Lecture 8 Flashcards
Mendelian genetics
demonstrates how genes segregate into gametes
what happens when genes do not obey the law of independent assortment
expected ratio does not match the observed ratio
fruit flies
a model organism for genetics
-lots of easy to se phenotypes
-short reproductive cycles
-wild type= normal phenotype in natural populations
-mutant= alternative alleles
Thomas Hunt Morgan
established the fly room at Columbia university where he carried out breeding experiments to understand inheritance
he suggested unexpected ratios can be explained by the fact genes may be located on the same chromosome
linkage
genes on the same chromosomes
recombinant
non parental type offspring
Morgan proposed recombinants resulted from physical exchange of genes between chromosomes (crossing over)
Recombination frequency
recombinants/ total offspring x100
recombinant frequency of a pair of linked genes
always the same
Alfred Sturtevant
predicted that the recombinant frequency was proportional to the distance between genes
larger distance= more chance of crossing over = higher % recombinants
calculating genetic distance
same as recombination frequency but with the units centiMorgans
Genetic maps
by carrying out 3 factor crosses and calculating the genetic distances from the % recombinants a genetic map can be made
why genetic distance effects crossing over
if genes are further apart on a chromosome its likely that two crossing overs will occur in between them
types of maps
Genetic maps- made from linkage
Physical map- from DNA sequencing and other methods
these are not always identical as the frequency of crossing over can vary along the chromosome
what can affect frequency of crossing over
reduced near the centromere
high in hot-spots of recombination
