Genetic Linkage and Recombination

Boveri/Sutton Theory (Chromosome Theory of Inheritance)

explains the underlying mechanism of Mendelian genetics by combining chromosomes with the paired factor postulate by Mendel

homologous chromosomes (one from each parent)

genetic linkage

if alleles are on the same chromosome and close enough together, they will sort together

Bateson, Saunders, and Punnet

used dihybrid crosses looking at flower color and pollen shape

observed phenotypes that were higher than the rest in the F2 generation that were the same as the parental generation

they got a completely different ratio in F2 generation than what Mendel said→ genetic linkage is the cause

Bateson, Saunders, and Punnet hypothesis

there is a connection between the parental alleles for flower color and pollen shape and the results of this connection resulted in deviation from Independent Assortment

sex linkage

genes on a sex chromosome

what gene is a sex factor in fruit flies?

eye color

Linkage

when two (or more) genes are inherited together

-loci on the same chromosome

-loci are located close together and travel as group during meiosis

-DO NOT assort independently

Complete Linakge

loci are very close together on the chromosome and crossover does NOT occur

2 out of the 4 expected phenotypes do NOT show up

crossing over

exchange of genetic information between non-sister chromatids

happens during prophase I

configuration

arrangement of alleles on homologous chromosomes

couple (cis-configuration)

normal (WT) alleles on one chromosomes, mutant alleles on the other

repulsed (trans-configuration)

each chromosome contains one normal (WT) allele and one mutant

what happens when two cis homologous chromosomes are crossed in complete linkage?

you will only see the parents in the F2 generation, not the trans configuration because complete linkage has no crossover

what do you see when trans chromosomes are crossed in complete linkage?

you will only see the recombinants (which are the parents) in the F2 generation, you will not see the cis configurations

what does it mean if you see parental and recombinants in the F2 generation?

you are no longer doing complete linkage because complete linkage gives you one or the other

what can you conclude if there are more parental offspring than recombinant offspring?

the parents are in the cis or coupled configuration

calculating recombination frequency

RF= number of recombinant progent/total number of progeny

recombination

exchange of unique genetic material between non-sister chromatids during meiosis

chisamata

the point of contact, the physical link, between two chromatids belonging to homologous chromosomes

incomplete linkage

recombination occurs between two loci

the amount of (or frequency) of recombination depends on how far apart the two loci are

why are there usually lower numbers of recombinants in offspring?

it takes energy to Recombinate and cells dont want to use that energy

what leads to a decreased RF?

decreased space between the alleles on the chromosome

they wont have a lot of space to recombine

what leads to an increased RF?

more space between the alleles on a chromosome

genetic mapping

methods used to identify the distance between genes

if a gene’s loci had a specific place on a chromosome, then the distance between any two genes was a measurable fixed number

distance of Gene A to Gene C

—-A———B————C—-

(gene A to gene B) + (gene B to gene C)

what does a RF of 50% tell you?

you have independent assortment ( then genes are too far apart from each other to recombinate)

double crossover between two loci

no change

double crossover including two loci

recombination

double crossover between three loci

recombination