Lecture 29

Inheritance

Importance of geneticsImportance of genetics• Understanding hereditary diseases and to Understanding hereditary diseases and to

develop new treatmentsdevelop new treatments• Donor matchesDonor matches• PaternityPaternity• ForensicsForensics• EvolutionEvolution

Genetic TestingWould you want to know?

• Ethical concerns• Cost• Insurance companies

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

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

• 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

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”

Mendel’s Three Principles

• Dominance

• Segregation

• Independent Assortment

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

(1822-1884)

Dominance

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

• Traits are not blended

Dominance Mechanism

• Two alleles are carried for each trait

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

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

• One trait is dominant, the other trait is recessive

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

Genetic Information

Genes are traits

“Eye color”

Ear lobe connectedness

Genes produce proteins

Enzymes are proteins

Homologous Chromosomes

gene: location

allele: specific trait

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

Punnett Square

If male & female are heterozygous for eye color

X

brown: 3/4 offspringblue: 1/4 offspring

male

female

PKUEach parent carries one gene for PKU.

P p

P pX

P

p

pP

P

P

P

p

p

P

p

p

Possible genotypes: 1PP 2Pp 1pp

Possible phenotypes:no PKU PKU

Compare this to what would have happened if one parent was homozygous for sickle cell.

HbA HbA

HbS HbS

X

HbS

HbS

HbAHbA

HbA

HbS

HbA

HbS

HbS

HbA

HbS

HbA

all offspring are carriers of sickle cell trait

Where Does Genetic Diversity Come From?

Where Does Genetic Diversity Come From?

• Mutation• Chromosomal Aberrations• Genetic Recombination

(e.g., from sexual reproduction)

• Mutation• Chromosomal Aberrations• Genetic Recombination

(e.g., from sexual 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

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?

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)

Tongue RollerTongue 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 FingerBent 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