linkage, recombination and deviations from mendelian ratios

sources of genetic variability

mutation, independent assortment, crossing over, random fertilisation

recombinant phenotype

combination of phenotypes differs from what is found in either parent

crossing over def

process of genetic recombination which gives rise to new combinations of linked genes

how and when does crossing over occur

occurs during pachytene phase in prophase 1 - starts with synapsis and a synaptonemal complex forming, homologous chromosomes are held together in the tetrad for crossing over

recombination frequency def

% of offpsring that inherit a combination of alleles which differ from either parent

recombination frequency formula

(no of recombinants/no of offspring) x 100

frequency for genes on different chromosome

50% parental, 50% recombinant

frequency for genes on the same chromosome

50%+ parental, 50%> recombinant - because crossing over happens at different locations in each meiosis

what do chromosome linkage maps show

locations of genes relative to each other on a chromosome

sex linkage

X and Y chromosomes are the sex chromosomes - Y chromosome doesn't have all the same genes that X does

incomplete dominance

dominant allele doesn't fully mask the effect of a recessive allele at the same locus - blended traits shows a diluted phenotype

codominance

where each allele affects phenotype in separate and distinguishable ways - no blending

pleitropy

a single gene has multiple effects on the phenotype

polygenic inheritance

a single trait is determined by multiple genes

epistasis

one gene masks or modifies the expression of another gene