22 Questions
What occurs when two or more genes specify enzymes that catalyze steps in a common pathway?
Gene interaction
What is the result of a recessive mutant allele at any of the three loci in gene interaction?
A mutant phenotype
What is the term used to describe the situation where a genotype can hide or mask the phenotypic expression of alleles at another locus?
Epistasis
What is the modified F2 ratio when there is epistasis?
Various combinations of 9:3:3:1
What is the genotype of the parents in the example of dominant epistasis in coat color in dogs?
BBII × bbii
What is the ratio of the F1 offspring in the example of dominant epistasis in coat color in dogs?
12:3:1
What is the function of the glycoprotein molecule on the surface of red blood cells?
It acts as a native antigen, providing biochemical and immunological identity to individuals.
What is the genotypic ratio of offspring produced by a mating between two heterozygous MN parents?
1:2:1
What is the maximum number of homologous gene loci that can be occupied by different alleles of the same gene in a diploid organism?
Two
What is the effect of the i allele on the production of A or B antigens in the ABO blood group system?
It does not produce any detectable A or B antigens.
What is the relationship between the IA and IB alleles in the ABO blood group system?
IA and IB alleles are dominant to i allele, but codominant to each other.
What is the phenotype of an individual with the genotype IA IB in the ABO blood group system?
AB
What is the chromosome number on which the gene controlling the ABO blood group system is located?
9
What is the term used to describe the inheritance pattern of the MN blood group system?
Codominant inheritance
What is the term for a location on a chromosome that may be occupied by different alleles of the same gene?
Gene locus
In a cross between a red-flowered snapdragon (R1 R1) and a white-flowered snapdragon (R2 R2), what is the phenotype of the F1 generation?
Pink
What is the ratio of the F2 generation in a monohybrid cross exhibiting incomplete dominance?
1:2:1
What is the term for a situation where neither allele is dominant?
Incomplete dominance
What is an example of codominant inheritance?
Inheritance of ABO blood groups
What is the term for an allele that occurs most frequently in a population?
Wild-type allele
What is the term for the interaction between genes that affect the same trait?
Epistasis
What is the term for multiple forms of a gene that occupy the same locus on a chromosome?
Alleles
Study Notes
Extensions of Mendelian Genetics
- Mendel's work was expanded upon by later research, which showed that phenotypes may not follow predicted ratios, but genotypes still obey the principles of Mendelian inheritance.
Definitions
- An allele is an alternative form of a gene.
- Wild-type allele is the most frequent allele in a population, which serves as a standard for comparing other mutations at the same locus.
- Gene loci are locations on a chromosome that may be occupied by different alleles of the same gene.
Incomplete Dominance
- Incomplete dominance occurs when neither allele is dominant.
- Example: flower color of snapdragons, where heterozygotes express an intermediate, blended phenotype.
- Genotypic ratio of F2 generation is 1:2:1, identical to that of Mendel's monohybrid cross.
- Phenotypic ratio is identical to genotypic ratio.
Codominant Inheritance
- Codominant inheritance occurs when two alleles of a single gene produce two distinct, detectable gene products.
- Example: MN blood group system in humans, controlled by a locus on chromosome 4, with two alleles (LM and LN).
- The two alleles produce distinct glycoprotein molecules on the surface of red blood cells, resulting in different blood types (M, MN, and N).
Multiple Alleles of a Gene
- Multiple alleles of a gene occur when three or more alleles of the same gene exist in a population.
- Example: ABO blood group system in humans, discovered by Karl Landsteiner, with IA and IB alleles producing A and B antigens, respectively.
- IA and IB alleles are dominant to the i allele, but codominant to each other.
Gene Interaction
- Gene interaction occurs when two or more genes specify enzymes that catalyze steps in a common pathway.
- Example: precursor P is converted to end product C through enzymes specified by genes g+1, g+2, and g+3.
- Recessive mutant alleles can produce defective enzymes, leading to a mutant phenotype when homozygous recessive at any of the loci.
- Epistasis occurs when the expression of one gene is dependent on the expression of another gene.
- Example: fur color in mice, coat color in dogs, and dominant epistasis (12:3:1) in coat color in dogs.
Quiz on advanced concepts of Mendelian genetics, including alleles, gene locus, epistasis, and inheritance patterns. Covers incomplete dominance, codominance, multiple alleles, and genetic interaction.
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