What is Biology Good For ? (#11)
Studying Inheritance of Human Disorders: Genetics Problems!

ANSWER KEY...but NO PEEKING! Questions like this WILL be on the exam, so you MUST know how to do these problems!

Genetics Problems: Please show work - use additional pages if needed. You may work with a friend, or in a group - you may get help from me or other members of the class - BUT - don't take the EZ way out - there will be problems just like this on the Exam. ((I promise! ))

Tip: Remember that for any gene, (doesn't matter what the 'letter' / gene is)
Homozygous dominant = "AA"
Heterozygous (‘carrier’) = "Aa"
Homozygous recessive = "aa"

This is the inheritance pattern for an Autosomal Recessive disorder	This is the inheritance pattern for an Autosomal Dominant disorder

Problems:

1. Freckles (F) is a dominant trait in humans.

a) By convention, the recessive allele for this gene is labeled ____f______
b) If a person is heterozygous for freckles, what is their genotype? ___Ff_____
c) If a person is homozygous dominant for freckles, what is their genotype? ____FF____
d) What is their phenotype? _____freckles!________

2. A couple has just found out that they are both carriers for PKU, a recessive metabolic disorder. What are the chances that their child will:

a) be phenotypically normal (KK or Kk)? ___75% or 3/4_____
b) be genotypically normal (homozygous dominant)? __25% or 1/4______
c) be a carrier for PKU (Kk)? __50% or 2/4______
d) have PKU (kk) __25% or 1/4______

3. John cannot curl his tongue but both his parents can curl their tongues. Tongue-curling (T) is a dominant trait. Give the genotypes of all persons involved.

John: ____tt_________ Mom:______(Tt)________ Dad: ___(Tt)____________

Hint:
1. Make a Punnitt square and fill in John FIRST; since he CANNOT curl his tougue, he MUST be (tt)
2. Then work backwards - the parents HAD to each give John a (t) and they also HAD to each have a (T) if they can curl their tongue, so they can ONLY be heterozygotes (Tt)
3. Do a reality check: what would happen if the parents were toungue-curlers who were homozygous dominant? TT

4. A woman is a carrier (heterozygous) for Tay-Sachs. What are the chances of her giving birth to a child with Tay-Sachs (a homozygous recessive disorder) if the father is normal (homozygous dominant?) What are the chances of giving birth to a carrier like herself?

Hint: Break the question into its pieces:
1. A woman is a carrier (heterozygous) for Tay-Sachs = Tt
2. the father is normal (homozygous dominant) = TT
3. What are the chances of her giving birth to a child with Tay-Sachs (a homozygous recessive disorder) (= tt)
4. Set up the Punnitt square...0% chance of a tt child. 50% chance of a carrier child Tt, 50% chance of a 'normal' child

5. Both you and your sister have attached earlobes (u) , yet your parents have unattached ones. Unattached earlobes (U) are dominant over attached. Give the genotypes of you, your sister, and your parents.

Hint:
1. Make a Punnitt square and fill in YOU AND YOUR SISTER first; since you have attached earlobes you MUST be (uu)
2. Then work backwards - your parents HAD to each give each of you a recessive allele (u) and they also HAD to each have a dominant allele (U) if they have attached earlobes, so they can ONLY be heterozygotes (Uu)
3. Do a reality check: what would happen if your parents were were homozygous dominant: UU for earlobes?

6. Parents who are carriers for have sickle-cell disease produce a child who has sickle-cell disease. What are the chances that their next child will have sickle-cell disease?

Hint: Break the question into its pieces:
1. Parents who are carriers for have sickle-cell disease = Cc
2. produce a child who has sickle-cell disease = cc
3. What are the chances that their next child will have sickle-cell disease? (=cc)
4. Set up the Punnitt square...25% chance of a cc child. (and 50% chance of a carrier child Cc, 25% chance of a 'normal' CC child)

7. A woman with PKU (kk) marries a man who is genotypically normal (KK). What are their chances of having a child who is

a) genotypically normal (KK), ______0%__________

b) a carrier for PKU (Kk), _________100%__________

c) or have the disease PKU (kk) ?____0%__________

Hint: Fill in the punnitt square: THEY CAN ONLY MAKE ONE KIND OF KID! 100% Kk (carriers). This is what MENDEL did with his initial purple x white flowers...100% of the F1 were purple (masking the white trait); and the white trait was only unmasked in the F2 generation

8. If both your parents have a continuous hairline (cc), what are your possibilities for hairlines? (show why this is) continuous hairline (cc)

Hint: Fill in the punnitt square: ...well guess what, all the kids will look like mom and dad!

9. Can a couple with achondroplasia (dwarfism), an autosomal dominant disorder, have a child without achondroplasia (aa) - of 'normal' height and stature? What happens to a conception that results in a zygote with the genotype AA?

Hint: Fill in the punnitt square: ...remember that this is a dominant disorder...anyone with one A allele will have a dwarf phenotype... YES, they can have a child without achondroplasia (aa) - of 'normal' height and stature (lower right box - aa) 25% chance. They have a 50% chance of a child with a dwarf phenotype Aa, and any child conceived with the AA genotype will die in utero.

10. A woman is heterozygous for polydactyly and has 6 fingers on each hand (polydactyly is a dominant trait). What are the chances of her giving birth to a child with polydactyly if the father is normal (homozygous recessive)?

Hint: Fill in the punnitt square: ...remember that this is a dominant disorder...anyone with one P allele will have the extra finger phenotype... Also notice that MOM is heterozygous (Pp) DAD is normal for fingers (pp) (watch your "Ps" - make sure you clearly distinguish a big P from a little p!) 50% chance of polydactyly (2 chances in 4) like mom; 50% 'normal' like dad

11. If a woman has Blood type AB, what are her possibilities for genotype (alleles)?

________IAIB only 1 possibility___________

If a man is Blood type O, what are his possibilities for genotype(alleles) ?

___________ii only 1 possibility____________________

Are these Blood types of kids possible if this woman and man have a baby together ? Yes or NO - AND list genotypes!!!!

A type AB baby? __NOPE, no IAIB possible from these parents___

A type A baby? ___YES, 50% chance of IAi___________

A type B baby? ___YES, 50% chance of IBi___________

A type O baby? __NOPE, no ii possible from these parents__

12. Joan (type A blood) and David (type B blood) have two children. All four members of this family have different blood types. List the blood types of the children and the genotypes of all 4 family members:

	Phenotype (Blood type)	Genotype (alleles)
Joan	(type A)	_IAi________
David	(type B)	_IBi________
Joni	(type _O___________)	__ii__________
Davy	(type _AB__________)	__IAIB________

HINT: Randomly choose one kid to be type O and the other to be type AB. Then Fill in these easy genotypes first...O = ii, AB= IAIB. THEN, it makes it EASY to fill in the parents. While it is techncally possible for them to be either homozygous dominant (IAIA; IBIB) or heterozygotes (IAi; IBi), they MUST be heterozygotes for A and B blood in this case to give birth to those two kids! I'll let YOU fill in the parents on that Punnitt square to confirm:

Note that if they have 2 more kids, they could end up with a family where each kid has a different BLOOD TYPE!

Woah! You are now a Genetics PRO!
Reminder: Yes, There will be problems like this on the test! There is no SUBMIT button because this Good For is due IN CLASS