Biology 2581B Chapter Notes - Chapter 9: Mendelian Inheritance, Zygosity, Gamete
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3 May 2020
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Mendel formulated theories of inheritance: heritable traits are determined by heritable factors called genes. They come in pairs: law of dominance: genes come in different versions called alleles. Dominant alleles can hide the presence of recessive alleles and determine appearance: law of segregation: during gamete production, each egg or sperm cell (gamete) receives one of the two alleles for a gene present in the parent"s dna. This is: law of independent assortment: genes from different traits are inherited random. independently of one another. An organism that has two different alleles for a gene. They produce gametes with different alleles, so are not true breeding. An organism that has a pair of identical alleles for a gene. They are true-breeding, because all their gametes contain the same allele. Has no noticeable effect on the organism"s appearance, if the dominant allele is present.
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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. |