Genetic inheritance
A short video explaining gene inheritance and demonstrating how to use a punnett square
Genetic key terms
- A Sex cell (sperm in males and ova/eggs in females). is a sex cell. In humans, gametes are sperm and eggs (ovums).
- Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being. is a large and complex polymer, which is made up of two strands forming a double helix. DNA determines the characteristics of a living organism. With the exception of identical twins, each person's DNA is unique.
- The structure made of DNA that codes for all the characteristics of an organism. are contained inside the cell's The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei.. These are long threads of DNA, which are made up of many genes. Chromosomes in a body cell are found in pairs. One chromosome is inherited from the mother and one is inherited from the father. The chromosomes in each pair carry the same gene in the same location.
- A The basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. is a small section of DNA on a chromosome, that codes for a particular sequence of amino acids, to make a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.
The diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes.
- One of a number of forms of a particular gene. or variants are different versions of the same gene (a variant). For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour.
- The The alleles that an organism has for a particular characteristic, usually written as letters. is the collection of alleles that determine characteristics and can be expressed as a The visible characteristics of an organism which occur as a result of its genes..
Alleles may be either dominant or recessive:
- A An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.allele is always expressed, even if only one copy is present. Dominant alleles are represented by a capital letter, for example, A. The allele for black fur in dogs is dominant. Only one copy of this allele is needed in order to have black fur. Two copies of the dominant allele will still produce black fur.
- A Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive gene will remain dormant unless it is paired with another recessive gene.allele is only expressed if the individual has two copies and does not have the dominant allele of that gene. Recessive alleles are represented by a lower case letter, for example, a. The allele for brown fur is recessive. A dog needs two copies of this allele to have brown fur.
- A This describes a genotype in which the two alleles for the characteristic are identical. individual has identical alleles for the same characteristic, for example AA or aa.
- A This describes a genotype in which the two alleles for a particular characteristic are different. individual has two different alleles for the same characteristic, for example Aa.
Some characteristics are controlled by a single gene, such as fur colour in animals and red-green colour blindness in humans. However, most characteristics are caused by the interaction of many different genes.