Given that Tay-Sachs disease is caused by an autosomal recessive allele (n): 1. Determine Charly's phenotype…

Question

Given that Tay-Sachs disease is caused by an autosomal recessive allele (n): 1. Determine Charly's phenotype, Portia's genotype, and Bill's genotype. 2. Explain why Patrick is normal but a carrier.

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2b (i) Chas's phenotype Step 1: Identify Chas in the pedigree. Chas is a white square, indicating an unaffected male. Step 2: Tay-Sachs disease is autosomal recessive, so unaffected individuals do not express the disease. Chas's phenotype is normal (does not have Tay-Sachs disease). normal 2b (ii) Ellen's genotype Step 1: Father is affected (tt), so passes t allele to all offspring. Step 2: Ellen is unaffected (white circle), so must have at least one T allele. Step 3: Ellen received t from father and T from mother. Ellen's genotype is Tt. Tt 2c Explain why Patrick is normal, but a carrier of Tay-Sachs. Step 1: Determine Seth's genotype. Seth is unaffected son of affected father (tt) and unaffected mother. Seth received t from father and T from mother, so Seth is Tt. Step 2: Patrick's mother (Seth's wife) is affected (black circle), so genotype tt. Step 3: Punnett square for Seth (Tt) × wife (tt): c|c|c & t & t T & Tt & Tt t & tt & tt Offspring: 50% Tt (normal), 50% tt (affected). Step 4: Patrick is unaffected (white square), so genotype Tt. Step 5: Patrick is normal because the dominant T allele masks the recessive t allele (heterozygous advantage). Step 6: Patrick is a carrier because he has one t allele, which he can pass to his offspring (risk of affected children if mate is carrier).

Given that Tay-Sachs disease is caused by an autosomal recessive allele (n): 1. Determine Charly's phenotype, Portia's genotype, and Bill's genotype. 2. Explain why Patrick is normal but a carrier.

Step-by-step solution

Identify Chas in the pedigree.

Tay-Sachs disease is autosomal recessive, so unaffected individuals do not express the disease.

Father is affected ( $tt$ ), so passes $t$ allele to all offspring.

Ellen is unaffected (white circle), so must have at least one $T$ allele.

Ellen received $t$ from father and $T$ from mother.

Determine Seth's genotype.

Patrick's mother (Seth's wife) is affected (black circle), so genotype $tt$ .

Punnett square for Seth ( $Tt$ ) $\times$ wife ( $tt$ )

Patrick is unaffected (white square), so genotype $Tt$ .

Patrick is normal because the dominant $T$ allele masks the recessive $t$ allele (heterozygous advantage).

Patrick is a carrier because he has one $t$ allele, which he can pass to his offspring (risk of affected children if mate is carrier).

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Given that Tay-Sachs disease is caused by an autosomal recessive allele (n): 1. Determine Charly's phenotype, Portia's genotype, and Bill's genotype. 2. Explain why Patrick is normal but a carrier.

Step-by-step solution

Identify Chas in the pedigree.

Tay-Sachs disease is autosomal recessive, so unaffected individuals do not express the disease.

Father is affected (tttttt), so passes ttt allele to all offspring.

Ellen is unaffected (white circle), so must have at least one TTT allele.

Ellen received ttt from father and TTT from mother.

Determine Seth's genotype.

Patrick's mother (Seth's wife) is affected (black circle), so genotype tttttt.

Punnett square for Seth (TtTtTt) ×\times× wife (tttttt)

Patrick is unaffected (white square), so genotype TtTtTt.

Patrick is normal because the dominant TTT allele masks the recessive ttt allele (heterozygous advantage).

Patrick is a carrier because he has one ttt allele, which he can pass to his offspring (risk of affected children if mate is carrier).

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Father is affected ( $tt$ ), so passes $t$ allele to all offspring.

Ellen is unaffected (white circle), so must have at least one $T$ allele.

Ellen received $t$ from father and $T$ from mother.

Patrick's mother (Seth's wife) is affected (black circle), so genotype $tt$ .

Punnett square for Seth ( $Tt$ ) $\times$ wife ( $tt$ )

Patrick is unaffected (white square), so genotype $Tt$ .

Patrick is normal because the dominant $T$ allele masks the recessive $t$ allele (heterozygous advantage).

Patrick is a carrier because he has one $t$ allele, which he can pass to his offspring (risk of affected children if mate is carrier).