BIOL 110 Chapter Notes - Chapter 16: Mns Antigen System, Quantitative Trait Locus, Mendelian Inheritance
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Incomplete dominance: complete dominance - one allele over the others (always looked like one of two phenotypes) Incomplete dominance - individuals who are heterozygous exhibit a phenotype that is an intermediate between individuals who are homozygous. Codominance: both alleles are expressed in the phenotype of individuals that have are heterozygous, ex: mn blood group. Mn are both expressed in the phenotype. The three types of dominance: complete: one over the other. Multiple alleles: human abo blood group provides an example of multiple alleles, ab, a, b, o, a parental genotype can be uncertain for this because a and b types have multiple possible genotypes. Pleiotropy: one gene can have multiple effects on the phenotype, ex: albino individuals also have a high frequency of crossed eyes. The gene that causes albinism can also cause defects in the nerve connections between the eyes and the brain. But these traits are not always linked. (demonstrates complexity)
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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. |