-
Phenotype: observable traits
- Feather color in Parakeets
- Mendel's pea garden observations
- Inheritance of traits follows strict patterns
- Multiple forms of genes exist for each trait
- Individuals have 2 "heritable factors" per trait
- Egg and sperm (pollen) each contribute 1 factor
- Dominant and recessive traits exist
- Examples of Mendel's crosses
- The Punnett square
- F1 and F2 generation
-
Genotype: gene
combinations
- Different forms of the same gene exist = alleles
- Alleles are carried on homologous chromosomes
- Sperm and egg only contribute 1 homologue = 1 allele per trait
- Phenotype is determined by the combination of 2 alleles
- Homozygous: both alleles same (PP or pp)
- Heterozygous: 2 different alleles (Pp)
- Principles of Inheritance
- Segregation of alleles: homologous chromosomes
- parental generation
- F1 generation
- F2 generation
- Rules of probability!
- Independent
assortment: for traits on different chromosomes
- Inheritance of trait A does not affect inheritance of trait B
- AaBb x AaBb yields 9:3:3:1 ratio of phenotypes
- Genetic Linkage
- Inheritance of traits A and B is linked
- AB stay together and ab stay together
- AaBb x AaBb yields 3:1 ratio of phenotypes
- Incomplete
(partial) dominance
- Heterozygotes have a unique phenotype
- Aa xAa yields 1:2:1 ratio of phenotypes
- Codominance
- Pleiotropy
- One gene has multiple phenotypic effects
- e.g. syndromes (sickle cell, Marfan's, CF)
- Multiple
gene traits:
- Epistasis
- Two genes interact to determine phenotype
- AaBa x AaBb yields 9:3:4 ratio of phenotypes
- Model: white --> brown --> black
- Environmental influence on inheritance
