BIOL 102 Lecture Notes - Lecture 22: Molecular Genetics, Hemoglobin, Y Chromosome
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Incomplete dominance: the phenotype of heterozygotes is intermediate between the. Alleles arise through mutation, and the same gene in different individuals may have different mutations, each producing a new allele. Therefore, although an individual can have at most two different alleles, a species may have multiple alleles of many of its genes. The human blood types are an example of multiple alleles of a single gene: blood types a, b, ab, and o arises from three different alleles of a single gene on chromosome 9. Codominance = the pattern of inheritance when heterozygotes express phenotypes of both of the homozygotes (ex. having both a and b glycoproteins for blood type). Polygenic inheritance = a form of inheritance in which the interaction of two or more genes contributes to a single phenotype. Human height, weight, skin color, and eye color are traits not governed by single genes but influenced by interactions among two or more genes, and interactions with environment.
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What is the difference between incomplete dominance and codominance?
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What is the difference between incomplete dominance and codominance?
1. In incomplete dominance, the dominant phenotype is expressed in heterozygotes. In codominance, both phenotypes are expressed in heterozygotes. |
2. The phenotype reveals the genotype only in codominance. |
3. In both types of inheritance, the heterozygotes express the phenotypes dictated by both alleles. |
4. In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes. |
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. |