Mendelian Inheritance Flashcards
Blending Inheritance
• Suggests variation will be lost over time
o Not what happens in most populations
Blending Inheritance Problem
o Rare variants will have no opportunity to increase in frequency even if they survive and reproduce more, since they will gradually disappear.
Modern Transmission Genetics
• Not traits transmitted, but genes
o Note: mendel didn’t know DNA responsible for passing info from one gen to the next, or what genes are
o 1946-64, pea plants to demonstrate
• Studied hybridization between 2 varieties of pea plant
Pea Plant Traits
o color of seeds • yellow, green o shape of seeds • round or wrinkled o color of pods • green yellow o shape of pods o color of flower • pink or white o position of flowers • stem or tip o plant height • dwarfed or tall
True Breeding
o Physical appearance of offspring in each successive generation is identical to previous one
o Inbred lines
o Makes homozygous for all traits
Breed out all heterozygoticy
Pea Plant Crossing Protocol
Take a flower, o anthers: produce pollen o ovules: receive • Cut off anthers, can’s self pollinate • Take mature pollen from plant with known traits o Put mature pollen onto stigma • Cover it with something so other pollen doesn't get in • Let seeds grow
Incomplete Dominance
• Tigerlilies • Red and White cross = purple o not complete dominance of one to the other • Take P1, produce F1 o Ok, we have incomplete dominance • Allow F1 to self pollinate o Genotype ratio reflects phenotype ratio o 1 Red: 2 Purple: 1White
Addition Rule
• Addition: when outcomes cannot occur simultaneously
Multiplication Rule
when outcomes can occur simultaneously and occurance o one has no effect on likelihood of the other
Principle of Segregation
o Individuals inherit 2 copies of each gene (1 from mom 1 from dad)
o When individuals form reproductive cells, 2 copies separate equally in eggs and sperm
Principle of Independent Assortment
o The 2 copies of each gene segregate into gametes independent of one another
Independent Assortment During Meosis
• Line up on metaphase plate without respect of where parental chromosome came from
o chromosomes line up on plate randoml
Some combo from mom and dad on either side
Epistasis
- Genes that modify phenotypic expression of other genes show epistasis
- In dihybrid cross (2 genes) where genes are epistatic, a deviation from expected ratios are observed
- Get deviation of 9:3:3:1
Brachydactyly
intermediate bones in hand don’t form correctly
o 50% children affected by trait
o Grandfather had it: He was heterozygous for trait
o Trait never skips a generation, in every generation
o Not on sex chromosomes because likely in both males in females
Trait Analysis: Yellow v Green Seed
Parental generation: P1
o different crosses
o reciprocal cross
o Cross in one direction, then do reciprocal cross
o Cross 2 true breeding parents with only one difference
• 1 has yellow seeds, one has green
