Genetic Variation Short Answer Quiz 1

The tortoiseshell cat has a combination of black and orange fur. The allele for black fur is represented by Xb and the allele for orange fur is represented by Xo. A tortoiseshell female cat (XbXo) mates with a black male cat (XbY).

(a) Determine the probable percentages of coat colour in the phenotype for the litter of kittens. Show all working. (2)

(b) Explain the tortoiseshell phenotype. (2)

(c) Explain why tortoiseshell cats are never male. (1)

The diagram below is a pedigree for albinism in humans. Albinism can be any one of a number of genetic conditions that cause lack of pigment in the eyes, skin and hair of sufferers.

(a) Is the allele responsible for albinism dominant or recessive? Justify your answer. (2)

(b) If individuals 10 and 11 in Generation II had a daughter, what chance would there be of
her being an albino? Show working. (3)

Mrs Richards is a brown-haired female married to Mr Jones, a brown- haired male. They have three children, a male (Jack) who is red-haired, a male (Mark) who is brown-haired and a female (Jill) who is red-haired. Jack marries a black-haired female and they have one red-haired female, one black-haired female and one red-haired male. Jill marries a brown- haired male and they have three children, two males and a female. All of Jill’s children are brown-haired.

(a) Using the key below, construct a pedigree to represent this information. (2)

(b) State the type of genetic inheritance for red hair colour in the family. (1)

The pedigree shows the incidence of haemophilia in the royal families of
Europe.

(a) Identify the type of inheritance and justify your choice. (1)

(b) Allocate appropriate genotypes to individuals 1, 2 and 3. (3)

(c) Prince Albert and Queen Victoria had nine children – 5 girls and 4 boys.

Explain, genetically, why their son Leopold was unlucky to inherit haemophilia. (2)

(d) Nicholas II of Russia and Alexandra had a haemophilic son and four daughters.

What was the probability of each of the daughters ( 4, 5, 6 and 7) carrying the allele for haemophilia? Show all working. (2)

Outline three mechanisms in sexually reproducing organisms that produce variability in offspring. (3)

Describe an example that demonstrates the effect of environment on phenotype. (2)

Phenotypes are affected by the environment. Siamese cats are darker on their extremities, due to temperature effects on phenotypic expression. Expression of phenotype is a result of the interaction between genes and environment. Siamese cats and Himalayan rabbits both have dark coloured fur on their extremities, but not on the rest of their bodies.

(a) Propose a mechanism by which the environment affects the phenotype of the
above species. (2)

Becker’s muscular dystrophy is a sex-linked muscular disorder which occurs in approximately 5 in 100,000 male births. Symptoms usually appear in men about age12, but may sometimes begin later. The average age of becoming unable to walk is 25-30. Women rarely develop symptoms. Below is a pedigree for the disorder.

(a) Is the disorder likely to be dominant or recessive? Give an explanation for your choice. (1)

(b) Predict the likely genotypic and phenotypic ratio of offspring of a mating between Z and a male that does not have the disease. (3)

Red Green colour blindness is a sex-linked recessive condition.
In a family a female grandchild is red green colourblind. She examines her parents and grandparents and only one of these six people is colourblind.

In the space below use a pedigree diagram to show all the above mentioned members of the family to explain how she inherited the condition.

Identify carriers and the relative who is also colourblind. (3)

(a) Name two processes that create genetic variation in sexually reproducing organisms during meiosis (excluding mutation). (2)

(b) Describe how variation is caused by each process you identified in (a). (2)

Compare the inheritance of a multiple allele trait with a trait that follows Mendelian inheritance. (2)

A non-infectious disease was observed in a mother and her four sons who live with her. She has no daughters. The father of these children does not have the disease and does not live with them. The woman’s parents and her two sisters who live overseas do not have the disease.
A geneticist suspects that the disease is inherited.
(a) Draw the family pedigree for this disease. (3)

(b) From the evidence, what indicates that the disease could be the result of a recessive allele and not be sex-linked? (2)

The diagram shows a model developed in the early 20th century of crossing over of homologous chromosomes.

Explain how the difference between this model and our current model of crossing over reflects an increased understanding of the way in which new combinations of genotypes are produced. Support your answer with a diagram. (4)