genetic diversity can arise as a result of mutation/meiosis Flashcards
Define a mutation
Change to the base sequence of DNA caused by errors during DNA replication
Explain why a mutation might not lead to a change in the amino acid sequence?
- Genetic code is degenerate so mutation may end up coding for the same amino acid as the original triplet
- Mutation may occur in an intron
Describe what a substitution mutation is
When a nucleotide in the DNA sequence is replaced by another
Describe what a deletion mutation is
When a nucleotide in the DNA sequence is lost, leads to a frameshift which means the entire amino acid sequence is different
What is a mutagenic agent?
They are things/factors that can cause an increase in the rate of gene mutations
Give examples of mutagenic agents
- X-rays
- UV light
- Chemicals in alcohol/tobacco
What is a chromosome non-disjunction
When chromosomes fail to separate correctly in meiosis, resulting in gametes with 1 more or fewer chromosomes than normal
Define meiosis
A form of cell division that produces 4 genetically different haploid cells known as gametes
What is a duplication mutation?
One or more bases are repeated
What is an insertion mutation?
One extra base is added
What is an inversion mutation?
A sequence of bases is reversed
What is a point mutation?
A change in a single nucleotide
When are mutations likely to occur?
DNA replication
Describe the differences between mitosis and meiosis
- Mitosis produces cells with the same number of chromosomes as the parent cell, meiosis produces cells with half the number of chromosomes as the parent cell
- In mitosis the daughter cells are genetically identical to the parent cell and to each other, in meiosis, the daughter cells are genetically different from one another and the parent cell
- Mitosis produces 2 daughter cells, meiosis produces 4 daughter cells
Define gametes
Gametes are sex cells
What is a zygotes
When a sperm cell and an egg cell fuse together in fertilisation
Define diploid
Each cell contains two of each chromosome from both parents (46 chromosomes)
Define haploid
Each cell contain one copy of each chromosome (23 chromosomes)
Describe what happens at fertilization
- Haploid sperm fuses with a haploid egg
- Making a cell with a diploid number of chromosome
- Half of the chromosomes are from the mum and dad
Describe random fertilization
Produces zygotes with different combinations of chromosomes to both parents
How is the mixing of genetic material advantageous to a species?
The mixing of genetic material in sexual reproduction increases genetic diversity within a species
Describe the cells before meiosis takes place
They are diploid cells (46 chromosomes)
Describe the cells after meiosis takes place
They are haploid cells (1/2 number of chromosomes)
Describe the steps of meiosis
- DNA unravels and replicates so there are 2 copies of each chromosome (chromatids)
- DNA condenses to form two sister chromatids joined together by a centromere
- Meiosis I - the chromosomes arrange themselves into homologous pairs
- Homologous pairs are separated, halving the chromosome number
- Meiosis II - the centromere of each sister chromatid is divided
- 4 haploid cells (gametes) that are genetically different from each other are produced
In which ways does meiosis produce genetic variation?
- Crossing over of chromatids during meiosis I
- Independent segregation of chromosomes
Explain how the independent segregation of chromosomes leads to genetic variation
- Homologous pairs of chromosomes are made up of 1 chromosome from each parent
- When they are separated in meiosis I, it is completely random which chromosome from each pair ends up in which daughter cell
- So the 4 daughter cells produced by meiosis have different combinations of maternal and paternal chromosomes
