Genetic Variation Flashcards
Define genetic variation
Genetic variation is the differences between genes of individuals (= having different alleles), and individuals having different combinations of alleles for genes, which results in different genotypes and phenotypes
in individuals
Define an allele frequency and give formula?
Allele frequency is the percentage (proportion) of each allele in a gene pool.
total number of allele/total number all alleles x100
Importance of genetic variation?
Genetic variation is significant/important because if there is more genetic variation in a population of a species it means the population has a greater chance to survive changes in their environment because there is a greater chance that there might be a genetic difference that allows some individuals to better survive the change
So the consequence of low genetic variation is that any change in the environment that has a negative impact will more likely affect every individual of the population, and so will more likely result in the whole population dying out because there is less chance that there are individuals that have a genetic difference that allows
them to survive the change.
Sources of variation within a Gene Pool?
Mutations are the only source of new alleles in a gene pool (“of differences in genes”). A new unique allele produced by a mutation that can be inherited will increase the size of the gene pool and genetic variation in the population
Sexual Reproduction produces variation through Meiosis, mate selection and random gamete fusion
Fertilisation
Environment
Define:
- Gene
- Allele
- Phenotype
- Genotype
- Gene pool
Gene – A Gene is a specific section of DNA (a specific
sequence of bases) that codes for a specific protein. Genes are the basic unit of heredity. (Heredity = the passing on of characteristics from a parent to its offspring). Each individual inherits two copies of a gene (one copy inherited from each parent)
Allele – An allele is an alternative (different) version of a gene
Phenotype – The phenotype is the physical appearance of a characteristic/trait in an individual
Genotype – The genotype is the alleles an individual carries for its genes/characteristics (= the genetic makeup of an individual for a characteristic)
Gene Pool – All the unique inheritable alleles present in a population
Define a mutation
A mutation is a random and permanent change in the base sequence of DNA.
Mutations are the only source of new alleles in a gene pool. A new allele produced by a mutation that can be inherited will increase the size of the gene pool and genetic variation in the population
How does random mate selection and random assortment increases variation.
Random Mate Selection can increase genetic variation because different combinations of alleles for genes can occur depending on which two parents reproduce
Random Fusion of Gametes at fertilisation can produce variation because different combinations of alleles for genes can come together depending on which two random gametes of the parents join together.
So in summary: sexual reproduction (meiosis) means there is the possibility that different combinations of alleles for genes might come together in offspring and so it increases genetic variation.
What are the effects mutations can have?
Lethal = kill the individual
Harmful = these lower the “fitness” of the individual (= lower their likelihood of survival and reproductive success)
Beneficial (useful) = increase the ‘fitness’ of the individual (= increase the likelihood of their survival and
reproductive success)
Neutral (silent) = no noticeable effect on the phenotype.
Causes of mutations
Mutagens are environmental factors (chemical or physical) that cause permanent changes in DNA e.g.
Mutagens such as:
X-rays
Ionising radiation (UV)
Chemicals in food, cigarettes, plastics etc….
Discuss gametic and somatic mutations.
Gametic mutations are mutations that have occurred in the DNA of sex cells (sperm or egg cells) so are able to be inherited (passed onto their offspring) because the sex cells are used in sexual reproduction/fertilisation (so offspring are produced with the mutated DNA of the gamete in every cell) e.g. cystic fibrosis, sickle cell anaemia. – so you can be born with an inherited gametic mutation that is in the DNA of every one of your
cells
of the body (soma) cells (e.g. skin cells) during an individual’s lifetime, and so cannot be inherited (so cannot enter the gene pool) because somatic (body) cells are not used in sexual reproduction/fertilisation to produce offspring, so they cannot be passed on e.g. melanoma (skin cancer), colon cancer – so you cannot be born with a somatic mutation because they occur during your life if mutagens or errors in DNA replication cause a mutation in the DNA of a body cell.
What is gamete redundancy
Gamete redundancy occurs because not every gamete goes on to be used in fertilization, so even if a gamete contains a mutation, it might not be used in fertilization, and so the gametic mutation would not be inherited and enter the gene pool
Explain the relationship between natural selection and mutations.
Natural selection will select against a harmful mutation/phenotype/allele reducing its frequency in the population because the individual with the harmful mutation will have a survival disadvantage and so will have less success sexually reproducing, so is less likely to pass on its alleles to offspring
Natural selection will select for the beneficial mutation/phenotype/allele increasing its frequency in the population because the individual with a beneficial mutation will have a survival advantage and so will be more likely to be successful in sexually reproducing and so pass on its alleles to offspring more often
