Question

3. Cystic fibrosis is a recessive genetic disorder that causes too much mucus to build up in the lungs. What rules of genetics do you need to use to solve this problem? a.

Answer 1

3-a) Cystic fibrosis is an autosomal recessive disorder that is inheritable and causes severe damage primarily to the lungs but also affect the digestive system of the body.

One should know about autosomal recessive in order to solve problems related with cystic fibrosis. This disorder is inherited when the offspring recieves a mutated copy of the gene (cystic fibrosis associated) from both the parents (law of dominance and law of segregation). This means when gene is present in the homozygous condition then only it will show the features of cystic fibrosis. One should also know the probability of genetics.

b) Jessica - cc (Cystic fibrosis)

Jon - Cc (carrier as he contains only one allele responsible for cystic fibrosis).

Cc/cc	c	c
C	Cc	Cc
c	cc	cc

Genotypic ratio = 1 (Cc) : 1 (cc)

Phenotypic ratio = 1 (carrier) : 1 (cystic fibrosis)

4-a) Freckles is a dominant trait which means that only one allele from either parent can cause freckles in the offsprings. One should know about law of dominance and law of segregation, probability in genetics, autosomal dominance (only one allele from either parent can cause freckles).

b) Marisa - Ff ( Heterozygous)

Ben - ff (homozygous recessive)

Ff/ff	f	f
F	Ff	Ff
f	ff	ff

Genotypic ratio - 1 (Ff) : 1 (ff)

Phenotypic ratio - 1 (freckles) : 1 ( no freckles)

5-a) ABO blood group system is a an example of Codominance and in order to solve problems related with ABO blood group, one should know about codominance, law of dominance, law of segregation, probability in genetics.

In this blood group system, three are responsible for the determination of blood groups. These alleles are - A, B and O where A and B alleles are completely dominant over O but when A and B are present together, they both function as dominant alleles (codominance).

b) Mother - O blood group (ii)

Father - AB blood group (AB)

AB/ii	i	i
A	Ai	Ai
B	Bi	Bi

Genotypic ratio - 1 ( Ai) : 1 (Bi)

Phenotypic ratio - 1 (A blood group) : 1 (B blood group)