Pedigree Chart Worksheet | PDF | Zygosity | Dominance (Genetics) - Free Printable

Looking at the colorblindness pedigree, I can see that the key indicates "half-shaded = carrier of disease." This suggests that this is likely an X-linked trait, as carriers are typically females who have one copy of the recessive allele on one of their X chromosomes.

Question 12 asks: "The pedigree to the right shows a family's pedigree for colorblindness. Which sex can be carriers of colorblindness and not have it?"

From the key and the pedigree, I can see that half-shaded circles (females) represent carriers. Males are either fully shaded (affected) or open (unaffected), with no half-shaded males. This is consistent with X-linked recessive inheritance, where females can be carriers (heterozygous) without showing symptoms, while males, having only one X chromosome, will express the trait if they inherit the mutant allele.

Answer to Question 12: Females can be carriers of colorblindness and not have it. This is because colorblindness is typically an X-linked recessive trait, and females have two X chromosomes. If a female has one normal allele and one mutant allele, she will be a carrier but not express the disease. Males, having only one X chromosome, will express the trait if they inherit the mutant allele.

Question 13: "With this in mind, what kind of trait is colorblindness (use your notes)?"

Based on the pattern observed (females as carriers, males more frequently affected, and the inheritance pattern shown in the pedigree), colorblindness is an X-linked recessive trait.

Answer to Question 13: Colorblindness is an X-linked recessive trait.

Question 14: "Why does individual IV-7 have colorblindness?"

Looking at the pedigree, IV-7 is a female (circle) who is fully shaded, indicating she is affected. For a female to be affected by an X-linked recessive trait, she must inherit the mutant allele from both parents. Her father (III-5) is affected (fully shaded square), so he must have passed his mutant X chromosome to her. Her mother (III-6) is half-shaded, indicating she is a carrier, so she must have passed her mutant X chromosome to IV-7. Therefore, IV-7 inherited the mutant allele from both parents.

Answer to Question 14: Individual IV-7 has colorblindness because she inherited the mutant allele from both parents. Her father (III-5) is affected and passed his mutant X chromosome to her, and her mother (III-6) is a carrier and also passed her mutant X chromosome to her. Since colorblindness is X-linked recessive, a female needs two copies of the mutant allele to be affected.

Question 15: "Why do all the daughters in generation II carry the colorblind gene?"

Looking at generation II, I can see that there are several daughters (circles) who are either half-shaded (carriers) or fully shaded (affected). The key question is why they all carry the colorblind gene. Looking at their parents, I can see that their father (I-1) is affected (fully shaded square). Since he is male and affected, he must have the mutant allele on his X chromosome. He passes this X chromosome to all of his daughters (since males pass their X chromosome to daughters and Y chromosome to sons). Therefore, all of his daughters will inherit the mutant allele and be at least carriers.

Answer to Question 15: All the daughters in generation II carry the colorblind gene because their father (I-1) is affected and passes his mutant X chromosome to all of his daughters. Since colorblindness is X-linked recessive, inheriting the mutant allele from their father makes them carriers (or affected if they also inherit a mutant allele from their mother).

Question 16: "Name 2 IV generation colorblind males."

Looking at generation IV, I need to identify males (squares) who are fully shaded (affected). I can see IV-1, IV-5, and IV-6 are affected males.

Answer to Question 16: Two IV generation colorblind males are IV-1 and IV-5 (or IV-6).

This completes the analysis of all questions in the pedigree worksheet.