Section 4 - Genetic diversity Flashcards
What is a gene mutation?
Any change to one or more nucleotide bases, or a change in the sequence of bases in DNA.
Why might a mutation not lead to a change in the amino acid sequence?
The genetic code is degenerate so a mutation may end up coding for the same amino acid as the original triplet.
The mutation may occur in an intron.
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another.
What is a silent mutation?
When a substitution of base still codes for the same amino acid as original.
(degenerate nature)
What is a mis-sense mutation?
When the base change leads to a different amino acid being coded for.
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost.
Why is a deletion mutation likely to be harmful?
The codon is no longer read in the same way, as all subsequent bases would shit forward.
FRAMESHIFT
What is an insertion mutation?
When a nucleotide is added to the DNA sequence.
What happens as a result of a deletion or insertion mutation?
A frameshift occurs.
Amino acid sequence will be different as the codon will be read in a different way.
What is a polyploidy chromosome mutation?
When organisms have 3 or more sets of chromosomes rather than 2
(plants mostly)
What is chromosome non-disjunction?
When individual homologous pairs of chromosomes fail to separate during meiosis.
Resulting in gametes with one more or less chromosome than normal.
What are 3 things are mutations caused by?
- X-rays
- Ionising radiation
- Chemicals
Why is a deletion gene mutation more likely to result in a change to an organism than a substitution gene mutation?
Deletion: all codons after deletion are affected, amino acids will be different, polypeptide will be significantly affected.
Substitution: only a single codon is changed so only 1 amino acid is different, effect on polypeptide is less severe.
Why might a mutation that is transcribed onto mRNA not result in any change to the polypeptide?
Mutation may be substitution.
As genetic code is degenerate, the changed codon may still code for same amino acid, making no change to the polypeptide.
Why are errors in DNA replication more damaging than errors in transcription?
Errors in DNA replication may be inherited and have permanent affect on whole organism.
Errors in transcription are usually only specific cells, temporary and not inherited.
What is meiosis?
A form of cell division that produces four daughter cells, each with half the number of chromosomes as the parent cell.
How does meiosis differ from mitosis?
Meiosis: produces 4 daughter cells with half the number of chromosomes as the parent cell
Mitosis: produces 2 daughter cells with the sane number of chromosomes as the parent cells.
What happens during meiosis |?
- Homologous chromosomes pair to form bivalents
- Crossing over occurs at the chiasmata as equivalent
portions of chromatids may be exchanged - Homologous pairs separate with one chromosome
from each pair going into 1 of the 3 daughter cells.
What is the centromere?
Where the chromatids are attached together.
What is the chiasmata?
Where 2 homologous pairs of chromosomes are held together.
PROPHASE 1
What is a bivalent?
A pair of homologous chromosomes
What happens in meiosis ||?
- Chromatids move apart, independent segregation of
sister chromatids. - Each cell divides again, producing 4 haploid cells.
What are the 3 types of genetic variation?
- Crossing over
- Random segregation
- Independent assortment
What is crossing over?
Chromatid breaks and re-joins to the chromatid of its homologous chromosome so that their alleles are exchanged.
MEIOSIS |
What is random segregation?
Shuffles whole chromosomes among the four gametes that result at the end.
What is independent assortment?
Separation of homologous chromosomes into the gametes.
What are 2 ways in which meiosis leads to an increase in genetic variety?
Independent segregation of homologous chromosome and recombination
What happens during meiosis division 2 and not division 1?
Division of centromere
What is the role of independent segregation in meiosis?
Increases genetic variation within population
Allows different combinations of maternal & paternal chromosomes
What happens during meiosis division 2 and not division 1?
Division of centromere
