week 4 handout - L ecture 8 INCOMPLETE DOMINANCE vs....

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Lecture 8 INCOMPLETE DOMINANCE vs. CODOMINANCE Incomplete dominance – the phenotype of the heterozygote is intermediate to the phenotypes of the two homozygotes Codominance – the phenotype of the heterozygote is both of the phenotypes of the two homozygotes Population Genetics Terms: Allele frequency—The frequency of a specific allele in a population. Population bottleneck—During migrations, new populations are often founded by a small number of people. If these founders had unusual allele frequencies, the new population will have lower genetic diversity and different allele frequencies. Genetic Drift—Random fluctuations in allele frequency as genes are transmitted from 1 generation to the next. Compare to changes in allele frequency due to selection. Haplotype – A group of tightly linked alleles on the same chromosome that are co-inherited. A haplotype is a chromosome region that has not been broken up by recombination Example: Haplotypes in a Genetic Cross 3 genes are located at the following positions in the rhinoceros genome: Gene A chrIV: 20,300,281 - 28,304,101 Gene B chrIV: 20,305,120 - 28,309,038 Gene C chrIV: 29,613,103 – 29,617,202 a) A male rhino with genotype A 1 B 1 C 1 / A 2 B 2 C 2 mates with a female rhino with genotype A 3 B 3 C 3 / A 3 B 3 C 3 (superscripts indicate different alleles). What are the possible genotypes of their offspring? Rank these genotypic outcomes in terms of their relative probabilities. b) Which two genes are likely to be part of the same haplotype? c) How is a haplotype an extension of the concept of “parental” genotype? (remember recombinants vs. parental types in determining linkage and calculating genetic distance)
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Lecture 9: Gene dosage Polyploid organisms have more than 2 copies of each homologous chromosome per cell before meiosis. Organisms can be triploid (3n), tetraploid (4n), hexaploid (6n) etc. Polyploid organisms often have an even number of chromosomes per cell due to the necessity of homologous chromosome pairing in meiosis. By contrast, polysomy refers to organisms that have one or more extra copies of a single chromosome per cell. For example, people with trisomy 21 (Down’s syndrome) have 2 copies of most of their chromosomes but 3 copies of chromosome 21. Polysomy is one type of aneuploidy, an abnormality in the number of chromosomes; the other type of aneuploidy involves the loss of one or more copies of a chromosome. Types of polyploidy -- Allopolyploid individuals have chromosomes that originally came from multiple different species. These chromosomes were united in a single individual during a hybridization event. -- Autopolyploid individuals have chromosomes that all originated in the same species. The awesome power of yeast genetics
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This note was uploaded on 01/28/2010 for the course MCB 104 taught by Professor Urnov during the Fall '09 term at University of California, Berkeley.

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week 4 handout - L ecture 8 INCOMPLETE DOMINANCE vs....

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