Gain-of-function mutations are a mutation that causes a gene to be expressed in an additional place where it is not normally expressed or during a stage of development when it is not normally expressed. This is usually associated with dominant mutant alleles. Dominant-negative mutations is defined as the protein encoded by the mutant gene acts antagonistically to the normal protein. This is usually associated with ______ alleles. Haploinsufficiency is when the dominant mutant allele is a loss-of-function allele. It is used to describe when a heterozygote exhibits an abnormal or disease phenotype. II. Chapter 4-4: Incomplete Dominance, Overdominance, and Codominance A. Section Learning Objectives: 1. Predict the outcome of crosses involving incomplete dominance, overdominance, and codominance. 2. Explain the underlying molecular mechanisms of incomplete dominance, overdominance, and codominance. 3. Use the terms listed below to correctly explain concepts, assigned figures, and specified end-of-chapter questions. B. Important Terms: Incomplete dominance: a pattern of inheritance in which a heterozygote that carries two different alleles exhibits a phenotype that is intermediate to the corresponding homozygous individuals Heterozygote advantage/Overdominance: A pattern of inheritance in which a heterozygote has a higher Darwinian fitness compared with either of the corresponding homozygotes Sickle cell disease: Malaria Multiple alleles: when the same gene exists in two or more alleles within a population ABO blood group: Codominance: a pattern of 3
inheritance in which two alleles are both expressed in the heterozygous condition C. Assigned Figures : 4.5*, 4.6*, 4.7*, 4.8*, and 4.9* (parts a and b); (* There is a video clip lecture for this figure in the Bb folder) D. Assigned Tables : None E. Assigned Comprehension Questions: 1 and 2 1. d 2. a F. Problem Sets and Insights – Assigned Solved Problems: S5 (Parts A-C) G. Problem Sets and Insights – Assigned Conceptual Questions : C1, C4, C9-C11 C1: in dominance, only one phenotype is expressed without any alteration. In incomplete dominance, the phenotype is intermediate between the corresponding homozygous individuals. In overdominance, a heterozygote has a greater reproductive success compared with either of the corresponding homozygotes. In codominance, two alleles are both expressed in the heterozygous individual. C4: If the normal allele is the dominant allele, it tells you that one copy of the gene produces a sufficient amount of the protein encoded by the gene. A homozygote with this protein does not alter the phenotype. If the allele is incompletely dominant, it means one copy of the normal allele does not produce the same trait as the homozygote C9: Types O and AB provide an unambiguous genotype. It is possible for a couple to produce children with all for blood types if one is I A i and the other is I B i.
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