Mutation and Meiosis Flashcards
When do mutations usually occur?
Replication
Cell division
What are mutations?
Any change to the DNA of an organism; either the quantity of DNA or the base sequence
What are the two type of mutation?
Gene
Chromosome
What are gene mutations?
A change in the base sequence of the DNA of an organism
Happens during DNA replication
What are chromosome mutations?
A change in the number or structure of whole chromosomes
Happens during cell division
Are mutations in somatic cells passed on? Why?
No
Inherited cells are only from gametes in meiosis
If you have a change in the base sequence of DNA what also changes?
Base sequence of mRNA Amino acid sequence Hydrogen bonds Tertiary structure of protein Protein function
What are the 3 main type of gene mutations?
Substitution
Addition
Deletion
What is a substitution mutation?
One base in the DNA is switched for a different base
What are addition and deletion mutations?
Addition - one base is inserted into the DNA
Deletion - one base is removed from the DNA
What are the consequences of a substitution mutation?
Non-sense mutation: results in a stop codon
Mis-sense mutation: causes a different amino acid to be coded for
Silent mutation: the substituted base code for the same amino acid = no effect
What are the consequences of addition and deletion mutations?
Frame shift
Causes all subsequent codons to be altered
Can be devastating if at the start of a gene
What causes mutations?
Ionising radiation Carcinogens Genetic/Inherited Age Random Microorganisms
What happens in meiosis?
DNA is replicated from the parent cell
The homologous pairs are separated
Then the chromatids are separated to form 4 genetically varied daughter cells each containing half the number of chromosomes of the parent cell
Why is it important the chromosome number is halved in meiosis?
DNA is halved so the diploid number is restored and we don’t double chromosomes every generation
How does meiosis lead to variation?
Crossing over
Independent segregation of homologous chromosomes
Independent segregation of homologous chromatids
How does sexual reproduction lead to variation?
Crossing over
Independent segregation of homologous chromosomes
Independent segregation of homologous chromatids
Random fusion of gametes
What is crossing over?
In prophase 1 and metaphase 1 the homologous chromosomes can tangle and some genes may swap between them
What is independent segregation of chromosomes?
How the chromosomes line up in metaphase 1 as orientation is random
What is independent segregation of chromatids?
How the chromatids are oriented which determines which pole they are moved to before separation into cells
How many divisions are there in meiosis? Resulting in?
2 divisions
4 genetically variable daughter cells that are haploid
Describe phase 1 of meiosis?
Genetic material is replicated, cell grows and organelles synthesised
Homologous chromosomes pair up
The homologous chromosomes line up along the equator (spindle fibres help)
The spindle fibres contract to separate the chromosomes to each pole which halves the chromosome number
Describe phase 2 of meiosis?
The chromosomes line up along the equator not in pairs
The chromatids separate when the spindle fibres contract
The membrane reforms and 4 haploid daughter cells are produced
How can you tell the difference between prophase 1 and 2?
In prophase 1 the chromosomes will be in pairs crossed over
How can you tell the difference between metaphase 1 and 2?
Metaphase 1 will have homologous chromosomes lined up side by side on the equator
Metaphase 2 will have chromosomes lined up alone
On a life cycle diagram where will fertilisation take place?
Just before the genetic material is doubled
On a life cycle diagram where will meiosis take place?
Just before the genetic information has split
What does asexual reproduction lead to?
Clones
Genetically identical
How can chromosomal mutations occur?
The failure of chromatids to separate in anaphase 2 of meiosis therefore you could end up with 1 too many or too few chromosomes
What is a chromosomal abnormality/disease?
Down’s syndrome
Extra 21st chromosome
What affects the risk of down’s syndrome? Why?
The age of the mother
The eggs are older therefore something going wrong in meiosis phase 2 is more likely
