Lecture 3 BIO 311D 2nd EditionOutline of Last Lecture I. Meiosis, “ploidy”, and life cyclesII. Sources of genetic variability in meiosisIII. Applying meiosis to Mendelian inheritance Outline of Current Lecture I. Mendelian Inheritance Current LectureI. Mendelian Inheritance A. Transmission: one gene locus controls the trait only two possible alleles per gene locusB. Types of Dominance1. Simple (complete dominance)2. Incomplete dominance- The heterozygote has a phenotype unlike either homozygote i.e. pink snapdragon- For example: when two palominos mate they can produce offspring colors of chestnut (homozygous RR), cream (homozygous R’R’), or palomino (heterozygous R’R)3. Co-dominance - The ABO blood group alleles are examples of multiple alleles (3 possible at this gene locus) and co-dominant alleles (both fully expressed in the phenotype)Genotype PhenotypeIAi or IAIAType AIBi or IBIBType BIAIBType ABii Type O C. Genotypes: the two alleles an individual has for that gene locusHint: Use the same letter of the alphabet for alleles at any given gene locusFor example:Homozygous AA [Use capital letter if simple dominance]Homozygous aa Heterozygous AaHomozygous A’A’ [Not simple dominance]Heterozygous A’AD. Practice Problems1. In the mating cross Rr X Rr, what proportion of the offspring will have the genotype “rr”? 1/42. In the mating cross Tt X TT, what proportion of the offspring will have the genotype “tt” 03. A mouse shows the dominant black phenotype but has unknown genotype. To do a test cross, you would mate this individual with any brown mouse. E. Recessive Traits: defined at the molecular level as loss-of-function mutations (a missing or non-functional protein, single gene locus)1. Hypercholesterolemia- lack of LDL receptor protein2. Cystic fibrosis- Lack of CI-ion transmembrane regulator protein- In humans, cystic fibrosis is inherited as a simple recessive trait. A normal woman (without cystic fibrosis) who carries the gene (i.e. she is heterozygous) marries a normal man who does not carry the cf allele. Child would not have CF3. Phenylketonuria (PKU): missing a critical enzyme- PKU symptoms due to lack of tyrosine and excessive phenylpyruvic acid and its breakdown products 4. Albinism is also a recessive trait F. Heterozygous Traits1. Achondroplasis: dwarfism is heterozygous condition. Homozygous dominant condition is embryonic lethal. Molecular basis: overactive fibroblast growth factor receptor gene (FGF Receptor 3), which leads to premature differentiation from cartilage into
View Full Document
Unlocking...