Red Poll cattle are homozygous for an allele which gives red coat colour.
While Shorthorn are homozygous for an allele which give white coat colour.
When crossed, the offspring all have a mixture of red and white hairs in their
coats, producing a colour called roan.
a) Suggest suitable symbols for the 2 alleles of the coat gene.
b) List the three possible genotypes for the coat gene and their
phenotypes.
c) Draw genetic diagrams to show the offspring expected from the
following matings:
i)
A Red Poll with a roan.
ii)
Two roans
In mice, the gene for eye colour has 2 alleles. The allele for black eyes is
dominant, while the allele for red eyes is recessive.
Choose suitable symbols for those alleles and then draw a genetic diagram to
show the probable results of a cross between a heterozygous black-eyed
mouse and a red-eyed mouse.
A species of poppy may have pink petals, or petals with a large black spot
near the base. If two plants with spotted petals are crossed, the offspring
always have spotted petals. A cross between unspotted and spotted plants
sometimes produces offspring which all have unspotted petals and sometimes
produces half spotted and half unspotted offspring. Explain these results.
In dalmatian dogs, the colour of the spots is determined by a gene which has
two alleles. The allele for black spots is dominant and the allele for brown
spots is recessive.
A breeder wanted to know the genotype of a black-spotted bitch. She
crossed her with a brown-spotted and a litter of three puppies was produced,
all of which were black. The breeder concluded that her bitch was
homozygous for the allele for black spots. Was she right? Explain your
answer.
Coat colour in rabbits is determined by a gene with 4 alleles. The alleles for
agouti (normal) coat is dominant to all of the other 3 alleles. The allele for
albino coat is recessive to the other 3 alleles. The allele for chinchilla (grey)
coat is dominant to the alleles for Himalayan (white with black ears, nose, feet
and tail).
a) Write down the 10 possible genotypes for coat colour and their
phenotypes.
b) Draw genetic diagrams to explain each of the following:
i)
An albino rabbit is crossed with a chinchilla rabbit producing
offspring which are all chinchilla. Two of these chinchilla
offspring are then crossed producing 4 chinchilla offspring
and 2 albino.
ii)
An Agouti rabbit is crossed with a Himalayan rabbit
producing 3 agouti offspring and 3 Himalayan.
iii)
2 agouti rabbits produce a litter of 5 young, three of whom
are agouti and 2 chinchilla. The chinchilla young are then
crossed producing 4 chinchilla offspring and 1 Himalayan.
A man of blood group B and a woman of blood group A have 3 children. One
is group A, one is group B and one group O. What are the genotypes of these
five people?
Draw a genetic diagram to explain why there is always an equal chance that a
child will be male or female. (You can do this in just the same way as the
other genetic diagrams you have drawn but using symbols to represent whole
chromosomes not genes.
Can a man with haemohilia pass the disease to:
a) His son.
b) His grandson.
Draw genetic diagrams to explain your answers.
One of the genes for colour vision in humans is found on the X chromosome
but not on the Y chromosome. The dominant allele of this gene gives normal
colour vision while a recessive allele produces red-green colour blindness.
a) Choose suitable symbols for these alleles and then write down all of
the possible genotypes for a man and for a woman.
b) A couple who both have normal colour vision have a child with colour
blindness. Explain how this may happen and state what the sex of the
colour blind child must be.
c) Is it possible for a colour blind girl to be born? Explain your answer.
One of the genes for coat colour in cats is sex-linked. The alleles Co gives
orange fur while CB gives black fur. The alleles are co-dominant and when
both are present the cat has patches of orange and black which is known as
tortoiseshell.
a) Explain why male cats cannot be tortoiseshell.
b) Draw a genetic diagram to show the expected genotype and
phenotypes of the offspring from a cross between an orange male and
a tortoiseshell female cat.
The allele for grey fur in a squirrel is dominant to white and the allele for long
tail is dominant to short.
a) Using the symbols G and g for fur coat colour and T and t for tail length,
draw a genetic diagram to show the genotypes and phenotypes of the
offspring you would expect from a cross between a pure-bred grey
animal with a long tail and a pure-bred white animal with a short tail.
b) If this first generation of offspring were bred together, what would be
the expected phenotypes in the second generation of offspring and in
what ratios would they occur?
In a species of plant, the allele for tall stem is dominant to short. The 2 alleles
for leaf colour giving green or white in the homozygous condition are codominant producing variegated leaves in the heterozygote.
A plant with tall stems and green leaves was crossed with a plant with short
stems and variegated leaves. The offspring from this cross consisted of
plants with tall stems and green leaves and plants with tall stems and
variegated leaves in the ratio of 1:1. Construct a genetic diagram to explain
this cross.