1-18 Genetic Variation Genome Mapping

Question 1

Segregation

Answer 1

Sexually reporducing organisms possess genes that occur in pairs and only one member of this pair is transmitted to the offspring

Question 2

Independent assortment

Answer 2

Genes at different loci are transmitted independetly

Question 3

Hardy-weinberg

Answer 3

In an ideal or model pop the relative proportions of different genotypes remain constant from one generation to another

p2 +2pq + q2 = 1 given p+q=1

Question 4

Assumptions made by Hardy-weinberg

Answer 4

1. no new mutation
2. no selection for or against particular gentoype
3. no chance fluctuations due to small pop size
4. no selection of partner on basis of genotype
5. no migration of new genes into gene pool

Question 5

Non-random mating affect HW

Answer 5

effects HW, results in increase in freq of homozygous genotypes at teh expense of heterosygoutes compared to what would be predicted by HW

stratification: pop in which there are subgroups that are genetically seperate (eg causcasin, AA, hisp)
assortative mating: choice of mate is not randome
consanguinity: mating between people with common haplotype have higher risk of congential anomalies (eg first cousins)

Question 6

non-constant allel freq affect HW

Answer 6

genetic drift: in small pop allele freq can deviate substatiannly one generation to next

founder effect

gene flow: occurs as pop migrates and beins to mate with another pop, through time will make 2 pops more similar to one another eg PKU once only celtic and now more widespread

Question 7

founder effect

Answer 7

small pop breaks off from larger pop and allel freq in small pop may differ from parent group and a rare allele will become over represented in these descendants

Question 8

heterozygote advantage

Answer 8

increased fitness over homozygous mutition and homo normal allele

ex sickle cell disease hetero resistant to malaria

Question 9

linked loci

Answer 9

transmitted together rather than independently

depends on physical distance btw genes on chrom

Question 10

recombination frequency

genetic distance

Answer 10

the % recomb seen btw 2 loci in a large series of meioses

genetic distance: unit measure of recom, centiMorgan, 1 cM = 1% recomb

Question 11

Logarithm of the odds “LOD score”

Answer 11

log (likelihood of observing the pedigree data if the loci are linked / likelihood of observing the pedigree data if the loci are unlinked)

unliked likehood: 0.5
ratio > 1 indicates more likely than random chance
ration < 1 more likely due to chance

LOD > 3 indicates the likelihood in favor of linkage is 1000x > than the likelihood against linkage significant

Question 12

genome wide association studies GWAS

Answer 12

tests for altered freq of allele or haplotype in affected individuals compared with normal controls

does not ID the disease gene, but uses a nearby (linked) polymorphism to ID the association