Inheritance (Edexcel GCSE Biology: Combined Science)

Figure 1 shows a list of key terms and definitions relating to inheritance but they are in the incorrect order. 

Figure 1

In humans, ear wax type has two distinct types, sticky and dry. Ear wax is an inherited trait which is controlled by a single gene. The allele for sticky ear wax (E) is dominant over the allele for dry earwax (e).

Explain how inheritance of biological sex is determined in humans.

Figure 2 shows a genetic diagram.

Complete the genetic diagram to show the genotypes of the parents and any offspring

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Figure 2

Describe what the term 'variation' means in the context of a population.

State why the following phrase is incorrect.

"Variation between individuals within populations is only caused by a variation in their genes" 

Variation in organisms can be caused by genetic and environment factors or a combination of both.

Figure 1 shows a list of characteristics in humans.

Complete Figure 1, placing a tick (✓)  in the appropriate column for each example characteristic.

Give an explanation for each of your answers in Figure 1.

Describe the differences between continuous variation and discontinuous variation.

The Human Genome Project was an international scientific research project to determine the sequence of all the bases that make up human DNA and to identify and map all of the genes.

State two potential applications of the Human Genome Project within medicine.

There is usually extensive genetic variation within a population of a species due to variations in alleles.

State how this variation arises.

State two factors that can lead to changes in the base sequence of DNA.

Most mutations don't significantly affect the phenotype.

Explain why this is.

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.

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

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Haemochromatosis can be inherited.

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

Figure 1 shows the inheritance of haemochromatosis in a family.

Figure 1

State and explain the genotype of female Z.

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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.

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

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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.

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A karyogram is a picture of the chromosomes found in the nucleus of a single cell.

Figure 1 shows a human karyogram.

State two reasons why this karyogram cannot be from a gamete (sex cell).

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(ii)

State the gender shown by this karyogram.

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(iii)

Complete the Punnett square to show how gender is inherited.

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A gene coding for a protein has two alleles.

Figure 1 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 1

Allele 2 has a mutation.

Figure 2 shows the key needed to predict the translated amino acid sequence of the protein.

Figure 2

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

Higher Tier Only

One gene can have several different alleles.

Explain why these alleles can produce proteins with different structures.

Sickle cell anaemia is another example of an inherited disorder whereby the alleles that cause it are codominant.

Sickle cell anaemia affects the shape of red blood cells, causing them to be shaped like sickles or crescent moons rather than their regular round shape. This means they can become rigid or sticky, which can slow blood flow. These red blood cells die much quicker than regular-shaped red blood cells.

Suggest why someone with sickle cell anaemia feel fatigued much more quickly than someone without sickle cell anaemia.

Figure 1 shows the inheritance of sickle cell anaemia in a family.

Figure 1

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Tay-Sachs is a rare inherited disorder that stops nerves from working properly and often leads to progressive damage to and the death of cells due to a build up.of a lipid called GM2 ganglioside

In unaffected individuals, an enzyme called β-hexosaminidase A helps to break down GM2 ganglioside.

Explain how a change in one amino acid in β-hexosaminidase A could stop the enzyme working properly. 

Tay-Sachs is caused by a recessive allele.

The diagram in Figure 1 shows the inheritance pattern for Tay-Sachs in a family.

Figure 1

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There are few known cures for DMD, but one type of treatment currently being researched is the use of stem cell therapy. This involves using stem cells from the patient to make healthy muscle cells, which could then be used to replace the damaged ones that cause DMD. The new muscle cells have a low risk of being rejected by the patient however the gene mutation may still affect some of these stem cells.

The graph in Figure 2 shows how patients categorised their DMD symptoms following treatment by stem cell therapy.

Figure 2

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