mutations · 2020-05-06 · all point mutations are a results of substitution( one nucleotide...

Mutations • Mutations are changes of an individual’s

genetic information.

Can occur in

Somatic cells (Body cells)

◼Cannot be inherited

◼ can lead to cancer- like skin cancer

Gametes (Sex cells- egg and sperm)

◼Can be inherited

◼These are more notable, because they introduce genetic diversity and possible phenotypic changes in the population

• Spontaneous mutations in somatic cells cause tumors, diseases, and cancer, but are not passed on.

• Spontaneous mutations in germ cells affect the offspring and future generations.

Causes of mutation

1. Spontaneous (natural)– Spontaneous mutations can occur

during genetic processes • Such as DNA replication, recombination, or repair

• Proof-reading mechanisms prevent most mutation from happening in DNA Replication, but they aren’t so good during protein synthesis

2. Induced (caused by mutagens)

– Physical Mutagens:

• Some forms of electromagnetic radiation (X-rays and Ultra Violetlight)

– Chemical Mutagens:

• Pesticides

• Tobacco smoke

• Environmental pollutants

6

Types of mutations

– Gene Mutations • Changes in a single base pair of a gene, also called point mutations

-Chromosomal Mutations

• Involves a change in the structure

• Or the number of chromosomes

Gene Mutations: Substitution

Gene Mutations 1) Point Mutations: occur at a single point. Change

in ONE letter (base) in the DNA.

All point mutations are a results of SUBSTITUTION( one nucleotide replaces another)!!!!

-Silent mutations: have no effect on the amino acid produced.

-Missense mutations: still code for an amino acid, but not the correct amino acid.

- Nonsense mutations: change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Gene Mutations 2) Frameshift Mutations

Gene Mutations 2) Frameshift Mutations: are mutations caused by insertion or deletion of the bases, which results in a shift of the “ reading frame” of the genetic message.

This type of mutation can change every amino acid that follow the point of the mutation and can alter a protein. Most dangerous type of mutation

Insertions and Deletions• Insertions: addition of nucleotide pairs in a gene

• Deletions: losses of nucleotide pairs in a gene

• Insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation

© 2011 Pearson Education, Inc.

Chromosomal Mutations • Changes to the number of chromosomes

• Changes to the structure of the chromosome

• Four types exist:

A B C D E F G HDeletion

A B C E G HF

A B C D E F G HDuplication

A B C B D EC F G H

A

A

M N O P Q R

B C D E F G H

B C D E F G HInversion

translocation

A B P Q R

M N O C D E F G H

A D C B E F HG

• Deletion: removes a chromosomal segment.

• Duplication: repeats a segment.

• Inversion:reverses a segment within a chromosome.

• Translocation: moves a segment from one chromosome to another, nonhomologous one.

The “good”, the “bad”, and the “indifferent”

• Based on their effects on fitness, mutations can be divided into three broad categories:

1. the ‘good’ or advantageous that increase fitness,

2. the ‘bad’ or deleterious that decrease it

3. and the ‘indifferent’ or neutral that are not affected by selection because their effects are too small.

Example: Point Substitution Mutation

Pedigree of Sickle-Cell Mutation

hh HH

HH

Hh HhHhHhHh

HhHhhh

What is a mutation?

A. the specific sequence of bases in a molecule of DNA

B. the perfect replication of a DNA molecule

C. the process by which a molecule of DNA makes a copy of itself.

D. a change in the genetic material.

Which type of mutation occurs when one base in DNA is replaced

by another?A. frameshift mutation

B. point mutation

C. chromosomal mutation

D. nondisjunction

1.

2.

3.

4.

Which type of mutations is shown?

A. insertion

B. substitution

C. duplication

D. translocation

A. insertion

B. substitution

C. duplication

D. translocation

Which type of mutations is shown?

What is the cause of the mutation shown in the

karyotype below?A. inversion

B. frameshift

C. nondisjuntion

D. translocation

Consider the following statements:

• I. Mutations always have a negative effect on an individual.

• II. Mutations can have a positive effect on an individual.• III. Mutations can have no effect on an individual.• IV. Mutations can have a negative effect on an individual.

Which statement above is/are true?

A. I onlyB. I and II onlyC. II, III, and IV onlyD. I, II, III, IV