William Bateson and Reginald Punnett used the sweet pea (Lathyrus odoratus) in genetics studies in the early 20^th century. Pure-breeding plants that produced purple flowers and long pollen grains were crossed with pure-breeding plants that produced red flowers and round pollen grains. The resulting offspring all produced purple flowers and long pollen grains. Two of the F₁ generation plants were crossed. The table shows the ratio of phenotypes in the F₂ generation. 

What is an explanation for these experimental results?

A. Purple flowers and long pollen grains are dominant and the alleles have assorted independently.

B. The genes for flower colour and pollen shape are linked and all plants producing long pollen grains are recombinants.

C. The genes for flower colour and pollen shape are linked and all plants producing red flowers are recombinants.

D. Plants producing purple flowers and round pollen grains arose through crossing over.

When a cell divides by meiosis, chiasmata can be observed. Which are features of chiasmata?

I. They are points of attachment between chromatids of non-homologous chromosomes.

II. They occur during meiosis I.

III. They increase stability of bivalents.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Which cell is a polyploid zygote produced by fusion of one haploid and one diploid gamete?

What can lead to reproductive isolation after just one generation?

A. Polyploidy

B. Increased mutation rate

C. Changed allele frequencies

D. Independent assortment of chromosomes

The graph shows the relationship between mass at birth and the percentage that die shortly after birth for Scottish Blackface lambs.

[Source: Dwyer, C.M., Conington, J., Corbiere, F., Holmoy, I.H., Muri, K., Nowak, R., Rooke, J., Vipond, J. and Gautier,
J.-M., 2016. Invited review: Improving neonatal survival in small ruminants: science into practice. Animal, 10(3),
pp. 449–459.]

What type of selection for the lambs is shown in the graph?

A. Disruptive selection, as there is a drop in mortality at intermediate birth masses

B. Stabilizing selection, as lambs with low or high birth mass are less likely to survive

C. Directional selection, as lambs with a high birth mass have high mortality

D. There is no evidence in the graph of selection, as survival frequency is not shown

Which process could cause non-disjunction if it occurred during meiosis?

A. Sister chromatids do not align in metaphase I.

B. Homologous chromosomes do not separate in anaphase I.

C. Sister chromatids do not align in metaphase II.

D. Homologous chromosomes do not separate in anaphase II.

The image shows variation in height of adult humans.

What can explain the variation?

A.  One pair of alleles and age

B.  Polygenic inheritance and nutrition

C.  Nutrition and age

D.  Autosomal inheritance only

What could account for this distribution of height in a population?

[Source: Graph adapted from Six Minutes http://sixminutes.dlugan.com/good-public-speaker-average/]

A. Gene linkage

B. Dominant alleles

C. Independent assortment

D. Multiple genes

A dihybrid cross was carried out between two plants to determine whether the genes for seed shape and colour are linked. If the genes are unlinked, the expected ratio of 9:3:3:1 should occur. A chi-squared test was carried out on the observed results of the cross. The critical value for chi squared at the 5 % level of significance in this test was 7.82. The calculated value for chi squared was 6.25. What can be concluded from this data?

A. The results prove that the genes are linked.

B. The results prove that the genes are unlinked.

C. There is significant evidence that the genes are linked.

D. There is significant evidence that the genes are unlinked.

Andalusian fowl have varied colours and types of feathers. The allele for black feathers is codominant with the allele for white, producing blue feathers in the heterozygote. The texture of feathers is controlled by another gene, with silky feathers recessive to normal. Blue silky birds are crossed with black silky birds. What is the expected proportion of blue silky offspring?

A. 0%

B. 25%

C. 50%

D. 100%

The genetic determination of dogs’ coats can be quite complex, with many different genes acting at the same time.

• The dominant allele E gives brown tones. The recessive allele e results in red tones.
• The colour intensity is due to another gene. The dominant allele B gives a dark colour, whereas the recessive allele b results in a light colour.

What would be the genotype of a light brown dog produced from a cross between a dark brown dog and a light red dog?

A. EEbb

B. EeBb

C. eeBb

D. Eebb

The graph shows variations in beak size for the bird Geospiza fortis on an island in the Galápagos archipelago.

What evidence from the graph indicates that disruptive selection is occurring?

A. An intermediate beak size is less common.

B. Median beak size is the most common.

C. Smaller beaks are favoured.

D. Larger beaks are favoured.

Fossil records show that black bears increased in size during the Ice Age and decreased in size with warmer temperatures. What type of selection do these changes in size represent?

A. Allopatric
B. Directional
C. Disruptive
D. Stabilizing

What is always passed to the next generation as a result of sexual reproduction?

A. Homologous chromosomes from the mother

B. A chromatid from every chromosome of the father

C. A haploid set of chromosomes from the mother

D. All alleles from each parent

What process occurs in both mitosis and meiosis?

A. Formation of chiasmata

B. Reduction division

C. Separation of chromatids

D. Exchange of alleles between non-sister chromatids

Which event happens in meiosis II but not in meiosis I?

A. Spindle microtubules attach to centromeres.

B. Crossing over occurs.

C. Sister chromatids move to opposite poles.

D. Chromosomes become shorter and thicker by coiling.

Many commercially produced bananas are triploid instead of diploid. The nucleus of a triploid cell has three sets of chromosomes. What is the effect of triploidy?

A. Seeds are larger.

B. Chromosomes cannot pair in meiosis.

C. Sexual reproduction is more rapid.

D. Mitosis cannot occur.

In fruit flies (Drosophila melanogaster), grey bodies (b⁺) are dominant to black bodies (b) and normal wings (vg⁺) are dominant to vestigial wings (vg). Homozygous vestigial winged, black bodied flies were crossed with individuals that were heterozygous for both traits. 2300 individuals were counted and the phenotypes observed were recorded as shown.

965 normal wings, grey bodies
944 vestigial wings, black bodies
206 vestigial wings, grey bodies
185 normal wings, black bodies

Which statement is valid?

A. The predicted phenotypic ratio was 9:3:3: 1.

B. There is independent assortment of wings but not body colour.

C. The expected number of vestigial winged, grey bodied flies was 575.

D. The traits are on different chromosomes.

What is polyploidy?

A. Having an extra set of chromosomes

B. Having an extra sex chromosome

C. Having an extra autosome

D. Having two or more nuclei

The cheetah (Acinonyx jubatus) is a large cat found in Africa. It has been discovered that organs could be transferred between any two individuals without rejection of the organ.

What is the probable reason for this?

A. Cheetahs have poor reproductive success.

B. Cheetahs have high heterozygosity.

C. Cheetahs have a large gene pool.

D. Cheetahs have a small gene pool.

Natural selection can operate in different ways. What is the effect of disruptive selection?

A. It eliminates individuals with intermediate forms of a characteristic.

B. It eliminates individuals at random regardless of their characteristics.

C. It favours individuals with intermediate forms of a characteristic.

D. It favours individuals at one extreme of the range of variation in a characteristic.

How do the concepts of gradualism and punctuated equilibrium differ?

A. The timing of evolution

B. The mechanism causing evolution

C. The sequence of evolutionary events

D. The reality of evolution

Which statement is valid regarding chromatids?

A. Sister chromatids separate during meiosis I.

B. Chiasmata form between non-sister chromatids.

C. Crossing over is the exchange of DNA between sister chromatids only.

D. Non-sister chromatids have the same combination of alleles.

Which gametes can result from the following crossover?

In a plant, dark leaves are dominant to pale leaves and yellow seeds are dominant to white seeds.

A heterozygous dark-leaved plant with yellow seeds was crossed with a pale-leaved plant with white seeds. A large number of offspring were produced. They were either dark-leaved with yellow seeds or pale-leaved with white seeds in equal number.

What is the most likely cause of this pattern?

A. Crossing over has occurred.

B. The two genes are linked.

C. The traits are polygenic.

D. The genes are codominant.

An individual is heterozygous for two linked genes .

To investigate the frequency of crossing over, a test cross is carried out between the individual and another that is homozygous recessive for both genes. What are the possible recombinants in the offspring of this cross?

Which example shows disruptive selection?

A. Giraffe necks have become longer over time.

B. Medium-sized beaks in hummingbirds have decreased in frequency over time.

C. The peppered moth became less common in polluted environments.

D. Human babies with a very high or a very low birth mass have a higher mortality rate. 

Some of the ratios that Morgan investigated in genetic crosses did not correspond with expected Mendelian ratios.  What was the cause?

A. The genetic crosses used insects rather than plants.
B. The results were counted more reliably than Mendel’s.
C. The genes in the genetic crosses were linked.
D. Drosophila has more genes than plants.

What forms when two different chromatids of the same homologous pair cross over?

A. Daughter centromere

B. Chiasma

C. Chromosome mutation

D. Telomere

A hunter tends to kill the bigger individuals of a population for their meat or for large ornamental trophies. Therefore, the population tends to have more individuals who are smaller. What is this an example of?

A. Directional selection

B. Disruptive selection

C. Natural selection

D. Stabilizing selection

Three-spined stickleback fish (Gasterosteus aculeatus) vary in the number of armour plates. The graph shows the frequency of individuals with low, partial or complete plating in a three-spined stickleback population living in Kennedy Lake, Vancouver Island, Canada.

[Source: Reprinted from Current Biology, 24, Marchinko, K.B., Matthews, B., Arnegard, M.E., Rogers, S.M. and Schluter, D., Maintenance of a Genetic Polymorphism with Disruptive Natural Selection in Stickleback.
2014.  pp.1289–1292 with permission from Elsevier.]

Which type of natural selection could result in this pattern of variation in the population?

A. Disruptive

B. Directional

C. Stabilizing

D. Convergent