Pedigree from other source attached:
Answer:
Condition A inheritance mode: Autosomal recessive
Condition B inheritance mode: X-linked recessive
Explanation:
1. Condition A appears in generation 2 when neither parent in generation I is affected. This means at least one of them must carry the allele for the trait. However, because neither parent displays the trait, it must be a recessive allele. Thus, individual 6 must have inherited two copies of the allele, meaning both parents are carriers.
Because we know both parents are carriers but do not display the trait, we can conclude that the trait is not X-linked, because even if it was recessive, the dad (generation I, individual 3) would display the trait (because he only has only 1 X chromosome).
2. Condition B is more common in males, suggesting it could be X-linked. This is shown to be the case if you look at generation 3. Individual 1 of generation II (father) is unaffected, as is individual 2 of generation II (mother), although her father is. If the trait is X-linked, then she must carry the allele. Therefore, all her sons would carry it and display the trait, this is true (generation II), meaning it is likely X-linked,
To determine whether it is dominant or recessive, we need to look at the females (who have 2 copies of the X chromosome and hence would not display a recessive trait). The only affected female is Generation IV, individual 2. She is also the only individual who might have 2 copies (parents III.2 and III.3). Other females that must have a copy (II.2) and (II.4) are unaffected, meaning it is X-linked recessive.
Sex-linked inheritance refers to genes linked to the sexual chromosomes, while autosomal inheritance refers to genes placed in autosomal chromosomes. Condition A: Option D / Condition B: Option C
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According to the pedigree, we can assume that
Let us first remember a few concepts,
Also, remember that in a pedigree,
Now, let us analyze each condition
Condition A.
If the condition was dominant, at least one of the parents should be heter0zyg0us expressing it. So we can assume that the condition is recessive and that female II6 is h0m0zyg0us recessive for that trait.
If the gene coding for this condition was sex-linked, then the mother of woman II6 should be heter0zyg0us, and the father should be affected.
The fact that individuals I-3 and I-4 (father and mother) do not express the condition, and only individual 6 does, suggests that the gene coding for this trait is autosomal recessive.
Both parents must be heter0zyg0us for the trait, the brothers might be either h0m0zyg0us dominant or heter0zyg0us, and the affected woman is h0m0zyg0us recessive.
So let us make a short cross:
Cross) man I-3 x woman I-4
Parentals) Aa x Aa
Gametes) A a A a
Punnett square) A a
A AA Aa
a Aa aa
F1) 3/4 AA + Aa ⇒ individuals II-5 and II-7
1/4 aa ⇒ individual II-6
According to this analysis, Condition A Inheritance Mode is Autosomal Recessive (Option D).
Condition B.
The fact that the condition is mostly affecting men, excepting for individual
IV-2, suggests that the gene coding for this trait could be sex-linked.
If it was dominant, at least one of the individuals II-1 and II-2 should carry the dominant allele and should express the trait.
The fact that these individuals do not express the trait, but their III-1 son does, suggests that this is a recessive trait.
According to this analysis, Condition B Inheritance Mode is X-linked Recessive (Option C).
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