BIOL 2500 - Topic 6 (part 4)

Sturtevant

Morgan’s undergraduate student who produced the first linkage map and is credited for discovering that we can use recombination frequencies to map genes

Smaller recombination frequencies =

Genes are closer together

Larger recombination frequencies =

Genes are further apart

Linkage maps

It shows the relative position of traits, based on how often cross over occurs

Units used for linkage maps

1 map unit (m.u.) = 1% recombination frequency

Maps are ________

Additive

Arrangement of genes

They are arranged in a linear order

What is the problem with using recombination frequency to produce linkage maps

You get multiple possible maps on the possible order of the genes

What can we do if we know the recombination frequency between two genes

We can predict the phenotypes of parentals and recombinants

If Morgan’s data show 11% recombinance, what is the recombination frequency of the parentals

100 - 11 = 89%

Therefore, each parental phenotype would be 44.5%

Proportion of parental to recombinant chromosomes depends on…

The frequency of crossing-over

Recombination frequency (definition)

The probability that we get a crossing over event between syntenic genes

Recombination frequency formula

r = number of recombinant offspring / total number of offspring

Interpreting recombination frequency in 2 ways

1.) Crossing over occurs at a higher rate between genes that are further apart than closer together OR

2.) Linked genes with higher recombinant frequencies are more distant from each other, than other linked genes with lower recombinant frequencies

Linked genes in humans

1.) Hair and eye colour

2.) Hereditary elliptocytosis

Hereditary elliptocytosis

1.) An autosomal dominant trait that results in elliptical RBCs instead of biconcave RBCs

2.) It has variable penetrance and expressivity

3.) It confers some resistance to malaria

Gene for hereditary elliptocytosis is close to…

It is close to the gene that determines your Rh factor, being only 4 map units away