C2 - C1 Mendels work showed that genetic determinants are inherited in a dominant/recessive manner This was readily apparent in many of his crosses

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C1. Mendel’s work showed that genetic determinants are inherited in a dominant/recessive manner. This was readily apparent in many of his crosses. For example, when he crossed two true-breeding plants for a trait such as height (i.e., tall versus dwarf), all the F 1 plants were tall. This is inconsistent with blending. Perhaps more striking was the result obtained in the F 2 generation: 3/4 of the offspring were tall and 1/4 were short. In other words, the F 2 generation displayed phenotypes that were like the parental generation. There did not appear to be a blending to create an intermediate phenotype. Instead, the genetic determinants did not seem to change from one generation to the next. C2. In the case of plants, cross-fertilization occurs when the pollen and eggs come from different plants while in self- fertilization they come from the same plant. C3. The genotype is the type of genes that an individual inherits while the phenotype is the individual’s observable traits. Tall pea plants, red hair in humans, and vestigial wings in fruit flies are phenotypes. Homozygous, TT, in pea plants; a heterozygous carrier of the cystic fibrosis allele; and homozygotes for the cystic fibrosis allele are descriptions of genotypes. It is possible to have different genotypes and the same phenotype. For example, a pea plant that is TT or Tt would both have a tall phenotype. C4. A homozygote that has two copies of the same allele. C5. Conduct a cross in which the unknown individual is mated to an individual that carries only recessive alleles for the genes in question. C6. Diploid organisms contain two copies of each type of gene. When they make gametes, only one copy of each gene is found in a gamete. Two alleles cannot stay together within the same gamete. C7. B. This statement is not correct because these are alleles of different genes. C8. Genotypes: 1:1 Tt and tt Phenotypes: 1:1 Tall and dwarf C9. The recessive phenotype must be a homozygote. The dominant phenotype could be either homozygous or heterozygous. C10. c is the recessive allele for constricted pods, Y is the dominant allele for yellow color. The cross is ccYy × CcYy. Follow the directions for setting up a Punnett square, as described in chapter 2. The genotypic ratio is 2 CcYY : 4 CcYy : 2 Ccyy : 2 ccYY : 4 ccYy : 2 ccyy. This 2:4:2:2:4:2 ratio could be reduced to a 1:2:1:1:2:1 ratio. The phenotypic ratio is 6 inflated pods, yellow seeds : 2 inflated pods, green seeds: 6 constricted pods, yellow seeds : 2 constricted pods, green seeds. This 6:2:6:2 ratio could be reduced to a 3:1:3:1 ratio. Note: smooth pods are the same as inflated pods. C11. The genotypes are 1 YY : 2 Yy : 1 yy. The phenotypes are 3 yellow : 1 green. C12. Offspring with a nonparental phenotype are consistent with the idea of independent assortment. If two different traits were always transmitted together as unit, it would not be possible to get nonparental phenotypic combinations. For example, if a true-breeding parent had two dominant traits and was crossed to a true-breeding
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This note was uploaded on 04/07/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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C2 - C1 Mendels work showed that genetic determinants are inherited in a dominant/recessive manner This was readily apparent in many of his crosses

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