Chapter 5 Flashcards
If p less than 0.05
statistically significant
confirm null hypothesis
null hyp is mendelian
Syntenic genes
genes on the same alleles
can be reshuffled when crossing over occurs
= recombinant chromosomes
if genes close together, called linked genes
Genetic linkage mapping
plots the position of genes and their relative distances from each other on chromosomes
looking at phenotypic ratios in offspring
Independent assortment
mendelian
50% parental
50% recombinant
Linked genes
no independent assortment
parental phenos more common than recombinant
physical relationship among genes located close to one-another
Complete vs incomplete genetic linkage
complete = no crossover
incomplete = crossover in 40% of gametes
The recombination frequency
r = number of recombinants / total number of progeny
further = recombine more
max value = 0.5
Who confirmed genetic linkage
Morgan
used red and white eye flies
did a test cross
worked bc in drosophila recombination only occurs during oogenesis
Test cross
between heterozygote and homozygous recessive parent
allows you to look at the alleles of the dihybrid (hetero) parent
Morgan’s crossing-over hypothesis
crossing over creates parental and non-parental gametes after segregation
First genetic linkage map
Sturtevant (morgan’s student) made the first chromosome map
discovered map units
Map units
1% recombination
= 1 map unit (m.u.)
= 1cM
Three point test cross
allows you to determine the location of three genes
cross a trihybrid individual with a homo recessive one
AaBbCc x aabbcc
Which recombinations are most common
parental most common
double least common
(middle is the one that differs)
Does data show evidence of genetic linkage
- if P value statistically significant, can accept genetic linkage hypothesis
- reject mendel independent assortment
Single recombinations
(double + double + single + single)/total
look where only one gene is different than parental
abc
bc
look at where c is different
Total gene distance
[(single + single + single + single) + 2(double)] / total
Theoretical double crossover frequency
= (Psingle) x (Psingle)
then multiply by the number of individuals
Is number of double crossovers usually higher or lower than expected
lower
due to interference
More interference suggests
increased distance than map distance
Coefficient of coincidence
C = (observed double recombinants)/(expected double recombinants)
Interference (I)
Interference (I) = 1-C
Negative interference
when there are more double recombinants than expected
I < 0
Recombination frequency ______ actual distance between genes
underestimates
Genetic analysis of humans
can’t ethically do crosses
human genome mapping done through mapping software
Genetic markers
genetic sequences that are polymorphic and used for genetic analysis
can be analysed from a DNA sample
locate markers that are linked to alleles that determine phenotypic variation
typically found in non-coding regions
VNTRs
variable number tandem repeats
shore 3-20 bp sequences of DNA
can be amplified by PCR
inheritance can be analyzed in a pedigree and show a codominant relationship
RFLPs
restriction fragment length polymorphisms
variable DNA sequences that are detected when extracting DNA and digesting it with restriction endonuclease enzymes
- number and length varies at specific regions
- VNTRs are usually RFLP markers
SLPs
single nucleotide polymorphisms
more commonly used
single nucleotide at a specific position that is variable among populations
some in coding, some in non-coding
used by 23andme (detect 60 000 SNPs)
Using genetic markers to detect disease
if close to gene of interest, usually inherited together and can be associated
ex. SNPs A and B with disease gene D
Haplotype
a series of linked SNPs on a specific chromosomal region
