9. Genetic diversity Flashcards
what is a gene mutation?
a change in the DNA base sequence of chromosomes
what difference often arises due to substitution mutation?
a single different amino acid.
why do some substitution mutations not affect the protein function at all?
degenerate DNA.
several codons can code for the same amino acid.
in a deletion mutation, why is it unlikely that they polypeptide coded for will function correctly?
frame shift occurs, all bases after the deletion shift one place to the left. This means that an entirely different set of triplets are created
what is the process called in which mutations in the number of chromosomes occurs?
chromosome non-disjunction
in sexual reproduction, what fuses to give rise to a new offspring?
gametes
what is a diploid number of chromosomes?
number of chromosomes. a diploid is two copies of each (2n)
how many chromosomes does the average human have?
- 23 pairs
define homologous chromosomes
pairs of matching chromosomes
in the first stage of meiosis, meiosis I, what seperates?
the homologous pairs
What separates during meiosis II?
The two chromosomes in the homologous pair split up
Name the two processes which increase genetic variation in the offspring which are a result of meiosis?
crossing over, independent segregation of chromosomes
outline the process which occurs in meiosis I which increases genetic variation
crossing over. The chromatids wrap around each other and swap bits of genetic information.
This means each chromatid has the same genes but a different combination of alleles
How many haploid daughter cells are produced from one diploid parent cell?
4
define genetic diversity
the number of different alleles in a species/population
outline natural selection
individuals with an allele that increases survival chance are more likely to survive, reproduce and pass on their genes. This leads to an increase of allele frequency of beneficial genes, which over time leads to evolution
What causes bacteria to be resistant to antibiotics?
mutation in their DNA allows some bacteria to survive the use of antibiotics.
This enables those bacteria to survive and reproduce, passing on the resistant alleles to their offspring.
what type of selection is exemplified by antibiotic resistant bacteria?
directional selection
why are human birth rates an example of stabilising selection
babies at the extreme ends often do not survive
give an example of anatomical adaptation that can result from natural selection
physical features such as an animals shape
give an example of physiological adaptations that can result from natural selection
can include the ability to make venom, but also more general functions such as temperature regulation
give an example of behavioural adaptations that can result from natural selection
can be inherited or learnt and include tool use, language and swarming behaviour
what is a substitution of bases mutation?
a nucleotide in the DNA molecule is replaced with a nucleotide that has a differing hydrogenous base
what effect does a substitution of bases mutation have on the final polypeptide?
the polypeptide produced will differ in a single amino acid.
this can affect the shape and function of the final protein
what is a deletion of bases mutation?
a nucleotide is lost from the normal DNA sequence
what effect does a deletion of bases mutation have on the final polypeptide?
the loss of a singular nucleotide can cause considerable changes in the DNA sequence
the amino acid sequence of the polypeptide is completely different, therefore the polypeptide is unlikely to function correctly
Why does a deletion of bases mutation have such a drastic effect on the final polypeptide?
because the sequence of bases is read in units of 3 bases, one deleted nucleotide causes all triplets to be shifted left by one base, and therefore read differently.
Resulting in the formation of an entirely different protein
what is a chromosome mutation?
changes in the structure or number of whole chromosomes
what are the 2 forms of chromosome mutation?
changes in whole sets of chromosomes
changes in the number of individual chromosomes
explain the chromosome mutation : changes in the whole sets of chromosomes
occur when organisms have three or more sets of chromosomes rather than the usual 2
What condition is caused by changes in the whole sets of chromosomes
polyploidy, occurs mostly in plants
explain the chromosome mutation : changes in the number of individual chromosomes
sometimes individual homologous pairs of chromosomes fail to separate during meiosis.
This is known as non-disjunction and usually results in a gamete having either one more or one fewer chromosome.
resultant offspring will have more of fewer chromosomes than normal in all their body cells
what condition is caused non-disjunction, changes in the number of individual chromosomes
downs syndrome
individuals have an additional chromosome 21
why is genetic variation considered a strength?
it allows a species to adapt to their environment through evolution
list the stages of meiosis
DNA is replicated pairing of homologous chromosomes crossing over occurs independent segregation occurs separation of chromatids production of haploid cells
define non-dysjunction
chromosomes fail to separate during meiosis division
How do you calculate the number of possible chromosome mutations?
2 to the power of n
where n = the number of pairs of homologous chromosomes
e.g an organism with 4 homologous pairs of chromosomes can produce 16 combinations
list the stages of ‘crossing over’ during meosis
when the chromosomes line up with their homologous partner in meiosis 1, the chromatids become twisted around each other
during the twisting, tensions are created and portions break off and then may recombine with the homologous partner (known as recombination)
there are always equal amounts crossed over so chromosomes stay the same length
crossing over means that the maternal and paternal alleles can be mixed
why do organisms differ, what factors contribute to this?
genetic diversity within a species
- gene mutation
- chromosome mutation
- random factors associated with meiosis and fertilisation
describe the three sources of genetic variation
mutation
gene flow
sexual reproduction
what effects do mutations have on a species?
mutations are not very common
mutations are usually harmful to a population
mutations are usually selected against through evolutionary processes unless they provide an advantage
how does genetic diversity lead to natural selection?
serves as a way for populations to adapt to changing environments
with more variation, it is more likely that some individuals in a population will posses variations of alleles that are better suited to the environment
those individuals are more likely to survive long enough to produce fertile offspring possessing that allele
why is genetic variation essential for natural selection?
essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population
whereas genetic variation offers the ability to introduce new ones to the population
what are selection pressures?
external agents which affect an organisms ability to survive in a given environment
different types of selection pressures.
negative - decreases the occurrence of a trait
positive - increases the proportion of a trait
selection pressures may not remain constant, leading to changes in what constitutes a beneficial adaptation.
describe natural selection.
predation, disease and competition means that there is competition for survival - each of these provide a different selection pressure
individuals with certain combinations of alleles have adaptations that makes them more likely to reproduce
their advantageous alleles are passed onto the next generations
over many generations, the frequency of the advantageous alleles increases and the frequency of the non-advantageous alleles decreases.
so the frequency of the successful phenotypes also increases in subsequent generations
types of genetic variations…
mutations
meiosis (crossing over)
random fertilisation (new combinations)
describe discontinuous variation
there are distinct categories with no overlap
are controlled by a small number of genes
are largely unaffected by the environment
describe environmental variation
genes set limits
environment determines where, within the limits, an organism lies
usually due to polygenes
graphs plot an example of a continuous variation
- no categories to plot individuals
- are controlled by a large number of genes
- are significantly affected by the environment
- normal distribution curve
what is an example of environmental variation
height and weight
name the 3 types of selection
directional
disruptive
stabilising
describe genetic drift
the change in the frequency of an allele in a population over time
when does genetic drift occur most often?
in smaller populations
how are genetic drift and population bottlenecks linked?
the ‘founding’ population is only made up of a small number of individuals with a small number of alleles
the new population has non-representative allele frequencies compared to the parent population
genetic drift causes allele frequency to become different to the parent population
describe speciation
the evolution of a new species from an existing species
- gene pool isolation (gene flow barrier)
- evolutionary changes (changes in allele frequency)
- reproductive isolation (organisms can no-longer breed to produce fertile offspring)
describe allopatric speciation
organisms are geographically separated
organisms in each population experience different selection pressures
different alleles will be advantageous in each population
mutations occur differently in each population
describe sympatric speciation
organisms live in the same habitat at the same time
random mutations occur that cause an organism to be reproductively isolated from the other individuals
normally requires the organisms to be able to reproduce asexually
what can reproductive isolation be a result of?
seasonal changes, e.g. a change in flowering/mating season
mechanical changes, e.g. genitalia are no longer complementary
behavioural changes, e.g. a change in courtship behaviour
chromosomal changes, e.g. a chromosome divides in two, or an organism becomes polyploid
