Genetics Linkage and Mapping

Question 1

linkage group

Answer 1

• genes located on the same chromosome belong to the same linkage group

Question 2

double crossover

Answer 2

• two crossovers
• smaller part of chromosome is switched (compared to with single crossover
• could rearrange dominant/recessive genes

Question 3

crossover limit

Answer 3

• after 1 crossover, it is less likely that there will be another crossover
• closer to the centromere–> less likely for crossover to occur

Question 4

Genes not linked (1/3 cases of genes that happens with cross over)

Answer 4

• Homozygous dominant and homozygous recessive individuals (AABB X aabb)
• genes are not linked–> shows normal random assortment
• test cross get 1:1:1:1 ratio of phenotype
• AaBb, Aabb, aaBb, aabb
• 50% nonparental (in dihybrid test cross w/ genes not linked)

Question 5

Genes completely linked (2/3 cases of genes that happens with cross over)

Answer 5

• do not show independent assortment
• do not crossover
• do not show genetic recombination
• Homozygous dominant and homozygous recessive individuals (AABB X aabb)
• A and B stick together–> not independently assorted (because they are physically close to each other
• test cross–> only get 2 phenotypes in 1:1 ratio (AABB, aabb)
• 2 offspring resemble parents–> 0 nonparental types

Question 6

Linked genes, with some distance between (3/3 cases of genes that happens with cross over)

Answer 6

• shows genetic recombination
• Homozygous dominant and homozygous recessive individuals (AABB X aabb)
• test cross–> 4 phenotypes in 9:9:1:1 ratio
• AaBa, aabb, Aabb, aaBb
• same offspring as when genes are not linked, but different ratio
• we get this ratio since this crossover happens rarely
• this ratio tells us that the genes are on the SAME chromosome, and they are genetically linked, they do NOT show independent assortment

Question 7

Parental types

Answer 7

• the parents that the offspring resemble

Question 8

recombinance

Answer 8

• breaking and rejoining DNA (crossing over)
• the farther apart the genes, genes are, the bigger the number for recombination percentage
• Farther apart, more likely to have nonparental types

Question 9

map unit

Answer 9

• relative distance between genes

- mapping- used to figure out where genes are on chromosomes

Question 10

trihybrid test cross

Answer 10

• result expected is 1:1:1:1:1:1:1:1 (8 different phenotypes all with equal distribution if genes are unlinked)
• parental types- highest number of offspring
• lowest numbers–> double crossover

Question 11

Chi square test

Answer 11

• Goodness of fit test
• Determining if idea of pattern inheritance you are seeing is correct or not
• TABLE: Classes, observed numbers, expected numbers (add up and divide by 4), deviation (difference between observed and expected)- should add up to 0, take deviation and square it, then take deviation square and divide by expected
• Chi squared number is the sum of the deviation^2/expected
• Degrees of freedom = The number of classes – 1