Congential Abnormalities And Genetic Linkage

Question 1

What did Morgan do?

Answer 1

He was the first to associate a specific gene with a specific chromosome

Question 2

Describe Morgans sex linkage hypothesis theory

Answer 2

Observations only make sense if the eye colour gene locus is on the X chromosome
Sex in drosophillia is determined by XY
Males are ‘hemizygous’ meaning it they only possess ONE allele of any sex- linked gene

Question 3

Describe genetic linkage

Answer 3

Genes on the same chromosome exists on the same strand of DNA and genes on any given chromosome are physically linked
If genes are very close they can be linked as a block
When genes are inherited as a linkage group they do not behave in the Mendelian fashion, they assort randomly

Question 4

Describe crossing over

Answer 4

Occurs during prophase of meiosis 1
Homologous portions of 2 non-sister chromatids exchange places
This gives rise the individual chromosomes that contain both maternal and paternal DNA

Question 5

How do you calculate recombination frequency?

Answer 5

RF= (number of recombinants/total number of offspring) x 100

Question 6

What does the RF value tell you?

Answer 6

If its 50%- Genes are unlinked
If its near 0- Genes are ver tightly linked (very close together)

Question 7

What did Sturtevant do?

Answer 7

Devised the 1st gene maps, high were a sequence of genes along a chromosome
He realised that you can work out how far apart genes are on a chromosome

Question 8

What did Sturtevant assume?

Answer 8

There’s an equal chance of crossing over along a length of a chromosome
Therefore a high RF value can be predicted for genes far apart and a low RF value can be predicted for genes close together

Question 9

Describe the mechanism of genetic recombination

Answer 9

Within the tetrad, non-sister chromatids physically exchange DNA at the chiasma forming a cross-linke configuration
This causes tension resulting in DNA duplexes breaking and rejoining crosswise