00:01
A test cross is used if the genotype of an organism with the dominant phenotype is unknown.
00:06
And we need to know what would happen if the unknown dominant organism were homozygous dominant, and if they were heterozygous.
00:14
So, a test cross, you have an individual who has the dominant phenotype.
00:21
Let's say we have two alleles, the dominant and the recessive.
00:25
We have an individual who has the dominant phenotype.
00:28
We know they have at least one.
00:30
Copy of the dominant allio, otherwise they wouldn't have the double phenotype.
00:35
We don't know what their second allele is, because whether it's a dominant or a recessive, could be either of these, they'd have the same phenotype.
00:45
So we perform a test cross.
00:48
And a test cross takes this individual, crosses them, with a homozygous recessive organism.
00:56
So a test cross.
00:59
What happens when you do this? let's do a punnet square.
01:03
So we have the parental alleles on the outside of the square, and then inside the square we will combine them to get the possible outcomes.
01:12
So this column is always the same...