I just need help with the last part where it asks to "give an example of a cross" and to provide an explanation.

Question

c.    What would happen if you crossed a heterozygous Parent 1 with a homozygous recessive Parent 2? Fill in the blanks below and do the Punnett square. 

Your key:       F = ____Smooth skin___

                       f = ____fuzzy skin

Genotype of Parent 1: ____Ff_____

Genotype(s) of Parent 1’s gametes (also write these above the columns): ____F and f________

Genotype of Parent 2: _____ff_____

Genotype(s) of Parent 2’s gametes (also write these to the left of the rows): __f and f_______

Percent(s) and phenotype(s) of offspring: 50% heterozygous

50% homozygous recessive

	F	f
f	Ff	ff
f	Ff	ff

d.   If you cross an individual with a dominant phenotype but unknown genotype with a homozygous recessive individual, that is an example of a ______________ cross.  Also, if you wanted to determine the genotype of an individual with a dominant phenotype but unknown genotype, explain why (in very simple terms!) why it would not be useful to cross an individual with a dominant phenotype but unknown genotype with a homozygous dominant individual. 

Explanation: ___________________________________________________________________ .

Answer 1

In Mendelian genetics, a dominant phenotype can be produced by a homozygous (FF) or heterozygous (Ff) organism. So, to find out which it is, you can perform a TEST cross.

Why is a test cross always between an unknown dominant phenotype and a homozygous (pure) recessive?

Consider the following:

If your unknown organism is FF or Ff, and you cross it with a homozygous (pure) dominant FF, all of the offsrping will express the dominant phenotype. But, if you cross your unknown with a homozygous recessive ff, 50% of your offspring will express the recessive phenotyoe IF your unknown is heterozygous Ff. Your chance of discovering the genotype of your unknown is better if your test cross is with a pure recessive.