1. GENETIC DISORDERS 1: Single Gene Disorders*
GENETIC DISORDERS 1: Single Gene Disorders
* Take notes from all pages with an asterisk in the corner – you can just read the other pages without taking notes.

3. Autosomes vs. Sex Chromosomes*
Autosomes vs. Sex Chromosomes
All chromosomes have hundreds of different genes on them
Some alleles cause severe disorders
The sex chromosomes are the final pair of chromosomes (pair #23 in humans)
Autosomes are the other 22 pairs
A karyotype is a photo of the chromosomes in a cell

4. Human Karyotype
All
others are Autosomes!!
Sex
Chromo-somes

5. * Autosomal Disorders Genes for these disorders are on the autosomes
They follow Mendel’s Laws
Examples-
Achondroplasia (dwarfism)
Huntington’s Disease

6. Achondroplasia
AKA, Dwarfism

7. “A” = without “chondro” = cartilage “plasia” = growth*
Achondroplasia
“A” = without “chondro” = cartilage “plasia” = growth
Caused by a dominant allele
Heterozygous individuals receive the dwarfism phenotype (Aa)
Homozygous dominant (dwarf) individuals die (lethal allele) (AA)
Homozygous recessive individuals grow to full height as adults (aa)

8. Achondroplasia
Dorothy meets and marries a dwarf from the “Lollipop Guild”
Can they have a normal child?
If they can, what are the odds that they will?

9. Achondroplasia A a Aa aa A a Dorothy = Standard Adult = aa
Lollipop = Dwarf = Aa A a Aa aa A a
Phenotype ratio= 1:1
Genotype ratio= 1:1
Final Answer: Yes, they have a 50% chance of having a child that grows to standard height, and a 50% chance of having a dwarf.

10. Achondroplasia
A member of the “Lullaby League” marries a member of the “Lollipop Guild”
Can they have a child of normal height?
If they can, what are the odds that they will?

11. Achondroplasia A a AA Aa aa A a Lullaby = Dwarf = Aa
Lollipop = Dwarf = Aa A a AA Aa aa A a
Phenotype ratio= 1:2:1
Genotype ratio= 1:2:1
Final Answer: Yes, they have a 25% chance of having a child that grows to standard height, a 50% chance of having a dwarf, and a 25% chance of having a child that will not survie.

12. * Huntington’s Disease Lethal autosomal disorder
Dominant allele on the fourth chromosome – so if you get the gene, you get the disease 
Degenerative disease of the central nervous system; causes involuntary dancelike movements
Strikes at age
Normal Brain
Brains with Huntington’s Disease

13. Huntington’s Disease, aka Huntington’s Chorea (Why is it similar to the word choreography?)
Normal Brain has small Ventricles (fluid-filled cavities) and large Striatum
Diseased Brain has large Ventricles (fluid-filled cavities) and small Striatum

14. Huntington’s Disease H = Huntington’s h = normal
Cross a heterozygous male with an unafflicted female.
What are the chances their children will develop Huntington’s disease?

15. Huntington’s Disease H h Hh hh Heterozygous male (Hh) crossed with
Unafflicted female (hh) H h Hh hh
Their children have a 50/50 chance of developing Huntington’s Disease
If this is a dominant lethal allele, why is it still in existence?
Because the trait does not kill people until after they have lived long enough to have children!
CAT scan of brain with
Huntington’s Disease

16. * Sex- Linked Disorders
These traits are controlled by alleles on the sex chromosomes
The traits they control are NOT related to gender
Both males and females can inherit these disorders, with modifications to Mendel’s Laws
Not related to gender, but often more common in males – why?
Examples-
Hemophilia (bleeding disorder – blood won’t clot)
Muscular dystrophy (muscles wear down over time)
Color blindness (can’t tell red from green)

17. * Hemophilia Recessive allele on the X chromosome
This disorder prevents blood from clotting – so they can easily bleed to death from a cut or a bruise
1: 10,000 ♂ versus
1 : 100,000,000 ♀

18. Hemophilia Genotypes & Phenotypes*
Hemophilia Genotypes & Phenotypes
X H = normal blood clotting
X h = hemophilia
X H X H = Normal Female
X H X h = Carrier Female
X h X h = Female Hemophiliac
X HY = Normal Male
X hY = Male Hemophiliac
Notice that both the X and the Y chromosomes are shown in the genotypes!
But why don’t the Ys have the h subscript like the Xs?
Because the gene is only on the X chromosome, and is missing from the Y!
Carrier = Does not have the trait, but can give it to their children (must be heterozygous)

19. Sex-Linked Punnett: Hemophilia*
Sex-Linked Punnett: Hemophilia
A heterozygous female marries a normal male. Describe the percent of sons and daughters with hemophilia.
Mom
X H X H
X H X h
X H
X HY
X hY
X H
X h Y
Dad
Final Answer
50% of the daughters are normal =
50% of the daughters are carriers =
50% of the sons are normal =
50% of the sons are hemophiliacs =

20. Muscular Dystrophy Recessive allele on the X chromosome
1: 10,000 ♂ versus
1 : 100,000,000 ♀
X D = normal
X d = abnormal

21. *
Muscular Dystrophy
Affected individuals lack gene coding for muscle protein dystrophin
Results in a progressive wasting of muscle mass. Always fatal.
Sex-Linked Recessive Trait, so more common in males than females
X D = normal X d = abnormal

22. Muscular Dystrophy X D = normal X d = abnormal
A carrier female and a normal male have a child. What are the child’s chances for being normal?

23. * Color Blindness Recessive disorder on the X chromosome
Affected individuals lack pigment needed for color vision
Red/ green is the most common form
8% ♂ vs. 1 %♀ population
XB= normal vision Xb= color blind

24. Color Blindness Test Patterns
If you can see the number within each pattern, you are not colorblind.

25. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
Hints:
XB= normal vision Xb= colorblind Y = male
Use a punnett square showing both sex chromosomes of both parents, since this is a sex-linked trait.
Give your final answers separately for sons & daughters.
Show all work for full credit!

26. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
X B = X chromosome with Color Vision allele
X b = X chromosome with Color Blindness allele
Y = Y chromosome without either allele for color vision

27. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
X B = X chromosome with Color Vision allele
X b = X chromosome with Color Blindness allele
Y = Y chromosome without either allele for color vision
Mother
Father
Phenotype
Carrier
Colorblind
Genotype
X B X b
X bY
Gametes
X B or X b
X b or Y

28. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
Mother
Father
Phenotype
Carrier
Colorblind
Genotype
X B X b
X bY
Gametes
X B or X b
X b or Y
X B
X b Y

29. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
X B
X b
X BX b
XbX b Y
X BY
X bY

30. Color Blindness Practice Punnett!*
Color Blindness Practice Punnett!
A carrier female marries a colorblind male. Describe the percents of sons and daughters with each kind of vision.
Final answer:
50% of males are normal, 50% of males are colorblind
50% of females are carriers, 50% of females are colorblind
X B
X b
X BX b
XbX b Y
X BY
X bY

31. So WHY are Sex-Linked Recessive Disorders more common in Males?*
So WHY are Sex-Linked Recessive Disorders more common in Males?
Since males only have one X chromosome, they only get one gene for sex-linked traits – this means that a recessive allele is ALWAYS expressed since there is no dominant allele to hide it.
Since females have two X chromosomes, they get two alleles for these traits. In order for the trait to show up in their phenotype, they must inherit two of the disorder genes, which is much less likely.

32. YAY!!
You are now a master of autosomal and sex- linked disorders!!!!