HL Paper 2
Dachshunds have three basic coat types: wire-, smooth- or long-haired. These are affected by two genes, W and K. The presence of W always results in wire hair.
[Source: American Kennel Club, 2007. Available at:
https://www.slideshare.net/ghinck/dachshund-power-point.]
When long-haired dogs are crossed among themselves, they always produce long-haired puppies. When dogs heterozygous for both genes are crossed, they produce offspring in the ratio 12 wire-haired:3 smooth-haired:1 long-haired.
A male wire-haired dog was crossed with several long-haired females and the phenotypic ratio of the puppies was approximately 2 wire-haired:1 smooth-haired:1 long-haired.
Identify the genotype of the male wire-haired dog.
Using a Punnett square, determine how a smooth-haired puppy could be produced in the offspring.
The biological insights of Mendel and Darwin in the 19th century remain important to this day.
Discuss the role of genes and chromosomes in determining individual and shared character features of the members of a species.
Outline the process of speciation.
Describe, using one example, how homologous structures provide evidence for evolution.
The diagram shows one of Thomas Hunt Morgan’s crosses of Drosophila in the early 20th century.
State the type of inheritance shown.
Identify the recombinants.
The chi-squared value was calculated as shown. Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio.
Outline the roles of helicase and ligase in DNA replication.
Explain how natural selection can lead to speciation.
Outline the features of ecosystems that make them sustainable.
List two causes of variation within a gene pool.
Describe how variation contributes to evolution by natural selection.
Outline what is required for speciation to occur.
Hemophilia is a sex-linked disease that affected some members of royal families in Europe during the 19th and 20th centuries.
The diagram shows the structure of two chromosomes after the first division of meiosis, assuming that there was no crossing over or chiasmata formation.
Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.
Deduce the genotype of Queen Victoria’s daughter Alice.
Draw the same chromosomes to show their structure at the same stage of meiosis if there had been one chiasma between two gene loci.
State the stage of meiosis where chiasmata formation may occur.
Explain gene linkage and its effects on inheritance.
Explain the mechanism that prevents polyspermy during fertilization.
Describe the process of crossing over.
Explain the reason for linked genes not following the pattern of inheritance discovered by Mendel.
Extensive areas of the rainforest in Cambodia are being cleared for large-scale rubber plantations. Distinguish between the sustainability of natural ecosystems such as rainforests and the sustainability of areas used for agriculture.
Describe the roles of the shoot apex in the growth of plants.
Research suggests that many living plant species are polyploid. Explain how polyploidy occurs and, using a named example, how polyploidy can lead to speciation.
A group of students used quadrat sampling and the chi-squared test to find out whether the distributions of two plant species were associated with each other or not. These two species were found in the ground vegetation in a woodland ecosystem.
[Source: (left) Pixabay.
(right) Topic, J., n.d. Veronica montana 2. [image online] Available at: http://www.freenatureimages.eu/Plants/
Flora%20S-Z/Veronica%20montana/#Veronica%2520montana%25202%252C%2520Bosereprijs%252C%2520Saxifr
aga-Jasenka%2520Topic.jpg [Accessed 3 December 2019].
The numbers of quadrats with one, both or neither species present were counted and recorded. The observed frequencies from 150 quadrats are shown in the following contingency table.
State the alternative hypothesis for this study.
To calculate chi-squared, expected values must first be calculated. Assuming that there is no association between the two species, calculate the expected number of quadrats in which both species would be present, showing your working.
State the number of degrees of freedom for this test to determine the critical value of chi-squared.
When the data in the table were used to calculate chi-squared, the calculated value was 0.056. The critical value is 3.84. Explain the conclusion that can be drawn from the calculated and critical values for chi-squared.
The karyogram shown is for the African marsh rat (Dasymys incomtus). In this species, sex is determined by X and Y chromosomes. Females are XX and males are XY.
[Source: adapted from https://embryology.med.unsw.edu.au]
Thomas Hunt Morgan established that genes for body colour and wing size in Drosophila are autosomally linked. The allele for grey body (b+) is dominant over that for black body (b) and the allele for normal wing size (vg+) is dominant over that for vestigial wing (vg).
Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.
Outline the causes of sickle cell anemia.
Identify, with a reason, the sex of this individual.
State the haploid number for this nucleus.
A fly that is homozygous dominant for both body colour and wing size mates with a fly that is recessive for both characteristics. In the table, draw the arrangement of alleles for the offspring of this mating and for the homozygous recessive parent.
The offspring, which were all heterozygous for grey body and normal wings, were crossed with flies that were homozygous recessive for both genes. The table shows the percentages of offspring produced.
Explain these results, based on the knowledge that the genes for body colour and wing size are autosomally linked.
Cells go through a repeating cycle of events in growth regions such as plant root tips and animal embryos. Outline this cell cycle.
Draw a labelled diagram of the formation of a chiasma by crossing over.
Explain the control of gene expression in eukaryotes.
Autosomal genes are located in chromosomes that are not sex chromosomes. The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the two types of inheritance, using the example of parents that are heterozygous for two genes A and B.
Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life.
Testis cells are eukaryotic cells. Identify the structures seen under the electron microscope in testis cells that are not present in prokaryotic cells.
More than 8 million different species are alive today but over the course of evolution, more than 4 billion may have existed.
Outline the criteria that should be used to assess whether a group of organisms is a species.
Describe the changes that occur in gene pools during speciation.
Discuss the process, including potential risks and benefits, of using bacteria to genetically modify plant crop species.
Draw a labelled diagram to show the structure of a single nucleotide of RNA.
Describe how DNA profiling can be used to establish paternity.
Explain the reasons for variation in human height.
The micrograph shows a plant cell of Lilium grandiflorum during meiosis.
Identify, giving reasons, the stage of meiosis shown by this cell.
Outline the law of independent assortment.
The genes for cystic fibrosis and blood group are not linked. Two parents are heterozygous for cystic fibrosis. One parent has blood group O and the other has blood group AB. Using a Punnett square, determine the probability that their child will have both cystic fibrosis and blood group A.
Outline how reproductive isolation can occur in an animal population.
Describe the different cell types in the seminiferous tubules that are involved in the process of spermatogenesis.
Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms.
Outline, using graphs, the effect of different factors that influence enzyme activity.
Describe the function of three named enzymes involved in DNA replication.
Explain how speciation occurs, including the different processes of isolation and selection.
RNA molecules play numerous roles in gene expression and so contribute to variation.
Draw labelled diagrams to show the structure of RNA nucleotides and how they are linked together to form a molecule of RNA.
Explain transcription.
Distinguish between continuous and discrete variation, using examples.