Genetic diagrams and pedigree analysis
- Created by: emews
- Created on: 18-11-17 17:26
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- Genetic diagrams and pedigree analysis
- Fertilisation leads to genetic variation because:
- alleles on the chromosomes control the characteristics of the zygote
- two gametes combine to form a diploid zygote
- For humans to reproduce, fertilisation needs to happen. Gametes are produced by meiosis. As a result of this type of cell division, each gamete is haploid.
- The cell’s nucleus contains chromosomes. These are long threads of DNA, each made up of many genes.
- Human body cells have 23 pairs of chromosomes in the nucleus.
- The two possible combinations are:
- an X chromosome from the mother and an X chromosome from the father - producing a girl
- an X chromosome from the mother and a Y chromosome from the father - producing a boy
- Huntington’s disease
- Huntington’s disease is an inherited disorder that causes damage to certain brain cells.
- It is caused by a dominant allele. In a genetic diagram:
- the recessive allele can be shown as h
- the dominant allele can be shown as H
- Codominance
- Some alleles are both expressed in the same phenotype, a situation called codominance.
- There are three possible genotypes: WW, BB and BW.
- Blood groups
- The gene controlling human ABO blood groups has three alleles, not just two:
- IA and IB are not dominant over one another
- both are dominant over IO
- The gene controlling human ABO blood groups has three alleles, not just two:
- Pedigree analysis
- Doctors can use a pedigree analysis chart to show how genetic disorders are inherited in a family.
- Fertilisation leads to genetic variation because:
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