Monohybrid inheritance

A pure-breeding plant with smooth stems was crossed with a heterozygous plant that had hairy stems. What ratio of hairy stems to smooth stems will appear in the offspring plants?

Feb/March 2016

The diagram illustrates the inheritance of ABO blood groups. The blood groups of some individuals are shown. What might Priya’s genotype be?

Feb/March 2016

The allele for brown coat colour is dominant over the allele for albino coat colour. A mammal that is homozygous for brown coat colour is crossed with a mammal that is heterozygous for brown coat colour. What percentage of the offspring are expected to be albino?

Feb/March 2017

A man with genotype $I^A I^O$ and a woman with genotype $I^B I^O$ have a child. What is the probability that the child will have the same blood group as one of the parents?

Feb/March 2017

Colour blindness in humans is the result of a defect in some of the light receptor cells in the retina of the eye. Rod cells and cone cells are the two kinds of light receptor.

Feb/March 2017

The diagram illustrates how fur colour is inherited in a small mammal. If the allele for white fur is dominant, which animal must be heterozygous for the gene that controls fur colour?

Feb/March 2018

The diagram illustrates the inheritance of fur colour in a small mammal. If the allele for white fur is dominant, which animal has to be heterozygous for the gene that controls fur colour?

Feb/March 2018

Which pair of parents could have offspring with blood group O?

Feb/March 2019

Fig. 2.1 depicts several flowers on a snapdragon plant, Antirrhinum majus. Snapdragons are insect-pollinated plants.

Feb/March 2019

Which cross will produce only pure-breeding offspring?

Feb/March 2020

Hair length in cats is determined by a single gene. The allele for short hair is dominant - H. The allele for long hair is recessive - h. Fig. 3.1 shows a photograph of two cats.

Feb/March 2020

A male who is heterozygous for the sickle cell anaemia allele, Hb$^{S}$Hb$^{A}$, has children with a female who is homozygous for the normal haemoglobin allele, Hb$^{A}$Hb$^{A}$. What is the chance that the first child will be resistant to malaria?

Feb/March 2021

In mice, the allele for black hair is dominant over the allele for brown hair. What proportion of the offspring would show brown hair if a homozygous black mouse is crossed with a heterozygous black mouse?

Feb/March 2023

Huntington’s disease is a hereditary disorder caused by a change in one gene. The allele for Huntington’s disease is dominant and is shown by the letter H. The allele for no Huntington’s disease is recessive and is shown by the letter h. Fig. 3.1 is a pedigree chart showing the inheritance of Huntington’s disease in one family.

Feb/March 2023

Pea seeds may be either smooth or wrinkled in shape. The allele for smooth is dominant, whereas the allele for wrinkled is recessive. Two heterozygous plants are crossed. What percentage of the offspring would be expected to have a smooth shape?

Feb/March 2024

Polydactyly is an inherited condition that can occur in cats. It causes the affected offspring to have extra toes. The allele for polydactyly is dominant and is shown by the letter T. The allele for not having polydactyly is recessive and is shown by the letter t. A cat with genotype Tt is bred with a cat with genotype tt. What is the chance of the offspring having polydactyly?

Feb/March 2025

A man with blood group A and genotype $I^{A}I^{O}$ has a child with a woman who has blood group B and genotype $I^{B}I^{O}$. What is the probability that the child will have blood group O?

Feb/March 2025

Albinism is a condition passed on through inheritance in which pigment fails to develop in the skin, hair and eyes. The albinism allele is recessive. What is the probability that parents who are albino will have an albino child?

May/June 2016

In pea plants, the allele for tall, $T$, is dominant over the allele for dwarf, $t$. Which cross would give plants in the ratio of $1$ tall : $1$ dwarf?

May/June 2016

In ABO blood-group inheritance, if two parents have the genotypes $I^{A}i$ and $I^{A}I^{B}$, which blood group will their offspring have?

May/June 2016

In ABO blood group inheritance, if two parents have the genotypes $I^{A}I^{A}$ and $I^{A}I^{O}$, what blood group would their offspring have?

May/June 2016

In the inheritance of ABO blood groups, if two parents possess the genotypes $I^{A} I^{A}$ and $I^{A} I^{o}$, what blood group will their offspring have?

May/June 2016

Sickle cell anaemia is controlled by the gene Hb. $Hb^{A}$ is the allele for normal blood. $Hb^{S}$ is the allele for sickle cell anaemia. Which pair of parents could produce some children who are resistant to malaria and some who have all normal red blood cells?

May/June 2016

Fig. 8.1 is a diagram of a cross-section of a human eye. Fig. 8.2 shows part of a family tree in which some of the individuals have the type of glaucoma caused by the recessive allele, g. In Fig. 8.2, shaded boxes show individuals who have glaucoma, while unshaded boxes show individuals with normal vision.

May/June 2016

Catalase is an enzyme that decomposes hydrogen peroxide within cells. Red blood cells contain catalase. In some dogs, an inherited disorder means catalase is not made. This disorder is called acatalasia, and it results from a mutation in the gene for catalase.

May/June 2016

Anthocyanin, a red pigment, is present in carnation flowers. Some carnation plants possess a gene that allows anthocyanin to be made.

May/June 2016

A female guinea pig that was pure-breeding for white fur was mated with a male guinea pig that was pure-breeding for brown fur. Every offspring had brown fur. One of the male offspring was then mated with a female with white fur. What proportion of white offspring would be expected from this cross?

May/June 2017

Dianthus flowers may appear in three colours: red, pink or white. A red flower is always homozygous, and a white flower is always homozygous. Pink flowers are heterozygous. If a red flower is crossed with a white flower, what percentage of the offspring will be pink?

May/June 2017

Dianthus flowers occur in three colours: red, pink or white. Every red flower is homozygous, and every white flower is homozygous. Pink flowers are heterozygous. If a red flower is crossed with a white flower, what percentage of the offspring would be pink?

May/June 2017

Dianthus flowers may occur in one of three colours: red, pink or white. A red flower is always homozygous, and a white flower is always homozygous. Pink flowers are heterozygous. If a red flower is crossed with a white flower, what percentage of the offspring will be pink?

May/June 2017

What term is given to an organism with two different alleles of a particular gene?

May/June 2018

The diagram illustrates the phenotypes of the blood groups in a family. Which statement about the parents’ genotypes is correct?

May/June 2018

Sickle-cell anaemia is an inherited disease. Which genotypes shown in the diagram would raise an individual’s resistance to malaria?

May/June 2018

Cystic fibrosis is a genetic disorder passed on through inheritance. The allele for cystic fibrosis is recessive. A woman is heterozygous, and her partner is homozygous dominant. What must be true for any children they have?

May/June 2018

State the name of the cell division that forms gametes.

May/June 2018

Which term is used for an individual who carries two identical alleles for one particular gene?

May/June 2019

One form of night-blindness is an inherited disorder that results from a dominant allele. The pedigree diagram shows how this disorder was inherited in one family. Person X marries a partner with normal sight. What is the probability that their first child will have night-blindness?

May/June 2019

In fruit flies, the allele for grey body, $G$, is dominant to the allele for black body, $g$. The outcome of a cross between two flies is shown below. Parent 1: grey-bodied fly \times Parent 2: black-bodied fly Offspring: 40 grey-bodied flies + 42 black-bodied flies What were the genotypes of the parents?

May/June 2019

Parents with alleles $I^A I^B$ and $I^O I^O$ can have children of which blood groups?

May/June 2019

The table lists some inherited characteristics. Which characteristics demonstrate co-dominance?

May/June 2019

Fig. 8.1 depicts a cat with an inherited condition that gives the cat extra toes. The allele responsible for this condition is dominant over the allele for the normal condition. Fig. 8.2 illustrates the inheritance of this condition in a family of cats.

May/June 2019

Sickle-cell anaemia is an inherited disorder. Fig. 5.1 shows a photomicrograph of some blood cells taken from a person with sickle-cell anaemia. The diagram identifies a red blood cell with a sickle shape.

May/June 2019

In a family, both parents show a characteristic produced by the dominant allele of a gene. They have two children. The family pedigree diagram is shown. Which row gives the genotypes of the parents for this gene?

May/June 2021

Two codominant alleles determine coat colour in cattle. Genotype $C^R C^R$ gives cattle a red coat. Genotype $C^W C^W$ gives cattle a white coat. Genotype $C^R C^W$ produces a roan coat; such cattle have both red hairs and white hairs in the coat. A red cow is mated with a roan bull. What is the expected ratio of coat colour in the offspring?

May/June 2021

Fig. 10.1 presents the outcome of crossing a red-flowered plant with a white-flowered plant. Each parent plant was homozygous for flower colour. Every offspring produced had red flowers.

May/June 2021

In humans, the ABO system contains four blood groups: A, B, AB and O. The gene that controls blood group has three alleles: $I^A$, $I^B$ and $I^o$.

May/June 2021

For rabbits, the allele for dark fur, $R$, is dominant over the allele for white fur, $r$. The diagram illustrates a cross between one rabbit with dark fur and one rabbit with white fur. What are the genotypes of the parents?

May/June 2022

If a horse with red hair (genotype $H^R H^R$) is crossed with a horse with white hair (genotype $H^W H^W$), the young produced show both red and white hair (genotype $H^R H^W$). Such horses are said to have roan-coloured hair. This is an instance of codominance. If two roan-coloured horses are crossed, what is the probability that their offspring will also be roan-coloured?

May/June 2022

Some fruit flies have orange eyes, while others have red eyes. If two orange-eyed fruit flies are crossed, every offspring has orange eyes. If two red-eyed fruit flies are crossed, the offspring may have orange eyes or red eyes. What conclusion can be drawn from these observations?

May/June 2022

A woman with normal colour vision is a carrier of the colour-blindness allele ($X^{B}X^{b}$). She has a male child with a man who has normal colour vision ($X^{B}Y$). What is the probability that the male child will be colour-blind?

May/June 2022

A single gene determines coat texture inheritance in guinea pigs.

May/June 2022

The pancreas is a human organ with roles in both the digestive and hormonal systems. Fig. 3.1 shows a section of the alimentary canal together with some of its associated organs.

May/June 2022

Red blood cells have the protein haemoglobin.

May/June 2022

During breeding, which pair of parents would be pure-breeding for a specific characteristic?

May/June 2023

In pea plants, the allele for round seeds, R, is dominant over the allele for wrinkled seeds, r. If plants with genotype Rr are crossed, what proportions of offspring are likely?

May/June 2023

In one mammal species, black fur colour is dominant, whereas brown fur colour is recessive. Two black-furred parents have offspring, and all of the first group of young are black-furred. Later in the same year, these same parents have more offspring. One of the new offspring has brown fur. Which statement about fur colour is correct?

May/June 2023

Which pair of parents could have a child with blood group O?

May/June 2023

The diagram illustrates how albinism is passed on within one family. Albinism is an inherited condition caused by a recessive allele. Which individuals must be heterozygous for this condition?

May/June 2023

A man with genotype $I^A I^O$ and a woman with genotype $I^B I^O$ have a child. What is the probability that the child will share the same blood group as either parent?

May/June 2023

The diagram displays the sex chromosomes of a woman and a man. Their genotypes for a recessive sex-linked condition are also given. What is the probability that their daughter will express the sex-linked condition?

May/June 2023

Which Punnett square represents a test cross used to identify a heterozygous parent?

May/June 2023

The pedigree diagrams illustrate how a genetic disorder is inherited in four families. This genetic disorder is not sex-linked. Which pedigree diagram shows that the genetic disorder must be due to a dominant allele?

May/June 2024

In mice, the allele for brown fur is dominant over the allele for white fur. The diagram illustrates how fur colour is inherited in a family of mice. Which two individuals are heterozygous for fur colour?

May/June 2024

Describe what the term gene means.

May/June 2024

Fig. 3.1 shows a pedigree chart for a plant species that may bear blue flowers or purple flowers. Blue flower colour is dominant over purple flower colour. The allele for blue flowers is shown by the letter B. The allele for purple flowers is shown by the letter b. These plants can therefore have genotypes BB or Bb or bb.

May/June 2024

Cystic fibrosis is an inherited disorder that develops when a person is homozygous for the recessive allele. If both parents are heterozygous for this characteristic, what is the probability that their first child will have cystic fibrosis?

May/June 2025

An individual’s genotype is Bb. Which description correctly matches this genotype?

May/June 2025

A farmer crossed male cattle with white hair and female cattle with red hair. Every offspring had roan hair (a blend of red and white). He then kept crossing two roan cattle with each other, and the offspring appeared in the ratio 1 red : 2 roan : 1 white. What accounts for the farmer getting this ratio?

May/June 2025

The diagram illustrates how a genetic condition is passed on in one family. What can be concluded about this genetic condition?

May/June 2025

The diagram illustrates the inheritance, within one family, of a sex-linked recessive disease. Which individuals in the diagram are heterozygous for this disease?

May/June 2025

The list below contains some claims about variation. Put ticks (✓) in the boxes to show which claims are correct. Variation is discontinuous when only a small number of phenotypes occur and there are no intermediates. Variation refers to similarities among individuals from different species. Variation is caused only by genes. Variation may be produced by mutation.

May/June 2025

A brown mouse is crossed with a white mouse. In the first set of offspring, there are 8 brown mice and 9 white mice. The same pair is then crossed again. In the second set of offspring, there are 9 brown mice and 7 white mice. What are the parents’ genotypes most likely to be?

Oct/Nov 2016

A farmer purchases a bull that has unusual curved horns. He wants to find out whether the bull is pure-breeding for curved horns. He mates the bull with cows in his herd, all of which are pure-breeding for straight horns. Which proportion of the calves would show that the bull is pure-breeding for curved horns?

Oct/Nov 2016

In mice, the allele for black hair is dominant over the allele for brown hair. If a homozygous black mouse is crossed with a heterozygous black mouse, what proportion of the offspring will have black hair?

Oct/Nov 2016

One parent is blood group A and the other parent is blood group B. Their first child is blood group O. Which blood groups could their next child have?

Oct/Nov 2016

$\text{Hb}^A$ denotes the allele for normal haemoglobin, and $\text{Hb}^S$ denotes the allele for abnormal haemoglobin that results in sickle-shaped red blood cells. Which row correctly links a genotype with its phenotype?

Oct/Nov 2016

Fig. 9.1 illustrates a genetic cross between a purple-flowered plant and a white-flowered plant. The parts of the cross are labelled U-Z.

Oct/Nov 2016

In some mammals, the allele for brown coat colour is dominant over the allele for white coat colour. What percentage of the offspring would have white coats if two heterozygous mammals are crossed?

Oct/Nov 2017

In some plants, $H$ is the dominant allele for hairy stems, while $h$ is the recessive allele for smooth stems. A mating pair of these plants has 37 offspring, of which 18 have hairy stems and 19 have smooth stems. What are the most likely genotypes of the parents?

Oct/Nov 2017

The pedigree diagram illustrates the inheritance of the ability to detect flowers called freesias. The allele for smelling freesias is dominant. Which individual’s symbol is incorrect?

Oct/Nov 2017

A pure-breeding white rat was crossed with a pure-breeding black rat, and every offspring produced was black. One offspring was then bred with a pure-breeding white rat. What is the most likely percentage of black rats among the offspring?

Oct/Nov 2017

A tall pea plant is bred with a short pea plant. Every offspring plant is tall. What are the genotypes of the tall parent plant and the offspring?

Oct/Nov 2017

In certain mammals, the allele for brown coat colour is dominant over the allele for white coat colour. What percentage of the offspring would be white if two heterozygous mammals are crossed?

Oct/Nov 2017

In some plants, $H$ is the dominant allele for hairy stems, while $h$ is the recessive allele for smooth stems. One pair of these plants has 37 offspring, of which 18 have hairy stems and 19 have smooth stems. What are the most likely genotypes of the parents?

Oct/Nov 2017

The pedigree chart illustrates the inheritance of the ability to smell flowers known as freesias. The allele for being able to smell freesias is dominant. Which individual's symbol is incorrect?

Oct/Nov 2017

A true-breeding white rat was mated with a true-breeding black rat. Every one of the young produced was black. One of these offspring was then mated with a true-breeding white rat. What is the most likely percentage of black rats among the offspring?

Oct/Nov 2017

Fig. 9.1 illustrates a cross involving two guinea pigs. The male guinea pig is pure-breeding for black fur colour, while the female guinea pig is pure-breeding for white fur colour. The allele for black fur colour is represented by B and the allele for white fur colour is represented by b. All four offspring had black fur.

Oct/Nov 2017

The flowers on pea plants can be pollinated by bees.

Oct/Nov 2017

The garden pea, Pisum sativum, is a species with flowers containing both male and female structures. P. sativum naturally undergoes self-pollination.

Oct/Nov 2017

Apple scab is a disease that affects apple trees. Fig. 3.1 shows apples taken from apple trees that are uninfected and from those that are infected. A gene controls whether apple trees are resistant to apple scab disease or not. This gene has two alleles: the disease-resistant allele, R, and the not disease-resistant allele, r.

Oct/Nov 2017

The genetic diagram illustrates a monohybrid cross. B is the dominant allele, while b is the recessive allele. Which of the parents and offspring are heterozygous?

Oct/Nov 2018

The allele for detached earlobes is dominant over the allele for attached earlobes. Both parents are heterozygous for detached earlobes. What is the probability that their first child will have attached earlobes?

Oct/Nov 2018

Two pea plants that produce white flowers are crossed. Among the offspring pea plants, some have red flowers while others have white flowers. Which statement about the parent pea plants is correct?

Oct/Nov 2018

Sickle-cell anaemia is an inherited disorder caused by the allele $\mathrm{Hb}^S$. $\mathrm{Hb}^A$ is the normal allele. A woman has no symptoms of the disease, but her brother does have symptoms. If her mother and father both have no symptoms, which statement is correct?

Oct/Nov 2018

Pure-breeding black-feathered chickens are crossed with pure-breeding white-feathered chickens. Every offspring in the F1 generation has both black and white feathers. What ratio of offspring phenotypes will be produced when two chickens from the F1 generation are crossed?

Oct/Nov 2018

Which genotypes can result in a person having blood group A?

Oct/Nov 2018

Fig. 7.1 depicts a goat with white fur. Fig. 7.2 gives a diagram showing how fur colour is inherited in a herd of goats.

Oct/Nov 2018

State what cell T is called in Fig. 6.1.

Oct/Nov 2018

A mouse with grey hair mates with a mouse with white hair, producing offspring with genotypes Bb, Bb, bb and bb. (B is the dominant allele for grey hair, and b is the recessive allele for white hair.) Which statement correctly describes the genotypes of the parents?

Oct/Nov 2019

For a plant species, the allele for red flowers, $R$, is dominant over the allele for white flowers, $r$. Homozygous red-flowered plants, $RR$, are crossed with homozygous white-flowered plants, $rr$. What flower colour will the offspring from this cross have?

Oct/Nov 2019