week 4 (gene linkage and mapping)

Question 1

define: syntenic genes (+ linked genes)

Answer 1

• genes on the same chromosome
• can be shuffled into recomb.
• close on chromo. = linked

Question 2

question: do unlinked genes assort independently or not? what about linked genes? why?

Answer 2

• unlinked = indep. assortment
  ⤷ bc genes are on diff. chromo. so they assort randomly and indep. of each other
• linked = no indep. assortment
  ⤷ bc genes are close together so they’re likely to be inherited together (and less likely to be separated by recomb.)

Question 3

question: what is recombination frequency?

Answer 3

r = # recombinants / total # progeny

• longer distance = larger recomb. freq.
• max = 0.5 (50%)
  ⤷ any larger and they genes are unlinked

Question 4

question: why is the max. recomb. freq. 50%?

Answer 4

• any larger than 50% = unlinked
• bc at 50%, it randomizes the inheritance (up to chance)
• no way to tell whether the genes are on different chromosomes or just very far apart on the same chromosome

Question 5

question: what does a short genetic distance mean for recombination?

Answer 5

• not much recombination
  ⤷ too close -> move together in a crossing over -> no change in how the alleles are inherited

Question 6

question: what are the parents in a two-point test cross?

Answer 6

• homo. rec.
• dihybrid parent (het.)
• bc easier to see recomb. if pheno. dep. entirely on het. parent
  ⤷ bc rec. can only give rec. which dep. on the other parent so see what the pheno. is

Question 7

question: how to determine which genes are closest to one another from a recomb. freq.?

Answer 7

• smaller r = shorter distance
  ⤷ harder to separate alleles in recomb. -> closer together

Question 8

question: in three-point test cross, how to determine which gene is the middle?

Answer 8

• compare parental and double cross genotypes and see which one differs

Question 9

question: when calculating distance for recomb. freq. for 2 genes apart, what is the numerator?

Answer 9

(# single recomb.) + 2(#double recomb.)

• bc need to consider all the crossovers

Question 10

define: interference (formulas)

Answer 10

• when one crossover reduces the likelihood of another nearby

1 - coefficient of coincidence

coefficient of coincident = observed double recomb. / expected double recomb.

expected double recomb. = product of two single recomb. freq.

Question 11

define: recomb. hotspot and coldspot

Answer 11

• hotspot = recomb. more freq. in that area (vv for coldspot)

Question 12

define: variable number tandem repeats

Answer 12

• short seq. of DNA that can be amplified for genotyping
• short sequence of nucleotides repeats itself a variable number of times

Question 13

define: restriction fragment length polymorphisms

Answer 13

• differences in DNA fragments detected when extracting w/ resctriction enzymes
• VNTRs are examples of RFLPs

Question 14

question: what is the most common genetic marker in humans?

Answer 14

• single nucleotide polymorphisms
  ⤷ single nucleotide at a specific position
• often used to ID disease causing genes