Genetic inheritance
Greg Foot explains gene inheritance using cats
Genetic key terms
- 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 strands of Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being., which are made up of many 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..
- A gene is a small section of DNA on a chromosome, that codes for a particular sequence of The building blocks that make up a protein molecule., to make a specific Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.. It is the unit of Genetic information that determines an organism's characteristics, passed on from one generation to another. To do with passing genes to an offspring from its parent or parents., and may be copied and passed on to the next generation.
- DNA is a large and complex polymer, which is made up of two strands forming a double helix. DNA determines the characteristics of a living Living entity, eg animals, plants or microorganisms.. With the exception of identical twins, each person's DNA is unique.
- DNA is made from base pairs which always come in the following combinations A-T, T-A, C-G and G-C. The order of these letters makes up an organism's genetic code.
- An organism's The complete set of DNA found in an organism. is one copy of all of their DNA. With the exception of identical twins, no two people's genomes are the same.
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 Different forms of the same gene..
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 of each pair is inherited from the mother and the other 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:
- Alleles 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 This describes a genotype in which the two alleles for the characteristic are identical. or two different ones, known as This describes a genotype in which the two alleles for a particular characteristic are different..
- 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 An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself. or 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.:
- A dominant allele is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter, for example you could use a B. The allele for brown eyes, B, is dominant. You only need one copy of this allele to have brown eyes. Two copies will still give you brown eyes.
- A recessive 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, b. The allele for blue eyes, b, is recessive. You need two copies of this allele to have blue eyes.
- Homozygous alleles are both identical for the same characteristic, for example BB or bb.
- Heterozygous alleles are both different for the same characteristic, for example Bb.
Most characteristics are a result of multiple genes interacting, rather than a single gene.
