BSC 2023 Lecture Notes - Lecture 26: Abo Blood Group System, Quantitative Genetics, Mendelian Inheritance
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Document Summary
Alternate forms of the same gene homozygous genotype. A genotype consisting of two identical alleles of a gene for a particular trait. heterozygous genotype. A genotype consisting of two different alleles of a gene for a particular trait. phenotype. The observable or detectable characteristics of an individual organism; the physical expression of a genotype. dominant allele. The general term for an allele that masks the presence of another allele in the phenotype. principle of independent assortment. Gregor mendel"s principle of genetic inheritance stating that different pairs of genes are passed to offspring independently so that new combinations of genes, present in neither parent, are possible. In other words, the distribution of one pair of alleles does not influence the distribution of another pair-- the genes controlling different traits are inherited independently of one another. homozygous recessive. The genotype that normally results in the expression of a recessive allele in the phenotype.
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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. |