X Linked Traits And Recombination

Question 1

What are sex linked traits

Answer 1

Traits involving genes on the sex chromosomes (X and Y) rather than autosomes
Subsequently, inheritance patterns differ between males (XY) and females (XX)
E.g. haemophilia - red/green colour blindness

Question 2

Outline the inheritance of eye colour in the Drosophilia

Answer 2

Eye colour is a sex-linked trait in drosophilia (gene at locus on female X chromosome)
Homozygous dominant ready eye female mating with hemizygous recessive white eyes male produces heterozygous daughters, and hemizygous dominant males

Homozygous recessive white eye female mating with hemizygous dominant red eye male produces heterozygous daughters, and hemizygous recessive males

Question 3

Outline the cross between a recessive male and a homozygous dominant female

Answer 3

Father with trait will transmit to all daughters but no sons. Daughters will be carriers, but display normal phenotype

Question 4

Outline the cross between a homozygous female and a dominant male

Answer 4

Mutation will be passed to half of the sons and half of the daughters. Sons with mutation will display mutated phenotype. Daughters will be carriers

Question 5

Outline the cross between a homozygous female and a recessive male

Answer 5

There is a 50% chance that each offspring will have the trait. Daughters without the trait will be carriers. Sons without the trait will be free of mutated allele

Question 6

How many genes are there in humans

Answer 6

Around 20,000

Question 7

How many chromosomes are there in humans

Answer 7

23 pairs

Question 8

How are linked genes inherited

Answer 8

Linked genes show bias towards parental genotypes

Question 9

How can order and location of genes within a chromosome be determined

Answer 9

Using recombinant frequencies

Question 10

What is recombination frequency

Answer 10

The proportion of recombinant gametes is termed the recombination frequency

Question 11

Outline recombination for linked genes

Answer 11

The smaller the distance between the 2 genes on a chromosome, the less likely a chiasmata to form between them
Distant (unlinked) genes have recombination frequencies around 50%
Close genes have recombination frequencies of 0-50%
There is a linear relationship between distance and recombination frequency