BIO 2133 Chapter 4: Module 5A Notes
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13 Mar 2017
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4. 3 neither allele is dominant in incomplete, or partial, dominance: sometimes, an allele is not dominant/recessive but the phenotypes of the parents will be a mix. Incomplete dominance: expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent. Also called partial dominance: an example is snapdragon flowers, a red and a white produce offspring, the offspring will be pink. This results in the enzyme that produces pigment to not produce enough pigment to make the flower red and therefore the flower will be pink. Bio2133 module 5a readings notes: this demonstrates the threshold effect: a normal phenotypic expression occurs anytime a certain level of gene product is attained. 4. 5 multiple alleles of a gene may exist in a population: multiple alleles: in a population of organisms, the presence of three or more alleles of the same gene, can only be studied in populations.
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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. |