Questions and Answers
What is the term for the pattern where a dominant allele is present but its effect is not visible?
In a case of incomplete dominance, what is the phenotype of the heterozygous offspring?
What is the term for the situation where the heterozygote has a more beneficial trait than either homozygote?
What is the reason for penetrance, according to the molecular perspective?
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What is the term for the pattern where the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype?
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Why may heterozygotes have increased resistance to infection by microorganisms?
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What is the result of a cross between homozygous red-flowered and homozygous white-flowered parents, in terms of flower color?
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In dominant and recessive alleles, what is the main difference between the dominant and recessive alleles?
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What is a characteristic of simple Mendelian inheritance?
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What is the main goal of examining different patterns of Mendelian inheritance?
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What is the term applied to the inheritance of alleles that obey Mendel's laws and follow a strict dominant/recessive relationship?
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What can occur when a single gene has three or more alleles?
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What is the result of a single copy of a dominant allele in a heterozygote?
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What is an example of a complex inheritance pattern?
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What is the relationship between genetic polymorphism and Mendelian inheritance?
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What is the result of a mutation in a gene?
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What is the blood type of an individual carrying the A and B alleles?
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In X-linked inheritance, what percentage of the protein produced by a single copy of the dominant allele is sufficient to produce the dominant trait in a heterozygous female?
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What type of inheritance pattern involves the effect of sex on the phenotype of the individual?
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Which type of inheritance pattern involves traits that occur in only one of the two sexes?
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What is the main difference between sex-influenced and sex-limited inheritance patterns?
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In X-linked inheritance, what is the expression of the copy of the gene that males carry?
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What is an example of codominance?
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What regulates the molecular expression of genes in sex-influenced and sex-limited inheritance patterns?
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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
Understanding inheritance patterns, including incomplete penetrance and how environmental influences affect gene expression.
