Genes Lecture 5- Gene Mapping

Question 1

A gene map shows

Answer 1

the relative order of genes on the chromosome
the distance between the genes

Question 2

positional cloning

Answer 2

identify genes linked to diseases or traits

Question 3

1 centiMorgan=? base pairs

Answer 3

1 Mb

Question 4

physical map

Answer 4

Based on dna sequence itself, based on the base pairs (how long the gene is and where location is on chromosome
e.g human genome project

Question 5

cytogenic map

Answer 5

Based on the banding patterns of chromosomes which refer to the genomic location

Process:
Chromosomes are stained with Giesma to see the light and dark bands
850 G-dark bands are visible on the 23 human chromosomes
Each band is assigned a different number
Standardized system: chromosome, arm type (short or long; p or q), region, band, subband
e.g ). For example, CF, the gene mutated in cystic fibrosis, is located at 7q31.2

Question 6

genetic/linkage map

Answer 6

Genetic/ linkage- Based on the crossover events that are happening in the genome between chromosomes, tell us the relative order

Question 7

what does genetic linkage go against?

Answer 7

Mendel’s second law of independent assortment

Question 8

linkage map principles

Answer 8

crossing over occurs at random positions along each chromosome
the frequency of crossing over between two gene loci is proportional to the physical distance between them on the chromosome

Question 9

the frequency of recombinant gametes is proportional to the…

Answer 9

frequency of crossing over

Question 10

independent assortment produces….

Answer 10

recombinant gametes

Question 11

what % of recombinant gametes does independent assortment of genes give

Answer 11

50%

Question 12

50% recombinant gametes tells us

Answer 12

genes are on different chromosomes
genes are far apart on the same chromosome

Question 13

less than 50% recombinant gametes tell us

Answer 13

genes are linked on the same chromosome
the smaller the RF, the closer the genes

Question 14

testcross

Answer 14

used to determine the genotypes of the gametes from the phenotypes of the offspring they produce
usually homozygous recessive

Question 15

what is genetic distance equal to

Answer 15

recombinant frequency

Question 16

recombinant frequency formula

Answer 16

(number of recombinant progeny) / (total number of progeny) x 100

units= centiMorgans (cM): 10% RF = 10 cM

Question 17

Why aren’t genetic distances
exactly additive?

Answer 17

1. Over large genetic distances double (or multiple) crossover events underestimate the true distance
2. Crossover events are not always independent, i.e. a crossover in one region can influence the probability of a crossover in an adjacent region: positive or negative interference
3. The frequency of crossing over varies in different regions of the genome