MutationsMutations

A change in the DNA structure

There are two categories of mutations

Gene MutationGene Mutation

1. A change in the DNA2. A change in the sequence of nitrogenous bases3. Mutagens can cause the change

What’s Happened to the DNA?

Both had one basesubstituted for another.

How was the DNA changed in these examples?

Comparing Gene MutationsComparing Gene Mutations

What can a changed protein do What can a changed protein do to an organism?to an organism?

Additional Ways DNA Mutated

Mutation: FrameshiftMutation: Frameshift

1. Changes the reading of the DNA2. Results in the formations of new mRNA

codons leading to a change in the polypeptide structure

3. Types are: insertion or deletion

Identify the category and Identify the category and type of mutation affecting type of mutation affecting this strand of DNAthis strand of DNA

1. AUGCCGUACCUUAUGGCUG 2. AUGC_GUACCUUAUGGCUG

1. AUGCACGUACCU…

2. AUGCGUACCUUA…

Mutated Strand reads:

Notice that the reading of the DNA will be shifted.Hence, these are frameshift mutations. The mRNAwhen translated will produce a different amino acidsequence.

A

Human Red Blood CellsHuman Red Blood Cells

1. Contain the protein, hemoglobin (Hb)2. O2 binds to Hb = oxygenated blood3. Red Blood Cells are doughnut shaped

cells

Sickle Cell AnemiaSickle Cell Anemia

1. RBC’s are “sickled shape”2. Hemoglobin protein has been altered -shape

has changed3. Cells stick to each other; Oxygen binding

capacity has been altered.4. Circulatory problems arise

Why?

Normal Hemoglobin:

Valine-Histidine-Leucine-Threonine-Proline-Glutamic Acid-Glutamic Acid

Abnormal Hemoglobin:

Valine-Histidine-LeucineThreonine-Proline-Valine-Glutamic Acid

Sickle Cell Anemia had change in the polypeptide chain:Glutamic acid is changed to Valine

Why??????? How can this be??????????????

Change Affects CodonChange Affects Codon

Normal HbDNA: CTTmRNA: GAA Amino Acid: Glutamic acid

…Proline-Glutamic Acid-Glutamic Acid…

Sickle HbDNA: CATmRNA: GUAAmino Acid: Valine

…Proline-Valine-Glutamic Acid…

What type of mutation caused the altered hemoglobin?A Point Mutation – base substitution

This is normal structureThis is normal structure

Codon Change Affects Protein Codon Change Affects Protein StructureStructure

Chromosomal MutationChromosomal MutationAlterations in chromosome number and/or structure

Figure 8.23A, B

Deletion

Duplication

Inversion

Homologouschromosomes

Reciprocaltranslocatio

n

Nonhomologouschromosomes

Str

uctu

ral C

hrom

osom

al

Mut

atio

ns

Read 8.22, 8.23, 8.24

Chromosome Number for a Species

Species # of chromosomes

Species# of chromosomes

Fruit fly 8 Human 46

Rye 14 Ape 48

Guinea Pig 16 Sheep 54

Dove 16 Horse 64

Snail 24 Chicken 78

Earthworm 32 Carp 104

Pig 40 Butterflies ~380

Wheat 42 Fern ~1200

Does the embryo have the correct Does the embryo have the correct number of chromosomes?number of chromosomes?

Eggcell

Spermcell

Chromosome Number Mutation

zygote

Does the zygote have the correct number ofchromosomes?

LE 13-10LE 13-10

Key

Maternal set ofchromosomes

Paternal set ofchromosomes

Possibility 1 Possibility 2

Combination 2Combination 1 Combination 3 Combination 4

Daughtercells

Metaphase II

Two equally probablearrangements ofchromosomes at

metaphase I

LE 13-7LE 13-7

Homologous pairof chromosomesin diploid parent cell

Interphase

Homologous pair of replicated chromosomes

Chromosomesreplicate

Meiosis I

Diploid cell withreplicatedchromosomes

Sisterchromatids

Meiosis II

Homologouschromosomesseparate

Sister chromatidsseparate

Haploid cells withreplicated chromosomes

Haploid cells with unreplicated chromosomes

A A karyotypekaryotype::a photographic inventory of an a photographic inventory of an individual’s chromosomesindividual’s chromosomes

To study human chromosomes microscopically, researchers stain and display them as a karyotype◦A karyotype usually shows 22 pairs of autosomes

and one pair of sex chromosomes

Additional information 8.19-20

Preparation of a karyotype

Figure 8.19

Blood culture

1

Centrifuge

Packed redAnd white blood cells

Fluid

2

Hypotonic solution

3

Fixative

WhiteBloodcells

Stain

4 5

Centromere

Sisterchromatids

Pair of homologouschromosomes

This karyotype shows three number 21 chromosomes

An extra copy of chromosome 21 causes Down syndrome

Let’s look at this Karyotype

Figure 8.20A, B

The chance of having a Down syndrome child goes up with maternal age…why?

Figure 8.20C

Beginning the KaryotypeBeginning the Karyotype

Karyotype LabKaryotype Lab

1. You will simulate the karyotyping task.2. You will create a karyotype and determine the

gender and developmental status of the baby.3. You must carefully cut out all chromosomes

and correctly match them up by:

a. Size of chromosomeb. Location of centromerec. Banding pattern on chromosome

Finished KaryotypeFinished Karyotype

Another KaryotypeAnother Karyotype Male or Female?