DNA: The Blueprints For Life 1

Chromosomes Recall: Gene Chromosome A segment of DNA that codes for 1 polypeptide. Chromosome A long strand of DNA tightly coiled to form a rod-shaped structure. May contain hundreds of genes. Humans have 46 chromosomes arranged in 23 homologous pairs Gene 1 Gene 2 2

10.2 Genetic Changes Mutation ANY change in DNA Most are harmful! A few turn out to be beneficial & provide the variation upon which natural selection acts to cause evolution. 3

Mutagens Examples: Environmental factors that damage DNA (cause mutations) Examples: Viruses Asbestos Cigarrette tar Radiation (UV, x-rays, etc) Chemicals Ames test Procedure used by researchers to identify mutagenic substances.

There are 2 Categories of Mutations: Point mutation Involves a change in 1 base pair Chromosome mutation Involves a change in MANY base pairs or even the loss or gain of a entire chromosome. * Affects many genes (therefore, many proteins) 5

There are 2 Types of Point Mutations: Substitution mutation One base is substituted for another: Ex: THE CAT ATE THE RAT THE MAT ATE THE RAT 6

Affects only 1 codon which may or may not affect the amino acid Substitution Affects only 1 codon which may or may not affect the amino acid “Silent” RNA 7

A single change in amino acid sequence can have disastrous effects: Sickle-cell Anemia 8

Sickle Cell Anemia

Sickle Cell Anemia Animation

Frameshift Ex: THE CAT ATE THE RAT Addition: THE TCA TAT ETH ERA T Results from the addition or subtraction of a single base pair. Ex: THE CAT ATE THE RAT Addition: THE TCA TAT ETH ERA T Subtraction: THE ATA TET HER AT C 11

* Affects every codon, therefore, every amino acid after the change!! Frameshift * Affects every codon, therefore, every amino acid after the change!! 12

There are 5 Types of Chromosome mutations 1. Deletion A piece of a chromosome breaks off and all the information on that piece is lost 13

Chromosome mutations Inversion A piece of a chromosome breaks off, flips over, and reattaches in reverse (Segment will be read backwards) 14

Chromosome mutations Translocation A broken piece attaches to a nonhomologous (different) chromosome 15

Chromosome mutations Insertion/ Duplication A broken piece attaches to a homologous (matching) chromosome. 16

Chromosome mutations Nondisjunction Occurs when a pair of homologous chromosomes fail to separate during meiosis (gamete production) 17

Nondisjunction One gamete gets an extra chromosome. If fertilized the resulting zygote will have three chromosomes instead of a pair - trisomy Ex: Trisomy 21 or Down’s syndrome One gamete is short a chromosome. If fertilized, the zygote will have only 1 chromosome instead of a pair- monosomy Ex: Turner’s Syndrome