linkage, recombination, and crossing over

Question 1

observations about genes that do not segregate randomly

Answer 1

Morgan: genes are linked if present on the same chromosome, the divergent from linkage is called recombination
Sturtevant: the frequency of recombination reflects distance between genes

Question 2

pairs of genes that don’t segregate independently example: Red and white flower cross

Answer 2

• genes are on the same chromosome and get inherited together
• new combinations of colours and seeds are formed as result of crossing over
• shows 24:1:1:7 phenotypic ratio

Question 3

possible explanation for new combinations in phenotype

Answer 3

• A and B genes are linked on the same chromosome
• AB and ab alleles segregate as linked genes
• some infrequent exchange between chromosomes that harbor AB and ab
• known as recombination

Question 4

crossing over vs recombination

Answer 4

crossing over: exchange of genetic material between alleles on the same chromosome
recombination: generation of new allele combination on homologous chromosomes (not parental)
- don’t necessarily happen together

Question 5

what makes genes more likely to cross over

Answer 5

the closer they are on a chromosome

Question 6

what makes genes more likely to recombine

Answer 6

the farther apart they are on a chromosome

Question 7

frequency of recombination

Answer 7

recombinant / (recombinant x parental)

Question 8

what will frequencies show if genes are not linked

Answer 8

in F1 you will get classes of offspring with equal frequencies (1/4)

Question 9

recombinant gametes

Answer 9

• parental genotype doesn’t have this combination
• very minor in the gamete pool
• found in equal proportions

Question 10

homologous recombination

Answer 10

• occurs during prophase I of meiosis
• a tetrad or bivalent is formed
• occurs at the chiasma

Question 11

true or false - multiple crossovers can be simultaneously taking place over the same tetrad

Answer 11

true