02BIS1012013XLinkLect3

Lrodriguez 11 morgans red eye white eye crosses a

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Unformatted text preview: 001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 10 Biology of Drosophila ­ Males and females are Males morphologically distinct morphologically ­ 2N = 8 ­ X and Y sex chromosomes ­ Female the homogametic Female sex sex ­ Males the heterogametic Males sex sex BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 11 Morgan’s Red Eye - White Eye Crosses ­ A spontaneous white-eyed mutant was found and bred to spontaneous white-eyed produce male and female mating stocks. Because white eyes are recessive to red, they were designated (w). are WW ww BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 12 Morgan’s Red Eye - White Eye Crosses Morgan performed the typical Mendelian monohybrid cross between a redeyed female (WW) and a white-eyed male (ww) and obtained the expected and ratios in the F1 and F2 progeny (all red eyes in the F1 and 3:1 red to white in F2. ratios progeny WW female female ww male male Parents BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 13 Reciprocal Monohybrid Cross ­ Mendel got the same F1 phenotypes whether the purple trait Mendel comes from pollen (male) or female (ovule) flower parts. comes BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 14 Morgan’s Exceptions to Mendel’s 1st Law ­ However, when Morgan performed a reciprocal cross, white-eyed female However, reciprocal white-eyed (ww) to red-eyed males (WW), he observed the first of two exceptions to ), Mendel's laws. First, eye-color in the F1 was divided by sex, females were Mendel's red-eyed and the males were white-eyed. Second, instead of a 3:1 ratio of red to white eyes in the F2, a 1:1 ratio was observed. red 1:1 Parents ww ww female female WW male BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 15 Milestones of Modern Genetics ­1853 Mendel begins pea breeding 1853 experiments experiments Mendel's First Law: The Principle of Equal Segregation. During the formation of gametes, the paired characters (alleles) segregate (or separate) equally so that half of the gametes receive one allele and half of the gametes receive the other member of the pair. Mendel's Five Assumptions: (1) Hereditary determinants (genes) are particulate in nature (therefore there is no blending of characters). (2) Each adult pea plant has a pair of genes (alleles) for each character (as can be seen in the F1, one member can be dominant and one recessive) (3) Members of each gene pair segregate equally into the gametes (pollen/ovule, sperm/egg) (4) Consequently, each gamete carries one member of each gene pair (5) The union of gametes from each parent (to form the zygote) is random. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 16 Mo...
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