1. Test Cross
a test cross of an individual of unknown genotype to an individual that is fully recessive
the phenotypes of the F1 generation of the test cross reveals whether the unknown genotype is homozygous or heterozygous
example:
you have a white ram (white is dominant “W” and black is recessive “w”) and want to know if it is heterozygous or homozygous for breeding purposes.

2. it must have a recessive genotype (ww)
do a test cross by crossing your unknown ram with one showing a recessive phenotype.
it must have a recessive genotype (ww) w ? w?

3. Test 1 Test 2 ♀ ww ♀ ww Ww ♂ ♂ Ww WW ww
If the ram is Heterozygous it will produce:
Phenotypic ratio: 50% white 50% black, or 2:2 or 1:1
Genotypic ratio:
2:2 or 1:1 hetero:homo recessive
If the ram is Homozygous it will produce:
Phenotypic ratio: 100 % White
Genotypic ratio:
100% heterozygous

4. Test 1 ♀ Rr Analyze: Analyze:
Heterozygous Seed shape crossed with a recessive seed shape
Analyze:
What are the predicted phenotypes and genotypes?
Phenotypic Ratio
50% round 50% wrinkled or 2:2 or 1:1, ½, 2/4,
Genotypic Ratio
50% hetero: 50% homo recessive, 2:2 or 1:1, hetero 2/4 or ½ homo recessive 2/4 or ½
Test 1
♀ Rr ♂ rr Rr

5. Example Problem
A horticulturist has seeds from a cross but does not know the genotype of the phenotype of the parents. Use the following information to figure out the parental phenotype and genotype
Offspring Phenotype
Numbers
round-seed peas
5472
wrinkle-seed peas
1850
Solution
because there is two different phenotypes one the parents must not be homozygous dominant

6. Tester round-seed peas 5472 wrinkle-seed peas 1850 Solution
Offspring Phenotype
Numbers
round-seed peas
5472
wrinkle-seed peas
1850
Solution
because there are two different phenotypes one the parents must not be homozygous dominant
Tester
♀ ?? ♂ RR R?
Solution
5472/1850 = 2.96
2.96/1 or 2.96 : 1
~ 3 : 1
to get a 3:1 ratio both parents must be heterozygous

7. Mendelian Genetics Proof RR rr Proof rr ♀ Rr ♂ Rr ♀ rr ♂ Rr
3:1 Phenotypic ratio
1:1 (50%) Phenotypic ratio