Ch_5_Extensions-1 - Extensions&Modifications...

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to Mendelian Genetics
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Lethal Alleles Lethal alleles causes death at an early stage of development Some genotypes may not appear A 2:1 ratio of phenotypes is observed (not the 3:1 ratio because ¼ die) The Mexican Hairless dog (Xolo) Individuals who are homozygous dominant (HH) die Individuals who are homozygous recessive (hh) are hairy Heterozygous (Hh) individuals are hairless Hh hh
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Manx cats have a dominant mutation for shortened or no tail Homozygous dominant individuals die
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5.17 modified When an alpine chipmunk with whites spots is crossed with another chipmunk that has no spots, approximately ½ of the offspring have white spots and ½ have no spots. When two chipmunks with white spots are crossed, 2/3 of the offspring posses white spots and 1/3 have no spots. Give the genotypes and phenotypes of all individuals in this cross. How would you produce alpine chipmunks that are true breeding for white spots?
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Acondroplasia is an autosomal dominant trait that is lethal in the homozygous form. A couple, both of which have acondroplasia, decide to have children. What is the probability that their first child will have acondroplasia? I II 1 2 ?
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Multiple Alleles In mallard ducks, 3 alleles produce feather patterns M R produces restricted pattern M produces wild-type mallard pattern m d produces dusky With the following phenotypes M R M R - restricted M R M - restricted M R m d - restricted MM - mallard M m d - mallard m d m d - dusky
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WP 5.1b and 5.1d The type of plumage found in mallard ducks is determined by 3 alleles at a single locus M R , which encodes restricted plumage M, which encodes mallard plumage m d , which encodes dusky plumage Restricted is dominant to mallard, which is dominant to dusky (M R > M > m d ). Give the expected phenotypes and proportions of offspring produced by the following crosses. b. M R m d x Mm d d. M R M x Mm d
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Dihybrid Cross Remember: Dihybrid cross with 2 genes and 2 traits gives 9:3:3:1 ratio of phenotypes in F2 generation
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Gene Interaction Dihybrid cross with 2 genes and 1 trait can also give 9:3:3:1
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Epistasis Sometimes the effects of gene interaction is that one gene masks the effects of another gene The observed ratios depend on the type of epistasis
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Recessive epistasis Black (B) is dominant Brown (b) is recessive (e) at another locus is recessive gold. Prevents pigment deposition, so hides effects of black or brown pigment alleles. Results in 9:3:4 ratio
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5.29a modified Your buddy, Lucas, decided that he wanted to start breeding dogs so he bought a yellow Labrador male and a brown Labrador female and mated them. Lucas never took genetics and he was shocked when all the puppies were black. Explain to him what happened.
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Dominant epistasis White (B) is dominant Colored (b) is recessive An allele (A) at another locus produces an enzyme that will cause an otherwise green squash to become yellow Results in 12:3:1 (white: yellow: green) ratio
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From text, pg. 109
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This note was uploaded on 01/30/2010 for the course ECOL 320 taught by Professor Weinert during the Spring '07 term at University of Arizona- Tucson.

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Ch_5_Extensions-1 - Extensions&Modifications...

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