L5

Question 1

What did Morgan propose which relates to one of the causes of variation in the progeny chromosomes

Answer 1

Morgan proposed that it was at the chiasmata seen at meiosis joining homologue chromosomes that were the sites of recombination and that genes on the same pair of chromosome show linkage; CHIASMA FORMATION LEADS TO MEIOTIC RECOMBINATIONS

Question 2

What is interchromosomal recombination

Answer 2

recombination, where genes are on different chromosomes, this results in equal frequencies (50%) of recombinant and parental classes; 1:1:1:1 ratio (2 genes of interest are on different chromosomes)

Question 3

what is intrachromosomal recombination

Answer 3

mediated by chiasma formation where the recombinant classes usually much less frequent; gene of interest linked on the same chromosome (will not behave independently of each other); test cross progeny deviate from 1:1:1:1 ratio; parental type result more; recombinant type result less

Question 4

what do chromosome maps represent

Answer 4

linear order of genes on the chromosome

Question 5

what is a common way of deriving a chromosome map

Answer 5

using the recombination frequency between linked genes, since this differs between different pairs of genes, this sort of map is called a linkage map

Question 6

true or false, crossovers between genes are relatively rare events

Answer 6

true

Question 7

true or false, genes that are closer together (tightly linked) will recombine less often than genes that are further apart

Answer 7

true

Question 8

what does it mean when a pair of genes show 10% recombination

Answer 8

means that these are 10 map units (mu) or centimorgans (cM) apart

Question 9

true or false, linked genes are on the same chromosome

Answer 9

true

Question 10

when does the chiasma form according to Morgan

Answer 10

during zygotene/ pachytene of meiotic prophase 1

Question 11

what is the equation for the frequency of recombination

Answer 11

total number of recombinants/ total number of progeny

Question 12

what does the frequency of recombination tell us

Answer 12

tells us how many map units these genes are from each other; shows us that these individuals have …% recombinants

Question 13

true or false, the farther apart the genes are the closer the recombinant frequency get to close to 50%

Answer 13

true

Question 14

true or false, recombinant frequencies cannot be greater than 50%

Answer 14

true

Question 15

who were the pioneers of linkage maps

Answer 15

Sturtevant and Morgan

Question 16

What did Sturtevant and Morgan find out

Answer 16

that different pairs of genes showed different amounts of recombination

Question 17

true or false, relative positions and physical positions are not necessarily the same

Answer 17

true

Question 18

true or false, map units are additive

Answer 18

true

Question 19

What does the linear map correspond to

Answer 19

correspond to the linear arrangement of genes on the single DNA molecule that makes up a chromosome

Question 20

what are the progeny of test cross ratio:

• independent assortment
• complete linkage
• linkage with some crossing over

Answer 20

• inpendent assortment: 1/4 :1/4 : 1/4 : 1/4 (1:1:1:1)
• complete linkage: 1/2: 1/2
• linkage with some crossing over: > 50% parental type and < 50% recombinant type

Question 21

in chromosomes, longer regions produce more crossing overs than shorter regions; true or false

Answer 21

true