Genetic Information And Reltionships - Meiosis And Mutation Flashcards
Chromosome definition
An independent DNA molecule
Gene definition
A base sequence of DNA that codes for a polypeptide or functional RNA
Allele definition
Different forms of the same gene
Locus definition
The fixed position of a gene on a particular chromosome
Homologous chromosomes definition
A pair of chromosomes which have the same genes at thee same gene loci but may have different alleles
Haploid cell definition
A cell containing one of each type of chromosome (n) e.g. a gamete
Diploid cell definition
A cell containing two of each type of chromosome as pairs (2n) e.g normal body cell
(N) meaning
The number of types of chromosomes in a cell
(2n) meaning
The total number of chromosomes in a diploid cell
What is a mutation
A change in the sequence of DNA bases
How does a mutation arise
Mutations can arise spontaneously during DNA replication and and include base deletion and base substitution
What is a substitution mutation
One base is swapped with another different base
What is a deletion mutation
One base is removed from the sequence
What are the possible effects of a substitution mutation on a protein
Sometimes none because of the degenerate nature of the genetic code
What is the effect of a deletion mutation on a protein
There is always an effect because the election of a base will cause a frame shift in all the base triplets after it
Name some possible mutagenic agents
Ionising radiation, UV radiation, some viruses, some chemicals
What is the role of mutagenic agents
Mutgenic agents increase the rate of chance of mutations
What happens during crossing over
- Homologous chromosomes come together as a pair formimg a bivalent
- Non-sister chromatids cross over
- The point of the cross is called chiasmata
- Getenic information is swapped
How does crossing over increase genetic variation
The resulting chromatids after crossing over contain the same genes but have a different combination of alleles
What is crossing over
The swapping of genetic information between homologous pairs of chromosomes
What is independent segregation
The random positioning of homologous pairs
What happens during independent segregation
- Homologous pairs line up on the equator randomly
- Once they separate in the 1st meiosis division it is completely random which chromosome from each pair ends up in which daughter cell
- The same happens in the second meiosis division
How does independent segregation increase genetic variation
at the end of meiosis there are different combinations of parental chromosomes in the 4 daughter cells
Compare and contrast mitosis and meiosis in terms of number of divisions
Mitosis has one division whereas meiosis has a total of 2 divisions
Compare and contrast mitosis and meiosis in terms of number of daughter cells produced
In mitosis 2 daughter cells are produced whereas in meiosis 4 daughter cells are produced
Compare and contrast mitosis and meiosis in terms of whether daughter cells are haploid or diploid
Mitosis results in diploid daughter cells whereas meiosis results in haploid daughter cells
Compare and contrast mitosis and meiosis in terms of whether daughter cells are genetically identical or different
In mitosis genetically identical daughter cells are produced whereas in meiosis genetically different daughter cells are produced
Compare and contrast mitosis and meiosis in terms of whether chromosomes cross over
In mitosis crossing over does not occur whereas in meiosis crossing over of chromosomes does occur
What is chromosome non-disjunction
- A type of chromosome mutation
- Homologous pairs do not separate in meiosis
- Gamete has 2 copies of a chromosome instead of 4
- Fertilisation leads to cells having 3 copies of a particular chromosome
What are the possible consequences of a non-disjunction event in organisms
Can lead to inherited conditions because there are the wrong number of chromosomes in the resulting gametes such as Down’s syndrome
How do you calculate number of possible chromosome combinations following meiosis
2^n
How do you calculate number of posssible chromosome combinations following random fertilisation
(2^n)^2
