Question

a) Define four of the following terms in layman’s terms:

1. DNA

2. Allele

3. Mutation

4. Single Nucleotide Polymorphism (SNP)

5. Homozygous

6. Heterozygous

7. Dominant

8. Recessive

b)Marfan syndrome is an autosomal ________________ (dominant or recessive?) disorder. Draw a Punnett square showing the potential offspring if mom is heterozygous for Marfan syndrome and dad is homozygous recessive. Circle the affected offspring (the offspring who would inherit Marfan syndrome).

Answer 1

1. DNA ( deoxyribonucleic acid) is the molecule that contains genetic code of an individual.

2. each gene may exist in alternative forms known as alleles, which code for different versions of a particular inherited character. in other terms, it can be defined as genes occupying corresponding positiions on homolgus chromosomes and controlling the same characteristic but producing different effects.

3. a sudden and heritable change in the sequence of an organism's genome that gives rise to alternate forms of any gene is called mutation.

4. SNP(single nucleotide polymorphism) shows the single nucleotide variation in the DNA sequence of an organism.

5. homozygous - indicates that they possess two identical alleles for a trait . (TT or tt)

6. heterozygous - indicates that they posses one of each allele for a particular trait. (Tt)

7. dominant- a dominant allele masks or hides expression of a recessive allele and it is represented by uppercase letter.

8. recessive- allele that exerts its effect only in the homozygous state and in heteroygous condition its expression is maskked by a dominant allele . it is represeted by lowercase letter.

b) marfan syndrome is an autosomal dominant disorder.

genotype of heterozygous mother - Dd ----> gametes will be D and d

genotype of homozygous recessive father is = dd ----> gametes will be d

so 1/2 of the offspring will inherit the disorder whereas 1/2 of the offspring will not inherit the disorder.

	d	d
D	Dd (marfan)	Dd (marfan)
d	dd	dd