From a mating of two dihybrid individuals (e.g. AaBb x AaBb) how many of the 16 possible zygote combinations would be expected to contain only two dominant genes?  (Assume that the two pairs of genes are located on different chromosomes).

In pea-plants, flower colour and height are determined by single pairs of alleles. The genes for red colour and tallness are dominant.

Two flowers were crossed, and the offspring (F1) were self-pollinated.  The results in the F2 generation were as follows: 280 tall red; 90 tall white; 94 dwarf red; 30 dwarf white.

Which one of the following is a possible description of the parental generation?

- Heterozygous tall red x heterozygous dwarf white

- Homozygous tall red x homozygous dwarf white

- Heterozygous tall red x homozygous dwarf white

- Homozygous tall white x heterozygous dwarf red

- Homozygous tall red x heterozygous dwarf red

What is the probability that the son of a female carrier of haemophilia and a normal male will be haemophiliac?

Red-green colour blindness in mammals is a sex-linked recessive trait.  If a colour-blind female is crossed with a normal male then what is the theoretical ratio of the offspring?

Assume that in a certain mammal the inheritance of skin colour is controlled by two pairs of genes, A-a and B-b, which are inherited independently.  The genes for dark pigmentation A and B are incompletely dominant and produce about the same amount of pigmentation.  If skin colour is proportional to the sum of the dominant genes present, how many classes of skin colour would be expected to be distinguishable from a mating between two doubly heterozygous individuals?

In the sweet pea plant, flowers may be either purple or white.  The colour is determined by two allelomorphic pairs of genes (R, r and S, s).  If at least one dominant gene from each allelomorphic pair is present, then the flower colour is purple.  All other genotypes are white.  If two purple plants each of the genotype RrSs are crossed, then what is the expected phenotypic ratio of the offspring?

A disease caused by a recessive gene has an incidence of one per cent of the population.  What percentage of the whole population would be expected to be carriers of the gene but unaffected by the disease?

If a mother has blood of group O and her daughter has blood of group A, what are the possible blood groups for the father?

A black rabbit crossed with an albino rabbit produces 14 black offspring. When the albino is crossed with a second black rabbit, 8 black and 6 albino kits are produced. What is the best explanation for this genetic situation?

What are the differences between sex chromosomes of the human male and female?

Using examples, explain how the sex chromosomes differ in some other animal species?

What phenotypic ratios of offspring would arise from the following genetic situations?

a) Monohybrid complete dominance, parents heterozygous x heterozygous

b) Monohybrid complete dominance, parents heterozygous x homozygous

c) Dihybrid (two trait cross) independent assortment, parents heterozygous x heterozygous for both genes

d) Sex-linked gene, mother a carrier and father not a sufferer of the condition

e) Monohybrid incomplete dominance, parents heterozygous x heterozygous

Red-green colour-blindness is caused by a sex linked gene and is recessive to normal colour vision. A boy has inherited colour-blindness from one of his grandparents.

- Which grandparent is most likely to have been colour-blind?

- What is the probability the boy's brother will be a carrier?

- What is the probability the boy's sister will not be a carrier

Two people have blood groups of A and B respectively. What is the probability they will have a child who is blood group AB?

Recent research at ARU has demonstrated that in squirrels the gene for fur colour can produce three different phenotypes, jet back, brown black and grey.

The offspring of a mating between two brown black squirrels produce 11 pups, of which 6 are brown black, 3 are black and 2 are grey.

- What is the simplest explanation for the inheritance of these colours in squirrels?

- What offspring would you predict from the mating of a brown black male with a grey female?

- What offspring would you expect from a mating between a  jet black female and a grey male                                                            

In wild dogs, dark coat colour is dominant over albino, and short hair is dominant over long hair. If these phenotypes are caused by independently assorting genes, give the genotypes of the parents of each of the crosses below.

            Parents                                               Progeny

dark                 dark                 albino              albino

short                long                 short                long

a) dark short  x                        89                    31                    29                    11

dark short

b) dark short  x                        20                    0                      21                    0

            albino long     

c) albino short  x                     0                      0                      28                    9

            albino short

d) dark long x                                     0                      32                    0                      10

            dark long

e) dark short  x                        30                    31                    9                      11

            dark long