Genetic inheritance
A short video explaining gene inheritance and demonstrating how to use a punnett square
Genetic key terms
- A gamete 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.
- 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 code 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.
Some characteristics are controlled by a single gene, such as fur in animals and red-green colour blindness in humans. Each gene might have different forms, and these are called alleles. The diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes.
- Chromosomes are found in the nucleus of a body cell in pairs. One chromosome is inherited from the mother and one is inherited from the father. The chromosome in each pair carries the same gene in the same location. These genes could be the same, or different versions.
- Different forms of the same gene. are different versions of the same gene. For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour. For any gene, a person may have the same two alleles, known as homozygous or two different ones, known as heterozygous.
- 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 one copy is present. Dominant alleles are represented by a capital letter, for example, A. The allele for brown eyes is dominant. You only need one copy of this allele to have brown eyes. Two copies will still give you brown eyes.
- 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 blue eyes is recessive. You need two copies of this allele to have blue eyes.
- This describes a genotype in which the two alleles for the characteristic are identical. alleles are both identical for the same characteristic, for example AA or aa.
- This describes a genotype in which the two alleles for a particular characteristic are different. alleles are both different for the same characteristic, for example Aa.
Most characteristics are a result of multiple genes interacting, rather than a single gene.