Genetic Diversity (Chapter 9) Flashcards
Describe the process of natural selection
1) Individuals vary/mutations take place
2) Some are better adapted to survival - so are more likely to reproduce and pass on alleles.
3) Over time the frequency advantageous alleles increase in the population.
Define Directional Selection
When there is an environmental change. Selective pressure for species to change in response to change. Favours individuals that are different e.g. antibiotic resistance.
Define Stabilising Selection
When there is no change in the environment - it remains stable. Individuals with phenotypes closest to mean are favoured for. Individuals with extreme phenotypes selected against - reducing them. The distribution curve becomes narrower e.g. human birth weights.
How does a distribution curve change with directional selection?
Individuals at one extreme of the range are selected for and those at the other end of the mean are selected against so there is a shift in the mean.
What does a mutation change?
Change in the sequence of bases in the DNA which changes the order of amino acids and therefore H/Ionic/Disulphide bonding and then the tertiary structure of a polypeptide.
Describe how mutations create non-functioning proteins (applied to enzyme)
1) Amino acid sequence is changed.
2) Change in H/Ionic bonds
3) Tertiary structure is altered
4) Shape of active site changes
5) No E-S substrate complexes can be formed
What is a substitute mutation?
A base is substituted for another. This can lead to a different amino acid being coded for, the same amino acid being coded for (degenerate) or a stop codon being coded for.
What is a deletion mutation?
A base is deleted causing a frame shift.
What is meiosis?
The process which makes 4 daughter cells (gametes)(haploid cells)
What are haploid cells?
Cells which have half the number of chromosomes as parents
Why is meiosis important?
Halves the number of chromosomes so diploid number is restored in fertilisation and introduces variation through crossing-over and independent segregation of chromosomes.
Describe the process of meiosis
1) Chromosomes line up in homologous pairs.
2) Chromosomes are pulled to opposite poles of the cell (one of each pair)
3) Crossing over and independent segregation happens to create variation and create new combinations of alleles.
4) (Meiosis 2) The same process as mitosis but starts with half as many chromosomes and ends with gamete.
Compare Meiosis and Mitosis
- In mitosis, chromosome number remains the same/produces diploid cells while in meiosis chromosome number is halved/ haploid cells are produced.
- In mitosis, identical cells are produced while in meiosis the cells are not identical.
- Mitosis has only one division/2cells produced while in meiosis two divisions happen which produces 4 cells
- Mitosis produces body cells while meiosis produces gametes.
What is non-disjunction?
When chromosomes do not sepaarte properly so cells have the wrong number of chromosomes which can cause mutations such as downs syndrome.
What is polyploidy?
Changes in whole sets of chromosomes and organisms have 3 or more sets of chromosomes.
