Genetics quiz 3

__ prevents independent assortment

physical linkage

What does the chi squared test for independent assortment assume? If chi square value =5.3 and critical chi square is 7.8 what is the conclusion?

Assumes normal segregation for all alleles and equal viability of all genotypes.

Fail to reject null hypothesis; normal segregation and equal viability of all genotypes

Recombination never exceeds __%. Why?

50%. This is because for every cross, even if genes aren’t linked, each individual crossover event involves only 2 nonsister chromatids out of the 4.

Determine gene order and map distances

What is genetic interference

Occurence of one crossover/recombination event on a chromosome reducing the likelihood of another crossover event occuring nearby

What is coefficient of coincidence?

Coc=1 →

CoC <1 →

CoC > 1 →

Used to measure interference.

Observed double crossovers/expected double crossovers

Coc=1 → no interference

CoC <1 → negative interference

CoC > 1 → positive interference

Difference between genetic and physical maps?

genetic linkage maps based on RF/recombination frequency

physical maps are based on base pair distance

What is the purpose of establishing linkage with microsatellites

To map genomes and ID physical genes associated with disease

Log odds (LOD) score vs coefficient of coincidence (CoC)

LOD: used to determine whether 2 genetic loci are physically linked on a chromosome (inherited together) vs assorting independently

CoC: determines interference: if one crossover influences another cross over

What is the purpose of a mapping function? How does the mean number of crossovers (m) relate to actual RF?

To convert observable RF (recombination frequency) into a reliable genetic map distance because raw recombination frequencies aren’t strictly additive over long chromosomal distances, this formula acts as a correction factor.

Uncounted multiple crossovers btn 2 genes causes map distances to be underestimated. larger distances also ahve less accurate recombination frequencies

what is admixture process

Genetic admixture happens when previously isolated populations interbreed, creating a new population with a combined gene pool from both source groups.

What does a GWAS graph help identify

which genes/allesl contribute to a trait/disease phenotype

What do these LOD values correlate to

LOD >=3

LOD <=-2

Interpret LOD=3

LOD>=3; supports linkage

LOD<=-2; strong evidence against linkage

LOD=3; pedigree data is 1000 times more linkage under the specific linkage model than under no linkage.

Change in sets of chromosomes:

Change in single chromosomes:

Change in sets of chromosomes: aberrant euploidy

Change in single chromosomes: aneuploidy

what is pathenogenesis

form of asexual reproduction where an embryo develops from an unfertilized egg cell without needing male fertilization

MOst monoploid animals are lethal because of ___

genetic load (which measures how much lower a population’s avg survival rate is because of deleterious genes

Triploids are crosses between __ and __. What are some applications of triploids?

diploid and tetraploid

meiotic sterility which is good for produces seedless plants/fruit

What is raphanobrassica and what is its significance

allotetraploid hybrid created by crossing two different genera in the Brassicaceae family

Is originally sterile (2n=18) but spontaneous doubling (4n=36) restores fertility creating new fertile species

What is a amphidiploid

Contains 2 distinct diploid sets of chromosomes, each derived from different parental species

Big strawberries are allo-octoploids, __ correlates to __

cell size is correlated to nuclear size

Features of meiotic nondisjunction:

Most nondisjunction events happen during ___

Mutations in crossing over result in high rates of __

Nondisjoined chromosomes are often __

Most nondisjunction events happen during Anaphase I

Mutations in crossing over result in high rates of high rates of aneuploidy

Nondisjoined chromosomes are often non-recombinant

What is the only viable human monosomic

turner syndrome

all other human monosomics spontaneously abort

frequency of trisomy 21 increases with maternal/paternal age

maternal

What is gene balance hypothesis

adding or subtracting a single chromosome (aneuploidy) causing severe phenotypic disruption because it upsets balance of dosage sensitive genes. In contrast, a whole-genome duplication (polyploidy) scales up all components evenly, preserving balance and causing milder effects

What causes structural chromosome changes and how do the mechanisms differ?

NHEJ (nonhomologous recombination): DNA breaks occur at different locations. Directly ligates broken ends back together, doesn’t require a homoologus DNA template

NAHR (nonallelic homologous recombination): displaced synapsis and crossing over between repetitive elements Occurs in regions where there is high sequence similarity but are located at diff genomic loci. Invovles crossover, recombination machinary similar to standard homologus recombination

Terminal vs interstitial deletion

Terminal: occurs at the very end of chromosome end, Caused by single chromosomal break. Ex. cri du chat syndrome (deletion of hTERT gene)

Interstitial deletion: occurs within chromosome Ex. Williams syndrome

What are the genetic properties of deletions

deletion loops in heterozygotes (large deletions only)

homozygous lethality

stability of recessive mutations (no reversion)

reduced recombination btn flanking genes

pseudodominance of recessive alleles

dsbreaks are repaired by

NHEJ

Paracentric vs pericentric inversion

paracentric: doesn’t involve centromere

pericentric: involves centromere

what happens during crossing over in paracentric vs pericentric inversions

paracentric: inversion loop

pericentric: dicentric acentric formation