Multiple Alleles
Biology: Cambridge International A Level, topic 16.2.4
Multiple Alleles
Although only two alleles per gene are found in an individual diploid organism, there may be multiple alleles at the population level. This means many possible combinations of alleles can exist.
Homologous chromosomes
- Chromosomes in diploid organisms exist in homologous pairs.
- Homologous chromosomes consist of the same genes in the same order.
- The only variation between homologous chromosomes is in the alleles.
- Two alleles can be present for one gene.
Multiple alleles
- Although only two alleles can be present in an organism, there could be multiple different alleles for a single gene.
- Multiple alleles provide many different genotype combinations.
- This creates large variation at the population level.
Rabbit coat colour
- Four phenotypes exist for the c gene (coat colour):
- CC - brown fur.
- cchcch - blacktipped white fur.
- chch - black fur on the extremities and white fur elsewhere.
- cc - white fur.
Dominance hierarchy
- Multiple alleles have a dominance hierarchy.
- E.g. rabbit coat colour.
- CC is dominant over all other allele combinations.
- cchcch is incompletely dominant over chch and cc.
- chch is dominant over cc.
Test yourself on Multiple Alleles
Which of the following statements are true for multiple alleles?
How many alleles can be present in an organism for one gene?