Linkage Mapping BSCI222

recombinant gametes

gametes with new combinations of alleles from crossing over

in meiosis what percent of gametes will be recombinant and parental?

50/50

complete linkage genes

crossing over never happens between alleles, always inherited together

incomplete linkage genes

crossing over sometimes happens between alleles, sometimes inherited together

unlinked genes

crossing over always occurs between alleles, never inherited together

OR two genes are on different chromosomes and independently assort during meiosis I

linked in repulsion

Ab/aB

- dominant alleles on different chromosomes

linked in coupling

AB/ab

- dominant alleles on one chromosome

what type of cross is preformed to test recombinant frequency?

test cross (heterozygous x homo. recessive)

if alleles are incompletely linked what percent of gametes will be recombinant?

<50%

how to calculate recombination frequency (RF)?

# recombinants / # progeny

recombination frequency

the percentage of recombinant offspring among the total

how to convert recombination frequency into centiMorgans (cM)?

0.__ -> % -> cM

example:

RF = 0.05 = 5% = 5cM

how to tell if a gene is linked using cM?

<50 cM apart

linkage group

represents all genes which may be linked in a part of or all of a chromosome

>50 cM

how to calculate recombination frequency when given cM

cM -> % -> 0.__ proportion

- even if genes are linked, still do this since there is a small change they won't be inherited together

genetic map

uses cM in linkage group to map chromosomes

cytogenetic map

uses chromosome banding pattern to map chromosomes

physical map

uses units of nucleotide base pairs to map chromosomes

wildtype vs non-wildtype

wildtype (+) = most common phenotype

non-wildtype (-) = less common phenotype

single cross over

single cross over between 3 alleles

double cross over

double cross over between 3 alleles

how to identify parental genotypes in a 3 point cross?

2 highest numbers of genotypes produced

how to identify double cross over recombinants in a 3 point cross?

2 lowest numbers of genotypes produced

how to identify which allele is in the middle in a 3 point cross?

compare parental and double cross over individuals genotypes, one different allele is the one in the middle

formula for recombination frequency in a 3 point cross

sum of (DR + genotypes from that point cross) / total progeny = probability which can be converted to centimorgans

interference

when one recombination event affects another

formula for interference

1 - (Observed DR / (total progeny P(cross over at point) P(cross over at other point))