Question

A true breeding swan flower plant with smooth petals is crossed with a true breeding swan flower plant with constricted petals. The offspring of this cross all have smooth petals. This indicates that

1) the offspring do not have a constricted allele in their genotype

2) smooth petals are dominant and constricted petals are recessive

3)constricted and smooth petals are not controlled by alleles

4) the F2 generation will have all smooth petals

5) constricted petals are dominant and smooth are recessive

Answer 1

According to law of dominance by Mendel -
• When both dominant and recessive alleles are present in a genotype then dominant allele shows it's phenotype.
• Or in other words, when two true breeding parents are crossed then in F1 generation or heterozygous condition, only Dominant character or phenotype is expressed.

Now, in question
• Two true breeding parents are crossed, so dominant phenotype will be expressed in offsprings. Smooth petels is expressed so smooth petels is dominant over constricted petels.

Monohybrid cross -
Alleles - S and s
SS and Ss = Smooth petels
ss = Constricted petels.

Parents = SS and ss
Gametes -
From parent 1 = S.
From parent 2 =s.

F1 generation = Ss

Now, F1 × F1.
Ss × Ss
Type of gametes = S and s.

F2 generation -
Phenotype ratio = 3 smooth petels (SS and Ss) : 1 constricted petels (ss).

Option (2) is correct answer.
• Smooth petels are Dominant and constricted flowers is recessive.