3.4.3 Genetic Diversity by Mutation or Meiosis Flashcards
What are the two types of cell division?
Mitosis: produces two diploid cells
Meiosis: produces four haploid cells
How many chromosomes do gametes have?
Haploid (half the number of a normal body cell)
What are the two divisions during Meiosis? (No explanation)
Meiosis 1
Meiosis 2
What is a gene?
A length of DNA that codes for a polypeptide
What is a locus?
The position of a gene on a chromosome or DNA molecule
What is an allele?
One of the different forms of a particular gene
What are homologous chromosomes?
A pair of chromosomes, one maternal, one paternal with the same gene loci
What is fertilisation?
The fusion of a male and female gamete
What is the process of prophase 1?
Chromosomes condense and become visible
Nuclear envelope breaks down
Contains 4n genetic material
What is the process of metaphase 1?
Homologous pairs of chromosomes line up next to each other
Spindle fibres connect to the centrioles
Contains 4n genetic material
What is the process of anaphase 1?
Homologous pairs are pulled apart to opposite poles of the cell
Contains 4n genetic material
What is the process of telophase 1?
Nuclei reform
Cytokinesis
Forms two cells with 2n genetic material each
What is the process of prophase 2?
Nuclei break down
Contains 2n genetic material
What is the process of metaphase 2?
Chromosomes lime up on the equator of the cell
Spindle fibres attach to the centromeres
Contains 2n genetic material
What is the process of anaphase 2?
Chromatids are separated by the contraction of the spindle fibres
They’re pulled apart to opposite poles
Contains 2n genetic material
What is the process of telophase 2?
Nuclei reform
Cell divides
Produces n genetic material per cell
What are the two forms of variation during meiosis? (No explanation)
Independent segregation
Crossing over
What is the process of independent segregation?
The homologous chromosomes randomly line up in meiosis 1 along the equator so the chromosomes at the poles are randomly selected
What is the process of crossing over?
During meiosis 1, the chromatids become twisted round each other
The twisting creates tension where portions are broken off
These portions rejoin with the partner chromatids
Usually equivalent portions of homologous chromosomes are exchanged
This creates new genetic combinations
What is the aim of meiosis?
To create gametes (haploid cells) with half the number of normal chromosomes
To create sperm and ovum
To introduce variation
What is a substitution reaction?
A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
This changes the amino acid and disrupts the primary structure
This could mess up the whole chain because the R groups affect the secondary and tertiary structure
A mutation could give you exactly the same amino acid and have little or no effect
It can change an enzyme’s active site so that it doesn’t work
What is a deletion mutation?
DNA bases shift to the left which completely changes the sequence, stops the polypeptide from functioning
What is meant by random fertilisation?
Any egg can be fertilised by any sperm which increases variation
What is crossing over?
When portions of DNA are swapped between non-sister chromatids
What is the role of the centromere during mitosis?
Centromere attaches to the spindle fibres
It allows separation in anaphase as centromere splits
