UNIT
3
The transmission of traits
WHAT IS A TEST CROSS?
Biology and Geology 4. Secondary Education.
UNIT
3
What is a test cross?
The additional experiment which Mendel
carried out, to prove that alleles come in
pairs and separate at the moment when
gametes form, consisted of crossing F1
(yellow seeds) with the pure paternal
line of green seeds (recessive
homozygote).
Let’s take the yellow seed to be Aa.
In this case, 50% green seeds and 50%
yellow seeds are obtained.
If the yellow seed had been AA, all of the
seeds would have been yellow (Aa).
Biology and Geology 4. Secondary Education.
Yellowamarilla
seed F1F1
Semilla
Aa
Green
Semillaseed
verde
x
a
aa
a
A
Aa
Aa
aa
aa
a