300816 Lecture 11: Cell biology patterns of inheritance
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16 Feb 2019
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Salient points: alleles, phenotype vs genotype, mendel, segregation. Inheritance: genetics can predict how genes may be passed on to future generations, this is affected by: How chromosomes are passed on during meiosis. Alleles: an allele is a specific version of a gene at the same position (locus) on a gene, different alleles code for different forms of the same protein. The different forms of the protein function differently- resulting in different characteristics phenotype vs genotype: diploid organisms have 2 copies of every gene. This means that one individual can have two different versions of a gene. The term allele is used to identify different versions of a gene phenotype: describes the organisms appearance as a result of its genotype genotype, describes the combination of alleles present in the organisms cell, homozygous: 2 copies of the same allele: heterozygous: Heterozygote is intermediate in phenotype between the two homozygous. Heterozygote shows some aspect of the phenotypes of both homozygotes.
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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. |