Part 3 - Treatment and ResultsA few weeks after their most recent check-up, Anna and Jared are back at the clinic. They're called into a room and the doctor appear, his face is solemn. He reveals that the tests came back positive and this means that Jared has Tay-Sachs disease. “At most Jared had 3-4 years left," he adds, because the disease has no cure. There are medications that are able to prolong his life and to relieve some of the symptoms as they get worse. There are technologies such as physical therapy, respiratory care, and gene therapy that will help. Still in shock from this news, Anna begins to cry.
3 years later… Jared is now a permanent resident at the hospice. He has breathing tubes that are attached to monitors and this was his connection between life and death. It was time. With Anna by his side, Jared slowly inhaled for the last time, peacefully slipping from this world. |
Part 3 - Questions
Question 1. What is the law of segregation? How does it relate to Tay-Sachs disease and the possibility to inherit the disease from unaffected, heterozygous parents? Use your knowledge of why the parents do not have the disease while their child does.
The law of segregation is Mendel's law of inheritance that states that all individuals have two copies of each gene. These copies segregate (separate) randomly during meiosis, resulting with each gamet receiving one copy of every gene. Unaffected parents have a dominant and a recessive gene and during meiosis, one of the affected chromosomes can be found in two of the four gametes produced. If an affected ovum and sperm join to form a zygote, then the child has two copies of the affected gene and that results in inheriting the disease.
Question 2. What is a monohybrid cross, a dihybrid cross, and a test cross? Explain their differences and their relation to the disease.
A monohybrid cross is the mating of two organisms following the inheritance of one trait. Dihybrid cross is the mating of two organism following the inheritance of two traits. Test cross is used to determine the genotype of a dominant phenotype by crossing the unknown genotype with a homozygous recessive. Tay-Sachs disease results in the inheritance of two copies of the affected trait, this would be a monohybrid cross.
Question 3. What is a lethal allele? List and explain the types. What is the genotype of the parents of a child with Tay-Sachs disease?
A lethal allele is an allele that causes an organism unable to survive. Lethal dominant is when the organism dies immediately and the gene doesn't remain in the gene pool. Lethal recessive is when an organism dies because they receive two copies of the recessive allele. Lethal dominant (late onset) is when an organism will eventually die but they may live long enough to pass it to their offspring. The parents of a child with this disease are both carriers, which are heterozygous. They may be normal but they may pass it on to their offspring.
Question 4. The parents of the affected child can have the allele related to the disease however they will show no signs or symptoms of the condition. What type of inheritance is demonstrated in Tay-Sachs disease?
This is a case of autosomal recessive inheritance. It is autosomal because the affected gene is found on one of autosomes (chromosome 15) and it is also recessive because an affected individual needs to be homologous in terms of recessive genes. Also, it is recessive because the disease doesn't have to show up in every generation.
The law of segregation is Mendel's law of inheritance that states that all individuals have two copies of each gene. These copies segregate (separate) randomly during meiosis, resulting with each gamet receiving one copy of every gene. Unaffected parents have a dominant and a recessive gene and during meiosis, one of the affected chromosomes can be found in two of the four gametes produced. If an affected ovum and sperm join to form a zygote, then the child has two copies of the affected gene and that results in inheriting the disease.
Question 2. What is a monohybrid cross, a dihybrid cross, and a test cross? Explain their differences and their relation to the disease.
A monohybrid cross is the mating of two organisms following the inheritance of one trait. Dihybrid cross is the mating of two organism following the inheritance of two traits. Test cross is used to determine the genotype of a dominant phenotype by crossing the unknown genotype with a homozygous recessive. Tay-Sachs disease results in the inheritance of two copies of the affected trait, this would be a monohybrid cross.
Question 3. What is a lethal allele? List and explain the types. What is the genotype of the parents of a child with Tay-Sachs disease?
A lethal allele is an allele that causes an organism unable to survive. Lethal dominant is when the organism dies immediately and the gene doesn't remain in the gene pool. Lethal recessive is when an organism dies because they receive two copies of the recessive allele. Lethal dominant (late onset) is when an organism will eventually die but they may live long enough to pass it to their offspring. The parents of a child with this disease are both carriers, which are heterozygous. They may be normal but they may pass it on to their offspring.
Question 4. The parents of the affected child can have the allele related to the disease however they will show no signs or symptoms of the condition. What type of inheritance is demonstrated in Tay-Sachs disease?
This is a case of autosomal recessive inheritance. It is autosomal because the affected gene is found on one of autosomes (chromosome 15) and it is also recessive because an affected individual needs to be homologous in terms of recessive genes. Also, it is recessive because the disease doesn't have to show up in every generation.