BIS 2B Lecture Notes - Lecture 10: Punnett Square, Gamete, Zygote
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23 Oct 2018
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Mendel"s inference from the results of monohybrid crosses: (pollen/sperm or egg) contains only one factor , but the zygote contains two - the zygote is produced from the fusion of two gametes. These factors are now known as genes . This lead to mendel"s first law of heredity: . When any individual produces gametes, the two copies of a gene separate/segregate so that each gamete only receives on copy. Thus from every parent of the p generation, every individual of the f 1 generation receives one gene copy chosen randomly . The location of a gene on a chromosome is called a locus . Variations of a gene are called alleles . When an individual has two of the same alleles, they are homozygous ( homozygotes ); when. The combination of each pair of alleles for a given gene is an organism"s genotype . The totality of all genes in an organism is the genome.
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These all relate to exceptions to the inheritance patterns encountered by Mendel.รขยย
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. |