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1. An introduction to genetic variation - variants - alleles, chromosomes, genotypes, phenotypes

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There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index of biology notes on genetic variation, and the causes, formation and consequences of mutations


(1) An introduction to genetic variation

Reminders: A chromosome as a thread-like structure of DNA, carrying genetic information in the form of genes.

A gene is a length of DNA that codes for a protein. An allele as a version of a gene.

A genetic change is a mutation and how new alleles are formed.

Reminder that in the biological science of genetics, inheritance is the transmission of genetic information from one generation to the next generation by chromosomes of DNA, BUT, things are not that simple!.

Different species of plants or animals have different genes.

Individual species look different from each other because they have different combinations of genes.

The gene differences within a species are very similar, BUT, not absolutely identical, just look around and see the variation in the human species!

You see differences in height, eye colour, hair colour, height, skin colour, all of which are characteristic features within the same species.

Characteristic features can be inherited from your parents via the gene combination when an egg is fertilised (genetic factors), though some characteristic features can develop due to your surroundings and lifestyle (environmental factors).

This page will help you understand that ...

Genetic variants are caused by alterations in the common nucleotide sequences in the DNA of genes - specifically the change in base sequence from a mutation.

The term variant can be used to describe the result of a genetic alteration that may be benign (harmless), pathogenic (harmful), or of unknown significance.

Variation is the differences between individuals of the same species.

Variants are key to successful evolution because genotype changes (usually of the smaller type) can lead to changes in phenotype.

Human genetic variation is the genetic differences both within and among populations.

There may be multiple variants of any given gene in the human population, that is two different alleles.

The different alleles, different versions of a same gene, can lead to difference in phenotypes - the characteristics an organism displays.

A mutation may defined as any change in a DNA compared to normal that results in a rare and abnormal variant.

See the evolution page for lots more notes on variation - genetic and environmental


Summary of learning objectives and key words or phrases

Be able to explain what genetic variation is and refer to different organisms have different gene variants of their genotypes expressed as phenotypes.


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INDEX of biology notes on genetic variation, causes, formation and consequences of mutations

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