Genetics - Variation Flashcards
What are the two types of variation?
Inherited and acquired
For inherited variation, what are the two types?
Discrete/discontinuous (only a few variations for a feature)
Continuous (many variations for a given trait)
What genetic substance determines our features?
The DNA in our genes
What is DNA?
Genetic material made up of repeating nucleotides, arranged in a double helix that codes for our features
What is a gene?
Small sections of DNA that are found on chromosomes that determine our features
What is a chromosome?
A long chain of DNA that contains genes
What is an allele?
Different versions of a gene
Explain how DNA determines your phenotype
The base sequence on DNA determines the type of protein formed which gives you your phenotype
Explain how different alleles for a gene give different phenotypes
Different alleles for a gene have different base sequences in their DNA. Therefore they produce different proteins and therefore produce different phenotypes
What type of cell division creates variation?
Meiosis
What is the purpose of meiosis?
A type of cell division that produces gametes (sex cells)
Where does meiosis occur?
In sex organs such as testes and ovaries
How does meiosis create variation?
Gametes are haploid (only have half the genetic information from each parent) which means they only have one chromosome from each homologous pair from each parent. When two gametes join during fertilisation they form a zygote which is diploid (chromosomes are now pairs again). The offspring is a combination of chromosomes and hence alleles from both parents and so is genetically unique
What processes occur during meiosis to ensure that each gamete produced is genetically different?
Independent assortment
Crossing over/recombination
Define independent assortment and explain how it creates variation
The random way different homologous chromosomes line up along the cell equator during meiosis. This means that each gamete receives a unique combination of chromosomes and hence alleles which increases variation.
Define crossing over/recombination and explain how it creates variation
When parts of homologous chromosomes are swapped during meiosis. This creates new allele combinations in the gametes that would not normally be possible which increases variation.
What other process creates variation but doesn’t necessarily occur during meiosis?
Mutations
Define a mutation and explain what they create
Any change in the base sequence of DNA. Mutations create new alleles that were not present before
What causes mutations?
Mutagens - radiation. certain chemicals
Explain how a mutation might create variation
A mutation is any change in the base sequence of DNA. This creates new alleles and therefore new proteins. This then leads to new phenotypes
When might a mutation be inherited?
If it is a gametic mutation it might be. These are mutations that occur in sex cells/gametes but the gamete would have to be involved in fertilisation
When will a mutation not be inherited?
If it is a somatic mutation in won’t be inherited. These occur in body cells (not cells in sex organs involved in meiosis). The mutation may affect the organism who has the mutation though providing it causes a change in the protein formed.
Why are mutations classified as the ‘ultimate source of variation’ but independent assortment and crossing over/recombination are not?
Mutations create new alleles and hence new proteins and phenotypes that were never present before. Independent assortment and crossing over/recombination simply rearranges existing alleles into new combinations.
