Inherited disorders

Cystic fibrosis is a genetic disorder.

Cystic fibrosis affects the movement of substances into and out of cells.

Which part of a cell controls the movement of substances into and out of the cell?

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Cystic fibrosis is caused by a recessive allele, b.

What name is given to the allele B ?

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Which term describes the genotype Bb ?

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Two people plan to have a child.

Both people have the genotype Bb.

Complete Figure 1 to show the possible genotypes of the child.

What is the chance that a child of these parents will have cystic fibrosis?

Use Figure 1.

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An embryo can be tested to find out its genotype.

What is the name of the testing process?

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Inherited disorders can be caused by changes in DNA.

What is the name of a change in DNA?

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Inheritance is one cause of variation in a population.

Environmental factors also cause variation in a population.

Suggest one environmental cause of variation in a human population.

Do not refer to inheritance or to changes in DNA in your answer.

AKU is a genetic disorder.

Figure 3 shows the inheritance of AKU in one family.

Describe how Figure 3 shows that the allele for AKU is recessive.

Which person is definitely heterozygous for AKU?

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A female who has AKU and a male who is heterozygous for AKU plan to have a child.

Determine the probability that the child will have AKU.

You should:

• complete Figure 4

• identify the phenotype of each offspring genotype

• use the symbols: A = dominant allele a = recessive allele.

A mutation is a change in a gene.

People who have AKU have a mutation that causes the production of a non-functioning enzyme.

Enzymes are proteins.

Suggest how a mutation can result in the production of a non-functioning enzyme.

Some people have In Vitro Fertilisation (IVF) treatment to increase the chance of becoming pregnant.

Describe how the process of IVF can result in pregnancy.

Embryos can be screened to detect inherited disorders.

Give two arguments against embryo screening.

Do not refer to religion in your answer.

Sexual reproduction in humans involves the production of egg cells and sperm cells.

Name the type of cell division that produces egg cells and sperm cells.

Sexual reproduction produces offspring that are genetically different from each other. Give two reasons why sexual reproduction causes variation in the offspring.

Polydactyly is an inherited disorder.

The allele for polydactyly is dominant, D. A person with two copies of the allele d will not have polydactyly.

A person with the genotype DD is homozygous. What word describes the genotype Dd ?

A person with the genotype Dd and a person with the genotype dd plan to have a child. Determine the probability that the child will have polydactyly. You should:

• complete the Punnett square diagram

• identify any offspring genotype that would have polydactyly.

Embryos can be screened for the alleles that cause inherited disorders. Give two advantages of embryo screening.

Sexual reproduction in humans involves the production of egg cells and sperm cells.

Name the type of cell division that produces egg cells and sperm cells.

Sexual reproduction produces offspring that are genetically different from each other. Give two reasons why sexual reproduction causes variation in the offspring.

Polydactyly is an inherited disorder.

The allele for polydactyly is dominant, D. A person with two copies of the allele d will not have polydactyly.

A person with the genotype DD is homozygous. What word describes the genotype Dd ?

A person with the genotype Dd and a person with the genotype dd plan to have a child. Determine the probability that the child will have polydactyly. You should:

• complete the Punnett square diagram

• identify any offspring genotype that would have polydactyly.

Embryos can be screened for the alleles that cause inherited disorders. Give two advantages of embryo screening.

This question is about genetics.

Crop plants are genetically modified (GM) for useful characteristics. Which useful characteristic are crops genetically modified for? Tick (✓) one box.

What is one concern about GM crops? Tick (✓) one box.

Some inherited disorders are caused by a faulty piece of DNA.

What is the name of a piece of DNA that codes for a characteristic?

DNA contains a code for making substances in the cell. What type of substance is made using the DNA code? Tick (✓) one box.

Cystic fibrosis (CF) is an inherited disorder. The allele for having CF is recessive (h). The allele for not having CF is dominant (H).

What is a recessive allele? Tick (✓) one box.

A man and a woman do not have CF. The man has the alleles Hh.

What word describes the alleles of the man? Tick (✓) one box.

The man and the woman want to have a child. Complete Figure 1 to show the possible genotypes of the child. Draw a ring around the genotype of a child who will have CF.

What is the chance that a child of the man and the woman will have CF? Tick (✓) one box.

The woman is pregnant. The woman can have embryo screening to find out if the child will have CF. Suggest one reason why the woman might not want to have embryo screening.

This question is about genetic disorders.

Some people are heterozygous for a genetic disorder. Define the term ‘heterozygous’.

Figure 6 shows the inheritance of a genetic disorder in a family.

Person 7 and person 8 plan to have another child.

Determine the probability that the child will be a male who has the disorder. You should:

• draw a Punnett square diagram

• identify the genotype of person 7 and the genotype of person 8

• identify the phenotype of each offspring genotype

• use the symbols: H = dominant allele h = recessive allele

Polydactyly is a different inherited disorder. Two parents do not have any alleles for polydactyly in their ordinary body cells. These parents produced a child with polydactyly. Explain how polydactyly suddenly occurred in this family.

This question is about inheritance. Humans have 23 pairs of chromosomes in each body cell. One pair of chromosomes determines sex.

Complete Figure 5.

Figure 5

In some families all children are the same sex. Give the reason why.

Cystic fibrosis (CF) is an inherited disorder.

A man and a woman do not have CF. The man and the woman have a child who has CF.

Draw a Punnett square diagram to find the probability that their next child will have CF. Use the symbols: T = dominant allele t = recessive allele Draw a ring around the genotype of any children with CF.

Embryo screening for CF can be done by two methods. Method 1

• The woman becomes pregnant by sexual intercourse.

• After 10 weeks of pregnancy a fine needle is inserted into the uterus.

• A sample of the fluid surrounding the embryo is taken.

• The DNA of the embryo is tested for CF.

The screening is done free by specialist hospitals for couples who are at risk of having a child with CF. There is a small risk of miscarriage.

Method 2

• The couple use In Vitro Fertilisation (IVF) to produce a small number of embryos.

• Each embryo is tested for CF.

• One or two embryos without CF are implanted in the woman’s uterus.

In 2017 the success rate for having a baby by IVF for women under 35 years was 30% IVF is a stressful, invasive procedure. In most UK areas the free public health service does not provide IVF for all women asking for it.

Suggest three reasons for choosing Method 1 instead of Method 2.

Suggest one advantage of Method 2.