Non-medelian Genetics Flashcards
Ways traits DON’T follow the ratios predicted by Mendel’s laws
- Varying degrees of dominance
- Many traits are produced through multiple genes acting together
- Some traits are determined by sex chromosomes
- Some genes close to each other on the same chromosome
- Some traits are the result of non-nuclear inheritance (chloroplast and mitochondrial DNA)
Incomplete dominance
Neither allele is fully dominant
-F1 generation has a phenotype that is a mix of those of the parental generation
Codominance
Two alleles for a trait are both expressed
-Ex. Human blood: AB blood, A & B both expressed
Multiple Alleles:
Genes that exist in forms with more than two alleles
Ex. Human blood group, height
Sex Chromosomes
Sex-linked genes: A gene located on either the X or Y chromosome
-Y and X- linked genes: Genes found on either chromosome
Inheritance of X-linked genes
-Father can pass X-linked alleles to all of their daughters but none of their sons
-Mothers can pass X-linked alleles to both daughters and sons
If an X-linked trait is due to a recessive allele:
-Females only express the trait if they are homozygous
-Because males only have one X chromosome, they will only express the trait if they inherit it from their mother
*hemizygous
*more likely to get x-linked disorders
X-inactivation
-During development one of the X chromosomes in each cell becomes inactive
-Inactive X in each cell of a female condenses into a Barr body which helps to regulate gene dosage
Genetic recombination
Production of offspring with a new combination of genes from parents
Parental Types:
Offspring with the parental phenotype
Recombinants:
Offspring with phenotypes that are different from the parents
Linked genes
Genes located near each other on the same chromosome that tend to be inherited together
Meiosis and random fertilization generate genetic variation in offspring due to
-Crossing over
-Independent assortment of chromosomes
-Any sperm can fertilize any egg
Linked genes show parental phenotypes in offspring at higher than…
50%
The further apart two genes are on the same chromosome…
The higher the probability that a crossing over event will occur between them and the higher the recombination frequency.