Component 2.5 - Mutations Flashcards
Why is a mutation being expressed rare in diploid organisms?
Because the mutation has to be dominant to be expressed in the phenotype. If it is recessive it causes no variation in phenotype.
What can the mutation rate be increased by?
Ionising radiation e.g gamma rays, UV, X-rays
Mutagenic chemicals e.g polycyclic hydrocarbons
In what ways can mutations happen?
1) Gene or point mutation - affects single bases in a gene (not copied correctly)
2) Chromosome mutation - affects many genes (Chromosomes break and repair themselves incorrectly)
3) Polyploidy : Number of chromosomes may double if the cell fails to divide following first nuclear division
Chromosome mutation (possible effect on gamete)
Chromosomes pair at chiasmata. If they don’t rejoin properly a mutation can occur (gametes may not be able to fuse properly)
How does someone get Down’s syndrome?
In oogenesis one daughter cell gets two copies of chromosome 21 and the other gets none.
When this secondary oocyte fuses with a normal sperm the person will have 3 of the 21 chromosome and this is Down’s syndrome
How an organism get polyploidy?
1) defect in spindle means all chromosomes move to same pole. Gametes with 2 of each chromosome.
Or
Replication of chromosomes not followed by cytokinesis
2) if two diploid gametes fuse - tetraploid
Why is polyploidy more common in plants?
Because humans become infertile when they have multiple sets of chromosomes
Plants
1) Can produce asexually
2) are hermaphrodite (chromosomes don’t determine sex)
What is a tumour suppressor gene?
They are genes which control cell division
If they are turned off they can cause cancer
What is an oncogene?
A proto-oncogene with a mutation that results in cancer
Proto-oncogenes cause cancer when they are turned on
In what cells is there a higher mutation rate?
Those with a short life and more frequent cell divisions
