Lecture 6 Flashcards
if R/r and Y/y are on the same chromosome and the distance between them is 20 mu, what is the relative ratio of F2s that are wrinkled and green if F1s are self-pollinated?
wrinkled and green = ry
must be selfed so the only way for progeny to be ry is if F1s are both ry
proportion of F1s that are ry is 10% (total recombinants is 20%, 2 possible recombinants so ry is 10%)
0.1 x 0.1 = 0.01
why are genetic crosses not feasible for mapping genes in humans? (3)
- controlled crosses not possible
- mating couples only have a few offspring
- experiments would take many years
what are molecular markers?
small DNA sequence differences/polymorphisms within a species, at specific chromosomal locations
why are molecular markers helpful?
they have no biological function/phenotype but can be used to map a gene by determining linkage btwn gene of interest and the molecular markers
what does SSLP stand for?
simple sequence length polymorphism
what are SSLPs?
multiple repeats of short DNA sequences at specific location
when do people have the same number of SSLPs?
if they are RELATED
describe inheritance of SSLPs
1 maternal set, 1 paternal set is inherited
how can we use SSLPs to see if ppl are related?
use primers that bind sequences that flank the SSLPs –> can see if they have similar patterns of SSLPs
how much of DNA is identical btwn 2 unrelated ppl?
99.9%
how much of DNA is different btwn 2 unrelated ppl? what are these differences?
0.1% –> most of the differences are SNPs
are SSLPs or SNPs more frequent?
SNPs
what classifies something as a SNP rather than a mutation?
SNP must be in 1% of people in a population
if not, it is just a mutation
SNPs can be common within _______
SNPs can be common within a specific population or ethnicity
3 possible locations for SNPs?
- intergenic
- within a gene
- in regulatory region
SNPs within a gene or in regulatory region may be involved in:
SNPs within a gene or in regulatory region may be involved in disease susceptibility or sensitivity to external factor
do most SNPs cause health effect?
most SNPs have no health effect
what does it mean if a specific set of SNPs is associated with disease? why?
the disease-causing gene must be close to those SNPs because things that are close to each other are often inherited together
what is a haplotype?
grouping of genomic variants/polymorphisms that tend to be inherited together bc they are close
what does it mean when specific haplotype is more common in certain population?
must be certain factors that favour the allele in that population
describe the adaptation of Tibetans to high altitude vs Chinese
Tibetans and Chinese are closely related –> SNP variants occur at similar frequency in both groups BUT Tibetan SNPs are linked to a helpful gene (EPAS1) at higher frequency
