BIOLOGY 1M03 Lecture Notes - Lecture 1: Allele Frequency, Genotype Frequency, Ecology
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14 Jun 2020
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Two de nitions of evolution: heritable changes in species traits over time, changes in allele frequency, genotype - the collection of an individual"s genes, phenotype - the collection of an individual"s (physiological and physical) traits. What we can usually observe about an individual. Phenotype is largely (but not entirely) determined by genotype. Analyzing genotype frequencies: make simple assumptions about how frequencies work, calculate expected frequencies under our assumptions, measure observed frequencies in the population, look for evidence of systematic (non-random) di erence between expected and observed frequencies. Assumptions: expected frequencies are usually calculated by assuming that alleles assort randomly and independently, like ipping two coins or rolling two dice. Hardy-weinberg distribution: the hardy-weinberg distribution is the distribution expected if alleles work like coins (random and independent) If p is frequency of allele a1 and q is frequency of allele a2, then: frequency of genotype a1a1 is p^2, frequency of genotype a2a2 is q^2, frequency of genotype a1a2 is 2pq.
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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. |