Chapter 9 - Genetic Diversity And Adaptation Flashcards
What is a gene mutation?
Any change to the quantity or the base sequence of the DNA of an organism
What is a substitution mutation?
When one base is substituted for another
Why are mutations bad?
The order of DNA bases in a gene determines the amino acid sequence which codes for a certain protein. If this is altered, it may lead to the protein lacking characteristics that are important for its role
What is a deletion mutation?
One base is deleted from the DNA sequence
Why do deletion mutations normally cause a large change to the organism?
Every base after the one that has been deleted experiences a frameshift and moves one to the left. Because bases are read in triplets, the codons aren’t read correctly
What will adding a base result in?
A frame-shift to the right
What is a silent mutation?
Because the DNA code is degenerate, a substitution mutation may result in the same amino acid being coded for and so have no effect on the organism
What is a mutagenic agent?
Something that increases the likelihood of a mutation, e.g. UV radiation and ionising radiation
What are chromosome mutations?
Spontaneous changes in the number of or structure of whole chromosomes
What are the two forms of chromosome mutations?
Changes in whole sets of chromosomes
Changes in the number of individual chromosomes
When will changes to whole sets of chromosomes occur?
When organisms have three or more sets of chromosomes rather than the normal two
What is a change to a whole set of chromosomes called?
Polyploidy and it occurs mainly in plants
What is non-disjunction?
When homologous pairs of chromosomes fail to separate during meiosis. This leads to changes in the number of individual chromosomes and sometimes syndromes like Down’s
What causes Down’s syndrome?
An extra copy of chromosome 21
How many daughter cells are produced from meiosis?
4
How many divisions take place during meiosis?
2
What is a haploid number?
The number of chromosomes gametes have - half of the normal amount
What is the diploid number?
The full set of 46 chromosomes
What happens during the first division of meiosis?
Homologous chromosomes pair up and their chromatids wrap around each other
One chromosome from each pair goes into one of the daughter cells
What happens during the second division of mitosis?
The centromere is divided and the sister chromatids move to each end of the cell
What is a gene?
A length of DNA that codes for a polypeptide
What is the locus?
The position of a gene on a chromosome or DNA molecule
What is an allele?
Different forms of a gene
What are homologous chromosomes?
One maternal and one paternal chromosome which have the same gene loci
Are daughter cells genetically different in meiosis or mitosis?
Meiosis
How many divisions are there in meiosis?
2
What is the first division of meiosis?
- arranged into homologous pairs (made up from one maternal/one paternal)
- crossing over - chromatids twist and swap (known as ‘chriasmata’
- same gene but different combination of alleles
- GENETIC VARIATION
What is the second division of meiosis?
- pairs of sister chromatids separate - halving the number (HAPLOID)
- random which chromosome ends in which daughter cell
- different combination
- GENETIC VARIATION
What is the formula for the possible number of chromosomes in each daughter cell?
2^n
N=number of homologous chromosomes
What is the formula for the number of chromosomes in each daughter cell, taking into account the random pairing of gametes?
(2^n)^2
What is independent segregation?
Happens in the second division of meiosis. It’s where the chromosomes randomly end up in each daughter cell which means that the daughter cells have a completely different combination of maternal and paternal genes
What is crossing over of chromatids?
This happens during the first division of meiosis. Chromatids twist. where the parts of the chromatids are twisted swap they with each due to the tension built up from twisting.
What is chiasmata?
Where the two points was chromatids break apart
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 or DNA molecule
What is the allele?
One of the different forms of particular genes
What is a homologous chromosomes?
A pair of chromosomes, one maternal and one paternal, that have the same gene loci
What is genetic diversity?
The total number of different alleles in the population
What is a population?
A group of individuals of the same species that live in the same place and can interbreed
How are species diversity reduced?
When a species have fewer different alleles
Finish the sentence:
The greater the genetic diversity, …………..
The more likely that some individuals in a population will survive an environmental change
Process of natural selection
- within any population of a species there will be a gene pool containing a wide variety of alleles
- randomly taken this may result in a new allele which in most cases it will be harmful
- in certain environments, the new allele might give its possessor an advantage
- these individuals will be better adapted and therefore more likely to survive in the competition with others
- these individuals will grow move rapidly and live longer, due to this they will have a better chance of breading successfully and producing more offsprings
- only individuals that reproduce successfully will pass on the allele to the next generation
- as the new individuals also have the new advantageous allele, they are more likely to survive and so reproduce successfully
What are the types of selection?
- directional selection
- stabilising selection
- disruptive selection
What is directional selection?
The population mean moves to the extreme in one direction changing the characteristics of the population.
What is a stabilising selection?
Selection may favour average individuals meaning it preserves the characteristics of the population
What is a disruptive selection?
Population will have two extremes have a large groups which become two different species
How does directional selection work, for example in bacteria?
A spontaneous mutation will occur in the alleles of a gene in a bacteria that enables it to make a new protein. The new protein was an enzyme that breaks down the antibiotic before it was able to kill the bacteria. The bacterium happened by chance to be in a situation where the antibiotic had been used to treat an individual before.The bacteria that survive will be able to divide by binary fusion to build up a small population of ‘antibiotic’-resistant bacteria. This will increase the population of the non-resistant meaning the population is normal distribution curve shifted in the direction of a population having greater resistance to the bacteria this will increase the population of the non-resistant meaning the populations normal distribution curve shifted in the direction of a population having greater resistance to the bacteria
How does stabilising selection work, for example, with babies’ birth weights?
When the babies birth weight is below 2.5 kg or above 4.0 kg there is a greater risk of infant death. Whilst those around the mean are less likely to die therefore the populations characteristics of preserved rather than changed.
What are the three types of adaptations?
- anatomical
- physiological
- behavioural
What is an anatomical adaption? Give an example
Changing the physical structure of the body.
Foxes in the arctic have shorter ears and thick fur
What is a physiological adaption? And give an example
Chemical reactions in the body. For example, Oxidising of fat rather than carbohydrate in kangaroo rats to reduce additional water in a dry desert environment
What is a behavioural adaptation? Give an example.
The way an animal acts. Autumn migration of swallows from the UK to Africa to avoid food storages in the UK winter
