BIOLOGY 1P03 Chapter Notes - Chapter 11 : Quantitative Trait Locus, Hemoglobin, Muscular Dystrophy
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6 Dec 2016
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A recessive hereditary condition caused by defective alleles of the genes that encode the enzymes require for melanin. Carrier: an individual who is heterozygous for a recessive condition; a carrier displays the dominant phenotype but can pass on the recessive allele to offspring. Codominance: the relation between two alleles of a gene, such that both alleles are phenotypically expressed in heterozygous individuals. Cross-fertilization: the union of sperm and egg from two individuals of the same species. Dominant: an allele that can determine the phenotype of heterozygotes completely. Gene linkage: the tendency for genes located on the same chromosome to be inherited together. Genetic recombination: the generation of new combinations of alleles on homologous chromosomes due to the exchange of dna during crossing over. Genotype: the genetic composition of an organism; the actual alleles of each gene carried by the organism. Hemophilia: a recessive, sex-linked disease in which the blood fails to clot normally.
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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. |