Genetic Diversity And Adaptation Flashcards
When may a mutation be inherited
When the mutation occurs during the formation of gametes
What is a GENE mutation
Any change to one or more nucleotide bases/ change in the sequence of bases, in the DNA
When can gene mutations arise
Spontaneously during DNA replication
What is a substitution mutation
Where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
What can happen due to a substitution mutation, what does the significance depend on
Original amino acid may be replaces so the polypeptide produces will differ in a single amino acid
Depends upon the rescues role of the original amino acid
What may be different in the new amino acid after substitution
Teh new amino acid may not form the same bonds to form the same tertiary structure
The protein then may be a different shape and therefore not function properly
Why is the effect of substitution different if the new triplet of bases still codes for the same amino acid as before
Due to the degenerate nature of the genetic code
No change in the polypeptide produces
Mutation will have no effect
What is a deletion
When a nucleotide is lost from the normal dna sequence
What is the effect of a deletion
Amino acid sequence is different so the polypeptide is unlikely to function correctly
Why is the polypeptide unlikely to function correctly after a deletion
The sequence of bases in DNA is red and units of three bases. One deleted nucleotide causes all triplets in the sequence to be red differently, due to a frameshift to the left by one base
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
What is a change a whole set of chromosomes in a chromosome mutation
What’s the condition called
When organisms have 3 or more sets of chromosomes rather than just the usual 2
Polyploidy and occurs mostly in plants
What is the changes in the number of individual chromosomes and how does it occur
Sometimes individual chromosomes fail to separate during meiosis
= non- disjunction
Resulting in a gamete having either one more or one fewer chromosome
What’s an example of non-disjunction of Down syndrome
Where individuals have an extra chromosome 21
What is non disjunction
A type of chromosome mutation, which results in the gamete, having either one more fewer chromosome.
on fertilisation with a gamete that has the normal complement of chromosomes.
The resultant offspring have more or fewer chromosomes than normal in their body cells.
What is hybridisation
Combining genes of different varieties of species of organisms to produce a hybrid
What is meiosis
Cell division producing 4 daughter cells, each with half the number of chromosomes as the parent cell
When does meiosis occur
In the formation of gametes
What happens when 2 haploid gametes fuse at fertilisation
The diploid number of chromosomes is restored
What’s the first step of meiosis
The meiosis 1
Homologous chromosomes pair up and their chromatids wrap around each other
Equivalent portions of these chromatids may be exchanges in crossing over
By the end of this division the homologous pairs have separated
One chromosome from each pair going into on of the 2 daughter cells
What happens in meiosis 2
The chromatids move apart
At the end of meiosis 2 4 cells have usually been formed
How many chromosomes are in each cell at the end of meiosis 2
23
2 ways in which meiosis brings about genetic variation
Independent segregation of homologous chromosomes
New combinations of maternal and paternal alleles by crossing over
What is crossing over
Process where homologous chromosomes exchange sections of their chromatids
When does crossing over occur
Meiosis 1 - prophase 1, when homologous chromosomes pair up
What’s a bivalent
A pair of homologous chromosomes that have come together during prophase 1 of meiosis
How many chromatids are in a bivalent
4
What’s the result of crossing over
New combinations of alleles on the chromatids (recombinant chromatids )
Genetic variation in gametes
Offspring are genetically unique
What’s independent segregation
Process where homologous chromosomes are separated randomly in meiosis 1
What does independent segregation produce
New genetic combinations
Events during crossing over
Chromatids of each pair become twisted around one another
Tensions are created and portions of the chromatid break off
These broken portions then rejoin with the chromatids of its homologous partner
Usually it is equivalent portions of homologous chromosomes that are exchanged
In this way new genetic combinations of paternal and maternal alleles are produced
What is recombination
Process where the broken off portions of the chromatid recombine with another chromatid
What’s the formula based on the number of chromosomes in an organism to determine the number of possible combinations of chromosomes for each daughter cell
2^n where n = number of pairs of homologous chromosomes
What’s the formula to calculate where the gametes come from different parents 2 genetic complements with different alleles are combined to provide more variety
(2^n)^2 where n = number of pairs of homologous chromosomes
How many different combinations of chromosomes are in an organism with 4 homologous pairs of chromosomes
256 different combinations of chromosomes in the offspring produces as a result of sexual reproduction
What does recombination mean for the possible number of chromosome combinations in gametes
Greatly increases the number
Calculate the number of possible chromosome combinations produced from the fertilisation of two dummies from separate individuals who is diploid number is 12
12/2 = 6 to find the pairs on homologous chromosomes
(2^6)^2 = 4096
Differences in what lead to genetic diversity
DNA
What is a gene
A section of DNA that codes for one polypeptide
What is genetic diversity
The total number of different alleles in a population
What is a population
A group of individuals of the same species that live in the same place and can interbreed
The greater the number of different alleles that all members of a species possess …
The greater the genetic diversity of that species
When is GD reduced
When a species has fewer DIFFERENT alleles
Why is it more likely that some individuals in a population will survive an environmental change if you have greater genetic diversity
A writer range of alleles and therefore a wider range of characteristics
Gives a greater probability that some individuals will posses a characteristic that suits it to the new environmental conditions
Genetic diversity is a factor that enables what to occur
Natural selection
Why are not all alleles of a population, equally likely to be passed the next generation
Because only certain individuals are reproductively successful and so pass on their alleles
Within a population of a species, there will be a … which contains a wide variety of alleles
Gene pool
It’s find the process of reproductive success and allele frequency
There will be a gene pool containing a wide variety of alleles within any population of a species
Random mutations of alleles within this gene pool may result in a new alleles of a gene, which in most cases will be harmful
However, the new allele of a gene might give its possessor an advantage over other individuals in a population
These individuals will be better adapted and therefore more likely to survive in their competition with others
These individuals are more likely to contain the available resources and so grow more rapidly and live longer. As a result, they will have a better chance of breeding successfully and producing more offspring.
Only those individuals that reproduce successfully will pass on the alleles to the next generation
Individuals with this advantageous allele are more likely to survive and so reproduce successfully
Over time The frequency of the new advantageous allele in the population increases while that of the non-advantageous ones decreases
What is selection
The process by which organisms that are better adapted to their environment survived and breed , while those who are less adapted tend not to
What is directional selection
Favours individuals that vary in one direction from the mean population
If the environment changes
If an organism has a phenotype which falls left or right to the mean what could hat lead to
Phenotype being more suited to the new conditions
More likely to survive and breed
Will therefore contribute more offspring to the next generation than other invidviduals
Antibiotic resistance in bacteria / penicillin steps
1 - mutation occurred in the allele of a gene in a bacterium
Gave the bacterium the ability to make a new protein which was an enzyme that can break down penicillin
2- antibiotic was introduced
Most of the bacteria were killed , but the resistant bacteria survived
3-the resistant bacteria were able to divide by binary fission and survive
4 the population of penicillin resistant bacteria increased as the frequency of the allele that enabled the production of the enzyme had increased in the population
5 the population is normal distribution curve shifted in the direction of the population having greater resistance to penicillin
Why is the total number of mutations in bacteria large
There are so many bacteria - not all are beneficial , may cause bacteria to die
What happens with continued use of antibiotics
There is a greater chance that the mutant population will out-compete and replace the original population
What does directional selection result in
Phenotypes at one extreme of the population been selected for and those at the other extreme being selected against
What is stabilising selection
If environmental conditions remain stable, it is the individuals with the phenotype closest to the mean that are favoured
And are more likely to pass on their alleles compared to being at the extremes
What does stabilising selection tend to eliminate?
Phenotypes at the extremes
What’s the example for stabilising selection
Human birth rates
How does a human birthrates illustrate, stabilising selection?
The morality is greater at the two extremes
What does stabilising selection result in?
Phenotypes around the mean population selected for and those at both extremes being selected against
What adaptations are there
Anatomical
Physiological
Behavioural
