Question

1. which members of the family above are afflicted with huntington’s disease?
2. there are no carriers for huntington’s disease- you either have it or you don’t. with this in mind, is huntington’s disease caused by a dominant or recessive trait?
3. how many children did individuals i-1 and i-2 have?
4. how many girls did ii-1 and ii-2 have? how many have huntington’s disease?
5. how are individuals iii-2 and ii-4 related? i-2 and iii-5?
6. the pedigree to the right shows a family’s pedigree for hitchhiker’s thumb. is this trait dominant or recessive?
7. how do you know?
8. how are individuals iii-4 and iii-5 related?
9. how would you name the 2 individuals that have hitchhiker’s thumb?
10. name the 2 individuals that were carriers of hitchhiker’s thumb.
11. is it possible for individual iv-3 to be a carrier? why?
12. the pedigree to the right shows a family’s pedigree for colorblindness. which sex can be carriers of colorblindness and not have it?
13. with this in mind, what kind of trait is colorblindness (use your notes)?
14. why does individual iv-7 have colorblindness?
15. why do all the daughters in generation ii carry the colorblind gene?
16. name two iv generation colorblind males.

Explanation:

Step1: Identify affected Huntington's members

From the first pedigree, shaded shapes = affected. Affected: I-1, II-2, II-3, II-5, III-3

Step2: Confirm Huntington's trait type

No carriers = dominant trait (dominant traits show in every generation, no hidden carriers)

Step3: Count I-1 & I-2 children

Count generation II offspring: II-1, II-2, II-3, II-4, II-5, II-6 → 6 children

Step4: Count II-1 & II-2's girls

Their children: III-1, III-2, III-3. Girls: III-2, III-3 → 2 girls. Affected girl: III-3 → 1

Step5: Determine relationships

III-2 & II-4: III-2 is II-4's niece; I-2 & III-5: I-2 is III-5's grandmother

Step6: Identify Hitchhiker's Thumb trait type

Unaffected parents (II-3 & II-4) have affected child (III-4) → recessive trait

Step7: Justify Hitchhiker's trait conclusion

Recessive traits skip generations; unaffected parents can have affected offspring if both are carriers

Step8: Relate III-4 & III-5

They are siblings (brother and sister)

Step9: Name affected Hitchhiker's Thumb individuals

Shaded shapes: III-4, IV-3

Step10: Name Hitchhiker's Thumb carriers

Unaffected parents of affected child: II-3, II-4

Step11: Assess IV-3 as carrier possibility

No; IV-3 shows the recessive trait, so has two recessive alleles (homozygous recessive), cannot be a carrier (carriers are heterozygous, unaffected)

Step12: Identify colorblind carrier sex

Colorblindness is X-linked; females (XX) can be carriers (one affected X, one normal X) without showing the trait

Step13: Classify colorblindness trait type

X-linked recessive trait (males show it with one affected X, females need two)

Step14: Explain IV-7's colorblindness

IV-7 inherited the affected X chromosome from her carrier mother (III-6) and no normal X from her father (who passes Y to sons, but here IV-7 is female? Correction: IV-7 is female, so she inherited two affected Xs: one from carrier mom III-6, one from affected dad III-8)

Step15: Explain generation II daughters' carrier status

Father I-1 is colorblind (has affected X), so he passes his only X to all daughters, making them carriers

Step16: Name IV generation colorblind males

Shaded males: IV-1, IV-5

Answer:

1. I-1, II-2, II-3, II-5, III-3
2. Dominant
3. 6
4. 2; 1
5. Niece and aunt; Grandmother and grandson
6. Recessive
7. Unaffected parents have an affected child, which is a hallmark of recessive traits that can skip generations.
8. They are brother and sister (siblings)
9. III-4, IV-3
10. II-3, II-4
11. No; IV-3 has the recessive trait, so she is homozygous recessive for the allele and cannot be a heterozygous carrier.
12. Females (XX)
13. X-linked recessive trait
14. She inherited two copies of the X chromosome with the colorblindness allele: one from her carrier mother (III-6) and one from her colorblind father (III-8).
15. Their father (I-1) is colorblind, so he can only pass his affected X chromosome to his daughters, making all of them carriers.
16. IV-1, IV-5