Monohybrid inheritance

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

Cystic fibrosis is a recessive genetic disorder.

Figure 10 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.

Scientists think that chickens were domesticated from red junglefowl thousands of years ago.

Figure 4 shows some information about these birds.

Describe how selective breeding has produced chickens that lay large numbers of eggs.

Chickens have 78 chromosomes in each of their body cells.

These chromosomes are in pairs.

Which term describes a chicken body cell?

State the number of chromosomes found in the gametes produced by chickens.

Complete the table to compare the production of body cells and gametes.

One box has been completed for you.

Some animal cells are stem cells.

Describe the function of stem cells.

Figure 8 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.

percentage =_........ %

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.

ratio_........ : 1

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.

Apple trees show genetic variation.

State one possible cause of genetic variation in apple trees.

The colour of an apple is an observable characteristic.

Which is the term for an observable characteristic?

Name the type of reproduction that produces genetically identical organisms.

Grafting is a technique used to grow some varieties of apple tree.

Figure 9 shows apple tree shoots grafted on to a rootstock.

Grafting can be used to produce apple trees that are genetically identical.

Give one advantage and one disadvantage of growing genetically identical apple trees.

advantage

disadvantage

As apples ripen, enzymes convert starch into sugars.

Devise a method to find the optimum pH of an enzyme that breaks down starch.

You may use standard laboratory equipment and the solutions listed in the box.

The optimum pH of an enzyme is pH 6.

Explain why this enzyme would not work at pH 10.

Alcohol is broken down by liver cells.

Which process moves alcohol from the blood into the liver cells?

If a person drinks too much alcohol, liver cells die and the person can develop cirrhosis of the liver.

The relative risk of developing cirrhosis of the liver is affected by two factors.

1. The volume of alcohol a person drinks in one week.

2. Whether the person drinks the alcohol on its own or with a meal.

Figure 5 shows how these two factors affect the relative risk of people developing cirrhosis of the liver.

Number of units of alcohol consumed per week

Figure 5

Person A drinks alcohol on its own.

Person B drinks alcohol with their meals.

Calculate the difference in risk for these two people when each one drinks 28 units of alcohol per week.

Using evidence from Figure 5, state two pieces of health advice for people about drinking alcohol.

Cystic fibrosis is a genetic condition that can also cause liver disease.

State where genes are found in cells.

Figure 6 shows the inheritance of cystic fibrosis in a family.

F represents the dominant allele that does not cause cystic fibrosis.

f represents the recessive allele that causes cystic fibrosis.

person A (Ff) person B

person C person D person E (ff)

Figure 6

A scientist states that the genotype of person B is Ff.

Explain why the scientist is correct.

State the genotype of person C.

Sickle cell disease is a recessive genetic disorder in humans.

Two parents are heterozygous for sickle cell disease.

Complete the Punnett square to show the possible genotypes of their children.

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

percentage probability =_........ %

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.

Figure 2 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.

Figure 3 shows the leaf of a wheat plant with a fungal disease.

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

Carrots have different physical characteristics such as colour.

Which genetic term describes the physical characteristics of a carrot?

Figure 4 shows some carrot sticks.

A student chose three carrot sticks and weighed each one.

The carrot sticks were placed in 50 cm³ of distilled water.

After two hours the student weighed each carrot stick again.

Figure 5 shows the results for these carrot sticks P, Q and R.

Give one reason why the student used three carrot sticks instead of just one carrot stick.

Give two ways that this method could be improved.

Calculate the percentage change in mass of carrot stick Q.

Use the equation

Give your answer to 2 significant figures.

percentage change =_........ %

Explain the change in mass of the carrot sticks.

Figure 5 shows how alcohol consumption increases the risk of developing liver cancer.

Someone who does not drink alcohol has a 1.0 risk of developing liver cancer.

One unit of alcohol contains 8 grams of alcohol.

Calculate the risk of developing liver cancer for someone who consumes 4 units of alcohol a day.

_........ risk of developing liver cancer

Describe how cancer develops in the liver.

Haemochromatosis is a disease that occurs when iron accumulates in the liver.

A person with haemochromatosis is treated by having 0.5 dm³ of their blood removed each week.

This lowers the level of iron in their blood.

Give two safety precautions needed when blood is removed from this person.

Haemochromatosis can be inherited.

Haemochromatosis occurs when a person inherits two copies of a recessive allele.

Figure 6 shows the inheritance of haemochromatosis in a family.

State and explain the genotype of female Z.