chapter 9 - genetic diversity Flashcards
1
Q
What is a gene mutation ?
A
- a change in the DNA base sequence
2
Q
How do mutations occur and what are thing that increase the rate of mutations ?
A
- they occur spontaneously if dna is misread during dna replication
- things that increase the rate of mutations are mutagens
- like ultraviolet/ionsing radiation, chemicals and viruses
3
Q
What are the three types of mutation ?
A
- substitution
- deletion
- insertion
4
Q
How do mutations affect the protein synthesis ?
A
- they can leas to a different amino acid sequence
- as the gene has changed
- this means we will get a different polypeptide
- and probably a different tertiary structure
5
Q
What are substitution mutations ?
A
- when one base is replaced by another
- which can cause the amino acid sequence to change
- but not all substitutions change the amino acid sequence
- because there is more than one triplet code that codes for the same amino acid
- this is the degenerate nature of dna
6
Q
What are deletion mutations ?
A
- when one base is removed from the sequence
- if a base is deleted, the base sequence shifts
- so all the triplets after the deletion change so the amino acid sequence also changes
- this is a frame shift
7
Q
What is an insertion mutation ?
A
- when one base is added to the sequence
- this also causes a frame shift
- and all the triplets codes after the insertion change so the amino acid sequence will also change
8
Q
What are missense, nonsense and frame shift mutations ?
A
- missence is when an amino acid is replace by another one because of a change to the triplet code
- nonsense is when there is a premature stop codon weaning not all the amino acids join the chain
- frame shift is when a base is added or removed so codons shift to either side so all the codons are read different so the amino acid is different
9
Q
What is chromosome mutation ?
A
- when there is a change to the structure or whole number of chromosomes
- these can happen spontaneously through cell division
10
Q
What are the two types of chromosome mutation ?
A
- polyploidy = when organisms have more than two sets of chromosomes, mostly seen in plants
- non-disjunction = when homologous chromosomes don’t separate during meiosis meaning there are gametes with extra or missing chromosomes , which leads to individuals with missing or extra chromosomes in all cells
11
Q
What is meiosis ?
A
- a type of cell division where a parent cell divides into 4 haploid cells where they are all genetically different from each other
- it involves 2 nuclear divisions
12
Q
What area the 2 stages of meiosis ?
A
- meiosis 1 - homologous chromosomes are separated
- meiosis 2 - chromatids are separated
-before this interphases happens so that each chromosome has 2 chromatids ( so each homologous chromosome has 2 chromatids )
13
Q
What are the 2 stages of meiosis that introduce variation ?
A
- independent segregation of homologous chromosomes
- crossing over between homologous chromosomes
- the both happen in meiosis 1
14
Q
Wha is crossing over ?
A
- during prophase 1, when the homologous pairs line up on either side of the equator , the form a bivalent
- and the chromatids ( from each chromosomes ) can become twisted around each other
- the crossing over is called a chiasma
- tension can then cause these chromatids to break off and attach to the other chromatid ( from the other homologous chromosome ) .
- this results in new combinations of alleles on each of the homologous chromosomes
15
Q
What is independent segregation ?
A
- when the homologous chromosmes line up on either side of the equator
- aka 23 pairs have lined up
- it’s random which side the paternal or maternal chromosome might line up on
- e.g all paternal chromosomes might be on one side
- there are 2^23 ways that the chromosomes could organise themselves
- formula for this is 2^n ( n = umber of homologous pairs )
16
Q
What happens in prophase 1 ?
A
- the chromosomes condense and homologous pairs line up
- centrioles migrtae to opposite sides of the cell and they each start to form spindle fibres
- the nucleolus disappears and the nuclear envelope breaks down which leaves the chromosomes free in the cytoplasm
17
Q
What happens in metaphase 1 ?
A
- homologous pairs line up at the equator of the cell
- each chromosome’s centromere attaches to the spindle
18
Q
What happens in anaphase 1 ?
A
- homologous chromosome pairs are separated an pulled to opposite poles of the cell
- but the chromatids are still joined together
19
Q
What happens in telophase 1 ?
A
- chromosomes reach opposites sides of the oil where they uncoil
- nuclear envelope forms around each set of chromosomes and the nucleolus starts to reform
- cytoplasm divides to form 2 cells
20
Q
What happens in prophase 2 ?
A
- chromosmes condense again
- centrioles migrate to opposite sides of the cell , each centrioles begins to form spindle fibres
- nucleolus disappears again and the nuclear envelope breaks down
21
Q
What happens in metaphase 2 ?
A
- chromosmes line up in the equator of the cell ( so 23 chromosomes line up )
- each chromosomes’s centromere attaches to a spindle
22
Q
What happens in anaphase 2 ?
A
- centromeres from each chromosomes divide and separate it to a pair of chromatids
- spindle fibres contract and shorten so chromatids are pulled to opposite sides of the cell
23
Q
What happens in telophase 2 ?
A
- chromatids reach the opposites sides poles of the cell whee they uncoil and become long and thin again
- nuclear envelope forms around each set of chromosomes and they form 2 nuclei and the nucleolus starts to reform
- cytoplasm divides and 4 cells are produced
24
Q
What is genetic diversity ?
A
- the number of different alleles of genes in a population
- this is what lets natural selection happen
25
What is a gene pool ?
- the collection of all the genes an alleles in a population at a particular time
26
What is allele frequency ?
- the proportion of organisms in a population that are carrying a particular allele
27
Describe the process of natural selection
- random mutations happens within the population
- this leads to genetic variation in the population
- some mutations give organisms an advantage to survive in their environment
- the new allele gives a reproductive advantage meaning the individual with new allele is more likely y reproduce and pass the allele to their offspring
- over many generations, the allele frequency of this allele will increase in the population
28
What can evolution be described as ?
- the change in allele frequency in a population
- it results in a species being better adapted for their environment
29
What are the 3 types of adaptation ?
- anatomical = spikes on a hedgehog, camouflage
- physiological = hedgehogs hibernating and slowing their metabolic reactions in winter , venom, water storage
- behavioural = hedgehogs curling up when they are in danger, courtship displays , seasonal actions ( like migration for birds )
30
What are the three types of selection ?
- stabilising
-directional
- disruptive
31
What is stabilising selection ?
- when the trait in the middle shams the selective advantage, extremes are eliminated
- the average if favoured
32
What is an example of stabilising selection ?
- human birth weight
- babies born with a middle birth weight have a selective advantage
- as extremely low and extremely high birth weights can lead to underdevelopment and complications during birth respectively
- so babies born with middle birth weights are more likely to survive and pass this allele on to their offspring
33
What is directional selection ?
- when extreme traits have a selective advantage
- and a once more rare phenotype becomes more common
34
What is an example of directional selection ?
- antibiotic resistant bacteria
- random mutations can leas to a bacteria developing a mutation that is resistant to the antibiotic
- then if the bacteria are exposed to this antibiotic only the one with the resistant allele will survive and reproduce and pass this allele to their offspring
- eventually most of the bacteria carry this allele
