MCAT Biology Practice Test 12: Genetics and Evolution

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1. What is the gene order of linked genes M, N, O, and P, given the following recombination frequencies?

MN: 6% NO: 18%

MO: 12% NP: 1%

MP: 5% OP: 17%

  • A. MOPN
  • B. NPMO
  • C. ONPM
  • D. PNMO

2. Suppose that in humans, the allele for black hair (B) is dominant to the allele for brown hair (b), and the allele for curly hair (C) is dominant to the allele for straight hair (c). When a person of unknown genotype is crossed against a person with straight, brown hair, the phenotypic ratio is as follows:

25% curly black hair

25% straight black hair

25% curly brown hair

25% straight brown hair

What is the genotype of the unknown parent?

  • A. BbCC
  • B. bbCc
  • C. Bbcc
  • D. BbCc

3. If a male with hemophilia (Xhch

  • A. 0%
  • B. 25%
  • C. 50%
  • D. 100%

4. If a test cross on a species of plants reveals the appearance of a recessive phenotype in the offspring, what must be true of the phenotypically dominant parent?

  • A. It must be genotypically heterozygous.
  • B. It must be genotypically homozygous.
  • C. It could be either genotypically heterozygous or homozygous.
  • D. It must have the same genotype as the test cross control parent.

5. Which of the following definitions is FALSE?

  • A. Penetrance—the percentage of individuals in the population carrying the allele who actually express the phenotype associated with it
  • B. Expressivity—the percentage of individuals in the population carrying the allele who do not express the phenotype associated with it
  • C. Incomplete dominance—occurs when the phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes
  • D. Codominance—occurs when multiple alleles exist for a given gene and more than one of them is dominant

6. In a species of plant, a homozygous red flower (RR) is crossed with a homozygous yellow flower (rr). If the F12

  • A. Codominance
  • B. Incomplete dominance
  • C. Penetrance
  • D. Expressivity

7. Which of the following statements is INCORRECT regarding inheritance of traits according to the modern synthesis model?

  • A. A mutation due to excessive amounts of ultraviolet light occurs in an unfertilized egg; this will affect the child who is born from that egg.
  • B. The muscular strength gained by a weight lifter during his lifetime is inherited by his children.
  • C. A green-feathered bird that survived all of the predators in the forest will pass on the green feather genes to its offspring.
  • D. A flower with a tasty nectar eaten by a butterfly is more likely to pass on its genes through the pollen spread by the butterfly then a flower with less desirable nectar.

8. Which of the following statements is FALSE based on Darwin's theory of evolution?

  • A. Natural selection is the driving force for evolution.
  • B. Favorable genetic variations become more and more common in individuals throughout their lives.
  • C. Natural selection can drive organisms living in groups to ultimately become distinct species.
  • D. Fitness is measured by reproductive success.

9. Which of the following is NOT a necessary condition for Hardy–Weinberg equilibrium?

  • A. Large population size
  • B. No mutations
  • C. Monogamous mating partners
  • D. No migration into or out of the population

10. As the climate became colder during the Ice Age, a particular species of mammal evolved a thicker layer of fur. What kind of selection occurred in this population?

  • A. Stabilizing selection
  • B. Directional selection
  • C. Disruptive selection
  • D. Speciation selection

11. At what point are two populations descended from the same ancestral stock considered to be separate species?

  • A. When they can no longer produce viable, fertile offspring.
  • B. When they look significantly different from each other.
  • C. When they can interbreed successfully and produce offspring.
  • D. When their habitats are separated by a significantly large distance so that they cannot meet.

12. In a nonevolving population, there are two alleles, R and r, which code for the same trait. The frequency of R is 30 percent. What are the frequencies of all the possible genotypes?

  • A. 49% RR, 42% Rr, 9% rr
  • B. 30% RR, 21% Rr, 49% rr
  • C. 0.09% RR, 0.42% Rr, 0.49% rr
  • D. 9% RR, 42% Rr, 49% rr

13. In a particular Hardy–Weinberg population, there are only two eye colors: brown and blue. Of the population, 36% have blue eyes, the recessive trait. What percentage of the population is heterozygous?

  • A. 24%
  • B. 48%
  • C. 60%
  • D. 64%

14. Which of the following was NOT a belief of Darwin's?

  • A. Evolution of species occurs gradually and evenly over time.
  • B. There is a struggle for survival among organisms.
  • C. Genetic recombination and mutation are the driving forces of evolution.
  • D. Those individuals with fitter variations will survive and reproduce.

15. A child is born with a number of unusual phenotypic features and genetic testing is performed. The child is determined to have partial trisomy 21, with three copies of some segments of DNA from chromosome 21, and partial monosomy 4, with only one copy of some segments of DNA from chromosome 4. Which of the following mutations could have occurred in one of the parental gametes during development to explain both findings?

  • A. Deletion
  • B. Insertion
  • C. Translocation
  • D. Inversion