Inheritance
- Created by: Anon
- Created on: 13-03-15 16:08
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- Inheritance
- Sex linkage
- In humans gender is determined by chromosomes rather than genes
- The X chromosome is much longer than the Y chromosome, which means that for most genes that appear on the X chromosome, there is no homologous pair
- The recessive characteristics on the X chromosome with therefore appear in males more frequently than females
- Because they only need a single recessive allele to express the characteristic
- Any gene that appears on the X or Y chromosome is described as sex-linked
- An example of a sex-linked disease is haemophilia
- Co-dominance
- Co-dominance occurs when both alleles are equally dominant
- Both alleles are therefore expressed in the phenotype
- When representing co-dominance we cannot use upper and lower case letters, as this implies one is dominant over the other, instead we use different letters
- An example is the snapdragon plant, both red and white flowers are equally dominant
- heterozygous plants will be pink
- Multiple alleles
- Multiple alleles occur when there are more than two alleles for the same gene
- An example is human blood groups
- Each blood type codes for an antigen
- IA codes for antigen A
- IB codes for antigen B
- IO does not code for any antigen
- A person can only have 2 of the 3 alleles
- IA and IB are co-dominant and IO is recessive to both
- Hardy-Weinburg
- The Hardy-Weinburg principle predicts that the proportion of dominant and recessive alleles will be the same from one generation to the next, provided that 5 conditions are satisfied
- 1. No mutations arise
- 2. The population is isolated so there is no flow of alleles
- 3. There is no selection of alleles
- 4. The population is large
- 5. Mating within the population is random
- The equation is: p squared + q squared + 2pq = 1.0
- p is the number of dominant alleles
- q is the number of recessive alleles
- The Hardy-Weinburg principle predicts that the proportion of dominant and recessive alleles will be the same from one generation to the next, provided that 5 conditions are satisfied
- Sex linkage
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