Probability and ratios in genetic crosses

In the 19th century, Gregor Mendel studied genetic inheritance in pea plants.

Mendel made the conclusion that characteristics in organisms were determined by the inheritance of ‘units’.

What are these ‘units’ of inheritance known as today?

Figure 20 shows one of Mendel’s experiments on the inheritance of pea shape.

plants that produced plants that produced

State the conclusion that Mendel was able to make about the wrinkled pea characteristic.

A scientist crossed two pea plants that were heterozygous for pea shape.

Complete the Punnett square to show the inheritance of the alleles for pea shape and the percentage probability of producing a plant with wrinkled peas.

Use the letter R for the allele for round shape.

Use the letter r for the allele for wrinkled shape.

percentage probability of producing a plant with wrinkled peas_........

Plants used to study inheritance are grown in controlled environmental conditions.

Suggest two ways of controlling these environmental conditions.

Some plants can reproduce asexually and sexually.

Complete the table by writing yes or no in each box to show the features of asexual and sexual reproduction.

A zygote with a diploid nucleus is formed by sexual reproduction.

State what is meant by a diploid nucleus.

In the 19th century, Gregor Mendel studied genetic inheritance in pea plants.

Mendel made the conclusion that characteristics in organisms were determined by the inheritance of ‘units’.

What are these ‘units’ of inheritance known as today?

Figure 5 shows one of Mendel’s experiments on the inheritance of pea shape.

plants that produced plants that produced

State the conclusion that Mendel was able to make about the wrinkled pea characteristic.

A scientist crossed two pea plants that were heterozygous for pea shape.

Complete the Punnett square to show the inheritance of the alleles for pea shape and the percentage probability of producing a plant with wrinkled peas.

Use the letter R for the allele for round shape.

Use the letter r for the allele for wrinkled shape.

percentage probability of producing a plant with wrinkled peas_........

Plants used to study inheritance are grown in controlled environmental conditions.

Suggest two ways of controlling these environmental conditions.

Some plants can reproduce asexually and sexually.

Complete the table by writing yes or no in each box to show the features of asexual and sexual reproduction.

A zygote with a diploid nucleus is formed by sexual reproduction.

State what is meant by a diploid nucleus.

Genetic disorders can be caused by mutations in the DNA of genes.

Cystic fibrosis is a recessive genetic disorder.

Figure 13 shows a family pedigree for the inheritance of cystic fibrosis.

Which row is correct for the mother, father and son?

Cystic fibrosis causes the build‑up of thick, sticky mucus.

Describe how the build-up of thick, sticky mucus affects the airways of a person.

Huntington’s disease is a condition caused by a dominant allele.

Explain the phenotypes of the offspring of a genetic cross between a person who is heterozygous for the Huntington’s allele and a person who is not affected.

Use the Punnett square as part of your answer.

*(c) Explain how DNA is extracted from strawberries.

Include in your answer:

• the reasons for each stage of the extraction process

• the structure of a DNA molecule.

Mendel crossed pea plants that always produced purple flowers with pea plants that always produced white flowers.

The flowers of the offspring were all purple, as shown in Figure 5.

Which conclusion can be made about the characteristic for purple flowers?

Mendel used two of the offspring with purple flowers in another cross.

The pea plants he obtained from this cross produced purple flowers or white flowers in a ratio of 3: 1.

Calculate the expected number of pea plants with purple flowers, in a sample of 160 pea plants.

A pea plant producing purple flowers had the genotype Aa.

This pea plant was crossed with a pea plant producing white flowers.

Complete the Punnett square to show the possible genotypes of the offspring.

Show the percentage of pea plants that produce white flowers in your answer.

Asexual reproduction can be used to produce flowering plants.

Give two advantages of using asexual reproduction to produce flowering plants.

Flower colour is controlled by genes.

Which is a definition of a gene?

The two strands of a DNA molecule are linked by complementary bases.

Describe how the complementary bases are linked in a DNA molecule.

Figure 12 shows some characteristics of pea plants.

The allele for purple flowers is dominant to the allele for white flowers.

Which term describes the allele for white flowers?

A scientist crossed a pea plant that produced round seeds (Rr) with a pea plant that produced wrinkled seeds (rr).

Complete the Punnett square.

State the percentage of the offspring that will produce round seeds.

The scientist crossed two purple flowering pea plants.

The offspring were:

• 133 plants with purple flowers

• 46 plants with white flowers

Calculate the ratio of offspring with purple flowers to offspring with white flowers.

Give your answer to the nearest whole number.

Explain why it was possible for this cross to produce some offspring with white flowers.

The cells in pea plants are diploid.

These cells have 14 chromosomes.

Explain why pea plant gametes have only seven chromosomes.

Describe what happens at fertilisation.

Gregor Mendel studied inheritance in pea plants.

Pea plants can produce either yellow pea pods or green pea pods.

Mendel crossed plants that always produce yellow pea pods with plants that always produce green pea pods.

Symbol A represents the dominant allele.

Symbol a represents the recessive allele.

Which is the genotype of the pea pods produced from this cross?

Mendel grew many plants from the seeds in these pea pods.

These plants were then crossed with each other.

The seeds from this second cross produced 5 496 plants with yellow pea pods and 1 832 plants with green pea pods.

Give this as a ratio in its simplest form.

Complete the Punnett square to show the outcome of a cross where both parent pea plants are heterozygous.

Show the percentage probability of homozygous recessive offspring in your answer.

percentage probability of homozygous recessive offspring_........

Some plants reproduce sexually.

Give one advantage of this type of reproduction.

Name the process that forms gametes for sexual reproduction.

3 (a) Sickle cell disease is a recessive genetic disorder in humans.

(i) Two parents are heterozygous for sickle cell disease. Complete the Punnett square to show the possible genotypes of their children.

(ii) State the percentage probability that their children could have sickle cell disease.

(iii) A father with the genotype dd and a mother with the genotype DD plan to have several children. Explain why none of their children will have sickle cell disease.

(b) Figure 4 shows some information about two types of cattle.

Describe how these types of cattle could be selectively bred to produce cattle that can survive high temperatures and have good meat quality.

(c) Figure 5 shows the leaf of a wheat plant with a fungal disease.

(Source: © Kazakov Maksim/Shutterstock)

Figure 5

Give two benefits of breeding wheat plants that are resistant to fungal disease.

10 (a) One gene can have several different alleles. Explain why these alleles can produce proteins with different structures.

(b) Monoclonal antibodies are proteins. Figure 16 shows the process of monoclonal antibody production.

mouse hybridoma

Figure 16

(i) Which type of cell is added to the B lymphocytes to produce the hybridoma?

(ii) A person with blood group A has the A antigen on the surface of their red blood cells. Monoclonal antibodies can be used to detect the A antigen on red blood cells to determine the blood group of a person. Explain why monoclonal antibodies, used to detect blood group A, would not react with the blood of a person with blood group B.

(c) The allele for blood group A and the allele for blood group B are codominant. Gregor Mendel investigated the inheritance of alleles using flowering plants. He showed that the allele for red flowers (I) is codominant with the allele for He showed that the allele for red flowers (I^R) is codominant with the allele for white flowers (I^W). A heterozygous plant produces pink flowers.

(i) Give the genotype for a plant producing white flowers.

(ii) Explain the outcome if two plants that produce pink flowers are crossed. You should complete the Punnett square as part of your answer.

(TOTAL FOR PAPER = 100 MARKS)

Gregor Mendel used pea plants in plant breeding experiments. He discovered the basis of genetic inheritance.

He cross-bred tall pea plants with short pea plants.

All the offspring were tall, as shown in Figure 16.

Explain why the offspring are all tall.

In this investigation, the parent pea plants were grown in a warm, closed greenhouse.

Give two reasons why the parent pea plants were grown in a warm, closed greenhouse.

Pea plants produce different coloured peas.

The allele for yellow‑coloured peas (A) is dominant to the allele for green‑coloured peas (a).

Two heterozygous parent plants were used in a genetic cross.

Predict, using the Punnett square, the percentage probability that this cross will have offspring that produce green‑coloured peas.

Explain one advantage to pea plants of using sexual reproduction to produce offspring.

Peas contain small amounts of fat.

Describe a test to identify fat.

Gregor Mendel used pea plants in plant breeding experiments. He discovered the basis of genetic inheritance.

He cross-bred tall pea plants with short pea plants.

All the offspring were tall, as shown in Figure 4.

Explain why the offspring are all tall.

In this investigation, the parent pea plants were grown in a warm, closed greenhouse.

Give two reasons why the parent pea plants were grown in a warm, closed greenhouse.

Pea plants produce different coloured peas.

The allele for yellow‑coloured peas (A) is dominant to the allele for green‑coloured peas (a).

Two heterozygous parent plants were used in a genetic cross.

Predict, using the Punnett square, the percentage probability that this cross will have offspring that produce green‑coloured peas.

Explain one advantage to pea plants of using sexual reproduction to produce offspring.

Peas contain small amounts of fat.

Describe a test to identify fat.

Figure 1 shows a pea plant with flowers.

Name the type of reproduction involving flowers.

What is the advantage of reproduction involving flowers?

The seeds produced by this pea plant can be round or wrinkled.

The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r).

A homozygous dominant round seeded plant was crossed with a homozygous recessive wrinkled seeded plant.

Complete the Punnett square to show the genotypes of the offspring.

State the percentage of the offspring that will produce round seeds.

Which scientist discovered the basis of genetic inheritance by crossing pea plants?

The blood group of a person is determined by their genotype.

Describe how a person inherits the blood group AB.

Transcription and translation are stages in the synthesis of proteins.

Which enzyme is involved in the process of transcription?

Describe how a mutation in the non-coding region of the DNA can prevent a gene being transcribed.

A gene coding for a protein has two alleles.

Figure 14 shows the first 5 codons of an mRNA strand for these alleles.

Allele 1 – AUG CCA CAG GAG UUC

Allele 2 – AUG CCA GAG GAG UUC

Figure 14

Allele 2 has a mutation.

Figure 15 shows the key needed to predict the translated amino acid sequence of the protein.

Explain how the mutation in allele 2 could affect the functioning of this protein.

*(c) The inheritance of different alleles affects the phenotype of an individual.

A child is blood group O.

The child’s mother is blood group A and the child’s father is blood group B.

Explain how this child is blood group O.

Use the Punnett square and probability in your answer.