Variation and Evolution Flashcards
What is heritable variation?
Heritable variation is caused by differences in genes and so can be passed on from parent to child e.g. hair/eye colour
What causes heritable variation? (DNA explanation)
Differences in the genotypes of organisms of the same species due to the presence of different alleles. It creates differences in phenotypes.
What is environmental variation?
Environmental variation is caused by the environment in which the organisms has developed. E.g. scars, piercings from diet, lifestyle, climate
What is continuous variation?
Continuous variation is where there is a continuous range with no ‘categories’ e.g. height, weight
What is discontinuous variation?
Discontinuous variation is where there are distinct groups e.g. gender, eye colour, blood group
What causes differences in offspring?
Offspring are genetically different from their parents as a result of sexual reproduction which involves an egg fusing with a sperm in the process of fertilisation. Meiosis produces genetically different gametes.
What happens during fertilisation?
One gamete from each parent fuses to form a zygote. Genetic information is mixed to form a unique individual.
What is a zygote?
Full set of chromosomes
What does asexual reproduction do?
Asexual reproduction does not create genetic variation as it involves mitosis which produces genetically identical daughter cells known as clones.
What is a mutation?
A random change in the structure of a gene.
What can cause a mutation?
A variety of factors e.g. exposure to some chemicals and ionising radiation.
What happens to mutations in gametes?
They will be passed on to the next generation
What happens to mutations in body cells?
They will not be passed on to the next generation.
What may mutations cause?
Mutations may cause a complete change in the sequence of amino acids. This could result in a non-functional protein and severe changes to phenotypes. (formation of harmful alleles)
What is cystic fibrosis?
A recessive condition resulting in the production of sticky mucus that affects the lungs and digestive system which makes breathing and digestion difficult.
What does it mean for the CF gene to be recessive?
The disease only appears when an individual has the allele for this gene on both chromosomes.
Some people have one CF allele and one “normal” allele. What does this mean?
These people are heterozygous for the recessive CF trait and will not suffer from the disease but can pass it on to any children they have. These people are called carriers.
What is gene therapy?
The name given to a range of techniques that can be used to remove the effects of a harmful allele.
What 2 methods of gene therapy are there?
Introducing a “healthy” allele into the person’s DNA.
“Switching off” the harmful allele.
What does introducing a healthy allele into the person’s DNA do?
It replaces the faulty allele and if the harmful allele is recessive a healthy dominant allele will counteract it. The recessive allele does not have to be removed.
What does “switching off” a harmful allele do?
This can be done in various different ways including the introduction of a completely new gene into the body.
What are the ethical issues of gene therapy?
The process is very expensive.
Some religious groups believe that humans should never alter the genes of living organisms.
What is evolution?
The process by which living species have gradually changed and developed from earlier forms over a long period of time.
What does evolution result in?
Organisms becoming better adapted to their environment.
