Variation
- Combining genes from two parents contributes to variation within a species.
- Single gene inheritance of characteristics shows discrete variation where measurements fall into distinct groups.
- Polygenic inheritance of characteristics shows continuous variation where there is a range of values between a minimum and a maximum.
- Polygenic inheritance of characteristics is controlled by more than one gene.
Genetic terms
- A gene is a section of chromosome which codes for proteins which expresses characteristics.
- An allele is a different form of a gene.
- Phenotype describes the physical expression of a gene.
- Genotype represents the two alleles possessed by an organism for a characteristic.
- A dominant allele is expressed if one or two copies of the allele are present in the genotype. Represented by a capital letter, eg H.
- A recessive allele requires TWO copies of the allele to be present for it to be expressed. Represented by a lower case letter, eg h.
- Homozygous is the term used to describe two matching alleles, eg HH or hh
- Heterozygous is the term used to describe two different alleles, eg Hh
- P is the letter used to represent the parental generation in a family tree
- F1 is used to represent the first generation of offspring in a family tree
- F2 is used to represent the second generation of offspring in a family tree
Reasons why predicted phenotype ratios among offspring are not always achieved.
- Fertilisation is a random process
- Involves an element of chance
Topic Summary
Related
