Font size
WorksheetsGenetic crosses 2
Total questions: 13
Worksheet time: 24mins
Cystic fibrosis is an inherited disease that occurs when an individual is homozygous for a recessive allele.
If parents are both heterozygous for this characteristic, what is the probability that their first child will have cystic fibrosis?
(a)
What determines the sex of a baby?
the father’s blood group
the father’s chromosomes
the mother’s blood group
the mother’s chromosomes
In cats, the allele for short hair is dominant to the allele for long hair. A short-haired cat gives birth to five kittens. Two of them have long hair.
Which statement must be correct?
Neither of the parents is heterozygous
One parent is homozygous
The female cat is heterozygous
The male cat is heterozygous
When white-flowered pea plants are crossed with red-flowered pea plants, the offspring (F1) all have red flowers.
If these F1 plants pollinate themselves, the next generation (F2) contains both red and white flowered plants.
Which statement explains this?
The allele for red flowers is dominant and the F1 plants are heterozygous
The allele for red flowers is dominant and the F1 plants are homozygous
The allele for red flowers is recessive and the F1 plants are heterozygous.
The allele for red flowers is recessive and the F1 plants are homozygous
Albinism in humans is caused by a recessive allele.
Parents who do not suffer from the condition produce an albino child.
What is the probability that their second child will be born albino?
(a)
An individual has the genotype Bb.
What is the correct description of this genotype?
heterozygous, with two different alleles of the same gene
heterozygous, with two different genes of the same allele
homozygous, with two different alleles of the same gene
homozygous, with two different genes of the same allele
The diagram shows the inheritance of flower colour in pea plants.
At which stages in the diagram does meiosis occur?
W and Y
W and Z
X and Y
X and Z
Most birds have a coloured pigment in their feathers, but in a few individuals, pigment is absent and the birds are albinos.
Albinism occurs when a bird is homozygous recessive for the gene which creates the coloured pigment.
If two albino birds mated, what describes the appearance of their offspring?
(a)
In an animal, the allele for straight fur is dominant to the allele for curly fur.
A pair of these animals mate and have nine offspring with straight fur and three with curly fur.
F represents the allele for straight fur and f represents the allele for curly fur.
What are the most likely genotypes of the parents?
(a)
A pure-breeding white mouse was crossed with a pure-breeding black mouse. All their offspring
were black.
Then, one of the offspring was bred with a pure-breeding white mouse. They produced 10 baby mice.
What are the most likely colours of these mice?
(a)
In pea plants, the allele for tall stems is dominant to the allele for short stems.
A heterozygous tall plant is crossed with a short plant, and 100 offspring are produced.
How many of the offspring are likely to be tall?
(a)
In a species of plant, the allele for red flowers (R) is dominant over the allele for white flowers (r).
Two red–flowered plants were crossed as shown in the diagram.
What are the genotypes of the parents?
(a)
short-toed animal was crossed with a long-toed animal of the same species. All the offspring had short toes. One of these offspring was crossed with another long-toed animal of the same species.
Which ratio of short-toed to long-toed animals should be expected?
(a)
