2.4 Variation And Inheritance Flashcards
What is discrete / single gene variation?
Discontinuous, where the values do not occur in a range and fall into distinct groups (usually descriptions e.g. colour).
What is continuous / polygenic variation?
Where there is a range of values on a scale e.g. height.
What are polygenic characteristics caused by and what do they show?
Many genes working together. They show continuous variation and very common phenotypes.
What is a gene?
A section of DNA which codes for a protein (characteristic).
What are alleles?
Different forms of a gene which control one characteristic.
What is a phenotype?
The visible physical characteristics you can see as a result of a gene.
What is a genotype?
The pair of alleles a person has which control one characteristic, e.g. AA, aa or Aa.
What is a dominant allele?
An allele which is always seen in a phenotype if it is present (in the genotype).
What is a recessive allele?
An allele which is only seen in the phenotype if there is no dominant allele present.
Define homozygous.
When a genotype has two alleles exactly the same, e.g. AA or aa.
Define heterozygous.
When a genotype has alleles which are different from each other, e.g. Aa.
Why are predicted ratios not always achieved?
Because fertilisation is a random process.
What do the terms P1, F1 and F2 mean in a genetic cross?
P1: The genotypes of the parents in the cross.
F1: The genotypes of the offspring from a cross.
F2: The genotypes of the offspring resulting if two of the original F1 offspring were crossed.
