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Transcript
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 crosses
USING SNAPDRAGONS
Multiple Alleles: some genes have
MORE THAN TWO ALLELES
Understand: A, B, O BLOOD TYPING
Phenotype
Type A
Type B
Type O
Type AB
Genotype
Understand: A, B, O BLOOD TYPING
Phenotype
Genotype
Type A
Type B
Type O
Type AB
AA or AO
Understand: A, B, O BLOOD TYPING
Phenotype
Genotype
Type A
Type B
Type O
Type AB
AA or AO
BB or BO
Understand: A, B, O BLOOD TYPING
Phenotype
Genotype
Type A
Type B
Type O
Type AB
AA or AO
BB or BO
OO
Understand: A, B, O BLOOD TYPING
Phenotype
Genotype
Type A
Type B
Type O
Type AB
AA or AO
BB or BO
OO
AB
Codominance: both alleles
EXPRESSED/DETECTED (e.g. AB)
Nature/Nurture: environment
INFLUENCES PHENOTYPE
Morgan, Flies, Sex Linkage - 1910s
Genes 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 F1
P Gametes: red/female X white/male
Let’s Show the P X P Cross to F1
P Gametes: red/female X white/male
XR
Xr
Y
XR
Xr
XR
XR Xr
XR
XR Xr
Y
XRY
XRY
Predictions: 50% RED FEMALES
50% RED MALES
Let’s Show the F1 X F1 Cross to F2
F1 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
Y
Xr
XR
XR
XR XR
Xr
Xr XR
Y
XR Y
Xr Y
Predictions: 50% RED FEMALES
25% RED MALES; 25% WHITE MALES
Is this consistent with observations?
Some Human Genetics
Pedigree Analysis: MASTER ALL RULES
Make 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