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Question 1
Tay-Sachs disease is a genetic disorder caused by a recessive allele, t. Tay-Sachs is caused by the absence of an enzyme called hexosaminidase A. |
a) | Explain how a change in an allele can stop an enzyme from being produced.
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The diagram below shows a pair of chromosomes from a newborn baby. |
b) | What is the baby's genotype? A homozygous dominant B homozygous recessive C heterozygous
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c) | What is the baby's phenotype?
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d) | The baby's father is homozygous dominant. What are the mother's possible genotypes?
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Question 2
DNA is made up of four different nucleotides, A, T, C and G. |
a) | Order the words allele, chromosome, genome and nucleotide to show their size from smallest to largest.
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b) | What is the meaning of the term allele?
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c) | The total number of nucleotides in a human body cell is 1.2 × 1010. The length of a DNA molecule increases by 0.34 nm for each nucleotide pair. What is the total length of double helix in a human body cell? Give your answer in metres.
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Question 3
DNA is the molecule of heredity. |
a) | Which statement correctly describes a DNA molecule? A two strands joined together by covalent bonds to form a double helix B two complementary bases twisted into a double helix by strong bonds C a double helix with strands joined by hydrogen bonds between bases D four complementary strands joined together with hydrogen bonds
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b) | Which structures in the nucleus of a human cell contain DNA?
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A student extracted DNA from a strawberry. The student followed the method below:
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c) | Give a reason for filtering the mixture.
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d) | Why did the student use ethanol?
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e) | The student wanted to compare the mass of DNA present in two different varieties of strawberries. The student repeated the process with a different variety of strawberry. |
State two variables the student must control when using this method to compare the mass of DNA from the two different varieties of strawberry.
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f) | The student repeated the experiment several times. Why did the student repeat the experiment?
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Question 4
The photograph below shows a sable antelope. The nucleus of an antelope's cell contains the same number of chromosomes as the nucleus of a human cell. |
a) | State the number of chromosomes in an antelope's muscle cell.
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b) | State the number of chromosomes in an antelope's sperm cell.
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c) | Scientists have been sequencing the DNA of all plants and animals on the planet. |
Humans share 80% of their DNA with mice. The human DNA contains 6,600 million bases. Calculate the number of bases that are the same as a mouse.
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Question 5
A karyogram is an image showing the chromosomes found in the nucleus of a cell. |
a) | How many chromosomes are present in each of this organism's cells?
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State the sex shown by this karyogram and explain your answer.
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c) | Give two reasons why this karyogram is from a somatic cell and not from a gamete.
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Question 6
Von Willebrand Disease (vWD) is a recessive disorder of dogs. Dogs with vWD lack a specific protein needed for their platelets to function correctly. vWD is the most common bleeding disease in dogs, and it is present in about 70% of all Doberman Pinschers. |
a) | Some of the dogs with vWD never show any symptoms. Others may spontaneously bleed from the nose and mouth. Suggest a reason why dogs with vWD bleed more than other dogs.
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b) | Give the percentage of offspring likely to have vWD if:
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c) | Explain why a dog breeder would want to use homozygous dominant dogs as parents.
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d) | A dog breeder buys a dog with no symptoms of vWD. The breeder mates this dog with a dog suffering from vWD in order to find out the dog's genotype. Explain:
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Question 7
Heredity is the process by which characteristics are given from a parent to their child through their genes. Some medical conditions are inherited. |
a) | What is the name of the chemical substance that makes up genetic material? A DNA B protein C carbohydrate D lipid
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b) | A gene often has two alleles, one dominant and one recessive. When is a recessive allele expressed by an organism? A when the dominant allele is not present B when the recessive allele is inherited from the male parent C when the recessive allele is inherited from the female parent D when the recessive allele is present on only one of the chromosomes
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c) | The sex of a baby is also determined by the chromosomes they inherit from their parents. Explain which parent determines the sex of the baby.
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d) | Modern medicine allows the treatment of a number of inherited conditions. In many cases, these conditions would be fatal without treatment. Explain what might happen to the frequency of alleles for these fatal inherited conditions, if medical treatment was not available.
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