Lecture 25: Sex-linkage, and recombination of linked genes

Question 1

In birds, females are _____ whereas males are ______. This means that….

Answer 1

• Heterogametic
• Homogametic
• Females have ZW
• Males have ZZ

Question 2

In Drosophila, an X chromosome with allele for white eye…

Answer 2

• Makes the male white-eyed hemizygous

- Also none of the males would be able to have white eyes because they only get the Y chromosome from dad

Question 3

Red-Green colour blindness is an _ linked trait. So if dad had the allele, (daughters/sons) carriers would be and (daughters/sons) normal.

Answer 3

• X
• Daughters
• Sons

Question 4

How many genes are there in humans?

Answer 4

• 20 000

Question 5

How many chromosomes are there in humans?

Answer 5

• 23 pairs

Question 6

There are about ____ genes per chromosome

Answer 6

• 1000

Question 7

In drosophila, a heterozygote female and a homozygote recessive male don’t give a 1:1:1:1 ratio like Mendel expected. Instead….

Answer 7

• Many turned out to look like mum or dad

- With only a little number of “recombinant types”

Question 8

Why does crossing over during meiosis occur?

Answer 8

• Evolution

Question 9

Recombination frequency formula…

Answer 9

• Combined/Total

Question 10

The smaller the distance between two genes - the ____ likely a chiasma will be formed between them

Answer 10

• Less

Question 11

What is a centimorgan? (cM)

Answer 11

• 100 x recombination frequency