Beyond Mendel, Sex Linkage, Human Genetics

Mendel studied only simple inheritance WELL-DEFINED, DOM/REC

Non-Mendelian Inheritance Patterns

Incomplete Dominance: INTERMEDIATE HET (Rr = PINK)

Homework - perform P, F1, F2 crossesUSING SNAPDRAGONS

Multiple Alleles: some genes have MORE THAN TWO ALLELES

Understand: A, B, O BLOOD TYPING

Phenotype Genotype

Type A

Type B

Type O

Type AB

Understand: A, B, O BLOOD TYPING

Phenotype Genotype

Type A AA or AO

Type B

Type O

Type AB

Understand: A, B, O BLOOD TYPING

Phenotype Genotype

Type A AA or AO

Type B BB or BO

Type O

Type AB

Understand: A, B, O BLOOD TYPING

Phenotype Genotype

Type A AA or AO

Type B BB or BO

Type O OO

Type AB

Understand: A, B, O BLOOD TYPING

Phenotype Genotype

Type A AA or AO

Type B BB or BO

Type O OO

Type AB AB

Codominance: both alleles EXPRESSED/DETECTED (e.g. AB)

Nature/Nurture: environment INFLUENCES PHENOTYPE

Morgan, Flies, Sex Linkage - 1910sGenes Shown on Chromosomes

By now, scientists could see CHROMOSOMES AND MEIOSIS

Drosophila melanogaster: FRUIT FLY

Autosomes (flies have 3 pairs): NOT GENDER DETERMINING

Sex Chromosomes (flies have 1 pair): GENDER DETERMINING, X AND Y

Wild Type: DOMINANT (e.g. RED EYES)Mutant: RECESSIVE (e.g. WHITE EYES)

Cross 1: True Parentals RED FEMALE X WHITE MALE

At first, Morgan assumed eye color was autosomal/Mendelian: F1 = Rr, F2 = 3:1

But F2 was half unexpected: where all females red, MALES 50:50 RED:WHITE

Morgan formed a new hypothesis: GENE FOR EYE COLOR ONLY ON X

Rule Three: For sex linkage, show alleles on X’s (e.g. XR) - none on Y’s. Prediction

must include gender. Use Mendelian letters for genes - not Morgan’s (+/-)

naming system.

Let’s Show the P X P Cross to F1P Gametes: red/female X white/male

Let’s Show the P X P Cross to F1P Gametes: red/female X white/male

XR XR

Xr

Y

Predictions: 50% RED FEMALES50% RED MALES

XR XR

Xr XR Xr XR Xr

Y XRY XRY

Let’s Show the F1 X F1 Cross to F2F1 Gametes: Het/Female X Red/Male

Let’s Show the F1 X F1 Cross to F2 F1 Gametes: het/female X red/male

XR Xr

XR

Y

Predictions: 50% RED FEMALES25% RED MALES; 25% WHITE MALES

Is this consistent with observations?

XR Xr

XR XR XR Xr XR

Y XR Y Xr Y

Some Human Genetics

Pedigree Analysis: MASTER ALL RULESMake sure you define shaded trait OR write phenotype below each person.

The following FYI traits are NOT on exam.

Gene Dom Allele Rec Allele

Chin Dimple + -

Free Ear Lobes + -

Widow’s Peak + -

Left Thumb Top + -

Iris Pigmentation + -

Sickle Cell Anemia

• REC AUTOSOMAL - SOME INC DOM

• African Americans - 1/400

• Carriers - 1/10

• Defective HEMOGLOBIN CHAIN

• Hom/Rec = LETHAL; Het = WEAK

Protects against tropical malaria - thus, selected among many equatorial races.

Cystic Fibrosis

• REC AUTOSOMAL

• European Caucasions - 1/2500

• Carriers - 1/24

• Defective Na/Cl TRANSPORTER

• High levels of secreted SALT, MUCUS

• If untreated, LETHAL BY AGE 5

Huntington Disease

• DOM AUTOSOMAL

• Unstable - EXPANDING MUTATION

• 30,000 HAVE, 150,000 AT RISK

• Gene function unclear

• Degenerative BRAIN FUNCTION

• No good treatment - LETHAL 35-45

Duchenne Muscular Dystrophy

• REC X-LINKED

• Male Bias - 1/3500

• Defective anchoring protein between…

• CYTOSKELETON AND MEMBRANE

• Degenerative MUSCLE DISEASE

• No good treatment - LETHAL 20-25