Ro_Lecture7 - The Big Picture an outline of the concepts...

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1 The Big Picture: an outline of the concepts covered to date 1. Genes are physical units of hereditary that carry information from one generation to the next 2. Mendel elucidated the following principles regarding the inheritance patterns of genes · A. Each individual contains two copies of a given gene · B. Genes have different forms called alleles. The form that is expressed phenotypically in the heterozygote is known as the dominant allele. It is an operational definition · C. These copies segregate from one another to form gametes with a single copy of each gene · D. Pairs of genes assort independently from one another during gamete formation 3. The inheritance pattern of genes parallels the behavior of chromosomes at meiosis. This generated the hypothesis that genes reside on chromosomes OR A a A a B b b B
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2 4. Exceptional patterns of chromosome segregation · Non-disjunction: homologous chromosomes migrate to the same pole during meiosis · The X/X and X/Y sex chromosomal system produces exceptional segregation patterns because males contain only one copy of X-linked genes 5. Exceptional expression patterns: Incomplete dominance, Co-dominance, Lethal alleles 6. Genes that reside close to one another on the same chromosome do not assort independently- linkage 7. Occasionally recombination occurs between these linked genes. The higher the frequency of recombination between any two genes, the greater the distance is between them. Recombination frequencies serve as a useful method of mapping genes along a chromosome. No exceptions to Mendellian laws at the level of the gene, but Phenotype ratios are modified
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3 Mendel studied 7 traits that assorted independently. The only explanation for this behavior is that the genes controlling these traits are located on different chromosomes. True False
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4 a b c d e f g 10 20 20 15 15 5 This map means that there is a 20% recombination frequency between the genes b and c and a 5% recombination frequency between the genes f and g Genes very far apart on the same chromosome will appear to assort independently How many map units between a and g? A-g = 85 cM Recombination freq is not 85% a f a f A F A F af P aF R Af R AF P Recombinant/total = 2/4=50% Maximum freq is 50% 50% also indicates NO LINKAGE If two genes are very far apart on the same chromosome, use markers between these genes to more accurately map the genes
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5 The largest distance that can be measured by this technique is 50MU. This is analogous to using a yardstick to
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