Pack 10 - Genetic Diversity: Mutations, meiosis and adaptation. Flashcards
What is a mutation?
Any change to the quantity or the base sequence of the DNA of an organism.
What is any change to one or more nucleotide bases, or a change in the sequence of the bases, in DNA known as?
A gene mutation.
When can gene mutations arise spontaneously?
During DNA replication
What is the type of mutation in which a nucleotide in DNA is replaced by another that has a different base known as?
A substitution
Explain how a substitution could lead to an enzyme not functioning.
- Change in nucleotide base will produce a different triplet which may translate to a different amino acid.
- This will produce a different polypeptide - different bonds formed.
- Different tertiary structure.
- The active site does not fit substrate.
Explain how the fact the genetic code is degenerate means a substitution may have no effect on the polypeptide produced.
- The substitution could lead to a triplet that codes for the same amino acid.
- Same amino acid used - same polypeptide.
What is the type of mutation in which a nucleotide in DNA is lost from the normal DNA sequence?
Deletion
Explain how the deletion of a single base can lead to a completely dysfunctional polypeptide.
- Deletion of one nucleotide shifts all subsequent bases.
- The code is read in triplets, so each subsequent amino acid is different.
- different bonds - different tertiary structure.
What is a frameshift mutation?
The insertion or deletion of a number of bases not divisible by three.
What is the name for the change in the structure or number of whole chromosomes?
Chromosome mutation.
What is the name for when organisms have three or more sets of chromosomes rather than two?
Polyploidy (mostly in plants)
What is the change in the individual number of chromosomes known as and how does it occur?
Non-disjunction - individual homologous pairs of chromosomes fail to separate during meiosis.
How many daughter cells does mitosis produce and how many chromosomes do they have?
2; same as the parent cell
How many daughter cells does meiosis produce and how many chromosomes do they have?
4; half the number of chromosomes
What is a gamete?
A sex cell.
What is the diploid number?
The number of chromosomes present in the body cells of an organism.
What is the haploid number?
The number of chromosomes present in the gametes.
When is the diploid number restored?
When two gametes fuse during fertilization.
Briefly - what happens during meiosis 1?
- Homologous chromosomes pair up and their chromatids wrap around each other - equivalent portions may be exchanged.
- Homologous pairs separate.
Briefly - what happens during meiosis 2?
The chromatids move apart - four cells have been formed.
Give two ways meiosis brings about genetic variation.
- Independent segregation of homologous chromosomes.
- New combinations of maternal and paternal alleles by crossing over.
What is a gene?
A length of DNA that codes for a polypeptide.
What is a locus?
The position of a gene on a chromosome.
What is an allele?
One of the different forms of a particular gene.
What are homologous chromosomes?
A pair of chromosomes that have the same gene loci.
Describe what independent segregation is during meiosis 1 and how it leads to genetic variation.
- When homologous pairs arrange themselves they do so at random.
- One of each pair will pass to each daughter cell.
- The homologous chromosome pairs line up at the equator independent of each other.
- Therefore the combination of paternal and maternal chromosomes in the daughter cells is a matter of chance.
- This produces new combinations of alleles.
Explain how random fertilisation leads to variation.
Each gamete produced contains different genetic make up. They fuse randomly so produce genetically different and varied offspring.
Describe the process of genetic recombination by crossing over in 5 steps.
- During meiosis 1, homologous chromatids pair up and become twisted.
- During this twisting tensions are created so portions of the chromatid break off.
- These broken portions might then rejoin with the chromatids of its homologous partner.
- Usually the equivalent portions of homologous chromosomes are exchanged.
- New genetic combinations of maternal and paternal alleles are produced within individual chromosomes.
When does crossing over occur?
Prophase 1
What is the process of crossing over? (1 point)
Chromatids crossing over many times during prophase 1.
What is the process of recombination? (1 point)
Broken off portions of homologous chromatids recombine with opposite chromosome.
When do homologous chromosomes pair up during meiosis?
Prophase 1
What is the formula for the number of possible chromosome combinations in an organisms gametes, where n is the number of homologous pairs of chromosomes? - assuming no crossing over.
2^n
What is the formula for the number of possible chromosome combinations of two organisms offspring, where n is the number of homologous pairs of chromosomes? - assuming no crossing over.
(2^n)^2
Genetically how do all individuals of a species differ and how are they all the same?
They are the same as they posses the same genes. Genome.
They differ as they all have different combinations of alleles for each gene.
Define genetic diversity.
The total number of different alleles in a population.
Define a population.
A group of individuals of the same species that can interbreed and live in the same place.
Why are species with a greater genetic diversity more likely to survive?
The wider the range of alleles the wider the range of characteristics. The greater the probability that some individual will possess a characteristic that enables it to survive an environment change.
Define allele frequency.
number of individual allele/total number of alleles of that gene
What is a gene pool?
All the alleles for all gene loci that exist for a specific population at a specific time.
Describe natural selection in 7 steps.
- Within a population there is a gene poll with a wide variety of alleles.
- Random mutation of alleles within the gene pool are mostly harmful
- Certain ones may give an advantage
- These individuals will be better adapted and more likely to survive
- More likely to live longer and reproduce successfully
- Only individuals that reproduce successfully will pass on their alleles. this new allele is the one that is likely to be passed on
- Over generations individuals with the advantages allele are more likely to reproduce so its allele frequency will increase. And visa versa.
What determines whether an allele is “advantageous”?
The current environmental conditions.
Define Selection.
The process by which organisms better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.
What determines selection?
The environmental conditions an organism is exposed to at the time.
What are the two types of selection? Describe how each effects the characterises of a population.
Directional - changes the characteristics of a population.
Stabilising - preserves the characteristics of a population.
What are polygenes?
Characteristics determined by more than one gene.
Which characteristics are more affected by the environment single gene or polygene?
polygene
What shape do you get when you plot a the variation of a population on a graph?
A normal distribution curve.
What does selection act upon? What does this have an indirect effect upon?
Phenotypes; the inheritance of alleles from one generation to the next
Describe directional selection in the context of penicillin resistant bacteria. (6 steps)
- Spontaneous mutation - in allele of a gene of a bacterium enabling the production of penicillinase.
- The bacteria happened to be in a situation where penicillin was used. Therefore the bacterium had an advantage. (Rest of the population was killed).
- This bacterium survived and so divided leading to a small penicillin resistant population.
- This population is more likely to survive and therefore multiply than others.
- This population increased at the expense of non-resistan bacteria. Therefore ALLELE FREQUENCY increased.
- NDC shifts in the direction of greater resistance to penicillin.
What is the original penicillin resistance caused by?
A chance mutation
Why are mutations not always advantageous? When are they?
They can cause death. When the environment gives the allele an advantage.
In stabilising selection which individuals are more likely to pass on their alleles?
- Phenotypes closest to the mean.
In stabilising selection which individuals are selected against?
Phenotypes that are extreme
Explain why stabilising selection occurs in terms of birth mass.
- Babies with high or low birth mass are selected against as they die and their alleles aren’t passed on so frequency decreases.
- Babies with mass closer to the mean are selected for -characteristic is preserved.
Natural selection results in species that are better adapted to their environment. What three types of adaptation may occur?
Anatomical - e.g. thick fur
Physiological - e.g. kangaroo rats oxidising fat rather than carbohydrate to produce edition water.
Behavioural - e.g. migration of swallows to avoid food shortage.
