L10 - linkage and chromosome mapping in eukaryotes

Question 1

how many combinations of chromosomes in gametes

Answer 1

2^23

Question 2

what is chiasma

Answer 2

recombination (crossing over) between homologous chromosomes in meiosis
(identical genes but possible different alleles)

Question 3

what ‘principle’ is used to create a genetic map

Answer 3

the no. of progeny produced by these recombination’s (chiasma) can be used to calculate the distance between genes on the same chromosome

Question 4

what does it mean if genes are close together on a chromosome

Answer 4

they are more likely to be inherited together

Question 5

define recombination frequency

Answer 5

proportional to the physical distance between two genes (loci)

Question 6

what is a test cross

Answer 6

deliberately crossing parents

Question 7

what types of genotypes have to be crossed to create a linkage map?

Answer 7

homozygous wild type X homozygous mutant
|
heterozygous (F1) X homozygous mutant 
| 
these progeny (F2) studied

Question 8

what is the expected ratio of a dihybrid testcross if there was no recombination?

Answer 8

1:1:1:1

Question 9

explain how a dihybrid cross can create a linkage map

Answer 9

F2 generation is studied

add up BOTH recombinant progeny
—————————————————– x 100
total progeny

Question 10

in a trihybrid cross how do you determine which gene is in the middle?

Answer 10

find the class with the least progeny (this is the double cross) 
whatever gene looks to be the odd one out (XYX xyz) is the gene in the middle

Question 11

why is mapping chromosomes difficult in humans?

Answer 11

1. cant cross humans

2. humans don’t produce 100s of progeny