QUIZ 2

Question 1

An embryo inherits t and B alleles from the sperm, and inherits T and b alleles from the oocyte. The T and B genes are on the same chromosomes. Correctly write the genotype of the embryo.

Answer 1

tB/Tb

Question 2

using the letter H for one gene and the letter G for the second gene. correctly write the genotypes (using ; and / symbols) of a cross btwn 2 dihybrids. What proportion of the offspring of that cross do you expect to show both dominant phenotypes?

Answer 2

9/16

Question 3

using the letter H for one gene and the letter G for the second gene, correctly write the genotypes (using ; and / symbols) of a cross btwn 2 dihybrids. What proportion of the offspring of that cross do you expect to show 1 dominant trait and 1 recessive trait?

Answer 3

6/16

probability that offspring G/-;h/h = 3/16
probability that offspring g/g;H/- = 3/16
mutually exclusive events (dominant for G, recessive for H or G, dominant for H), use law of the sum
3/16 + 3/16 = 6/16

Question 4

This question provides info for both Qs 4 and 5. Tay-Sachs is a recessive lethal disease. It leads to neurological deterioration soon after birth an death usually by the age of 4. this disease is rare in the population overall but is found at relatively high frequency in Ashkenazi Jews from Central Europe. A woman (Mary) whose brother had the disease is trying to determine the probability that she and her husband could have an affected child. What is the probability that Mary is a carrier? Hint: Draw the pedigree for mary’s family to help you with this question and remember that people who have the disease do not become adults

Answer 4

2/3

Question 5

The allele that can result in Tay-Sachs is also present in mary’s husband/s family. Specifically, his mother’s sister (his maternal aunt) died of the disease at an early age. What is the probability that Mary and her husband could have an affected child?

Answer 5

1/18

probability that mary is a carrier = 2/3
probability that mary gives recessive allele = 1/2
probability that Mary’s husband’s mother is a carrier = 2/3
probability that Mary’s husband’s mother gives recessive allele= 1/2
probability that mary’s husband gives recessive allele = 1/2
all independent events, use the law of the produce

2/3 x 1/2 x 2/3 x 1/2 x 1/2 = 4/72 = 1/18

Question 6

For Q6 & 7, chickens normally have neck feathers. An allele has a dominant recessive effect on viability, causing the chickens to die early. Let N be the naked neck allele and n the wildtype, neck feather allele. male chickens with naked necks are crossed to females with normal neck feathers. Write the genotypes of those chickens. Among te F1 progeny, what % naked neck vs normal neck feather adult chickens do you expect?

Answer 6

50% naked neck, 50% normal neck

Question 7

Male chickens with naked necks are crossed to females with naked necks. Write the genotypes of those chickens. Among the F1 progeny, what % naked neck vs normal neck feather adult chickens do you expect?

Answer 7

50% naked neck, 50% normal neck

Question 8

Male chickens with naked necks are crossed to females with naked necks. write the genotypes of those chickens. Among the F1 progeny, what % naked neck vs normal neck feather adult chickens do you expect?

Answer 8

66% naked neck, 33% normal neck

Question 9

codominance would be suggested by which of the following phenotypic ratios?

Answer 9

1:2:1

Question 10

Sickle cell anemia is a recessive trait in humans. A male with sickle cell anemia marries a female who is a carrier (ex: heterozygous for a mutant allele). What is the probability that their first 3 children will NOT have sickle cell anemia?

Answer 10

1/8

probability that dad gives recessive allele = 1
probability that mom gives dominant allele = 1/2
each child = independent event, use law of the product

1 x 1/2 x 1 x 1/2 x 1 x 1/2 = 1/8