TOPIC 4- genetic diversity can arise as a result of mutation or during mitosis Flashcards
what is a mutation?
A change in the base sequence of DNA.Often arises spontaneously during DNA replication.
why might a mutation not lead to change in the amino acid sequence?
- genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet.
-mutation may occur in intron
what is a substitution mutation?
nucleotide in DNA sequence is replaced by another.
- more likely a quiet mutation, so there is no change in amino acid sequence
what is a deletion mutation?
- nucleotide in DNA sequence is lost
-harmful and significant as it leads to FRAMESHIFT which means entire amino acid sequence will be different.
what is a mutagenic agent? examples?
- factors that increase the rate of gene mutation
eg:
-X-rays
-UV light
-gamma rays
-certain chemicals eg. in alcohol or tobacco
what is a polyploidy chromosome mutation?
where an individual has three or more sets of chromosomes instead of two.
what is chromosome non-disjunction?
- chromosomes fail to separate in meiosis
-results in gametes with one more or less chromosomes than normal
what is meiosis?
- cell division
- forms 4 genetically different haploid cells
known as gametes
what does haploid mean?
cells with half the number of chromosomes found in the parent cells.
how does meiosis differ from mitosis?
MEIOSIS:
- 4 genetically different
-haploid cells produced
MITOSIS:
-two genetically identical daughter cells
- diploid (same number of chromosomes in parent cells)
what happens during meiosis 1?
homologous chromosomes pair up whereby crossing over at the chiasmata may take
place. The cell then divides whereby each daughter cell contains one chromosome from each
homologous pair.
what happens during meiosis 2?
the chromatids of each chromosome are separated and they divide producing 4 haploid daughter cells.
Give two ways in which meiosis produces genetic variation?
- crossing over during meiosis I
- independent assortment (random segregation) of homologous chromosomes and sister chromatids.
Results of new combinations of alleles
What is crossing over?
When homologous pairs line up opposite each other at equator, chromatids cross over, chromatid breaks, broken part of chromatid recombine with another chromatid.
