dna lecture 009. gregor mendel rosalind franklinfrances crick & james watson x-ray diffraction...

DNALecture 009

Gregor Mendel

Rosalind Franklin Frances Crick & James Watson

X-ray diffraction photograph of DNA, 1953

Proposed double helix model 1953

Cell

Nucleus

DNA

What is DNA?What is DNA?• DNA, or deoxyribonucleic acid, is the genetic

instruction set.

• It is composed of a linear sequence of units called nucleotides.

• There are four different kinds of nucleotides (designated by the letters A, G, C, & T; sometimes called “bases”).

• An individual DNA strand (or chromosome) may consist of 100,000’s of nucleotides.

• The sequence of the nucleotides of a DNA strand determines the genetic code.

Polymers made up of individual nucleotides

Nucleotides contain• Phosphate group• Five carbon sugar• Ring shaped nitrogen base

DNA contains information for almost all cell activities

Nitrogen Base

adenine guanine

Purines

cytosine thymine

Pyrimidines

Deoxyribose

DNA is Double StrandedDNA is Double Stranded

Base Pairing in DNA

Base Pairing in DNA

ChromosomesChromosomes

Chromosomes Come in PairsChromosomes Come in Pairs

Beliefs about Heredity

Fig. 1. De la propagation du genre humain, ou manuel indispensable pour ceux qui veulent avoir de beaux enfants de l’un ou l’autre sexe (Paris, Year VII). Image courtesy of the Bibliothèque Interuniversitaire de Médecine, Paris.

Homunculus

How is “heredity passed on:

Spermist vs Ovists

Spermist conception of a

human sperm

Homunculus

Leeuwenhoek’s black male and white female rabbit experiments: spermist “proof”

Darwin

What he got right. What he got wrong.

• Acquired characteristics

Ex. Blind cave animals

• Sex. Repro.- gemmules from all over body are packed in sperm and egg

• Blended inheritance

• Likes produce likes• Change can be

permanent• There is no limit to

cumulative change

Mendel’s Three Principles

• Dominance

• Segregation

• Independent Assortment

The foundation of “classical” scienceThe foundation of “classical” science

(1822-1884)

• Genes- genetic material on a chromosome that codes for a specific trait

• Genotype- the genetic makeup of the organism

• Phenotype- the expressed trait• Allel- an alternative form of a

gene

Genetic Definitions

Dominance Mechanism

• Two alleles are carried for each trait

• In true-breeding individuals, both alleles are the same (homozygous).

• Hybrids, on the other hand, have one of each kind of allele (heterozygous).

• One trait is dominant, the other trait is recessive

Dominance

• Traits of both parents inherited, but one shows over the other

• Traits are not blended

Segregation

• Half the gametes (egg or sperm) will carry the traits of one parent and half the traits for the other parent

Pairs of alleles are separated (=segregated) during meiosisPairs of alleles are separated (=segregated) during meiosis

Two different parental characteristics will be inherited independently of one another during gamete formation.

Independent Assortment

Example: flower color and leaf shape

Complexities

• Multiple genes for one trait

• Example: eye color

• Blended traits (“incomplete dominance”)

• Influence of the environment (UV, smoking, alcoholism)

Complexities

• Co-dominance-neither allele is recessive and the phenotypes of both alleles are expressed.

• Blood types- AB (not O); sickle cell anemia

heterochromia

Disorders

Down’s Syndrome (chrom 21)

Huntington’s (chrom 4)

Alzheimer’s (chrom 1, 10, 14, 19, 21)

Genetic Information

Genes are traits

“Eye color”

Ear lobe connectedness

Genes produce proteins

Enzymes are proteins

Homologous Chromosomes

allele: specific traitallele: specific trait

gene: locationgene: location

Allele Example

Gene = “eye color”

Alleles

brownbluegreenlavender

Allele Examples

appearance

eye color:homozygous

Allele Examples

appearance

eye color:heterozygous,brown dominant over blue

Genotype vs Phenotype

homozygous(dominant)

heterozygous

homozygous(recessive)

genotype phenotype

appearanceappearance

Phaner = visible

Punnett Square

If male & female are heterozygous for eye color

X

brown: 3/4 offspringblue: 1/4 offspring

male

female

Sickle Cell AnemiaEach parent carries one gene for sickle cell

S s

S sX

S

s

sS

S

S

S

s

s

S

s

s

Possible genotypes: 1SS 2Ss 1ss

Possible phenotypes:no sickle cell sickle cell

Autosomes and Sex Chromosomes

Red-Green Color BlindnessSex-linked trait

XC Y

XC Xc

X

XC

Xc

YXC

XC

XC

XC

Y

Xc

XC

Y

Xc

Normal male

Normal female recessive gene

Possible outcomes: XCXC XCXc XCY XcYNormal female

Normal Female(carrier)

Normal male

Color-blind male

E unconnected earlobee connected earlobeE unconnected earlobee connected earlobe

alleleallele genegene

P EE x ee

gametes E e

F1 Ee

unconnected

connected

F1 Ee x Ee

gametes1/2 E 1/2 e1/2 E 1/2 e

E

e

E e

EE Ee

Ee ee

F2 1 EE 2 Ee 1 ee

PunnettSquare

Genotypes Phenotypes

Experiment to determinedominant vs. recessiveExperiment to determinedominant vs. recessive

Genetic Sleuthing

My eye color phenotype is brown.

What is my genotype?

Where Does Genetic Diversity Come From?

Where Does Genetic Diversity Come From?

• MutationMutation• Chromosomal AberrationsChromosomal Aberrations• Genetic Recombination Genetic Recombination

(e.g., from sexual (e.g., from sexual reproduction)reproduction)

mutationmutation

Sickle Cell Mutation

CTG ACT CCT GAG GAG AAG TCTLeu Thr Pro Glu Glu Lys Ser

CTG ACT CCT GAG GTG AAG TCTLeu Thr Pro Glu Val Lys Ser

NORMAL Hb

SICKLE CELL

Difference between Meiosis and MitosisDifference between Meiosis and Mitosis

Meiosis IMeiosis I

Interphase Prophase I Metaphase I Anaphase I Telephase I

Crossing Over of Nonsister Chromatids between Homologous Chromosomes

Meiosis IIMeiosis II

Prophase II Metaphase II Anaphase II Telephase II

Genetic Testing

Genetic Testing

• Predisposition to disease• Alzheimer's case (Feb. 2002)• Amniocentesis & Chorionic villa• Family history• >35 years old• Donor match• Paternity• Forensics

Gel electrophoresis

• PCR way of copying specific DNA fragments from small sample DNA material "molecular photocopying"

• It’s fast, inexpensive and simple

Polymerase Chain Reaction

Genetic Testing

Paternity Test $99

$299, looks at specific diseases

23 and me

Genetic TestingWould you want to know?

• Ethical concerns• Cost• Insurance companies

Tongue Roller

R = Tongue Rollerr = Unable to Roll Tongue

Widow’s Peak

W = Widows Peakw = Lack of Widow’s Peak

Free Ear Lobe Attached Ear Lobe

E = Free Ear Lobee = Attached Ear Lobe

Hitchhiker’s Thumb

Hi = Straight Thumbhi = Hitchhiker’s Thumb

Bent Little Finger

Bf = Bent Little Fingerbf = Straight Little Finger

Mid-digital Hair

M = Mid-Digital Hairm = Absence of Mid-Digital Hair

Dimples

D = Dimplesd = Absence of Dimples

Short Hallux

Ha = Short Halluxha = Long Hallux

Short Index Finger

Ss = Short Index FingerS1 = Long Index Finger

*Sex-Influenced Trait*Sex-Influenced Trait

http://www.youtube.com/watch?v=gCPuHzbb5hA