Linkage QuestionsLinkage Questions

Chapter 6Chapter 6

Questions 1Questions 1 Genetic recombination occurs during crossing Genetic recombination occurs during crossing

over in Meiosis I. When two homologous over in Meiosis I. When two homologous chromosomes form chiasma genes from a chromosomes form chiasma genes from a paternal chromosome ay cross over to the paternal chromosome ay cross over to the maternal chromosomematernal chromosome

This involves physical breaking and This involves physical breaking and recombination of two chromosomesrecombination of two chromosomes

Recombination leads to new combinations of Recombination leads to new combinations of genes that will be included in gametesgenes that will be included in gametes

The increase in genetic variability insures the The increase in genetic variability insures the ability of organisms to adjust to the environment ability of organisms to adjust to the environment and thereby offers a better possibility of survival and thereby offers a better possibility of survival of the species.of the species.

Question1 ( con)Question1 ( con) The increase in genetic variability insures the The increase in genetic variability insures the

ability of organisms to adjust to the environment ability of organisms to adjust to the environment and thereby offers a better possibility of survival and thereby offers a better possibility of survival of the species.of the species.

This is reshuffling of the genes resulting in new This is reshuffling of the genes resulting in new combinationscombinations

Question 2Question 2

The cytological evidence for crossing The cytological evidence for crossing over is the presence of synaptinemal over is the presence of synaptinemal complexescomplexes

These are chromosomes connected These are chromosomes connected by chiasma undergoing cross oversby chiasma undergoing cross overs

Cross overs involves only two of the Cross overs involves only two of the four sister chromatidsfour sister chromatids

Questions 3Questions 3

More crossing over occurs between More crossing over occurs between more distantly related genesmore distantly related genes

Two genes that are at a distant have Two genes that are at a distant have space for their chromosome arms to space for their chromosome arms to cross and thereby insure the cross and thereby insure the possibility of genetic exchange possibility of genetic exchange between homologous chromosomesbetween homologous chromosomes

Question 5Question 5

Double cross overs are expected in Double cross overs are expected in lower frequencies becauselower frequencies because

Two genes must be exchanged Two genes must be exchanged simultaneouslysimultaneously

Cross over events on one Cross over events on one chromosome inhibit the cross over chromosome inhibit the cross over events on another chromosomeevents on another chromosome

Question 8Question 8

dp---------------------cl--------apdp---------------------cl--------ap

Question 9Question 9 a + b are on separate chromosomes – random a + b are on separate chromosomes – random

assortment takes place and the gametes are assortment takes place and the gametes are formed by independent assortment and formed by independent assortment and segregationsegregation

a+ b are linked and far apart so that crossing over a+ b are linked and far apart so that crossing over occurs 100% and therefore appears to be like aoccurs 100% and therefore appears to be like a

a + b are linked so that there is no space for the a + b are linked so that there is no space for the exchange to occurexchange to occur

A+ b are on the same chromosome about 10 map A+ b are on the same chromosome about 10 map units apart. They have a total of 10 % crossing units apart. They have a total of 10 % crossing over between these two physical points on the over between these two physical points on the chromosomechromosome

Question 10Question 10 Colored green 88Colored green 88 Colored yellow 12Colored yellow 12 Colorless green 8Colorless green 8 Colorless yellow 92Colorless yellow 92

Total = 200Total = 200 Cross overs = 20Cross overs = 20 20/200 = 10% or 10 map units between the coat 20/200 = 10% or 10 map units between the coat

color gene and the plant color genecolor gene and the plant color gene

Question 13Question 13

Order of the genesOrder of the genes

d---b---pr---vg---c---adpd---b---pr---vg---c---adp 31 31 4848 54 67 75 8354 67 75 83

Question 15Question 15

Order of the genesOrder of the genes

sc---------v----ssc---------v----s

33 1033 10