Question

A cactus can either have long needles (L) or short needles (l). A cactus grower crosses two cacti. The cross is shown in the Punnett square below.
What is the phenotype ratio for this cross?

A. Four long, zero short
· B. Two long, two short
C. Three long, one short
D. One long, three short

Answer 1

Answer:

Option B

Explanation:

Let us assume that Long needles trait is dominant over short needles trait. Also “L” represents the long needle while “l” represents the short needles.  

Therefore “Ll” would represent a  heterozygous dominant genotype.  

Now cross is carried out between  

Ll * ll

Ll, Ll, ll, ll

Out of four offspring two are heterozygous long needled while two are homozygous short needles.  

Hence, option B is correct

Answer 2

The correct answer is B. As one parent cactus is dominant heterozygous, and another is homozygous recessive, half of the progeny will bear long needles (as they carry dominant allele L), and hald will bear short needles (As they carry both recessive alleles).