BIOL 1201 Chapter : Chapter 14
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Mendel was a monk who was trained in science at the university of vienna. Homologous chromosomes carry the same kinds of genes for the same characteristics. Genes for the same characteristics are found at the same loci (plural for locus) on both homologous chromosomes. Genes for a characteristic found on homologous chromosomes may not be identical. Alternative versions of genes found at the same gene locus are called alleles. If a mutation occurs in gametes, the cells that become sperm or eggs, then the mutation can be passed on from parent to offspring. Mutation is not always a bad thing. An organism"s two alleles may be the same or different. If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous or true-breeding at that locus. If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus, also called hybrid.
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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. |