Topic 10 - Variation and Evolution Flashcards
What is variation?
Variation describes differences in the characteristics of individuals.
What is variation the result of?
Genetics and the environment
What is genetic variation?
All genetic variation is the result of mutations, some of which are then inherited and passed onto the next generation.
What is continuous variation?
Continuous variation results in a range of phenotypes between two extremes e.g. height
What is discontinuous variation?
Discontinuous variation results in a limited number of phenotypes with no intermediates, usually caused by genes alone e.g. tongue rolling
What is a mutation?
Mutations are random and permanent changes to the base sequence of existing genes, creating new alleles.
Do mutations always affect the phenotype?
Most mutations do not affect the phenotype. Mutations that do affect phenotype can have positive or negative effects.
What rate do mutations happen at?
Mutations are rare. The rate of mutations can be increased by ionising radiation and some chemicals.
What happens if the mutation helps an organism to survive?
This organism will be better adapted to environmental changes than the rest of the population, so it is likely to spread throughout the population over a few generations.
What are the features of asexual reproduction?
Cells divide by mitosis, offspring are clones, no gamete fusion and only one parent.
What are the features of sexual reproduction?
Cells divide by meiosis, offspring are non-identical, gamete fusion and two parents.
How can disorders be inherited?
If parents have certain (usually recessive) alleles.
What is cystic fibrosis?
Cystic fibrosis is a disorder of cell membranes. It causes thick, sticky mucus to build-up in the lungs and digestive system.
What kind of allele causes CF?
Recessive
What is gene therapy?
Gene therapy involves replacing the diseased allele in the cells of a patient with a normal allele of the same gene.
What are the advantages of gene therapy?
This can reduce the symptoms of cystic fibrosis and increase a patient’s life expectancy and quality of life.
What are the disadvantages of gene therapy?
Since the diseased allele is in every cell, it is difficult to replace the gene so it doesn’t always work. It may wear off as healthy cells are replaced by the patient’s cells with the diseased gene.
