Lecture 13(2)

Lecture 13(2) - Lecture 13 Heredity, DNA and its...

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Unformatted text preview: Lecture 13 Heredity, DNA and its Replication How Do Genes Interact? A cross between two different true- breeding homozygotes can result in offspring with stronger, larger phenotypes: Hybrid vigor or heterosis . First discovered with corn by G.H. Shull. Figure 12.15 Hybrid Vigor in Corn How Do Genes Interact? Environment also affects phenotype. Light, temperature, nutrition, etc., can affect expression of the genotype. Siamese cats and certain rabbit breeds the enzyme that produces dark fur is inactive at higher temperatures. Figure 12.16 The Environment Influences Gene Expression How Do Genes Interact? Effects of genes and environment on phenotype: Penetrance : Proportion of individuals with a certain genotype that show the phenotype Expressivity : Degree to which genotype is expressed in an individual How Do Genes Interact? Mendels characters were discrete and qualitative. For more complex characters, phenotypes vary continuously over a range quantitative , or continuous, variation. Quantitative variation is usually due to both genes and environment. What Is the Relationship between Genes and Chromosomes? Some crosses performed with Drosophila did not yield expected ratios according to the law of independent assortment. Some genes were inherited together; the two loci were on the same chromosome, or linked. All of the loci on a chromosome form a linkage group . Figure 12.19 Crossing Over Results in Genetic Recombination (Part 1) Figure 12.19 Crossing Over Results in Genetic Recombination (Part 2) What Is the Relationship between Genes and Chromosomes? Recombinant offspring phenotypes (non- parental) appear in recombinant frequencies : Divide number of recombinant offspring by total number of offspring. Recombinant frequencies are greater for loci that are farther apart . Figure 12.20 Recombinant Frequencies What Is the Relationship between Genes and Chromosomes? Recombinant frequencies can be used to make genetic maps showing the arrangement of genes along a chromosome. Distance between genes = map unit = recombinant frequency of 0.01. Map unit also called a centimorgan ( cM ). Figure 12.21 Steps toward a Genetic Map Figure 12.22 Map These Genes (Part 1) Figure 12.22 Map These Genes (Part 2) Figure 12.22 Map These Genes (Part 3) Figure 12.22 Map These Genes (Part 4) Figure 12.22 Map These Genes (Part 5) What Is the Relationship between Genes and Chromosomes? Mammals: Female has two X chromosomes (XX). Male has one X and one Y (XY). Male mammals produce two kinds of gameteshalf carry a Y and half carry an X. The sex of the offspring depends on which chromosome fertilizes the egg. In other animals, sex determination by chromosomes is different from mammals....
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This note was uploaded on 10/11/2011 for the course BIS 2A taught by Professor Grossberg during the Summer '08 term at UC Davis.

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Lecture 13(2) - Lecture 13 Heredity, DNA and its...

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