Lecture 20 - x-linked traits and recombination

Question 1

Define the terms carrier and hemizygous.

Answer 1

carrier: individual who has a recessive trait but does not show it in their phenotype
hemizygous: an individual who has X and Y sex chromosomes

Question 2

If you cross a homozygous red eyed female with a hemizygous white eyed male, what are the sex, genotypes and phenotypes of the offspring?

Answer 2

all daughters are red eyed heterozygous

all sons are red eyed hemizygotes

Question 3

If you cross a homozygous white eyed female with a hemizygous red eyed male, what are the sex, genotypes and phenotypes of the offspring?

Answer 3

all daughters are red eyed heterozygous

all sons are white eyed hemizygotes

Question 4

Why are there no carrier males?

Answer 4

males only have 1 X chromosomes so they can not ‘carry’ because a single recessive X chromosome will case the disease

Question 5

What does it mean when we talk about linked genes?

Answer 5

when genes are close together on the same chromosome so they are less likely to separate during crossing over

Question 6

How does linked genes affect males and females differently.

Answer 6

males are more likely to be affected by x-linked problems because they only have 1 X-chromosome so 1 copy of the recessive allele can cause problems whereas females need 2 recessive alleles to be affected

Question 7

How are linked genes inherited?

Answer 7

Linked genes show biases towards parental genotypes