Lecture 6: Extensions to Mendels rules Flashcards
Genetic linkage
The tendency of alleles that are close together on a chromosome to be inherited together during meiosis. Linked genes will segregate together and not obey mendels 2nd law
Linkage disequalibrium
Non random association of alleles at different loci.
Loci are said to be in linkage disequilibrium when the frequency of association of their alleles is different than what would be expected if the loci were separating independtly
Complex inheritance
Genetic traits usually dont follow simple inheritance pattern.
Polygenic traits
Traits that are produced by the interplay of many sets of genes
Is it possible for a recessive phenotype to be displayed given a dominant genotype
Yes, in the case of hermaphrodite snails, there is a maternal effect that can override genotype.
Mother produces a substance that causes the phenotype of her offspring to reflect her genotype, regardless of the offsprings actual genotype
One of the earliest and most important events during embryological development is
Establishing polarity
Medels traits exhibit what type of dominance
Complete dominance
Complete dominance
Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes
Incomplete dominance
Phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes
Codominance
Phenotype of heterozygote includes phenotypes of both homozygotes
Penetrance
The percentage of individuals having a particular genotype that express the expected phenotype
Expressivity
The degree to which the character is expressed
Complete penetrance
Everyone who inherits the disease causing allele has same symptoms
Incomplete penetrance
Some individuals do not express the phenotype even though they inherit the alleles
Variable expression
Symptoms vary in intensity in different people
-for example, two extra digits vs three extra digits in polydactyly
Lethal allele and affects
Causes death at an early stage of development, some some genotypes do not appear among the progeny
-Affects the mendelian genotypic and phenotypic rates in progeny
Factors that affect penetrance
Sex and the parent who contributed the mutation affect the risk of expression of the phenotype
Type O
Can donate to any recipienct
Type AB
Can receive from any donor
Type A genotype
AO
AA
Type B genotype
BO
BB
Type AB genotype
AB
Type O genotype
OO
Gene interaction
Effects of gene at one locus depend on the presence og genes at another locus
- Gene interaction with epistasis- one gene masks the effect of another
- Gene interaction can produce novel genotypes
Recessive epistasis
Genotypes at both the H locus and the ABO locus determine the ABO blood type
Bombay phenotype
People with homozygous recessive hh genotype fail to convert the intermediate into H.
Blood type O can result from the absence of a terminal sugar on compound H, or from the absence of compound H.
