s thumb is NOT an X-linked trait

c. In this pedigree, straight thumbs is not a very common phenotype. Propose an explanation for why the only individuals on this pedigree that have the recessive phenotype are the offspring of III-1 and III-2 and not any of the other matings shown on the pedigree

Answer 3

Related individuals are more likely to carry the same recessive alleles. That means their offspring are more likely to inherit the recessive allele from both parents and express the recessive phenotype

Question 4

Domestication of animals frequently results in predictable changes in physical traits that are not directly being selected; examples include floppy ears, short/curly tails, white face markings, curly hair, etc. Describe two genetic mechanisms that might explain why these traits are consistently more common in domesticated animals than their wild relatives.

Answer 4

It is possible these genes are linked. If genes contributing to tameness are on the same chromosomes as genes relating to floppy ears, curly tails, etc, then breeding for tameness will also increase these other traits in the population. It is also possible that the genes for tameness are pleiotropic and also impact these physical traits directly

Question 5

The pedigree below shows the inheritance of alkaptonuria, a biochemical disorder. This is NOT an X-linked trait. Males are shown with boxes and females with circles, purple shapes represent individuals with alkaptonuria

a. Is this condition caused by a dominant allele or a recessive allele? Provide evidence from the pedigree to support your answer.

Answer 5

Recessive. Carla has the condition and neither of her parents do (they must be heterozygous and she inherited the recessive alleles)

Question 6

The pedigree below shows the inheritance of alkaptonuria, a biochemical disorder. This is NOT an X-linked trait. Males are shown with boxes and females with circles, purple shapes represent individuals with alkaptonuria

b. Which individuals’ genotypes can be deduced from this pedigree? Label all the persons whose genotype can be determined. Which individuals’ genotypes cannot be determined?

Answer 6

All purple individuals are aa.
Ann, Michael, George, Sam, Daniel, Alan must be Aa.
Sandra, Tina, Christopher are A_, we cannot determine the second allele with certainty