Transcript testcross

TEST CROSSES
TESTCROSS
used to tell what genes an organism has
Example: The genes of a TALL
PARENT are UNKNOWN
- COULD HAVE _____
TT
Tt
- COULD HAVE _____
BOTH LOOK ALIKE !
http://mac122.icu.ac.jp/BIOBK/BioBookgenintro.html
TESTCROSS
used to tell what genes an organism has
Cross an UNKNOWN parent with a
HOMOZYGOUS RECESSIVE
____________________________
and see results
Offspring give a clue about the
unknown parent’s genes
TESTCROSS
T
T
t
t Tt
Tt
t Tt
tt
Tt
t
Tt
t
tt
T
All offspring will
be TALL
Tt
50% will be TALL
50% will be SHORT
DEAF DOGS
Deafness in dogs is caused by a
recessive allele. Deaf dogs have
the genotype dd.
A HEARING dog could have 2
possible GENOTYPES
Dd
DD
______
______
How do we tell which one it is?
TESTCROSS
HEARING PARENT WITH DEAF PARENT
D
D
d
Hear
Hear
d
d
Hear
Hear
d
D
d
Hear
Deaf
Hear
Deaf
deaf puppies, you know
If you get some _______
parent genotype was Dd NOT DD.
D
d
Hear
d
Hear
D
Hear
Hear
D
d
d
Hear
Deaf
d
Hear
Deaf
What if ALL the puppies can HEAR?
BOTH
________Dd
and DD parents
COULD
MAKE Hearing dogs
________________
CAN’T tell genotype of unknown parent;
NEED TO DO ANOTHER _________________
TESTCROSS