Inheritance, Variation and Evolution Flashcards
What is DNA and what does it stand for?
It stands for DeoxyriboNucleic Acid which is a chemical a cell’s nuclear genetic material is made from.
[it is also a polymer made up of two strands coiled into a double helix]
What are chromosomes?
Long molecules of DNA that normally come in pairs.
What are genes?
A small section of DNA found on a chromosome.
What are genomes?
An entire set of genetic material of an organism.
What is sexual reproduction?
Where two parents go through the process of the cell division, meiosis and mitosis, to produce an offspring containing a mixture of the parents’ genes.
What happens during meiosis?
[produces cells with half the normal number of chromosomes]
① the cell duplicates its genetic information.
② the cell divides and each new cell has one copy of each chromosome.
③ both cells divide again to make four gametes. Each gamete only has a single set of chromosomes.
[all the gametes produced are genetically different]
What is an allele?
A version of a gene.
What is a dominant allele?
An allele that is always expressed.
What is the recessive allele?
An allele that is only expressed when two copies are present.
What is homozygous?
When an organism has two alleles for a particular gene that are the same.
What is heterozygous?
When an organism has two alleles for a particular gene that are different.
What is a genotype?
Combination of alleles of an organism.
What is a phenotype?
The characteristics an organism has.
What are inherited disorders?
Disorders caused by certain alleles that are inherited from the parents.
What is polydactyly?
A genetic disorder where a baby’s born with extra fingers or toes and is caused by a dominant allele.
What is cystic fibrosis?
A genetic disorder of the cell membranes and is caused by a recessive allele.
What are the disadvantages of embryonic screening?
> screening is expensive.
people might want to screen their embryos so they can pick the most ‘desirable’ one.
it implies that people with genetic problems are ‘undesirable’.
What are the advantages of embryonic screening?
> it will help to stop people suffering.
testing disorders costs the government a lot of money.
there are laws to stop it going too far.
What is meant by the term variation?
The differences in the characteristics of organisms.
What do mutations do?
They cause the differences in genes and occur continuously.
What is the effect of mutations on phenotype?
MOST MUTATIONS ⟶ none.
SOME MUTATIONS ⟶ slight.
VERY FEW MUTATIONS ⟶ new phenotype.
What are fossils?
Remains of organisms from many thousands of years ago.
What are the ways that fossils form?
> gradual replacement by minerals.
↳ happens to slow decaying parts.
casts and impressions.
↳ e.g. footprints, burrows and rootlet traces.
preservation.
↳ in places where conditions prevent decay, parts of organisms can be preserved.
What is meant by the term extinction?
When no individuals of a species remain.
