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MCB Extensions to Mendelian Genetics

Terms in this set (31)

Lethal alleles
alleles that are incompatible with life result in missing or dead genotypic classes
Recessive lethal
2 copies required for death
- homozygous recessive is missing or dies
- examples: cystic fibrosis, sickle cell anemia
Dominant lethal
1 copy required for death
- heterozygotes and homozygous dominant are missing or die
example: Huntington's disease
Complete dominance
heterozygote is the same as one parent
Incomplete dominance
heterozygote has an intermediate phenotype
- monohybrid cross results in 1:2:1 genotypic and phenotypic ratio
- example: hypercholesterolemia
Co-dominance
full and independent phenotype expression of both alleles
- all 3 genotypes phenotypically distinct
- heterozygote has both phenotypes simultaneously (not an intermediate)
- monohybrid genotypic and phenotypic ratios are 1:2:1
- example: ABO blood groups
Gene interaction
genes at multiple loci determine a single phenotype
- combine to produce phenotype
Epistasis
one gene hides/masks the effect of another gene at a different locus
Pleiotropy
single gene impacts many characteristics
example: cystic fibrosis
Sex-linked
genes on the X and Y chromosomes
Sex-influenced
genes in autosomes more readily expressed in one sex
Sex-limited
autosomal genes expressed only in one sex
Pseudoatuosomal regions
PAR1 and PAR2
- 5% of the chromosome
- contain genes shared with X chromosome
SRY and AZF
SRY= stimulates male development
AZF = required for sperm production

Both part of MSY (male specific region) which is on 95% of the chromosome
Monogenic disorders
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Complex disorders
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Continuous phenotypic variation
continuous traits are often measured and given a quantitative value - quantitative genetics
examples: height, skin color
Discontinuous phenotypic variation
like Mendel's peas - all or none so just yellow or green no in between color
Additive inheritance
- additive effects of alleles at different genes
- dominant allele (A) = active
- adds one increment of the trait
- recessive allele (a) = inert
- has no effect on the trait
- phenotype = sum total of additive and inert effects
Additive alleles
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Dominant/Active allele
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Recessive/Inert allele
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Environmental effects
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Continuous characteristics
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Multifactorial or complex traits
result of both gene action and environmental influences
Polygenic trait
phenotypic outcome depends upon more than one gene
penetrance
% of individuals with a particular genotype that express the expected phenotype
incomplete penetrance
genotype does not produce expected phenotype
expressivity
degree to which a trait is expressed
calculate % penetrance
x people who express the characteristic/y people who have the gene
genomic imprinting
genes whose expression is influenced by sex of transmitting parent
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