Cambridge OCR A Level · Biology A - H420
5 multiple-choice questions marked as you go, and 2 written questions with worked solutions. All on Patterns of inheritance.
A scientist studies a population of rodents where fur length is a polygenic trait influenced by several genes. The distribution of fur lengths in the population follows a normal distribution curve. Over several generations of extreme cold, the average fur length in the population increases significantly, and the curve shifts to the right.
Which type of selection is being described and what is its effect on the genetic diversity of the population?
A population is in Hardy–Weinberg equilibrium for a gene with two alleles, \(A\) and \(a\). The frequency of the recessive phenotype in the population is 0.09.
What is the frequency of the heterozygous genotype (\(Aa\)) in this population?
In a species of plant, flower color is controlled by a single gene with two alleles. A plant with red flowers was crossed with a plant with white flowers. All the \(F_1\) offspring had pink flowers. When these \(F_1\) plants were self-pollinated, the \(F_2\) generation showed a phenotypic ratio of 1 red : 2 pink : 1 white.
Which of the following best describes this pattern of inheritance and the genotypes of the pink flowers?
In humans, red-green color blindness is a sex-linked recessive trait (\(X^b\)). A woman with normal vision, whose father was color-blind, marries a man with normal vision.
What is the probability that their first child will be a son who is color-blind?
In the fruit fly Drosophila melanogaster, the genes for body color and wing shape are located on the same autosome. Gray body (G) is dominant to black body (g), and normal wings (V) are dominant to vestigial wings (v). A heterozygous gray, normal-winged fly was crossed with a black, vestigial-winged fly. The following offspring were obtained:
Gray, normal: 965
Black, vestigial: 944
Gray, vestigial: 206
Black, normal: 185
What is the calculated crossover frequency (recombination frequency) for these two genes?
In a dihybrid cross between two pea plants heterozygous for both seed shape (Rr) and seed color (Yy), where round and yellow are dominant, a phenotypic ratio of 9:3:3:1 is expected in the offspring.
Calculate the probability of an offspring having the genotype \( rrYy \).
Write your answer out first, then check it against the worked solution.
In a population of 500 individuals, 80 individuals show the recessive phenotype for a trait governed by two alleles at a single locus.
Assuming the population is in Hardy-Weinberg equilibrium, calculate the number of individuals expected to be heterozygous carriers (\( 2pq \)) of the recessive allele.
Write your answer out first, then check it against the worked solution.
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