Topic 4 - Mutation Flashcards
What is gene mutation?
A change in the DNA base sequence
What are the three types of gene mutation?
1) Substitution.
2) Deletion.
3) Insertion.
What is a substitution mutation?
One base is replaced by another
What is a deletion mutation?
One base is removed from the sequence.
What is an insertion mutation?
One base is added into the sequence.
What is meiosis?
A type of cell division in which aparent cell divides to form four haploid cells, each genetically distinct from one another.
What are chromosome mutations?
Involve changes in the structure or number of whole chromsomes, Mutations to chromosome number can arise spontaneously through errors in cell division.
What are the two main types of mutations to the number of chromosomes?
1) Polyploidy
2) Non-disjunction
What is a polyploidy mutation?
This is when organisms have more than two sets of chromosomes, and is mostly seen in plants.
What is a non-disjunction mutation?
This occurs when homologous chromosomes fail to separate in meiosis, resulting in gametes with extra or missing chromosomes and leads to individuals with extra or missing chromosomes in all cells.
What are the two cell divisions that take place in meiosis?
1) Meiosis I.
2) Meiosis II.
What happens in prophase I?
1) The chromosomes condense and homologous chromosomes pair up.
2) Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres.
3) The nucleolus disappears and the nuclear envelope starts to break down, leaving the chromosomes free in the cytoplasm.
What happens in metaphase I?
1) Chromosomes line up along the equator of the cell in their homologous pairs.
2) Each chromosome attaches to the spindle by their centromere.
What happens in anaphase I?
Homologous chromosome pairs are sepearted and pulled to opposite poles of the cell.
What happens in telophase I?
1) The chromosomes reach the opposite poles of the cell where they uncoil.
2) A nuclear envelope forms around each set of chromosomes and the nucleolus starts to reform.
3) The cytoplasm divides to form two cells (cytokinesis)
What happens in prophase II?
1) The chromosomes condense and are now visible under a microscope.
2) Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres.
3) The nucleolus disappears and the nuclear envelope starts to break down.
What happens in metaphase II?
1) The chromosomes line up at the equator of the cell.
2) Each chromosome attaches to the spindle by their centromere.
What happens in anaphase II?
1) The centromeres divide and separate each pair of chromatids.
2) The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell.
What happens in telophase II?
1) The chromatids reach the opposite poles of the cell where they uncoil to become long and thin again.
2) A nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform.
3) The cytoplasm divides (cytokinesis) and four cells are produced.
What is the function of meiosis?
Production of gametes
What type of reproduction is meiosis?
Sexual
What type of cells does meiosis produce?
Haploid
How many daughter cells are produced in meiosis?
4
How many cell divisions are there in mitosis?
2
Is there genetic variation in meiosis?
Yes
In what stage of meiosis do homologous chromosomes separate?
Yes, in anaphase I
What are the two important roles of meiosis?
1) Production of haploid gametes - allows sexual reproduction.
2) Creates genetic variation - increases, diversity, allowing natural selection to take place.
What are the two events within meiosis that lead to genetic variation?
1) Crossing over (or recombination).
2) Independent Segregation (or random assortment).
When does crossing over occur?
Crossing over occurs during prophase I of meiosis
Describe the process of crossing over.
1) During prophase I, the homologous chromosomes condense and pair up.
2) The chromatids of each chromosome then twist around one another, forming a chiasmata.
3) When the chromosomes are separated during anaphase I, the chromatids break at the chiasmata and then reconnect to the chromatid from the homologous chromosome.
What is independent segregation?
When the paternal and maternal chromosomes line up along the cell’s equator in metaphase I, whether they appear on the left or righ tin completely random. Which chromosomes end up in each daughter cell is random.
