Question

1)Dimples is a dominant trait and represented as “D”. No Dimples is a recessive trait and represented as “d”. The dimples/no dimples alleles follow Mendelian genetics.

What is the genotype of an individual who is heterozygous for the dimples trait?

Dd

DD

dd

Dimples

No dimples

2) Dimples is a dominant trait and represented as “D”. No Dimples is a recessive trait and represented as “d”. The dimples/no dimples alleles follow Mendelian genetics.

Person A has dimples and is homozygous for that trait. Person B does not have dimples. If person A and person B have offspring, how many of their offspring will have dimples?

A. all of them

B. none of them

C. about half of them

D. 1 in 4

3)Freckles is dominant (no freckles is recessive). The freckles trait is inherited in a “Mendelian” fashion. Both of my parents have freckles and are heterozygous for that trait. What percent of their children will have freckles?

A. 0%

B. 25%

C. 50%

D. 75%

E. 100%

4)Recall that hemophilia is a recessive X-linked disease. If a normal female (non-carrier) for hemophilia were crossed with a male with hemophilia, what is the percentage that their son will have hemophilia?

A. 0%

B. 25%

C. 50%

D. 75%

E. 100%

Answer 1

1.

• Alleles are alternate form of genes.
• One form is designated as dominant and the other as recessive.
• Dominant allele is one which expresses the phenotype when present in heterozygous form or along with the recessive allele.
• Thus if D is dominant, the effect of D will be observed as DD and Dd.
• Recessive alleles will be expressed only if two copies of the same allele are present or homozygous condition of two recessive alleles, like dd.

Answer: Dd

2.

Representation:

Dimples: Dominant trait

Homozygous genotype = DD

Heterozygous genotype =Dd

No dimples: Recessive trait

Homozygous genotype = dd

Cross: True breeding - Person A (DD) x person B (dd)

DD xdd

	d	d
D	Dd	Dd
D	Dd	Dd

F1: All are Dd = All are with dimples.

Answer: A. All of them

3.

Representation:

• Freckles= Dominant = FF/Ff
• No Freckles = Recessive = ff
• Cross Ff x Ff

	F	f
F	FF	Ff
F	Ff	ff

Freckles: non-freckles = 3:1

Thus, freckles = 75%

Answer: D. 75%

4.

• Factor VIII hemophilia is inherited as X-linked recessive state.

Representation:

Since the affected condition is caused by recessive state, representing Factor VIII affected condition as h, corresponding normal state as H.

Thus, genotypes may be represented as:

• Affected Male: X^hY (hemizygous, recessive)
• Normal Male: X^HY (hemizygous, dominhnt)
• Affected Female: X^hX^h (homozygous, recessive)
• Carrier female: X^HX^h (heterozygous, dominant)
• Normal female: X^HX^H (Homozygous dominant)

X^hY x X^HX^H

	Femhle
Male	XH	XH	F1
Xh	XH Xh	XHXh	Female
Y	XHY	XHY	Male

Thus, there are no males or females with Hemophilia

Answer: A.0%