3.4.3 Production of genetic diversity Flashcards
How does mitosis and meiosis differ?
Mitosis: produce 2 daughter cells - one division
Meiosis: produce 4 daughter cells - two divisions
Mitosis: genetically identical cells
Meiosis: genetically different cells
Mitosis: chromosomes aren’t pair with homologous pair during metaphase 1
Meiosis: chromosomes pair with homologous pair during metaphase 1
Mitosis: no crossing over
Meiosis: crossing over
What happens in meiosis I?
- Prophase I
Chromatin condenses - coils into chromosomes ( become visible)
Nuclear envelope breaks down
Formation of spindle fibres - Metaphase I
Chromosomes line up with homologous pair at equator, spindle fibres attach to one side of centromere per chromosome - Anaphase I
Homologous pair are pulled apart towards opposite poles
(Sister chromatids are not seperated) - Telophase I
Chromosomes unwind into chromatin
Nuclear envelope reforms
5.Cytokinesis
Cell is divided into two daughter haploid cells
What happens in meiosis II?
Same as mitosis
Produces 4 daughter cells
What is the biological importance of reducing the chromosome number when the cell divides by meiosis?
During fertilisation, chromosome number could be restored
What are two ways meiosis creates genetic variation?
Independent segregation
Crossing over
How does independent segregation creates genetic variation?
The combination of chromosomes when lined up at equator (position of material and paternal chromosome) is completely random
Therefore during metaphase I, when homologous pair are pulled apart, there are many combination of how many maternal/paternal chromosomes will move to each pole
How does crossing over create genetic variation?
Chromosomes in homologous pair twist around each other and pieces of chromatids may break off. When rejoining, they may attach to the wrong chromosome
This generates an infinite number of possible combinations
What is a mutation?
A rare, random and heritable change in the base sequence of DNA
What does it mean when a mutation is heritable?
Mutated DNA is passed onto daughter cells when DNA is replicated during interphase
Mutation in gametes are also heritable to offspring as all cells in fetus will therefore have the mutation
What are the two types of mutation?
Substitution
Deletion
What is substitution mutation?
Where a base is replaced by an incorrect base
This will lead to a change in the primary structure (different triplet code), which leads to a change in secondary structure (hydrogen/ionic/disulfide bonds are changed), which will lead to a change in tertiary structure
For an enzyme, the change in tertiary structure will lead to a change in active site, making it no longer complementary to its substrate
When does a mutation not have an effect on the primary structure of proteins?
When substitution mutation occurs in:
Non-coding DNA - not in gene
Introns (removed during splicing)
Degenerate code - causing silent mutation as amino acid coded for remains the same
What is deletion mutation?
Where a base is removed from DNA sequence
This causes frameshift - changes all codon after deleted base to shift up one
Changes reading frame - where in sequence to start reading triplets
How could gene length be changed?
What is premature stop codon caused by:
A substitution of a base producing a stop codon
What causes an overly long DNA?
A removal of a base in stop codon - causing frameshift, stop codon no longer coded
A substitution of a base in stop codon - stop codon no longer coded
What is chromosome mutation?
A change in the structure or number of whole chromosomes
What are examples of chromosome mutation?
Number: polyploidy
Structure:non-disjunction, translocation
What is non-disjunction and its consequence?
When spindle fibres fail to separate homologous pair properly during anaphase I as spindle fibres have attached to an extra/ one less chromosome in metaphase I
2 haploid daughter cells are not produced - don’t have the same number of chromosomes - will be inherited by daughter cells
What is translocation and its consequence?
The uneven number of crossing over between homologous pairs
The crossing over between non-homologous pairs
