3.4.3 Genetic Diversity Can Arise As A Result Of Mutation/ Meiosis Flashcards
(29 cards)
What are gene mutations?
A change in the DNA base sequence of chromosomes
When do mutations happen?
Spontaneously during DNA replication
What are the types of mutation?
Base deletion/ insertion
Base substitution
Gene mutations occur …
Randomly
How can mutations be corrected?
Most mistakes/mutations in the base sequence of DNA are spotted and corrected by a proofreading mechanism within the cell.
What are mutagenic agents/ What do they do?
Increase the rate of mutations
Examples of mutagenic agents
Ionising radiation
UV radiation
some chemicals
biological agents (viruses, or bacteria)
How many cells are produced by meiosis?
Four haploid daughter cells
What kind of cells are produced by meiosis?
Genetically different haploid cells
What happens at fertilisation in terms of haploid and diploid cells?
At fertilisation a haploid sperm and a haploid egg fuse form a diploid zygote
Fertilisation is …
Random as any sperm may fertilise any egg
What does fertilisation being random produce?
Produces zygote with different combinations of chromosomes to both parents and any other offspring
What are homologous chromosomes?
Pairs of chromosomes that have the same genes at the same loci, but may or may not have different alleles
Why is meiosis needed for sexual reproduction?
Because it produces daughter cells with half a number of chromosomes of the parent cell.
Where does meiosis occur?
In the reproductive organs
What happens before meiosis?
The DNA unravels and replicate so there are two copies of each chromosome called chromatids.
What happens in prophase 1?
-DNA condenses deformed double armed chromosomes each made from 2 chromatids joined by a centromere
-Other steps of profs prophase
How many stages does meiosis have?
Two stages
What happens during meiosis one?
Goes through PMAT same as mitosis but homologous pairs are replicated meaning each cell produced has chromosomes with two sister chromatids
What happens during meiosis two?
Goes through PMAT Sam is mitosis. But homologous pairs are separated so each cell contains a chromosome with only chromatid
How does meiosis cause variation?
Independent segregation
Crossing over
Explain independent segregation?
each homologous pair of chromosomes is made up of one chromosome from the father and one from the mother. When homologous pairs are separated during meiosis one it is random which chromosome from each pair ends up in which daughter cell
When does crossing over happen?
During prophase one
What happens during crossing over?
Homologous pairs of chromosomes come together and pair up
Chromatids twist around each other and bits of chromatid crossover
