HMB265H1 Lecture : Notes taken during lecture

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redtermite204

28 Jan 2011

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Law of segregation still held but geno-pheno relationship modified. Independent assortment come into play with dihybrid crosses. cannot self animals but cross f1 male with f1 female: expect in f2 1:2:1 ratio of walnut, rose, and pea. single phenotype showed up a fourth: cannot be accounted for because mendel has 3 phenotypes, cannot break down into one to two to one ratio. saw numbers as nine to three to three to one ratio: instead of two genes influencing two different traits, actually two genes influencing one phenotype. cf. pleiotropy one gene with multiple phenotypes: actually recover expected ratios good, walnut double heterozygote since parents were inbred lines, two genes contributing to one phenotype but everything else fits with. crossed f1 white and blue result. To get blue, must have dominant phenotype at two genes: at least one big a and at least one big b.

Related Questions

These all relate to exceptions to the inheritance patterns encountered by Mendel.â

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.

-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.

-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.

-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.

-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.

-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.

-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.

-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.

Which of Mendel's findings provided the best evidence for the principle of independent assortment?

		A tall plant and dwarf plant will produce all tall offspring.
		Homozygous recessive traits are always rare.
		A dihybrid cross will result in non-parental phenotype combinations (not seen in original P generation)
		A monohybrid cross will result in a 1:2:1 genotype ratio.

1. Using the multiplication rule, calculate the probabilities of each genotype occurring from a given cross.

2. Using the multiplication rule and the addition rule, calculate the probabilities of a certain combination of genotypes occurring as the result of a genetic cross.

3. Distinguish between incomplete dominance and codominance, multiple alleles and pleiotropy, epistasis and polygenic inheritance.

4. Explain how each of the following impact the phenotype; incomplete dominance, codominance, multiple alleles, pleiotropy, epistasis, polygenic inheritance, environmental influence.

5. Explain the role of the environment in the phenotypic range of some genes.

HMB265H1 Lecture : Notes taken during lecture

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