Genetic Diversity And Adaptation Flashcards
What are mutations?
Any change to the quantity of the base sequence of DNA and multiple of these is called a gene mutation
What is a substitution mutation?
Where a nucleotide in DNA is replaced by another.
Can cause the synthesis of a different amino acid which will lead to change in protein structure however due to DNAs degenerate nature the change may make no difference and still code for the correct amino acid which will
What is a deletion mutation?
When a nucleotide is lost from the normal DNA sequence which causes a shift in triplets making the code completely different this then means the polypeptide is unlikely to function correctly
What are chromosome mutations?
Changes in the structure or whole number of chromosomes
State and explain the 2 forms of chromosome mutations
-changes in whole sets e.g three sets called polyploidy
-changes in the number of individual chromosomes e.g homologous pairs failing to separate during meiosis resulting in the gamete having one more or less which is called non-disjunction
Importance of meiosis
Allows for the number of chromosomes in offspring to be kept constant.
Give a brief description of meiosis
1- first division homologous chromosomes line up and are separated forming 2 daughter cells
2- second division chromatids move apart forming overall 4 daughter cells
State the two ways in which genetic variation occurs during meiosis
-indepentant segregation
-crossing over
What is a gene?
A length of DNA that codes for a polypeptide
What is a locus?
Position of a gene on a chromosome or DNA molecule
What is an allele?
Versions of a particular gene
What are homologous chromosomes?
Pair of chromosomes one is maternal and one is paternal and they have the same gene loci
Describe how independent segregation occurs
During meiosis one when the homologous chromosomes line up this is done in a complete random way. This therefore means that when one of each pair goes to each daughter cell this is random meaning that whether the maternal or paternal chromosome goes to the cell is by chance
Describe crossing over
Occurs when homologous pairs line up
1) chromatids of each pair become twisted around each other (form bivalents and chismata)
2) during twisting tension is created and portions of chromatids break off
3) rejoin to chromatids of homologous pair (recombination)
4) usually the same portions are exchanged
5) new genetic combination’s
State the equation to calculate the possible chromosome combinations following meiosis in an organism
2^n or (2^n)2
What is genetic diversity?
Total number of different alleles in a population , the greater the number of alleles the greater the diversity
What is a population?
Group of individuals of the same species that live in the same place and can interbreed
How does genetic diversity affect survival?
Greater the diversity more likely individuals will survive environmental change as a wider range of alleles will cause a wider range of characteristics. Therefore there will be a greater probability that some individuals possess the trait which suits new environment. So genetic variation allows for natural selection to occur
Explain Allele frequency through natural selection
1)random mutation of an allele in a gene pool may result in a new allele of a gene which in most cases is harmful
2) allele may be advantageous and give individual better chance at surviving e,g in competition
3)they are more likely to obtain resources so grow quicker and live for longer
4)better chance a reproducing successfully passing on the allele
5)process occurs again and the number of individuals with the advantageous alleles increases
State the two ways in which selection can occur
-directional selection (selection may favour individuals that vary in one direction from the mean of the population and causes a change in the population)
-stabilising selection (may favour average individuals and preserves the characteristics of a population)
How are most characteristics affected?
Mostly affected by polygenes which are more affected by the environment
Describe the 3 types of adaptation
-anatomical (e.g shape of ears)
-physiological (chemical and biological processes)
-behavioural (migration)
Describe evolution
- a change in the characteristics of a species across several generations, sometimes leading to the development of a new species from pre-existing one
Phenotypic Variation
Differences in phenotypes in a population/species
Polygenic traits
-most genetic traits are polygenic meaning they are due to multiple action of many genes and there protein product.
-example is variation in size
-can be presented using a histogram or density plot
Steps of natural selection
1) Random mutation - new alleles of a gene
2) Threat to survival - competition, predation, lack of food , disease, change to environmental conditions
3) Natural selection - some individuals are better adapted
4) Reproduction - better adapted individuals will survive to breed
5) Increase in allele frequency - advantageous alleles will increase in frequency and less advantageous alleles will decrease
Directional Selection
Allele frequency moves towards one phenotype extreme and away from the other
Stabilising Selection
Allele frequency moves towards the mean value/phenotype and against both phenotype extremes
Disruptive Selection
Allele frequency moves towards both extremes of the phenotype and away from the mean value/phenotype
