Question

Monohybrid Problems

Among rabbits, short hair is dominant over long hair. What would be the appearance of the rabbits if a heterozygous short hair female were mated with a homozygous short hair male?

Dominant allele: ____ Recessive allele: ____			Genotypes of offspring: ___________________
Genotypes of parents: _________ Phenotypes of parents: _________			Phenotypes of offspring: ___________________

Among roses, red color is dominant over white color. What would be the appearance of the roses from a cross between a homozygous red rose and a heterozygous red rose?

Dominant allele: ____ Recessive allele: ____			Genotypes of offspring: ___________________
Genotypes of parents: _________ Phenotypes of parents: _________			Phenotypes of offspring: ___________________

Answer 1

Among rabbits, if we denote the allele for short hair as H, then the allele for long hair will be h. This is because conventionally, the dominant allele is denoted by capital letter and the recessive allele by its lower case.

So, Dominant allele is H (for short hair)

Recessive allele is h (for long hair)

Short hair individuals can have 2 genotypes

• HH (homozygous for short hair)
• Hh (heterozygous for short hair){remember than expression of the recessive alele is masked by the dominant allele, leading to phenotype of the dominant allele}

Given that the female parent is heterozygous for short hair. So her genotype is Hh. Gamates produced are H and h

Given that the male parent is homozygous for short hair. So his genotype is HH. Gamates produced are H and H

Therefore, genotypes of parents: Hh,HH

and phenotype of parents: short hair for both parents

The genotype and phenotype of offspring can be determined using punnet square.

Gametes	H	H
H	HH	HH
h	Hh	Hh

So, genotypes of offspring: HH and Hh

Phenotypes of offspring: All have short hair (this is because all offspring have a dominant H allele)

Among roses, if we denote the allele for red colour as R, then the allele for white colour will be r. This is because conventionally, the dominant allele is denoted by capital letter and the recessive allele by its lower case.

So, Dominant allele is R (for red colour)

Recessive allele is r (for white colour)

Short hair individuals can have 2 genotypes

• RR (homozygous for red colour)
• Rr (heterozygous for red colour){remember than expression of the recessive alele is masked by the dominant allele, leading to phenotype of the dominant allele}

Given that one parent is homozygous for red colour. So its genotype is RR. Gamates produced are R and R

Given that the male parent is heterozygous for red colour. So its genotype is Rr. Gamates produced are R and r

Therefore, genotypes of parents: RR,Rr

and phenotype of parents: red colour for both parents

The genotype and phenotype of offspring can be determined using punnet square.

Gametes	R	R
R	RR	RR
r	Rr	Rr

So, genotypes of offspring: RR and Rr

Phenotypes of offspring: All roses are red (this is because all offspring have a dominant R allele)

Note: If you wonder why incomplete dominance was not considered here, we are clearly given a heterozygous "red" rose. That is, the heterozygous rose is not pink. This is indeed proof that incomplete dominance exists only in certain plants like Snapdragon.