9.1 - 9.4 Genetic diversity Flashcards
Define mutation
A change in the structure or quantity of an organisms DNA
Define gene mutation
A change to one or more nucleotide bases
Define chromosome mutation
A change in the structure or number of chromosomes
Define polyploidy
Changes in whole sets of chromosomes
When are gene mutations most likely to arise?
During DNA replication
What are the six type of gene mutations?
- Substitution - replace a base
- Addition - add a base
- Deletion - remove a base
- Inversion - flip a sequence of bases so they are read backwards
- Translocation - move a sequence of bases from one place to another
- Duplication - repetition of a sequence of bases
Explain how a substitution of one base could result in a non-functional protein
- Base triplet on DNA is different
- Different codon on mRNA following transcription
- Different tRNA binds to mRNA during transcription
- Different amino acid is incorporated into polypeptide chain
- Hydrogen/ionic/disulphide bonds form in different places
- The tertiary structure of the protein is changed so it is non-functional
Define mutagenic agent
Something that can increase the rate of gene mutation
Give examples of a mutagenic agent
High energy radiation:
- Can ionise chemicals in DNA and change the overall structure
- e.g X-rays, gamma rays and UV radiation
High energy particles:
- Can ionise chemicals in DNA and change the overall structure
- e.g alpha or beta particles
Chemicals:
- Can alter bases
- e.g benzene, mustard gas, tobacco tar, pesticides
Define non-disjunction
When a chromosome fails to separate into to two chromatids during anaphase. This leaves one daughter cell with an extra chromosome.
What is meiosis?
Nuclear division that produces 4 genetically different daughter cells. The cells produced are gametes (sex cells).
What is the importance of meiosis?
- Chromosome number is halved (produces haploid daughter cells) - So when gametes fuse they maintain the correct number of chromosomes
- Genetic variation is introduced (all gametes genetically unique) - Enables natural selection
What are the two ways meiosis introduces genetic variation?
- Crossing over during meiosis 1
- Independent segregation in meiosis 1 and 2
Define independent segregation
When homologous chromosomes line up randomly during meiosis 1 meaning the daughter cells receive a random combination of maternal and paternal chromosomes
What is the formula for the number of possible combinations during independent segregation?
2ⁿ
n = The number of homologous pairs