Chapter 12: Mutations And Gene Pools

Question 1

• What are species?
• What are alleles?
• Define population
• What do scientists mean when they speak of a ‘gene pool’?
• Define allele frequencies
• Define ‘mutation’
• Define mutant
• What are the two main types of mutations?
• What are mutagens (or mutagenic agents)
• Explain the difference between somatic and germline mutations?

Answer 1

• Group of individuals sharing many characteristics and are able to interbreed to produce fertile offspring.
• An alternative form of a gene; an individual normally has 2 alleles of each gene (one from each parent).
• Group of organisms of the same species living together in a particular place at a particular time.
• Sum of all the alleles in a given population.
• How often each allele of a gene occurs in a population.
• A random change in DNA resulting in a new variation with characteristics that differ from either parent.
• An organism with a characteristic resulting from a mutation.
  1. Gene mutations: changes in a single gene so that the traits normally produced by that gene are changed or destroyed.
  2. Chromosomal mutations: all or part of a chromosome is affected.
• Agents that increase the rate at which mutations occur.
• Somatic mutations occur in the DNA of body cells that cannot be passed on to offspring; whereas germline mutations occur in the gametes and are passed on through reproduction.

Question 2

• When there is no history of Duchenne muscular dystrophy in a family, how are they thought to arise?
• Why do most gene mutations produce a recessive allele?
• Describe the 5 types of chromosomal mutations

Answer 2

• The disease is X-linked recessive therefore it must be from a mutation in the mother that is passed onto her children. It wouldn’t be from a mutation in the father as if he had a mutated X chromosome, he would of showed the disorder but no one in the family has it.
• Prevents mutated genes from producing unwanted proteins that will be able to function in the body.
• (Deletion: part of chromosome lost) (Duplication: Section of chromosome occurs twice when part of a chromatid breaks off and joins on the wrong chromatid) (Inversion: Breaks occur in a chromosome and broken piece joins back but wrong way around) (Translocation: Part of chromosome breaks off and re-joins to wrong chromosome) (Non-disjunction: During meiosis a chromosome pair doesn’t separate so 1 daughter cell has an extra chromosome and the other has 1 less)

Question 3

• Describe Down syndrome (trisomy 21)
• Describe Patau syndrome (trisomy 13)
• Define partial monosomy
• List 5 examples of mutagenic agents
• Why does special care need to be taken when pregnant women require X-Ray’s?
• What is a lethal recessive?
• Give an example of trisomy, monosomy and partialsomy conditions.
• Describe Duchenne muscular dystrophy.
• Describe X-linked recessive diseases

Answer 3

• A condition from non-disjunction where the patient has 3 of chromosomes 21 instead of 2
• Non-disjunction condition where patient has 3 chromosome 13. Results in mental retardation, small head and extra fingers.
• Where part of a pair of chromosomes is missing.
• Mustard gas, antibiotics, UV light, X-rays and radiation.
• Radiation from X-Rays can cause mutations in the developing foetus.
• Recessively inherited alleles that can cause death in offspring. They must inherit 2 of the lethal recessive alleles, 1 from mother and father.
• Down syndrome, Turner’s syndrome and Cri-du-chat syndrome.
• A X-linked recessive disease that results in wasting of leg muscles and then arms, shoulders and chest.
• Diseases where the recessive allele is carried on the X chromosome. Males can have the disorder with 1 recessive allele, as they only have 1 x-chromosome. Whereas females need 2 recessive alleles.

Question 4

• Explain how Klinefelter’s syndrome and Turner’s syndrome come about.
• Explain how mutations could change the proportion of certain alleles in a gene pool.
• The more often cells divide, the greater risks of errors and mutations. For this reason, scientists have hypothesised that when a baby is born with a congenital disorder caused by an error in cell division, the father is the parent more likely to have contributed the gene with the mutation. Explain the reasons scientists have formulated this hypothesis.
• Define point mutation
• Describe albinism
• Describe Tay-Sachs disease (TSD)

Answer 4

• Both arise from non-disjunction during meiosis of gametes. The resulting individual will have either trisomy or monosomy. Klinefelter’s syndrome is trisomy XXY; Turner’s syndrome is monosomy X.
• If mutation results in a lethal recessive allele, then patients die before passing on their genes therefore removing those alleles from gene pool over time. If mutation results in mutated allele with survival advantage patients will survive and pass on mutation and over time increasing the proportion of the mutant alleles in gene pool
• Male reproductive cells undergo more meiotic divisions.
• A change in 1 of the bases in a DNA molecule .
• A condition caused by point mutation that results in absence of pigment in hair, skin and eyes.
• A recessive disorder of lipid metabolism where a missing enzyme causes accumulation of fatty substances in the N.S. Results in mental retardation and physical abilities after birth resulting in death.