Topic 8 Origins Of Genetic Variation Flashcards
what are three genetic reasons for genetic variation?
- mutations
- random independent assortment
- random fertilisation
- crossing over in meiosis
what are two types of mutations?
- point mutation (change in bases)
- chromosome mutation
what are 3 types of point mutations?
- deletion
- insertion
- substitution
why do point mutations happen?
- random
- mutagens increase rate of mutations (eg chemicals, radiation)
who is affected by somatic cell mutations?
only the individual
who is affected by gamete mutations?
generations to come, passed onto offspring
when does independent assortment happen during meiosis?
metaphase I and II
when does crossing over happen during meiosis?
prophase I
what are two types of chromosome mutations?
- translocation
- non disjunction
what is translocation mutation?
when a chromosome breaks off and joins a non-homologous chromosome
what is non-disjunction mutation?
when a homologous pair fail to separate correctly, some gametes have abnormal number of chromosomes
what are two types of non-disjunction?
monosomy and polysomy
what is an example syndrome of monosomy?
Turner’s syndrome
what is an example syndrome of polysomy?
Down’s syndrome
what is the chi squared equation?
(O-E)^2
———– (divide by)
2
What is the definition of polygenic? 2 marks
- A characteristic influenced by 2 or more genes (1)
- in different loci (1)
- common to see variation in traits (eg hair colour)
Justify why xxx is a recessive condition - 3 marks
- 2 recessive alleles are needed to have X condition
- individuals A and B do not have X but some of their children do
- therefore A and B must be heterozygous
What is the definition of a gene pool
total number of genes of every individual in a population
what are allele frequencies?
proportion of each allele within a gene pool
what are 2 types of selection?
- stabilising
- disruptive
(- directional)
what is transient polymorphism?
selective advantages changes overtime (disruptive selection)
3 factors that can influence allele frequencies in a population:
- founder effect
- genetic bottlenecks
- genetic drift
what is a genetic drift?
changes in gene pool bcs of random selection of alleles
what is the founder effect?
when small groups of individuals leave a larger pop and develop new isolated pop
- alleles in offspring are determined by the founders
what are population bottlenecks?
when entire species are wiped out except for a small group of survivors
so numbers and diversity fall dramatically
what is the hardy weinberg equation and what do they stand for?
p^2 + 2pq + q^2 = 1
p^2 = homozygous dominant
q^2 = homozygous recessive
2pq = heterozygous
p + q = 1
p= dominant ALLELE
q= recessive ALLELE
in chi squared hypothesis testing, when do we accept or reject H0?
when calculated chi2 value > value on table (n-1, 0.05), reject H0.
How does inbreeding cause genetic defects? (2 marks)
Reduced gene pool
Increasing chance of homologous recessive genotypes for genetic defects
What is a gene locus? 2 marks
Where the allele is located on a chromosome
What are conditions for the Hardy-Weinberg equation?
- no mutations
- random mating
- large population
- no selection pressures
Do alleles mutate due to selection pressure?
NO!!!
They mutate randomly
Not ‘due to’ selection pressure
Explain HOW breeding programs in zoos can maximise genetic variation in populations before reintroduction to their natural habitat. (2 marks)
- stud book to log mating between individuals
- so prevents closely related individuals mating
- exchange alleles between zoos
Explain why a person who is heterozygous does not show the symptom of XYZ. (2 marks)
- heterozygotes have one dominant copy of the allele, so it’s expressed
- so protein can still be made
