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Inheritance P2
AQA A-level biology inheritance year 13
| Term | Definition |
|---|---|
| Autosomal linkage | Where 2 or more genes are located close together on the same autosome (non-sex chromosome) and are inherited together more frequently than they would have alone |
| How autosomal linkage makes 2 gene combinations more likely to be inherited together | Because the 2 genes are physically very close on the chromosome it is unlikely that they will undergo crossing over and recombination |
| How to tell if a question is referring to autosomal linkage | If the ratio of dihybrid inheritance isn’t the normal 9:3:3:1, if there are intermediate phenotypes then it is codominance, sex linkage will be made clear in the question, and everything else is autosomal linkage |
| Epistasis | The expression of one gene (epistasic gene) masks or modified the expression of a gene on a different locus (hypostatic gene) |
| Why men with an X chromosome sex linked disease can’t be unaffected carriers | If men inherit a sex linked disease on their X chromosome then since they don’t have another copy of this allele, whatever they inherit must be expressed meaning that they can’t be both a carrier and unaffected |
| Sex linked disease | A type of genetic disorder linked to the sex chromosomes (X and Y) but typically the X chromosome. Due to females having 2 copies of the X chromosome and males only having 1, inheritance patterns affect males and females differently |
| Type O blood: genotype and antibodies | Has I^O I^O genotype (recessive), has no blood antigens on its surface and doesn’t produce blood antigen antibodies |
| Type AB blood: genotype and antibodies | Has I^A I^B genotype (codominant), has A and B antigens on its surface and doesn’t produce blood antigen antibodies |
| Type B blood: genotype and antibodies | Has either I^B I^B or I^B I^O genotype (dominant), has B antigens on its surface and produces anti-A antibodies |
| Type A blood: genotype and antibodies | Has either I^A I^A or I^A I^O genotype(dominant), has A antigens on its surface and produces anti-B antibodies |
| Codominance | Both alleles in a heterozygous pair are fully expressed in the phenotype, this means that neither allele is dominant or recessive to each other |
| Dominant | Alleles of the heterozygote and the homozygous that will always be expressed in the phenotype |
| Recessive | The allele of the heterozygote that is not expressed in the phenotype, both copies must be present in order to be expressed in the phenotype |
| Population genetics | Study of allele frequencies in a population and comparing it to different populations at different times |
| Hardy-Weinberg formula | p^2 + 2pq + q^2 = 1 p^2 = frequency of homozygous dominant genotype (AA) 2pq = frequency of heterozygous genotype (Aa) q^2 = frequency of homozygous recessive genotype (aa) 1 = 100% of total population |
| Gene flow | Transfer of genetic material (specifically alleles) between different populations of a specie |
| Genetic drift | Random, non-selective change in allele frequencies within a population over time due to chance events that can lead to allele fixation and loss |
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