Questions and Answers
What is the term for when a dominant allele is not expressed even though an individual carries it?
What is the result of a cross between homozygous red-flowered and homozygous white-flowered parents?
Why does a heterozygote not express the same trait as a homozygote?
What is the term for when a heterozygote has a trait that is more beneficial than either homozygote?
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What is an example of a dominant trait that is not expressed?
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What is the term for when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype?
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Why may a heterozygote have increased resistance to infection by microorganisms?
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What is the result of molecular interactions between proteins encoded by different alleles?
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What is the primary focus of the chapter on extensions of Mendelian inheritance?
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What is the relationship between the molecular expression of a gene and the trait itself?
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What is the definition of simple Mendelian inheritance?
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What is the purpose of examining different patterns of Mendelian inheritance?
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What is the blood type of an individual carrying the A and B alleles?
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What is the term applied to the inheritance of alleles that obey Mendel's laws?
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What is an example of genetic polymorphism?
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What is the characteristic of codominant alleles?
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What is the result of 50% of the protein produced by a single copy of the dominant allele in the heterozygote?
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In which type of inheritance pattern do males have one copy of genes and females have two copies?
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What is the focus of Table 4.1?
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What is the effect of sex hormones on the molecular expression of genes in sex-influenced inheritance?
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What is an example of a sex-limited trait?
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What is the relationship between X-linked alleles in a heterozygous female?
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What is the effect of a single copy of a dominant X-linked allele in a heterozygous female?
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In which type of inheritance pattern do sex hormones regulate the molecular expression of genes?
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Study Notes
Inheritance Patterns
- Incomplete Penetrance: A dominant allele is present, but its effects are not seen due to environmental influences or counteracting proteins from other genes.
Incomplete Dominance
- A heterozygote has a phenotype that is intermediate between the two corresponding homozygotes, e.g., a cross between red-flowered and white-flowered parents produces pink-flowered offspring.
Overdominance
- A heterozygote has a trait that is more beneficial than either homozygote.
- Three ways heterozygotes gain benefits:
- Increased resistance to infection by microorganisms
- Producing more forms of protein dimers with enhanced function
- Producing proteins that function under a wider range of conditions
Extensions of Mendelian Inheritance
- Mendelian inheritance describes patterns that obey two laws: the Law of Segregation and the Law of Independent Assortment.
- Simple Mendelian inheritance involves a single gene with two different alleles that display a simple dominant/recessive relationship.
Codominance
- The codominant alleles encode proteins that function slightly differently from each other, and the function of each protein in the heterozygote affects the phenotype uniquely.
- Example: blood typing, where an individual carrying the A and B alleles will have an AB blood type.
X-linked Inheritance
- Inheritance of genes located on the X chromosome.
- In mammals and fruit flies, males have one copy of X-linked genes, whereas females have two copies.
- If a pair of X-linked alleles shows a simple dominant/recessive relationship, 50% of the protein produced by a single copy of the dominant allele in a heterozygous female is sufficient to produce the dominant trait.
Sex-influenced Inheritance
- The effect of sex on the phenotype of an individual.
- Some alleles are recessive in one sex and dominant in the opposite sex.
- Sex hormones may regulate the molecular expression of genes, influencing the phenotypic effects of alleles.
Sex-limited Inheritance
- Traits that occur in only one of the two sexes.
- Example: breast development in mammals.
- Sex hormones that are primarily produced in only one sex are essential to produce a particular phenotype.
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Description
This quiz covers concepts related to inheritance patterns, including penetrance and molecular influences on gene expression. It explores how dominant traits can be affected by environmental factors and more.
