BIOL 1020 Lecture Notes - Lecture 25: Mendelian Inheritance, Meddle, Epistasis
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11 Nov 2016
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Inheritance patterns are often more complex than predicted by s imple mendelian g enetics. T he relations hip between g enotype and phenotype is rarely as s imple as in the pea plant characters meddle s tudied many heritable characters are not determined by one g ene with two alleles. E xtended mendelian g enetics for a s ing le g ene. In c odom inanc e two dominant alleles affect the phenotype in s eparate, dis ting uis hable ways. A dominant allele does not s ubdue a reces s ive allele; alleles dont interact. Alleles are s imply variations in a g enes nucleotide s equence. **f or any characteris tics , dominance/reces s ivenes s relations hips of alleles depends on the level at which we examine the phenotype. D ominant alleles are not neces s arily more common in populations than reces s ive alleles. D ominant alleles s how up in f 1 g eneration.
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These all relate to exceptions to the inheritance patterns encountered by Mendel.รขยย
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. |