Human Genetic Traits

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

develop new treatmentsdevelop new treatments• Organ donor matchesOrgan donor matches• PaternityPaternity• ForensicsForensics• EvolutionEvolution

Genes- genetic material on a chromosome that codes for a specific traitGenotype- the genetic makeup of the organism for a trait

Phenotype- the physically expressed trait (what you look like)

Allele- alternative forms of a gene (comes in dominant & recessive)

Gregor Mendel’s Law of Complete Dominance

• 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).• The dominant allele form covers the

recessive allele form

Genetic InformationGenes produce proteins

Proteins (brown eye pigment, hair shape)

Trait (how you look; phenotype)

Homologous Chromosomes-pair of chromosomes that contain the same genes (one from mom/one dad)

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Allele ExampleGene = “eye color”

Alleles (gene forms possible)

brownbluegreenlavender

Allele Examples

appearance

eye color:Homozygous (both alleles same)

Allele Examples

appearance

eye color:Heterozygous (Bb),Two different alleles (brown dominant over blue)

Genotype vs Phenotype

homozygous(dominant)

heterozygous

homozygous(recessive)

genotype phenotype

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Punnett SquareIf 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

PP

Pp

pP

pp

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 HbSX

HbS

HbS

HbAHbA

HbA

HbS

HbA

HbS

HbS

HbA

HbS

HbA

all offspring are carriers of sickle cell trait

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

Dominance

Most traits show complete dominance

Blending unexpected

E unconnected earlobee connected earlobe

allele gene

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

P

F1

F2

EE, ee

Ee

EE, 2 Ee, ee

50%

100%

75%

1:1

1:1

1:1

generation genotypes unconnected E:e

Basis of the Castle-Hardy-Weinberg Law

phenotypes

ratio of alleles in the population

Genotypes Phenotypes

Experiment to determinedominant vs. recessive

Genetic Sleuthing

My eye color phenotype is brown.

What is my genotype?

Pedigree phenotypes

infer genotypes

Alternative:look directly at the DNA

Complexities

Multiple genes for one trait

Example: eye color

Blended traits (“incomplete dominance”)

Influence of the environment

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 PeakWidow’s Peak

W = Widows Peakw = Lack of Widow’s Peak

Free Ear LobeFree Ear Lobe Attached Ear Lobe

E = Free Ear Lobee = Attached Ear Lobe

Hitchhiker’s ThumbHitchhiker’s Thumb

Hi = Straight Thumbhi = Hitchhiker’s Thumb

Bent Little FingerBent Little Finger

Bf = Bent Little Fingerbf = Straight Little Finger

Mid-digital HairMid-digital Hair

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

DimplesDimples

D = Dimplesd = Absence of Dimples

Short HalluxShort Hallux

Ha = Short Halluxha = Long Hallux

Short Index FingerShort Index Finger

Ss = Short Index FingerS1 = Long Index Finger

*Sex-Influenced Trait*Sex-Influenced Trait

Presentation created by J. Kenyon

Pttttthhhhhhhtttt!

Kiss me, you fool.

Genetic Testing

Would you want to know?

• Ethical concerns• Cost• Insurance companies

see GATTACA