X-linked Trairs And Recombination

Question 1

Sex - linked traits

Answer 1

Involving genes on the sex chromosome (X or Y) - rather then autosomes
- as a result their inheritance patterns differ between males (XY) and females (XX)

E.g haemophilia and red green colour blindness

Question 2

Sex determination

Answer 2

• X.Y determine the sex of an individual

Question 3

Sex linked traits results

Answer 3

Father w trait will transmit the mutant allele to all daughters but no sons. When the mother is homozygote dominant, the daughters will have the normal phenotype but will be carries of the mutation

A carrier who mates with a normal male will pass the mutation to half her sons and half her daughters. The sons will have the disorder. The daughters will be carriers.

A carrier mates with a male with the trait, there is a 50% chance that each that each child will have the trait. Daughters who do not have the trait will be carries. Males without the trait will be completely free of the allele.

Question 4

How many genes in humans

Answer 4

20,000

Question 5

How many chromosomes in humans and how many linked genes per chromosome

Answer 5

• 23 pairs
• 1000 linked genes per chromosomes

Question 6

How Arte linked genes inherited

Answer 6

• linked genes show biases towards parental genotypes

Question 7

How can you determine the order and location of genes within a chromosome

Answer 7

• by using recombination frequencies

Question 8

Expected phenotypic ratio when crossing a heterozygote and a homozygote ressesive

Answer 8

1:1:1:1

These are the results expected from mendels 2nd Law (independent assortment of alleles) - not linked genes

Question 9

What happens when two genes are linked on the same chromosome during a test cross

Answer 9

• the two genes do not sort independently
• this results in a much higher ration of parental types to recombinant types (obtained by morgan)

Question 10

When genes are linked why don’t all gametes have a rental phenotypes?

Answer 10

• crossing over during prophase 1 explains recombination
• two chromatids of a tetrad (one from each pair) cross over at random points and swap genetic material
• this is a simple cross where only one chiasma has formed
• the proportial of recombinant gametes is termed the recomimbination frequency
• number of recombinant is determinant on how close genes are

Question 11

How to calculate the recombination frequency

Answer 11

Recombinants total divided by all recombinants and parental phynotypyes
- shows how many of the gametes contain a chromosome that has formed a chiasmata between the two genes

Question 12

What decreases the chances of a chaismata being formed between two alleles

Answer 12

• the distance between the,
• distant (unlinked) genres have recombination frequencies of 50% - half recombinant and half parental
• close genes have recomibmination frequencies of 0-50%
• there is a line at relationship between distance and recombination frequency