What are mutations?
- a change in the DNA base sequences
- mutations occurring in a gene can stop the production of the protein the gene normally codes for, or a different protein might be made instead
Why are most mutations harmful?
-the production of the wrong protein or no protein can be very bad, especially if the protein was an important enzyme
How are some mutations beneficial or of no effect?
- the new protein created could give an organism a survival advantage over the rest of the population and natural selection will take place, e.g.bacteria with resistant strains
- some mutations don’t change the protein being coded for, so they have no effect on the organism
How is the chance of mutation increased?
- through ionising radiation, and radioactive substances, and certain chemicals that are know to cause mutations (mutagens)
- if the mutations produce cancer then the chemicals are often called carcinogens
What are the advantages of being multi-cellular?
- means you are bigger, meaning you can travel further, get your nutrients in a variety of ways, and fewer things can squash or eat you
- allows for differentiation, you can have different cells that do different jobs, instead of one cell doing all the jobs. Your cells can be specially adapted to do their jobs
- this means we can be more complex–have specialised organs, different shapes and behaviour and adapt specifically to our particular environments
What does being multi-cellular mean for an organism?
having specialised organ systems:
- communicate between different cells, e.g. nervous system
- supply cells with nutrients they need, e.g. circulatory system
- control the exchange of substances with the environment, e.g. respiratory system
What is mitosis and how does it work?
-when a cell reproduces itself by splitting to form two identical offspring
1-before mitosis starts, DNA in cells replicate
2-at the beginning of mitosis, DNA coils into double-armed chromosomes, the arms contain exactly the same DNA
3-chromosomes line up at centre of cell and then divide as cell fibres pull them apart. The two arms of each chromosome goes to opposite poles of one cell, membranes form around each of these two sets of different chromosomes
4-the cytoplasm divides, and you get two new cells
How are sperm cells adapted for their function?
- small and have a long tail so they can swim to the egg
- lots of mitochondria to provide the energy needed to swim the distance
- an acrosome at the front of the head, which releases the enzyme needed to digest its way through the egg cell
How does fertilisation create genetic variation?
- at fertilisation a male and female haploid gamete form to make a diploid zygote
- the zygote’s characteristics are controlled by the combination for genes on its chromosomes, which it inherited from two parents, so it will show features of both, but not look exactly like them.
What is meiosis and how does it work?
-the formation of gametes
1-DNA replicates and curls to form double-armed chromosomes
2-chromosomes arrange themselves into pairs, chromosomes in a pair contain information about the same feature, one from mum and one from dad
3-the chromosomes in each pair move to opposite poles of the cell. In the new cells there are no pairs at all, just one of each 23 different types
4-the chromosomes in both cells line up at the centre and a pulled apart by the cell fibres, and one arm ends up in each new cell
5-you end up with 4 new cells, they are genetically different as the chromosomes are shuffled up during meiosis and the gamete has only half of them, at random
What is a diploid?
-a cell with two copies of each chromosome in the nucleus
What is a haploid?
-a cell with one copy of each chromosome in the nucleus
