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Genetics Exam 1
| Question | Answer |
|---|---|
| Complementary genes | 9:7 ratio; at least 1 dominant allele at each locus needed for dominant phenotype |
| Additive genes | 9:6:1 ratio; AAbb and aaBB have the same effect. Think of the squash shape example |
| Duplicate genes | 15:1 ratio; only one dominant allele needed from either gene for dominant phenotype. Only aabb gives a recessive phenotype |
| Suppressor genes | 13:3 ratio; one recessive allele reverses the effect of the other gene's recessive allele. Of the offspring recessive for one gene (4 out of 16), 1 in 4 (1 in 16) displays the dominant phenotype. |
| Recessive epistasis | 9:3:4 ratio; a recessive epistatic gene "covers" the expression of 4/16 of offspring; the remaining 12 display a normal 3:1 (9:3) phenotypic ratio. |
| Dominant epistasis | 12:3:1 ratio; a dominant epistatic gene "covers" the expression of 12/16 of offspring; the remaining 4 display a normal 3:1 phenotypic ratio. |
| Back cross | Organism is crossed with its parent, or another organism with the parental genotype |
| Reciprocal cross | A recessive male is crossed with a homozygous dominant female and vice versa to see if sex affects inheritance |
| Test cross | A dominant individual is crossed with a homozygous recessive one to determine its genotype |
| Complementation test | To test whether 2 recessive mutants have mutations in the same gene, cross them. If the 2 are mutated at the same locus, offspring will also be mutant. If they're complementary, ie, each mutated at different loci, they'll show the dominant phenotype. |
| Balanced polymorphisms | There is selective pressure both in favor of and against a mutation. Example: Sickle cell anemia |
| Polygenic | Affected by multiple different genes. Example: Height |
| Hemizygous | Having only one copy of a chromosome. Males and individuals with Turner Syndrome are hemizygous for the X chromosome |
| Pleiotropy | 1 gene influences multiple seemingly unrelated traits. Example: Marfan Syndrome causes elongated arms, curved spine, and pectus excavatum. |
| Penetrance | Percent of individuals with a given genotype that exhibit the associated phenotype |
| Expressivity | Extent to which a gene is expressed in the phenotype |
| Genetic anticipation | The expression of a gene becomes stronger each generation |
| Loss of function mutation | Most recessive mutations are loss of function mutations |
| Haploinsufficiency | Dominant loss of function mutation; one wild-type allele is not enough for the wild-type phenotype to be expressed |
| Gain of function mutation | Dominant mutations that often lead to disorders |
| Conditions for Hardy Weinberg Equilibrium | 1) Infinitely large population (no genetic drift) 2) No immigration or migration 3) Random mating 4) No mutation 5) No selection Numbers 2 and 4 introduce new alleles into the population |
| Mendel's Law of Segregation | Each organism has 2 alleles for each gene, 1 of which will be passed down to offspring |
| Mendel's Law of Independent Assortment | The allele passed down for 1 gene has no bearing on the allele passed down for another gene (excluding cases of linkage) |
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