Mutations & Meiosis Flashcards
What is a gene mutation?
A spontaneous change in the sequence of DNA bases in a gene, occurring during DNA replication.
Changes in order of DNA bases ->
-> changes order of amino acids -> changes position of R groups -> changes position of bonds -> changes tertiary structure -> changes active site (if an enzyme)
What are the different types of gene mutation?
- Addition
- Deletion
- Substitution
- Silent
- Nonsense
- Missense
What is an addition gene mutation?
When a new base or triplet is incorporated into the original DNA base sequence.
Causes a frame shift that changes the amino acid sequence.
If at start it can change whole protein or change the start codon so that it no longer starts
If at end it can have little effect unless is in the stop codon.
What is a deletion gene mutation?
When a base or triplet is deleted from the original DNA base sequence.
Causes a frame shift that changes the amino acid sequence.
If at start it can change whole protein or change the start codon so that it no longer starts
If at end it can have little effect unless is in the stop codon.
What are the different types of substitution gene mutations?
- Silent
- Nonsense
- Missense
What is a silent (substitution) gene mutation?
As the genetic code is degenerate the new triplet simply codes for the same amino acid
What is a substitution gene mutation?
The replacement of a base or triplet with another. Chances to not cause a mutation due to degenerate genetic code.
What is a nonsense (substitution) gene mutation?
The change in the triplet causes a stop codon to be created early, which would result in a non-functioning protein.
What is a missense (substitution) gene mutation?
The change in the base or triplet codes for an alternative amino acid.
What is genetic diversity?
How much variation there is.
Arises because of differences in what genes are present in an organism and due to presence of different alleles of a gene
What causes variation?
- Mutation via producing new alleles
- Random assortment
- Crossing over
- Random fusion of gametes
What are the potential results of a mutation?
Mutation may be:
- Advantageous
- Neutral
- Disadvantageous
What are examples of mutagenic agents?
- High energy radiation (X and gamma rays)
- Bacteria & viruses
- Certain chemicals
What are the chromosomal mutations?
- Inversion
- Duplication
- Translocation
What is an inversion chromosomal mutation?
A section of the DNA is detached, rotated and then reattached at the same point in the gene.
Flips the order of amino acids in this section.
What is an duplication chromosomal mutation?
One or more bases are repeated causing a frame shift, altering the amino acid sequence and many create a non-functioning protein.
What is an translocation chromosomal mutation?
A group of bases from one chromosome becomes detached from one chromosome and attaches to another.
Leads to a significant alteration in not only that amino acid sequence but the entire phenotype of the organism.
Can lead to cancer and other genetic disorders.
HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 which codes for this protein receptor. This mutation results in a non functional protein receptor.
Explain how this mutation can result in the production of a non functional protein receptor. (4)
- Change in DNA base/nucleotide (sequence);
- Change in amino acid (sequence)/primary structure;
Alters (position of) hydrogen/ionic/disulphide bonds; - Change in tertiary structure (of receptor);
How many divisions do chromosomes go through in meiosis?
2
How many daughter cells produced in meiosis?
4 genetically different daughter cells are produced
What happens to the homologous chromosomes in the first meiotic division (simply) ?
Homologous chromosomes are separated
What happens to the chromatids in the second meiotic division (simply)?
Chromatids are separated
How does meiosis introduce variation?
- Crossing over
- Random assortment
