Genetics, Population, Evolution & Ecosystems

• In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r. Male fruit flies are more likely than female fruit flies to have white eyes. Explain why?

  1. Males have one allele
  2. Females need 2 recessive alleles
• In fruit flies, the genes for body colour and for wing development are not on the sex chromosomes. The allele for grey body colour, G, is dominant to the allele for black body colour, g. The allele for long wings, L, is dominant to the allele for short wings, l. A geneticist carried out a cross between fruit flies with grey bodies and long wings (heterozygous for both genes) and fruit flies with black bodies and short wings. Explain the results in the table?

  1. The two genes are linked
  2. No crossing over occurs
  3. Only GL and gl gametes produced

  
• Mutation is one cause of genetic variation in organisms. Give 2 other causes of genetic variation?

  1. Random fertilisation
  2. Independent segregation
• In a species of flowering plant, the T allele for tallness is dominant to the t allele for dwarfness. In the same species, two alleles CR (red) and CW (white) code for the colour of flowers. When homozygous red-flowered plants were crossed with homozygous white-flowered plants, all the offspring had pink flowers. Name the relationship between the two alleles that code for flower colour?

  1. Co-dominance
• In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why?

  1. Epistasis
  2. Small sample size
  3. Random fertilisation (of gametes)
• What is meant by the term phenotype?

  1. Expression of genotype/genetic constitution
  2. (Due to) environment
• Name the type of gene interaction shown in the diagram?

  1. Epistasis

  
• A student investigated the monohybrid inheritance of eye shape in fruit flies. Two fruit flies with bar (narrow) eyes were crossed. Of the offspring, 1538 had bar eyes and 462 had round (normal) eyes. Using suitable symbols, give the genotypes of the parents. Explain your answer?

  1. Genotype - Bb
  2. Both parents have bar eyes, but some offspring have round eyes, so parents must be carriers of recessive allele for round eyes
• This fruit fly has another characteristic controlled by a pair of codominant alleles, WN and WV. What is meant by codominant alleles?

  1. Both alleles are expressed in the phenotype
• Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results? Give the reason for your choice of statistical test?

  1. Chi-squared
  2. Categorical data
• What is a gene pool?

  1. All the alleles in a population
• Guppies with large brains are better at identifying predators. The scientists found that only female guppies with large brains were attracted to male guppies bright in colour. Suggest and explain the advantage of this behaviour to the population of guppies?

  1. Females with large brains will mate with males bright in colour
  2. Their male offspring would be more likely to be bright in colour
  3. The male offspring will attract larger brained females
  4. Population could evolve to have larger brains
• Describe how the behaviour of female guppies could result in sympatric speciation?

  1. Not geographically isolated
  2. (Leading to) reproductive isolation
  3. Changes in allele frequencies
  4. Cannot breed to produce fertile offspring
• Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different. Using this information, suggest how these two species of palm tree arose by sympatric speciation?

  1. Occurs in the same habitat
  2. Mutation causes different flowering times
  3. Reproductive isolation
  4. Change in frequency of alleles
  5. Disruptive selection
  6. Eventually species can no longer interbreed to produce fertile offspring
• There are nine subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to six of these subspecies should be classified as different species. Explain how different subspecies of giraffe may have evolved from a common ancestor. Use information from the passage in your answer?

  1. Geographical isolation
  2. Mutation linked to different markings/colours
  3. Survival linked to different markings
  4. Adapted organisms breed
  5. Change in allele frequency
• Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that six of the nine subspecies are separate species. Suggest how they came to this conclusion?

  1. Comparing DNA base sequence
  2. Different in six species
• Explain how crossing over can contribute to genetic variation?

  1. Sections of chromatid are crossed over
  2. Resulting in alleles being exchanged
  3. Creating new combination of alleles that may not have existed before
• Explain how changes in ecosystems lead to speciation?

  1. Geographical isolation
  2. Separate gene pools
  3. Variation due to mutation
  4. Different selection pressures
  5. Differential reproductive success, leads to change in allele frequency
  6. Species can no longer interbreed to produce fertile offspring
• Explain how populations evolve adaptations to an environment?

  1. Variation due to mutation
  2. Some better adapted
  3. Greater reproductive success
  4. Change in allele frequencies
• Lake Malawi in East Africa has more species of fish than any other lake in the world. Suggest and explain how this speciation may have occurred?

  1. Variation due to mutation
  2. Allopatric speciation
  3. Different lakes have different environmental conditions
  4. Reproductive isolation
  5. Change in frequency of alleles
  6. Eventually different species cannot breed to produce fertile offspring
• Succession occurs in natural ecosystems. Describe and explain how succession occurs?

  1. Colonisation by pioneer species
  2. Pioneer species change the environmental conditions
  3. Environment becomes less hostile for new species
  4. Increase in biodiversity
  5. To climax community
• Describe how you could estimate the size of a population of sundews in a small marsh?

  1. Use a grid
  2. Use a computer generator to obtain random coordinates
  3. Count number in a quadrat
  4. Large sample and calculate mean per quadrat
  5. Mean number of plants per quadrat multiplied by number of quadrats
• Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation?

  1. Capture, mark and release
  2. Leave time for mosquitos to disperse before second sampling
  3. Population = number in first sample x number in second sample divided by number of marked in second sample
• Explain how the data in the table provides evidence of succession?

  1. Increase in species richness
  2. B. quilleri and P. guttipennis are pioneers
  3. Pioneers provide food for other species
  4. New species colonise once there is a change
  5. B. quilleri is outcompeted as succession continues

  
• Give 2 features of a climax community?

  1. Populations stable
  2. Same species present (over long time)
  3. Abiotic factors constant over time