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Questions and Answers
What is the reason behind the non-expression of a dominant allele in an individual despite its presence?
What is the reason behind the non-expression of a dominant allele in an individual despite its presence?
- The protein encoded by the gene may not exert its effects (correct)
- Genetic polymorphism
- The presence of a lethal allele
- Environmental influences
What is the term for the pattern of inheritance where the heterozygote has a trait that is more beneficial than either homozygote?
What is the term for the pattern of inheritance where the heterozygote has a trait that is more beneficial than either homozygote?
- Incomplete dominance
- Overdominance (correct)
- Co-dominance
- Dominance
In a cross between homozygous red-flowered and homozygous white-flowered parents, what is the expected phenotype of the heterozygous offspring?
In a cross between homozygous red-flowered and homozygous white-flowered parents, what is the expected phenotype of the heterozygous offspring?
- No flowers
- Red flowers
- Pink flowers (correct)
- White flowers
What is the term for the pattern of inheritance where both alleles are expressed simultaneously without forming an intermediate phenotype?
What is the term for the pattern of inheritance where both alleles are expressed simultaneously without forming an intermediate phenotype?
What is the potential benefit of being heterozygous for a particular gene?
What is the potential benefit of being heterozygous for a particular gene?
What is the term for the phenomenon where a dominant allele is not expressed despite its presence?
What is the term for the phenomenon where a dominant allele is not expressed despite its presence?
What is the primary goal of examining different patterns of Mendelian inheritance?
What is the primary goal of examining different patterns of Mendelian inheritance?
What is the reason behind the beneficial effects of being heterozygous for a particular gene?
What is the reason behind the beneficial effects of being heterozygous for a particular gene?
What term is commonly applied to the inheritance of alleles that obey Mendel's laws and follow a strict dominant/recessive relationship?
What term is commonly applied to the inheritance of alleles that obey Mendel's laws and follow a strict dominant/recessive relationship?
What is a characteristic of alleles that display a dominant/recessive relationship?
What is a characteristic of alleles that display a dominant/recessive relationship?
What is the term for the pattern of inheritance where the heterozygote has a phenotype that is intermediate between the two homozygotes?
What is the term for the pattern of inheritance where the heterozygote has a phenotype that is intermediate between the two homozygotes?
What is an example of a trait that deviates from the simple dominant/recessive relationship?
What is an example of a trait that deviates from the simple dominant/recessive relationship?
What is the effect of a lethal allele on the phenotype of an organism?
What is the effect of a lethal allele on the phenotype of an organism?
What is genetic polymorphism?
What is genetic polymorphism?
What can be a result of a mutation in a gene?
What can be a result of a mutation in a gene?
What is the relationship between the molecular expression of a gene and the trait itself?
What is the relationship between the molecular expression of a gene and the trait itself?
What is the characteristic of codominant alleles at the molecular level?
What is the characteristic of codominant alleles at the molecular level?
In X-linked inheritance, what is the effect of a single copy of a dominant allele in a heterozygous female?
In X-linked inheritance, what is the effect of a single copy of a dominant allele in a heterozygous female?
What is the defining feature of sex-influenced inheritance?
What is the defining feature of sex-influenced inheritance?
In sex-limited inheritance, what is the essential factor for producing a particular phenotype?
In sex-limited inheritance, what is the essential factor for producing a particular phenotype?
What is an example of a sex-limited trait?
What is an example of a sex-limited trait?
In codominance, what is the effect of the function of each protein in the heterozygote?
In codominance, what is the effect of the function of each protein in the heterozygote?
What is the characteristic of X-linked alleles in males?
What is the characteristic of X-linked alleles in males?
What is the difference between sex-influenced and sex-limited inheritance?
What is the difference between sex-influenced and sex-limited inheritance?
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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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