12.4 MUTATIONS

I. Kinds of MutationsMutations are changes in the

genetic material A. Gene mutations – changes in a

single gene 1. point mutation – changes in

one or a few nucleotides

3 TYPES OF MUTATIONS

a. substitution – one base is changed to another

* usually affects only one amino acid

b. insertion or deletion – a base is added or removed from DNA sequence

FRAMESHIFT MUTATIONS

i. Insertion & Deletion are known as frameshift mutations because the reading frame of the genetic message is shifted when a base is added or removed

ii. may change every amino acid that follows the point of mutation

iii. can alter a protein so much that it can not function

Substitution InsertionDeletion

Gene Mutations: Substitution, Insertion, and Deletion

CHROMOSOMAL MUTATIONS

B. Chromosomal mutation – changes in the number or structure of chromosomes

1. Four types of chromosomal mutations:

a. Deletion – all or part of chromosome is lost

CHROMOSOMAL MUTATIONS

b. Duplication – produces extra copies of parts of a chromosome

c. Inversion – reverses the direction of parts of chromosomes

d. Translocation – part of one chromosome breaks off and attaches another chromosome

Deletion

Duplication

Inversion

Translocation

 Chromosomal Mutations

MUTATIONS

II. Significance of Mutations A. many mutations are neutral and

have little or no effect on expression of a gene or function of protein

1. mutations allow genetic diversity in a species

MUTATIONS

B. harmful mutations are the causes of many genetic disorders or even cancer

C. beneficial mutations produce proteins that can be helpful in different environments

MUTATIONSMeiosis is a process where gametes

(sex Cells) half the number of chromosomes.

a. Nondisjunction occurs when a complete set of chromosomes fails to separate during Meiosis.

b. gametes (sperm & egg) may produce triploid (3N) or tetraploid (4N) organisms

What happens if nondisjunction occurs?

• The gamete will die or result in conditions known as trisomy or monosomy.

• Trisomy - a person has more than 2 copies of the same chromosome.

• Monosomy – a person only has one copy of a chromosome.

How can you tell that?

• Take a picture of the chromosomes• This is known as a karyotype.

Normal Female Karyotype

Normal Male Karyotype

Abnormal Karyotype-Trisomy #21

Down’s Syndrome

Abnormal Karyotype – Monosomy of the X chromosome

Turner’s Syndrome