Explain to them the probability of future offspring being normal or having the disease (assume
that this is an autosomal disease). Be sure to tell them whether the disease is brought about by a
dominant or recessive allele and what fraction of their children (if any) could be carriers for the
disease. Be sure to incorporate the following into your explanation: DNA and chromosomes,
genes, dominant and recessive alleles, paired alleles on homologous chromosomes, and
segregation of alleles during gamete production. You can use words and drawings/diagrams.
Sally and Steve are concerned about cystic fibrosis. Neither of them has it, nor do their parents or
grandparents, yet each one has a sibling with cystic fibrosis (Sally\'s sister and Steve\'s brother).
Sally and Steve want to have a second child (the first one, age 4, appears unaffected). Jess and
Jessie want to get married and have children. Unfortunately, they have the same great-
grandmother (not the same great-grandfather). The great-grandmother suffered from polycystic
kidney disease. No other family members suffered from the disease, but they were told
(correctly) that their great-grandmother had passed on the possibility of the disease.
Solution
Ques-1:
Aetiology and Pathophysiology: It is autosomal recessive disease (mode of inheritance), which is
familial. Gene for cystic fibrosis is located on the chromosome 7 & this recessive allele
propogated to the offspring via parental gamete formation by reduction division & problem will
be at segregation of chromosomes. A protein called, CF transmembrane -this gene produces
regulator (CFTR). In case of Pleiotrophy one affects 2 or more apparently not linked phenotypic
traits there by more gene could be affected (cystic fibrosis).
For instance, Sally and Steve are concerned about cystic fibrosis. Neither of them has it, nor do
their parents or grandparents, yet each one has a sibling with cystic fibrosis (Sally\'s sister and
Steve\'s brother) i.e. both Sally & Steve are carriers of the disease. Therefore, 2/3 (67%), of
probability with unaffected child. Sally and Steve want to have a second child but the first child
age-4 has no cystic fibrosis
Cystic fibrosis is an autosomal recessive condition. In the given example, the unaffected parents
will have an affected children Assume that the gene coding for the normal allele is C, and the
gene coding for the cystic fibrosis is c and C is dominant over c. Now, cross between two
heterozygotes will have the offspring with the following genotypes.
Cc* Cc = CC, Cc, Cc, cc (means, 3/4th are unaffected (out of these 2/4 are carriers) and the ¼
are affected -having disease).
C
c
C
CC
Cc
c
Cc
cc
C
c
C
CC
Cc
c
Cc
cc.
Explain to them the probability of future offspring being normal or h.pdf
1. Explain to them the probability of future offspring being normal or having the disease (assume
that this is an autosomal disease). Be sure to tell them whether the disease is brought about by a
dominant or recessive allele and what fraction of their children (if any) could be carriers for the
disease. Be sure to incorporate the following into your explanation: DNA and chromosomes,
genes, dominant and recessive alleles, paired alleles on homologous chromosomes, and
segregation of alleles during gamete production. You can use words and drawings/diagrams.
Sally and Steve are concerned about cystic fibrosis. Neither of them has it, nor do their parents or
grandparents, yet each one has a sibling with cystic fibrosis (Sally's sister and Steve's brother).
Sally and Steve want to have a second child (the first one, age 4, appears unaffected). Jess and
Jessie want to get married and have children. Unfortunately, they have the same great-
grandmother (not the same great-grandfather). The great-grandmother suffered from polycystic
kidney disease. No other family members suffered from the disease, but they were told
(correctly) that their great-grandmother had passed on the possibility of the disease.
Solution
Ques-1:
Aetiology and Pathophysiology: It is autosomal recessive disease (mode of inheritance), which is
familial. Gene for cystic fibrosis is located on the chromosome 7 & this recessive allele
propogated to the offspring via parental gamete formation by reduction division & problem will
be at segregation of chromosomes. A protein called, CF transmembrane -this gene produces
regulator (CFTR). In case of Pleiotrophy one affects 2 or more apparently not linked phenotypic
traits there by more gene could be affected (cystic fibrosis).
For instance, Sally and Steve are concerned about cystic fibrosis. Neither of them has it, nor do
their parents or grandparents, yet each one has a sibling with cystic fibrosis (Sally's sister and
Steve's brother) i.e. both Sally & Steve are carriers of the disease. Therefore, 2/3 (67%), of
probability with unaffected child. Sally and Steve want to have a second child but the first child
age-4 has no cystic fibrosis
Cystic fibrosis is an autosomal recessive condition. In the given example, the unaffected parents
will have an affected children Assume that the gene coding for the normal allele is C, and the
gene coding for the cystic fibrosis is c and C is dominant over c. Now, cross between two
heterozygotes will have the offspring with the following genotypes.
Cc* Cc = CC, Cc, Cc, cc (means, 3/4th are unaffected (out of these 2/4 are carriers) and the ¼
are affected -having disease).
C
c
