Genetic diversity can arise as a result of mutation or during meiosis Flashcards
define meiosis
form of cell division that gives rise to four daughter cells that are genetically different
differences between mitosis and meiosis
meiosis = 2 divisions, haploid cells, genetic variation, 4 daughter cells
mitosis = 1 division, diploid cells, genetically identical cells, 2 daughter cells.
what is the main role of meiosis
production of haploid gametes
define gene mutation
change in the base sequence of
chromosomes
Why do most mutations not alter the polypeptide or only alter it slightly so that its structure or function is not changed?
because the genetic code is degenerate
mutation
any change to the base sequence of DNA
gene mutation
Changes of the base sequence in DNA
how do gene mutation occur
-they can arise spontaneously during DNA replication (interphase)
-Involves base deletion / substitution
chromosome mutation
changes in the number of chromosomes
mutagenic agents
increase the rate of gene mutations by causing damage to the DNA, e.g. smoking, radiation, UV light, some viruses.
substitution mutation
occurs when a nucleotide is replaced by another nucleotide that has a different base.
base deletion
When a nucleotide (base) is lost from the normal DNA sequence.
CONSEQUENCES OF DELETION MUTATION
-One nucleotide / base removed from DNA sequence
-This causes frameshift where all triplets in a sequence are read differently because each has been shifted to the left by one base.
-Changes sequence of codons on mRNA
-Changes sequence of amino acids in primary structure of polypeptide.
-Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein
-Changing the tertiary structure of the protein and leaving it potentially unable to carry out its function.
define mutagenic agent
factor that increase the rate of gene mutation
examples of mutagenic agent
High energy radiation
Ultraviolet light
Alpha particles
where does meiosis takes place
-reproductive organs
interphase in meiosis
-DNA unravels and replicates to form 2 copies of each chromosome.
-DNA condenses into double armed chromosomes - each with 2 sister chromatids joined at centromere.
meiosis I (first division, homologous pairs separate)
-Chromosomes arrange themselves into homologous pairs (one mum, one dad)
-Crossing over occurs in prophase 1.
-Homologous chromosome pairs line up at middle of the cell double file.
-Independent segregation in metaphase 1 (random if mum or dads is on top)
-Pairs of chromosomes separate.
-This halves the number of chromosomes (23 chromosomes, 46 chromatids).
MEIOSIS II (second division, chromatids separate)
the pairs of sister chromatids separate and pulled by spindle fibres to poles (centromere divided)
END RESULT
-four haploid gametes are produced, each genetically different from each other. Each has (23 chromosomes, 23 chromatids, as all have centromere).
examples of genetic variation
-crossing over
-independent segregation
- random fusion of gametes
-mutation
