Mutation and Genetic Disorders: visual lesson, ISC Class 12 Biology

Lesson

Mutation and genetic disorders

Part 2 — changes in DNA and chromosomes, and the disorders they cause.

In this lesson you will

Distinguish spontaneous and induced mutations and kinds of point mutation
Describe the Mendelian disorders phenylketonuria, thalassaemia, colour blindness and sickle-cell anaemia
Describe Down’s, Klinefelter’s and Turner’s syndromes

Concept

Spontaneous and induced mutations

Mutations arise spontaneously (from errors in DNA replication or natural causes) or are induced by mutagens.

Table of spontaneous and induced mutations
Type	Cause	Example
Spontaneous	Natural errors in replication or repair	Occur at a low natural rate
Induced	Physical mutagens	UV radiation, X-rays and other ionising radiation
Induced	Chemical mutagens	Certain chemicals that alter bases

Diagram

Gene (point) mutations

A point mutation changes a single base pair. In a substitution, one base replaces another: a transition swaps a purine for a purine or a pyrimidine for a pyrimidine; a transversion swaps a purine for a pyrimidine or the reverse. Insertion or deletion of bases causes a frameshift.

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