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Introduction to [email protected]

Office : NI lab

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What is DNA?

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April 2003

Human Genome Project

determined the entire DNA

sequence of a human

(3 billion letters)

What is DNA?

April 1953

Drs. James Watson and

Francis Crick determined

the structure of DNA

(double helix)

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Variations in DNA can cause visible

changes in different individuals

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Traits can be inherited!

Arlene Chambers

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Traits are inherited through genes

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http://www.biotechnologyonline.gov.au


Genes are on chromosomes

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One chromosome inherited

from each parent

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One chromosome inherited

from each parent

We have two copies of each

chromosome, and thus, two

copies of each gene

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Different versions of genes are alleles

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2 different alleles


For each gene, you might have

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2 different alleles

2 of the same allele

OR



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2 different alleles

2 of the same allele

OR



Combinations of alleles determine what traits you have

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Can you roll your tongue?

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Yes! You carry a copy ofthe dominantallele.

OR

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OR

No! You have two copies ofthe recessiveallele.

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OR


If you inherit both alleles, the dominant one is expressed.

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OR


Dominant does NOT mean more common!

If you inherit both alleles, the dominant one is expressed.

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The Genetic Wheel

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Single-gene Traits

L dimples

(dominant)

ll no dimples

(recessive)

LaughDim

ples

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L

l l

If you have laugh dimples, your genetic

wheel will look like this

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Single-gene Traits

Tongue

Rolling

T can roll tongue(dominant)

tt cannot roll tongue(recessive)

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Single-gene Traits

C left thumb on top(dominant)

cc right thumb on top(recessive)

HandClasping

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Single-gene Traits

P pinkies bend away

(dominant)

pp pinkies are straight

(recessive)

Pinkie

s

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Single-gene Traits

E ear lobe is free(dominant)

ee ear lobe is attached(recessive)

EarLobes

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Single-gene Traits

W has widows peak

(dominant)

ww no widows peak

(recessive)

WidowsPeak

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Single-gene Traits

B thumb is straight(dominant)

bb thumb bends back(recessive)

ThumbBend

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32ww bb 32

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32

There are 128 possible

combinations from the

7 traits illustrated on the

genetic wheel.

Are you the same as

anyone else?

Genetic Wheel Results

71

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32

There are 128 possible

combinations from the

7 traits illustrated on the

genetic wheel.

Are you the same as

anyone else?

Genetic Wheel Results

71

If this much genetic variation exists in traits that are visible,

imagine how different we all are in ways that we cant see!

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Some DISEASESare also caused by our

GENESand can be inherited

G t i i t ti

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Genes contain instructions

to make proteins

Information is stored in

DNARNA Synthesis

(transcription) RNA copy

Protein Synthesis

(translation)

Protein

Amino acids

Proteins do most of the work in a cell and provide much of its structure

A change in a gene may result in

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A change in a genemay result in

a change in a protein


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SAM AND TOM ATE THE HAM CCT|GAG|GAG|AAG|CTG



(DNA)

(Protein)


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Possible Change:A I

Possible Change:A C

(DNA)

(Protein)


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SAM AND TOM ATE THE HIM CCT|GAG|GCG|AAG|CTG

Possible Change:A I

Possible Change:A C

(DNA)

(Protein)

Result:Changed meaning or function


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Result:Changed meaning or function

A change in DNA is called a mutation

SAM AND TOM ATE THE HIM CCT|GAG|GCG|AAG|CTG

Possible Change:A I

Possible Change:A C

(DNA)

(Protein)

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Variations in the DNAof different individuals

can cause changes in physical appearanceor can even cause disease.

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Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPointLecture Presentations for

BiologyEighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 14

Mendel and the Gene Idea

Overview: Drawing from the Deck of Genes

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Overview: Drawing from the Deck of Genes

What genetic principles account for the passing

of traits from parents to offspring?

The blending hypothesis is the idea that

genetic material from the two parents blends

together (like blue and yellow paint blend to

make green)

Copyright 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

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The particulate hypothesis is the idea that

parents pass on discrete heritable units

(genes)

Mendel documented a particulate mechanism

through his experiments with garden peas


Fig. 14-1

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Concept 14 1: Mendel used the scientific approach

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Concept 14.1: Mendel used the scientific approachto identify two laws of inheritance

Mendel discovered the basic principles of

heredity by breeding garden peas in carefully

planned experiments


Mendels Experimental Quantitative Approach

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Mendel s Experimental, Quantitative Approach

Advantages of pea plants for genetic study:

There are many varieties with distinct heritablefeatures, or characters (such as flower color);character variants (such as purple or whiteflowers) are called traits

Mating of plants can be controlled

Each pea plant has sperm-producing organs(stamens) and egg-producing organs (carpels)

Cross-pollination (fertilization between differentplants) can be achieved by dusting one plantwith pollen from another


Fig. 14-2

TECHNIQUE

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TECHNIQUE

RESULTS

Parentalgeneration(P)

StamensCarpel

1

2

3

4

Firstfilialgener-ation

offspring(F

1)

5

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Mendel chose to track only those characters

that varied in an either-or manner

He also used varieties that were true-breeding

(plants that produce offspring of the same

variety when they self-pollinate)


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In a typical experiment, Mendel mated two

contrasting, true-breeding varieties, a process

called hybridization

The true-breeding parents are the P

generation

The hybrid offspring of the P generation are

called the F1generation

When F1individuals self-pollinate, the F2

generation is produced


The Law of Segregation

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The Law of Segregation

When Mendel crossed contrasting, true-

breeding white and purple flowered pea plants,

all of the F1hybrids were purple

When Mendel crossed the F1hybrids, many of

the F2plants had purple flowers, but some had

white

Mendel discovered a ratio of about three

to one, purple to white flowers, in the F2

generation


Fig. 14-3-1

EXPERIMENT

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EXPERIMENT

P Generation

(true-breeding

parents) Purpleflowers

Whiteflowers

Fig. 14-3-2

EXPERIMENT

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EXPERIMENT

P Generation

(true-breeding


Whiteflowers

F1Generation

(hybrids)All plants hadpurple flowers

Fig. 14-3-3

EXPERIMENT

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EXPERIMENT

P Generation

(true-breeding


Whiteflowers

F1Generation

(hybrids)All plants hadpurple flowers

F2Generation

705 purple-flowered

plants

224 white-flowered

plants

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Mendel reasoned that only the purple flower

factor was affecting flower color in the F1hybrids

Mendel called the purple flower color a dominant

trait and the white flower color a recessive trait

Mendel observed the same pattern of inheritance

in six other pea plant characters, each

represented by two traits

What Mendel called a heritable factor is what

we now call a gene


Table 14-1

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Mendels Model

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Mendel s Model

Mendel developed a hypothesis to explain

the 3:1 inheritance pattern he observed in F2

offspring

Four related concepts make up this model

These concepts can be related to what we now

know about genes and chromosomes


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The first concept is that alternative versionsof genes account for variations in inheritedcharacters

For example, the gene for flower color in pea

plants exists in two versions, one for purpleflowers and the other for white flowers

These alternative versions of a gene are now

called alleles Each gene resides at a specific locus on a

specific chromosome


Fig. 14-4

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Allele for purple flowers

Homologous

pair ofchromosomes

Locus for flower-color gene

Allele for white flowers

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The second concept is that for each characteran organism inherits two alleles, one from eachparent

Mendel made this deduction without knowing

about the role of chromosomes

The two alleles at a locus on a chromosomemay be identical, as in the true-breeding plants

of Mendels P generation Alternatively, the two alleles at a locus may

differ, as in the F1hybrids


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The third concept is that if the two alleles at

a locus differ, then one (the dominant allele)

determines the organisms appearance,

and the other (the recessive allele) has no

noticeable effect on appearance

In the flower-color example, the F1plants had

purple flowers because the allele for that trait is

dominant


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The fourth concept, now known as the law ofsegregation, states that the two alleles fora heritable character separate (segregate)during gamete formation and end up in differentgametes

Thus, an egg or a sperm gets only one of thetwo alleles that are present in the somatic cellsof an organism

This segregation of alleles corresponds to thedistribution of homologous chromosomes todifferent gametes in meiosis


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Mendels segregation model accounts for the3:1 ratio he observed in the F2generation ofhis numerous crosses

The possible combinations of sperm and egg

can be shown using a Punnett square, adiagram for predicting the results of a geneticcross between individuals of known geneticmakeup

A capital letter represents a dominant allele,and a lowercase letter represents a recessiveallele


Fig. 14-5-1

P Generation

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P Generation

Appearance:Genetic makeup:

Gametes:

Purple flowers White flowers

Fig. 14-5-2

P Generation

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P Generation


Gametes:


F1Generation

Gametes:

Genetic makeup:

Appearance: Purple flowers

1/2

1/2

Fig. 14-5-3

P Generation

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P Generation


Gametes:


F1Generation

Gametes:

Genetic makeup:

Appearance: Purple flowers

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F2Generation

Sperm

Eggs

3 1

Useful Genetic Vocabulary

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f y

An organism with two identical alleles for a

character is said to be homozygous for the

gene controlling that character

An organism that has two different alleles for a

gene is said to be heterozygous for the genecontrolling that character

Unlike homozygotes, heterozygotes are not

true-breeding


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Because of the different effects of dominant

and recessive alleles, an organisms traits do

not always reveal its genetic composition

Therefore, we distinguish between an

organisms phenotype, or physicalappearance, and its genotype, or genetic

makeup

In the example of flower color in pea plants,

PP and Ppplants have the same phenotype

(purple) but different genotypes


Fig. 14-6

Phenotype Genotype

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Purple

Purple3

Purple

1 White

(homozygous)

(homozygous)

(heterozygous)

(heterozygous)

1

1

2

genetic 1

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