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S142 – TMA01 Question 1 (a) (b) (c) (d)
S142 – TMA01 Question 2
S142 – TMA01 Question 3

S142 – TMA01
Question 1 (a)
Pedigree chart showing three generations of members of a family and whether they are affected by the Piebald trait.

KEY: Names which have been circled are those persons who are affected by the
Piebald trait.
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Question 1 (b)
Piebald trait appears to be a dominant trait related to an autosomal gene.
Looking at the people who are affected, only one parent in each case is also affected; for a dominant trait to manifest, only one copy of the affected gene is needed. A recessive trait would require two copies of the affected gene, one from each parent.
A female child gets her father’s X chromosome, and a male child gets his father’s Y chromosome, and they both get an X chromosome from the mother. If Piebald trait was X-linked, only Adam’s daughters would be affected. However, in this case,
Adam’s son Paul, who got his father’s Y chromosome, is also affected, so it is not Xlinked.
(118 words)
Question 1 (c)
(i) Steve’s probable genotype would be a heterozygous PT pt; PT meaning affected by Piebald trait, and pt meaning unaffected by Piebald trait. His mother Mia is affected so she carries the dominant PT allele. His father Tom, who is unaffected, carries the recessive pt allele. Because Steve is also affected, it means he received the PT from his mother and the pt from his father.
Tom - pt

Tom - pt

Mia - PT

PT pt

PT pt

Mia - pt

pt pt

pt pt

Mating diagram showing the possible genetic outcomes of Tom and Mia’s children. (ii) Because Steve has the probable heterozygous genotype PT pt, any gametes he produces can have either the PT allele or the pt allele, selected at random. The gametes have an equal chance of getting either variation. The chance of Steve transmitting Piebald trait is 1 in 2, to reflect these equal outcomes.
Question 1 (d)
(i) GTG TTT ACC CTC AAA GGG TCT TTG TCC GAC
(ii) GUG UUU ACC CUC AAA GGG UCU UUG UCC GAC
(iii) Valine Phenylalanine Threonine Leucine Glycine Serine Leucine Serine
Aspartate
(iv) The mutation in the TTT codon has changed it to TTG, meaning the template
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codon would read AAC instead of AAA. Instead of producing the correct amino acid Lysine, it would be instructed to produce Asparagine.
Question 2
DNA consists of a double-helix of strands of nucleotides, which consist of a sugar-phosphate ‘backbone’, and a base which connects via hydrogen bonding to a base on the opposite strand. There are four different bases: adenine (A), thymine (T), cytosine (C) and guanine (G). Bases are arranged together along the strands in a unique order and act as a code which specifies the genetic makeup of individuals. When proteins are required by the body, they are created using DNA. First, the double helix of strands unfold and the hydrogen bonds break, creating two separate strands. During a phase called transcription, one of the strands, the template strand, is used to create a ribonucleic acid (RNA) strand, where DNA bases T, G, C and A are paired with RNA bases A, C, G, and U (uracil) respectively.
An enzyme called RNA polymerase facilitates this process. Once the RNA, or messenger RNA (mRNA), strand is complete, the bases are divided into groups of three, called codons. Because there are four different RNA bases, and there are three bases per codon, there are sixty-four possible codon combinations (4 x 4 x 4
=64).
These codons are then translated into amino acids. There are twenty different amino acids, so each one has three or four different codons. Transfer RNA (tRNA) molecules are used to link amino acids to their corresponding codons. The tRNA consists of an anticodon at one end, which pairs with a codon on the mRNA strand, and at the other end, a unique binding site for a specific amino acid. A tRNA molecule, with its amino acid already attached, connects with a start codon at the beginning of the strand, beginning the protein-building process. As the next tRNA molecule joins the RNA strand, the amino acids join to each other, forming a chain. Once joined, the first tRNA molecule breaks away. More tRNA molecules join the chain, their amino acids attach, and they break away again. This process continues until they reach a stop codon at the end of the RNA strand. The new line of amino acids forms the protein.
(350 words)
Question 3
(a) Inherited mutations occur in the gamete-producing cells of the sperm or ova, and are passed from one generation to the next. An inherited mutation of the
BRCA1 or BRCA2 genes could increase the risk of breast cancer being passed from parent to child.
Somatic mutations can occur in almost any cell in the body (except gameteproducing cells), and can be influenced by environmental factors. An
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accumulation of several mutations in a particular cell over many years can lead to cancer. Exposure to cigarette smoke, for example, can lead to potentially cancerous cell mutations in the mouth, throat and lungs. (95 words)
(b) (i) Generalised medicine is used to treat the patient with regards to their diagnosis and the symptoms they are getting. In stratified cancer treatments, the genetic makeup of the cancerous cells is examined to determine which mutations occurred and which treatments are most likely to be effective to combat those mutations. (ii) The stratified treatment is much more patient-specific and may produce a more promising outcome for the patient, either by successfully treating the cancer, or by prolonging the life of the terminally ill patient. It is possible that stratified treatments may be cost-effective to the NHS if the right treatments are prescribed in the first instance, as opposed to trying various treatments before a successful one is found.
(c) (i) Although treatments could be more specific to the patient as an individual, there is a possibility that the focus on treatment could be more on their genetic makeup than on other factors that influence response to cancer treatments.
Patients may also have concerns about how the information in their genetic sequencing is used by professionals. Who will have access to the information?
How else might it be used without the patient’s awareness? Is it confidential enough? (ii) If family members are informed about particular genetic mutations that have contributed to their relative’s cancer, they may be concerned that they themselves could be susceptible to the same cancer. This could lead to anxiety amongst the family.
(iii) Healthcare providers would need to consider the costs of genome sequencing for all cancer patients, as well as the costs of hiring suitably trained staff for the purposes of counselling patients effectively, testing patients, and advising on the right cancer treatments.
(iv) As awful as it sounds, pharmaceutical companies do profit from the ineffective use of treatments on patients. Sometimes, more than one type of treatment is needed. With stratified medicine, there is more chance of getting the treatment right first time, meaning less money going to the pharmaceutical companies. Page 4 of 4