Inheritance: Practice Questions

Which of the following best defines the term genotype?

In a certain population, the frequency of a recessive disorder caused by a single gene is 1 in 10,000. Assuming the population is in Hardy-Weinberg equilibrium, what is the frequency of the heterozygous carriers in this population?

A researcher performed a dihybrid cross between two organisms heterozygous for two autosomal genes, \(A\) and \(B\). The observed offspring numbers were:
Phenotype AB: 240
Phenotype Ab: 10
Phenotype aB: 12
Phenotype ab: 78

Using a \(\chi^2\) test against the expected 9:3:3:1 ratio, the calculated \(\chi^2\) value is significantly higher than the critical value at \(p = 0.05\). Which of the following is the most likely biological explanation for this result?

In a species of flowering plant, the allele for red flowers \(R\) is codominant with the allele for white flowers \(W\). Heterozygous plants have pink flowers. If two pink-flowered plants are crossed, what is the expected ratio of phenotypes in the offspring?

In summer squash, fruit colour is determined by epistatic interactions. A dominant allele \(W\) at one locus results in white fruit regardless of the genotype at a second locus. At the second locus, the dominant allele \(G\) produces green fruit and the recessive allele \(g\) produces yellow fruit. If two plants with the genotype \(WwGg\) are crossed, what proportion of the offspring is expected to have yellow fruit?

In a diploid population of insects, a specific gene for eye pigment has four different alleles: E₁, E₂, E₃, and E₄. Explain why any single individual in this population can possess a maximum of only two of these alleles.

The Himalayan rabbit has a genotype that allows for black fur production, but this is only expressed in body parts where the temperature is below \(25^{\circ}C\). Explain why this organism demonstrates the definition of phenotype as an interaction between the genetic constitution and the environment.

Explain how the distance between two genes on the same chromosome influences the probability of crossing over occurring between them and the resulting phenotypic ratios.

In a specific species of pea plant, the allele for axial flowers (A) is dominant over the allele for terminal flowers (a). A plant known to be homozygous for axial flowers is crossed with a plant that has terminal flowers.

(a) State the genotype and phenotype of the \(F_1\) generation produced from this cross.
(b) If individuals from the \(F_1\) generation are allowed to self-fertilize, calculate the probability that an offspring in the \(F_2\) generation will possess the same phenotype as the original parent with terminal flowers.
(c) Define the term locus in the context of these two alleles.

Red-green color blindness is a sex-linked recessive disorder in humans, caused by a gene located on the non-homologous region of the X chromosome. A woman who has normal color vision but whose father was color-blind has children with a man who has normal color vision.

(a) Using the symbols \(X^B\) for the normal allele and \(X^b\) for the color-blind allele, state the genotypes of the woman and the man.
(b) Use a genetic diagram or reasoning to determine the probability that a daughter born to this couple will be a carrier for color blindness.
(c) Explain why sex-linked recessive traits like color blindness are phenotypically expressed more frequently in males than in females in a population.