Mutations

Question 1

Examples of gene and chromosomal mutations

Answer 1

Gene: Sickle cell anaemia, PKU.

Chromosomal: Trisomy-21, Klinefelters.

Question 2

Harmful mutations

Answer 2

• Any mutation which decreases the quality of life.
• E.g. Tay-Sachs disease, PKU.

Question 3

Neutral mutations

Answer 3

• Mutations which occur in the non-coding sections of DNA.
• Therefore, don’t affect protein synthesis and often remain unknown.

Question 4

Beneficial mutations

Answer 4

• Any mutation which increases the quality of life.
• E.g. The apoA-1 Milano mutation allows Italian people to withstand high cholesterol levels.

Question 5

Causes of mutations

Answer 5

• Caused by mutagens (mutation inducing substances).
• Chemicals and high energy radiation.
• Environmental factors e.g. sunlight.
• Microorganisms and viruses.

Question 6

Causes of variation

Answer 6

1. Crossing Over - when chromatids share genetic info and recombine.
2. Law of Segregation - the determination of where each allele goes after being separated in anaphase.
3. Independent Assortment - random separation of chromatids in metaphase.
4. Non-Disjunction - the failure of a normal pair of chromosomes to separate during M1.
5. Random Fertilisation - sperm randomly fuse with eggs.
6. Mutations.

Question 7

Point mutations

Answer 7

• Changes in a single nucleotide.
• Nucleotide can either be inserted, substituted, or deleted.
• E.g. Sickle cell anaemia, albinism.

Question 8

Frameshift mutation

Answer 8

Occurs when bases have been added or removed to a sequence of DNA which pushes the three-amino acid coding sequence to start at another base. This throws the DNA sequence off and fails to code for the missed protein.

• Insertion or deletion.

Question 9

Chromosomal mutations

Answer 9

• Duplication - a section of a chromosome occurs twice.
• Inversion - a section of a chromosome is inverted.
• Translocation - a section of a chromosome breaks off and rejoins itself to another chromosome.
• Insertion/deletion/substitution

Question 10

Lethal recessive

Answer 10

• An allele that causes death to an organism either pre-natally or later in the organism’s life.

Question 11

Phenylketonuria (PKU)

Answer 11

• The ‘fish one’.
• Autosomal recessive.
• Germ-line mutation.
• Gene mutation.
• Affects the gene that helps create the enzyme needed to breakdown phenylalanine hydroxylase.
• These people can’t break down Phe well, so toxic levels of it build up in their bodies.
• Those affected must refrain from eating proteins and must maintain a vegetable-based diet.
• Amino acids build up in the blood and body tissue, which results in mental retardation and disruptions to brain development.

Question 12

Duchenne muscular dystrophy

Answer 12

• Sex-linked recessive.
• LR
• Only occurs in boys.
• Results in muscle weakness and wastage which causes a short life span of 20-25 years.

Question 13

Cystic fibrosis

Answer 13

• Gene mutation (on chrom. 7).
• LR
• If one protein is incorrect, then the passage of chloride ions across the membrane is affected.
• Results in lung congestion and infection, malabsorption of nutrients by the pancreas, coughing, salty skin, wheezing, pneumonia.

Question 14

Tay-Sachs disease

Answer 14

• Autosomal recessive.
• LR
• Caused by the enzyme for lipid metabolism being missed due to a chromosomal mutation in the HEXA gene.
• The nervous system then accumulates fat which then causes physical and mental difficulties.
• Death usally occurs in early childhood.

Question 15

Sickle cell anaemia

Answer 15

• Gene mutation.
• LR
• Autosomal recessive.
• Gene responsible for haemoglobin production is affected.
• Anaemia causes death (as cells become sickled) whereas the trait provides resistance against malaria.
• Results in the reduced ability for oxygen to be carried in the blood.

Question 16

Trisomy-21 (Down’s Syndrome)

Trisomy-13 (Patau Syndrome)

Answer 16

• Non-disjunction occurs on chromosome 21.
• Chrom. 21 then has 3 chromosomes.
• Causes mental retardation, a distinct facial appearance, and developmental struggles.
• Non-disjunction occurs on chromosome 13.
• Produces individuals with intellectual disabilities, microcephaly, an extra two fingers, a cleft palate and lip, and ear and eye malformations.
• Death usually occurs within months of birth.

Question 17

Klinefelter’s Syndrome

Answer 17

• Non-disjunction of X and Y chromosomes.
• Develops in adulthood.
• Boy’s testes fail to grow, sperm is not produced well, breasts become enlarged, body hair becomes sparse and occasionally mental retardation.
• The person is XXY or XYY (Jacob’s Syndrome).

Question 18

Monosomy-X (Turner Syndrome)

Answer 18

• One X-chromosome in females instead of two.
• Females are short, lack secondary sexual characteristics, have webbed necks, infertile, but can still lead a normal life

Question 19

Define mutation

Answer 19

A spontaneous and permanent change to an organism’s base sequence of their DNA.