Lectures 1-3 Flashcards
Recognizing Dominant Traits in Pedigrees
Affected offspring always have at least one affected parent. Vertical pattern of inheritance I.e. shows up in every generation. If one parent is a homozygote then all offspring will be affected
Monohybrid
Individual with two different alleles for a single trait
Recognizing recessive traits in pedigrees
Affected individuals can be offspring of two unaffected parents. All offspring of two affected parents should be affected. Horizontal pattern of inheritance. May show vertical pattern of inheritance if the allele is very common in the population.
Incomplete dominance
Heterozygote has a phenotype intermediate between homozygotes. Mono hybrid cross = 1:2:1, phenotype ratios reflect the genotype ratios.
Codominance
Heterozygote has both the traits found in each homozygote. For example AB blood types in humans. Both alleles are expressed and genotype ratios reflect phenotype ratios.
Allele frequency
Percentage of total number of gene copies for one allele in a population
Wild type allele
Most common allele
Mutant allele
Rare allele
Monomorphic gene
Genes with only one common wild type allele in wild populations however there can be many alleles found in animals artificially selected for such as lab mice
Polymorphic gene
Gene with more than be common allele
Pleiotropy
A gene which affects multiple traits. Ex, the A^y agouti gene in mice. Dominant to the A gene for yellow coat color but recessive for pre-implementation lethality
Mendel’s law of segregation
The two alleles for each trait separate during gamete formation then unite at random, one from each parent during fertilization.
Mendel’s law of independent assortment
During gamete formation, alleles of different genes segregate independently of each other
Polygenic trait
Trait determined by several genes. No simple Mendelian inheritance patterns
Monogenic traits
Mendelian inheritance patterns
Complimentary gene action
Two genes compliment each other to determine phenotype. For example pea flower color.
A- + B- leads to purple pigment. If either of the genes are homozygous recessive no pigment will be produced.
Eg: seed color in lentils. A-B- brown, A-bb tan, aaB- gray, aaB green
Epistasis
An allele of one gene masks the effects of the alleles of another gene.
Recessive Epistasis
Two copies of a recessive allele blocks the effects of the alleles of another gene. For example coat color in labs. B-E- black, B-ee yellow, bbE- brown, bbee yellow
Another example: Bombay blood group. H gene: hh blocks the effects of the I gene
Dominant Epistasis
One gene is dominant and cover the effect of another gene. Example: summer squash colors. A gene: 2 alleles dominant is yellow and recessive is green. B gene is dominant and epistatic to both A gene alleles. b allele allows the expression of the A gene. A-B- or aaB- creates a white color. A-bb yellow, and aabb green. 12:3:1 ratio.
Heterogeneous Trait
A trait caused by mutations in different genes causing the same phenotype. Eg deafness in humans can be separately caused by mutations in each of about 50 genes.
Test of complementation
Used to determine whether two mutations that cause the same phenotype are mutation in the same gene or in different genes. Can only be used for recessive mutations but not dominant. Take a female who is homozygous for recessive mutation 1 and a male homozygote for mutation 2. If the progeny has no mutant phenotype but rather the wild type, the mutations are in different genes and complimentary to each other. If the mutant phenotype is observed, the mutations are in the same gene and are not complimentary
