BIOL239 Lecture Notes - Lecture 8: Meiosis, Chromosome, Genotype
Set 8: Linkage and Recombination
●Some genes on the same chromosome assort together more often than not
●In dihybrid crosses, departures from a 1:1:1:1 genotypic ratio of F1 gametes indicates that
the two genes are on the same chromosome – not completely independent of each other;
can see this in F2 offspring
oThey are in close proximity to one another and therefore tend to assort together –
genetically linked
oSome genes are more closely linked than others
●Parental class – phenotype of P generation (not parents of F2)
●When genes are linked, parental combinations (more P features expressed) outnumber
recombinant types Drosophila
– model for genetics
o in testcross…
o 82% similar to either one of the parents (ie. no crossover event)
o 18% result from recombinations (crossing over; nonparental; random and rare)
o therefore 9:3:3:1 ratio may not show; still we see dominance of parental
phenotypes
▪ knowing that some genes travel closely together
●~75% of known human disease genes have a similar gene match in Drosophila
genome
●~50% of fly protein sequences have a similar protein match in mammals
●Used in research on neurodegenerative diseases, e.g. Parkinson’s, Huntington,
Alzheimer’s; research on processes of aging, diabetes, drug abuse
●Only concerned with phenotype when classing
●Recombination between non-sister chromatids during meiosis (pachynema) gives rise to
recombinant phenotypes (trading of alleles)
●The number of individuals in the recombinant phenotype classes varies with how closely
the genes are linked
●The number in the recombinant class will always be less than the number in the parental
class if the genes are linked
Document Summary
Some genes on the same chromosome assort together more often than not. Parental class phenotype of p generation (not parents of f 2 ) When genes are linked, parental combinations (more p features expressed) outnumber recombinant types drosophila model for genetics o o o o in testcross . 82% similar to either one of the parents (ie. no crossover event) 18% result from recombinations (crossing over; nonparental; random and rare) therefore 9:3:3:1 ratio may not show; still we see dominance of parental phenotypes knowing that some genes travel closely together. ~75% of known human disease genes have a similar gene match in drosophila genome. ~50% of fly protein sequences have a similar protein match in mammals. Used in research on neurodegenerative diseases, e. g. parkinson"s, huntington, Alzheimer"s; research on processes of aging, diabetes, drug abuse. Recombination between non-sister chromatids during meiosis (pachynema) gives rise to recombinant phenotypes (trading of alleles)