3.4.4 MUTATIONS + MEIOSIS Flashcards
Gene mutations involve…
a change in the base sequence of chromosomes
Gene mutations can arise..
Spontaneously
Gene mutations occur during…
DNA replication and can involve deletion and substitution
Due to the ………. nature of the genetic code, not all base ………… cause a change in the sequence of amino acids:
- degenerate
- substitutions
What increase the rate of a gene mutation?
Mutagenic agents
How do mutations in chromosomes occur?
- spontaneously
- by chromosome non- disjunction
- during meiosis
Materials which may increase the risk of a mutation:
- ultraviolet/ ionising radiation
- chemicals
- viruses
What happens in substitution?
One base is replaced by another
What happens in deletion?
One base is removed from the sequence
What happens in insertion?
One base is added into the sequence
Will substitution result in a change to the amino acid sequence of a protein?
Not always- may still code for the same amino acid
Will deletion result in a change to the amino acid sequence?
Yes, they are more likely to change the amino acid sequence because they cause a frame shift- this changes all the triplets after the deletion and so also changes the amino acid sequence
Will insertion cause a change to the amino acid sequence?
More likely to because they cause a frame shift
What is a polyploidy chromosome mutation?
When organisms have more than two sets of chromosomes- mostly seen in plants
How many daughter cells does meiosis produce?
4
Are the daughter cells from meiosis genetically different of the same as one another?
Different
Are the daughter cells produced in meiosis haploid or diploid?
Haploid
How many divisions occur in meiosis?
2
What are genetically different daughter cells a result of in meiosis?
Independent segregation of homogolous chromosomes
Crossing over of homologous chromosomes results in…
Further genetic variation among daughter cells
What is independent segregation of homologous chromosomes?
During meiosis I, each chromosome lines up alongside its homologous partner randomly, since the pairs line up randomly, the combination of chromosomes of maternal and paternal origin that go into the daughter cell at meiosis I is also a matter of chance
Variety from new genetic combinations:
Each member of a homologous pair of chromosomes has exactly the same genes and therefore determines the same characteristics (tongue rolling), however the alleles of these genes may differ (they may code for rollers or non rollers), the independent assortment of these chromosomes may produce new, genetic combinations
What is a gene?
A length of DNA that codes for a polypeptide
What is an allele?
One of the different forms of a particular gene
What is a locus?
The position of a gene on a chromosome or DNA molecule
What are homologous chromosomes?
A pair of chromosomes, one maternal and one paternal, that have the same gene loci
Genetic recombination by crossing over:
- during meiosis 1, each chromosome lines up alongside its homologous partner randomly, the following then takes place:
- the chromatids of each pair become twisted around one another
- during this twisting process tensions are created and portions of the chromatids break off
- these broken portions might then rejoin with the chromatids of its homologous partner
- usually it is the equivalent portions of homologous chromosomes that are exchanged
- in this way new genetic combinations of maternal and paternal alleles are produced
The chromatids cross over one another many times..
Process known as crossing over
What is recombination?
The broken off pieces of chromatid after crossing over recombine with another chromatid
What kind of division is meiosis?
Reduction- diploid to haploid
What happens before meiosis starts?
DNA is replicated during interphase so that each chromosome contains two chromatids
2n =
Diploid
N=
Haploid
What happens in meiosis 1?
Homologous chromosomes are separated
What happens in meiosis 11?
Chromatids are separated
What happens in prophase 1?
- chromosomes condense and homologous chromosomes pair up
- centrioles migrate to opposite poles of the cell where they each start to form spindle fibres
- the nucleolus disappears and the nuclear envelope starts to break down, leaving chromosomes free in the cytoplasm
What happens in metaphase 1?
- chromosomes line up along the equator of the cells in their homologous pairs
- each chromosome attaches to the spindle by their centromere
What happens in anaphase 1?
- homologous chromosome pairs are separated and pulled to opposite poles of the cell by spindle fibres
- chromatids stay joined together
What happens in telophase 1?
- the chromosomes reach opposite poles of the cell where they uncoil
- a nuclear envelope firms around each set of chromosomes and the nucleolus starts to reform
- the cytoplasm divides to form two cells in cytokenesis
What happens in prophase 2?
Same as prophase 1 except chromosomes are now visible under a microscope
What happens in metaphase 2?
Same as metaphase 1
What happens in anaphase 2?
- centromeres divide and separate each pair of chromatids
- spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell
What happens in telophase 2?
- the chromatids reach opposite poles of the cell where they uncoil to become long + thin again
- a nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform
- cytoplasm divides in cytokenesis
- 4 daughter cells produced
Function: mitosis vs meiosis
Growth and repair VS production of gametes
Type of reproduction: mitosis VS meiosis
Asexual VS sexual
Diploid or haploid?: mitosis VS meiosis
Diploid VS haploid
Amount of daughter cells: mitosis VS meiosis
2 VS 4
Number of cell divisions: mitosis VS meiosis
1 VS 2
Creates genetic variation?: mitosis VS meiosis
No VS yes
Separates homologous chromosomes?: mitosis VS meiosis
No VS yes in anaphase 1
