Ch 5: Linkage and Chromosome Mapping

linkage

genes near each other on a chromosome tend to be inherited together

testcross

cross to an individual that carries only recessive alleles for the trait, is dominant heterozygous or homozygous

via microscopy of meiotic chromosomes

Evidence of chiasmata?

linkage mapping

determines relative position of genes by following phenotypes

locus (loci = plural)

location of a certain gene on a chromosome

Poisson distribution

describes distribution of “successes” in samples when the average probability of successes is low

map distance

expected frequency of multiple exchanges between 2 genes predicted from distance between them

Interference

inhibition of further crossover events, usually by another crossover event nearbyCo

Coefficient of coincidence

calculated to quantify disparities that result from interference

observed DCO/expected DCO

coefficient of coincidence formula

1-C

interference formula

Positive interference

fewer DCO events than expected to occur

Negative interference

more DCO events occur than expected

• Autosomal recessive/dominant, X-linked recessive/dominant

• highly penetrant

• rare

• little to no environmental component

Medelian genetic diseases

• Polygenic, variable age onset

• Heterogeneous/variable expressivity

• Common

• Variable penetrance

• Environmental component

Non-mendelian genetic diseases

non-nuclear inheritance, only transferred by mother

Mitochondrial

Cystic fibrosis, sickle cell anemia, huntington disease

Rare mendelian diseases

Asthma, diabetes, hypertension, schizophrenia, bipolar disorder, multiple sclerosis

Complex non-medelian diseases

• Blood groups

• HLA types

• Serum protein electrophoretic variants

Human genetic markers that map disease to phenotypes, looking for recombination

• single nucleotide polymorphisms

• 1 in every 1.2 kb

• found throughout genome

• used to identify and locate genes

SNPs

short, repeated sequences of DNA that are scattered throughout the genome, can be 2, 3, 4, etc nucleotide repeats, 1 in every 30 kb

microsatellites

• microsatellites

• SNPs

Human genetic markers that map disease to DNA sequences, GWAS

Genome wide association studies

GWAS

Rare variant

genetic difference present in < 1% of alleles in population (too hard to find)

Polymorphism

genetic difference present in ≥ 1% of alleles in population (common)

not in equilibrium, not independently assorting, linked

disequilibrium

dichromatism

patterns of 2 coloration

sexual dimorphism

the difference in size, shape, or other traits between males and females of the same species, driven by evolutionary processes like sexual selection