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Questions and Answers
Which is the inheritance pattern where an allele is dominant in one sex and recessive in the opposite sex?
A trait that is expressed in only one sex and not seen in the opposite sex shows ______ inheritance.
sex-limited
Male birds often have more ornate and colorful feathering patterns than female birds. This is an example of ______.
sexual dimorphism
A lethal allele usually shows a(n) ______ inheritance pattern.
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A gene that codes for a product that is necessary for the survival of an organism is called a(n) ______ gene.
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For ______ inheritance, a given allele is dominant in one sex and recessive in the opposite sex.
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A temperature-sensitive allele that causes the death of an organism only with exposure to a specific range of temperatures is a(n) ______ allele.
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Which inheritance pattern is shown for a trait occurring in one sex but not in the opposite sex?
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G6PD deficiency results from a deficiency of an enzyme that is especially important for protecting red blood cells from harmful oxidizing agents. The allele for G6PD deficiency would be described as a ____ lethal allele.
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A phenomenon involving animals of the same species, but of opposite sexes, that have different physical features is called ____ ____.
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Suppose that there are two male mice who are homozygous for the same allele. Which type of allele is likely to be responsible for the death of one mouse despite identical conditions?
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An allele that can lead to the death of an individual is a(n) ______ allele.
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Huntington disease is a lethal condition for which symptoms begin to appear in middle age. The age at which a person begins to show disease symptoms is called the ___ of ___.
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A gene that produces a beneficial product that is not absolutely required for survival of the organism is called a(n) ______ gene.
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The pattern where one gene affects many traits is called ______.
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An allele that leads to the death of the organism only under specific environmental influences is called a(n) ______ allele.
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Why does an organism that inherited one or more temperature-sensitive lethal alleles survive at low temperatures?
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Pleiotropy can be caused by ______.
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An allele that causes death in some, but not all individuals in a population is a(n) ______.
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Corn kernels can have a purple color due to the dominant allele of one gene. This is an example of ______.
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Parents can unknowingly pass on a dominant lethal allele for Huntington disease to their offspring because the ______.
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When Blue-Eyed Mary plants inherit at least one dominant allele for a gene for flower color, their petals are blue. The effect of the second gene on the first flower color gene is called ______.
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The allele for sickle cell anemia leads to multiple changes in the individual's phenotype, including the onset of anemia and reduced susceptibility to malaria. The name for these multiple effects on phenotype is ______.
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The following pathway is proposed to explain the inheritance of purple flower color in pea plants: Colorless Precursor→Colorless Intermediate→Purple Pigment. An explanation for why plants with the ccPp genotype have white petals while plants with the CcPp genotype have purple petals is ______.
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For summer squash, the dominant allele Y for gene 1 leads to yellow color while the recessive allele y leads to green color. What is the fraction of offspring that will be white when YyWw is crossed with YyWw?
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Which choice does NOT represent an explanation for pleiotropy?
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Suppose that the covering on corn kernels can have a purple color due to the dominant allele P of gene 1. What is the effect of gene 2 on gene 1 for the genotype Ppcc?
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The pattern where allelic variants of two different genes affect a single trait is called ______.
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For summer squash, the dominant allele for one gene leads to yellow color while the recessive allele for this gene leads to green color. How many phenotypes would be observed among the offspring of the cross YyWw x YyWw?
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Suppose there is a biochemical pathway for producing blue flower color that involves a dominant allele for gene 1 and gene 2. A plant that has the homozygous recessive genotype for gene 1 would have ______ petals.
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What is the phenotypic ratio produced for the cross BbCc x BbCc in cats where gene 1 specifies coat color?
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When a geneticist produces an organism that is homozygous for a loss-of-function allele, the change is called a(n)
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For summer squash, the dominant allele Y for gene 1 leads to yellow color while the recessive allele y leads to green color. The dominant allele W leads to white squash while the recessive allele w does not interfere with color development. For the cross PpCc x PpCc, what fraction of the plants are expected to have a colorless covering on their corn kernels?
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The pattern where one gene compensates for the loss of function of another gene is called ______.
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Genes that may differ slightly in sequence but were derived by duplication during evolution are called?
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A quantitative trait is defined as a trait that ______.
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Characteristics that are determined by several genes and are also influenced by environmental factors are called ____ traits.
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A trait that does not fall into discrete categories is referred to as a(n) ____ trait.
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In bread wheat, the color of the hull can be dark red, white, or various intermediate shades of red. Genetic analysis of this trait has demonstrated that it is controlled by ______.
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A frequency distribution is a graph that shows the ______.
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Quantitative traits tend to show a continuum of variation because they are usually ____.
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Which of the following are examples of quantitative traits?
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The graph shows a hypothetical situation in which seed weight is controlled by three genes. If the environmental effect were high, ______.
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The graphs show the relationship between seed weight and genotype for a single gene that influences seed weight. Graph A shows a low environmental effect. What does Graph B show?
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Study Notes
Inheritance Patterns
- Sex-influenced inheritance occurs when an allele is dominant in one sex but recessive in the opposite sex.
- Sex-limited inheritance describes traits expressed in only one sex and not in the opposite.
- Sexual dimorphism refers to differences in physical features between male and female animals of the same species.
Alleles and Their Effects
- Lethal alleles generally exhibit a recessive inheritance pattern.
- Conditional lethal alleles lead to death under specific environmental conditions, such as temperature-specific alleles.
- Semilethal alleles cause death in some individuals within a population but not others.
- Essential genes are critical for an organism's survival, while nonessential genes produce beneficial products that are not necessary for survival.
Pleiotropy and Gene Interaction
- Pleiotropy describes a single gene affecting multiple traits, which can occur if the gene influences different stages of development, different cell types, or various cell functions.
- Gene interaction is illustrated when allelic variants of two genes affect a single trait, evidenced by dominance and epistasis in phenotypic expression.
Phenotypic Ratios and Crosses
- When crossing two dihybrid plants (e.g., YyWw x YyWw), ratios of phenotypes can be predicted, such as 12/16 showing white squash due to epistatic interactions.
- In specific crosses, like BbCc x BbCc in cats, the phenotypic ratio produced would be 9 black:3 chocolate:4 albino.
Complex and Quantitative Traits
- Complex traits are influenced by multiple genes and environmental factors.
- Quantitative traits can be numerically described; examples include seed weight and human blood pressure, often showing continuous variation and polygenic effects.
Development and Gene Duplication
- Gene redundancy occurs when one gene can compensate for the loss of function of another, often due to the presence of paralogs, or genes derived from duplication.
- Gene knockouts, which involve producing organisms homozygous for loss-of-function alleles, help study gene functions and mechanisms.
Frequency Distributions
- Frequency distribution graphs display the number of individuals in various phenotypic categories, allowing analysis of trait variation.
- High environmental effects can increase the overlap in trait expression among genotypes, demonstrating the interaction between genotype and environment.
Specific Traits and Their Mechanisms
- The color of corn kernels is influenced by two genes, where recessive alleles can mask dominant alleles, leading to variations like purple (P allele) and colorless (pp genotype).
- Threshold traits result from the quantitative contributions of many genes, demonstrating how complex traits are inherited.
Key Terms
- Epistasis describes a situation where one gene affects the expression of another.
- Complementation refers to different mutations preventing the color in plants occurring in different genes.
- Continuous traits do not fall into discrete categories and illustrate the nuances of genetic expression influenced by multiple factors.
Studying That Suits You
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Description
Test your knowledge on key concepts of genetics from Chapters 24 and 28. This quiz covers topics such as sex-influenced and sex-limited inheritance patterns. Perfect for reviewing essential terms and definitions in genetics.
