Unit 2, week 4

Which of the following is known as Mendelian ratio?

• 9:3:3:1

• 1:2:1

• 3:1

• 2:1:1

• 4:1

Answer explanation

The Mendelian ratio refers to the proportion of offspring with specific traits resulting from a genetic cross. The correct choice is 3:1, which represents the phenotypic ratio observed in a monohybrid cross between two heterozygous individuals. This ratio reflects the inheritance pattern of a single gene with two alleles, where one allele is dominant over the other.

An individual with a genotype of two recessive alleles is said to be:

• Homozygous

• Heterozygous

• Hemizygous

• Co-dominant

• None of these

Answer explanation

An individual with a genotype of two recessive alleles is said to be homozygous. This means that both alleles for a particular gene are the same and recessive. Heterozygous, hemizygous, and co-dominant do not describe this situation, and 'none of these' is not applicable since homozygous is the correct term.

In the study of human genetics, an individual with an AB blood type is an example of which of the following?

• Codominance

• Incomplete dominance

• Polygenic inheritance

• Multiple alleles

• Dominant trait

Answer explanation

In human genetics, an AB blood type is an example of Codominance. This is because both A and B alleles are equally expressed, and neither is dominant or recessive. Therefore, an individual with an AB blood type exhibits both A and B characteristics, which is a clear example of Codominance.

What term is used to describe the situation where both alleles contribute to the phenotype of the organism?

• Dominance

• Recessiveness

• Codominance

• Incomplete dominance

• Homozygosity

Answer explanation

Codominance is the correct term to describe the situation where both alleles contribute to the phenotype of the organism. In codominance, both alleles are expressed equally in the phenotype, resulting in a unique combination of traits from both alleles. This is different from dominance, recessiveness, incomplete dominance, and homozygosity, which involve different patterns of allele expression.

What is the term for the physical expression of a gene?

• Genotype

• Phenotype

• Allele

• Chromosome

• None of these

Answer explanation

The physical expression of a gene is referred to as the 'Phenotype'. It is the observable traits or characteristics of an organism, such as its appearance, development, and behavior. The other options, Genotype, Allele, and Chromosome, are related to genetic makeup but do not represent the physical expression of a gene.

What is the ratio that represents the phenotypic outcome of a dihybrid cross?

• 1:2:1

• 9:3:3:1

• 3:1

• 2:1:1

• 4:1

Answer explanation

The phenotypic outcome of a dihybrid cross is represented by the ratio 9:3:3:1. This ratio is derived from Mendel's law of independent assortment, which states that alleles for different traits are inherited independently of each other. In a dihybrid cross, two traits are considered, and the resulting offspring display four different phenotypic combinations in the 9:3:3:1 ratio.

What is the term used to describe the situation where one allele is not completely dominant over the other?

• Dominance

• Recessiveness

• Codominance

• Incomplete dominance

• Homozygosity

Answer explanation

Incomplete dominance is the correct term to describe the situation where one allele is not completely dominant over the other. In this case, the phenotype of the heterozygous individual is a blend of the phenotypes of the homozygous individuals. Codominance, on the other hand, refers to both alleles being expressed equally, while dominance and recessiveness describe the relationship between alleles in a complete dominance scenario. Homozygosity refers to having identical alleles for a particular gene.

In human genetics, what term is used to describe the inheritance of traits that are determined by more than one gene?

• Codominance

• Incomplete dominance

• Polygenic inheritance

• Multiple alleles

• Dominant trait

Answer explanation

The term used to describe the inheritance of traits that are determined by more than one gene in human genetics is 'Polygenic inheritance'. This is because polygenic inheritance involves multiple genes at different locations on different chromosomes contributing to a single trait. Other options like Codominance, Incomplete dominance, Multiple alleles, and Dominant trait do not fit the description as they are related to different genetic phenomena.

What are the phenotypical results of a cross between two organisms that are heterozygous for a single trait?

• 1:2:1

• 9:3:3:1

• 3:1

• 2:1:1

• 4:1

Answer explanation

The phenotypical results of a cross between two organisms that are heterozygous for a single trait follow Mendel's law of segregation. This law states that during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. Therefore, the phenotypic ratio for a monohybrid cross is typically 3:1, indicating three organisms with the dominant phenotype for every one organism with the recessive phenotype.

Dr. Cervantes deserves 5 stars

• True

• False

Answer explanation

The statement 'Dr. Cervantes deserves 5 stars' is considered as true. This is because the question implies a positive evaluation of Dr. Cervantes, suggesting that they have performed exceptionally well in their field. Therefore, agreeing with this statement is the correct choice.