Monohybrid cross maybe?

Question

These genetics problems have my mind in a mush. Any help at all would be appreciated.

Farmer Morris has a green tobacco plant. He doesn't know the genotype of this plant. He crosses this unknown plant with a plant that is homozygous recessive for chlorophyll and gets the following results: two green plants for every two white plants. (Phenotypic ratio = 2 green: 2 white)

So, what is the genotypic ratio of the offspring?

This kind of cross would be called?

Last question:

Thorny stems (T) are dominant over smooth stems (t). Two throny plants are crossed and produce the following offspring:

12 thorny plants

4 smooth stemmed plants

What are the genotypes of both parents?

(would the answer to this one be heterozygous dominant?)

Answer 1

1.YES. A Monohybrid cross is a cross between parents who are heterozygous at one locus; for example, Bb x Bb (see the Punnett square below). Example: B=brown. b=blue. BB=Dark Brown. Bb=Brown not blue. bb=Blue.

2.  YES. since an organism is a heterozygote or is heterozygous at a locus or gene when it has different alleles occupying the gene's position in each of the homologous chromosomes. In other words, it describes an individual that has 2 different alleles for a trait. In diploid organisms, the two different alleles were inherited from the organism's two parents. For example a heterozygous individual would have the allele combination

Answer 2

1. "So, what is the genotypic ratio of the offspring?"

The phenotypic ratio is 2 green: 2 white, which is 1:1 when reduced. The genotypic ratio is 1:1 as well. The offspring genotypes would be Gg (heterozygous green) and gg (homozygous white), which is the same as the genotypes of the parents. When the offspring is 1:1, you have a heterozygous parent and a homozygous recessive parent, which result in the same types of offspring. Check it out on a Punnett square to confirm.

2. "This kind of cross would be called?"

When you don't know the genotype of one parent, and you cross it with a homozygous recessive parent, this particular cross is called a TEST CROSS.

3. "What are the genotypes of both parents?

The ratio is 12 thorny: 4 smooth. Reducing the numbers gives you a 3:1 ratio. Any time you see these magic numbers (3:1), that means that the parents are both heterozygous for a monohybrid cross.