4.3 Mutations And Meiosis Flashcards
What are mutations?
Mutations are changes to the base sequence in the DNA.
Three types of mutation
- Addition - base(s) is added
- Deletion - base(s) is taken away
- Substitution - base(s) are switched out
Causes of mutation
- Error when replicating
- Mutagenic agents e.g. chemicals, radiation
Describe the process of meiosis
The chromosomes in the cells replicate to produce an identical copy of each other.
The chromatids condense to form a double-armed chromosome. Each arm is made from one chromatid and is joined by a centromere.
Homologous pairs arrange themselves at the centre of the cell
The homologous chromosomes are separated and pulled to opposite ends of the cell by the spindle fibres.
This process is random (random segregation)
As the homologous chromosomes are separated, the cell divides into two cells.
One chromosome from a pair is separated into each cell.
This division is called meiosis I.
Meiosis I produces two genetically different cells.
The sister chromatids are separated by the spindle fibres and pulled to opposite ends of the cell.
The separation of the sister chromatids is random.
As the sister chromatids are separated, the cell divides into two cells.
One chromatid from a chromosome is separated into each cell.
This division is called meiosis II.
Meiosis II produces four genetically different haploid cells.
Which processes during meiosis cause genetic variation in gametes
- Random segregation - homologous chromosomes are randomly separated
- Crossing over - Sections of DNA are swapped between homologous chromosomes during meiosis I causing a new combination of alleles to form
- Random fertilisation of gametes - mix of chromosomes from two unrelated organisms
Meiosis vs mitosis
Meiosis:
- Produces four cells
- Genetically different
- Produces haploid cells
- Produces gametes
Mitosis:
- Produces two cells
- Genetically identical
- Produces diploid cells
- Produces body cells
