Worksheet for problem set #10 March 27, 2006

1. Reciprocal translocation: the mutual exchange of segments between two non-homologous chromosomes.

There are three ways the chromosome pairs segregate (recall that in meiosis, normally homologous centromeres move toward OPPOSITE poles at Anaphase I).

Adjacent 1 segregation occurs when adjacent chromosomes with nonhomologous centromeres move to daughter cells (i.e. 1 and 2 above)- resulting in a duplication of one terminal segment, and a deficiency of the other.

Adjacent 2 segregation occurs when adjacent chromosomes with homologous centromeres move to daughter cells (i.e. 1 and 3 above)- resulting in a duplication of one proximal segment, and a deficiency in the other.

Alternate segregation occurs when alternate chromosomes with nonhomologous centromeres move to daughter cells (i.e. 1 and 4 above)- resulting in half of the gametes receiving both parts of the reciprocal translocation, and half receiving normal chromosomes.

Note that only alternate segregation leads to balanced gametes!

Population genetics

By convention A=p and a=q

To calculate allele frequency: p+q=1

If p+q=1, then p=1-q and q=1-p

Using p and q language

p2=the frequency of the AA genotype

q2=the frequency of the aa genotype

2pq=the frequency of the Aa genotype

With our 2 allele system, the genotype percentages add up to 100%, so we can say

p2+2pq+q2=1 (Hardy-Weinberg equation)

This is the same as saying AA+Aa+aa=1

fitness: relative reproductive success of a genotype in a population, i.e. the fitness is the RS of one genotype compared with the RS of other genotypes within the population.

Fitness ranges from 0-1.

To calculate fitness for each genotype, take the average number of offspring produced by a genotype and divide it by the mean number of offspring produced by the most prolific genotype.