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BIOL 190 Lecture Notes - Lecture 20: Dihybrid Cross, Epistasis, Heterogametic Sex

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copperwoodchuck239

19 Oct 2016

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University of San Diego

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Biology Courses

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Professor

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Document Summary

Birds, snakes, and butter ies hav zz zw chromosomes. Females are heterogametic sex: same rules as for x-linked, but ipped reproductive repercussions. Modi cations to mendelian patterns: dominance, all traits we have discussed thus far are completely dominnat, phenotype of heterozygous is same as homozygous, amount of functioning protein is not majorly hampered by only one function protein. Incomplete penitence - less than 100% of a population displays the expected phenotype with a given genotype the degree to which one individual expresses a phenotype: expressivity. Ex: polydactyly (extra digits) - dominant allele: not always seen in people with allele - 75% penetance, some people have fully formed extra ngers, others very small. Lethal alleles: genotypes that, when combined, are lethal, causes deviation in expectation of genotype proportions, ex: lucien cu not"s mice, y is dominant, but yy is lethal, so.

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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.