TEST CROSSES

TESTCROSSused to tell what genes an organism has

Example: The genes of a TALL PARENT are UNKNOWN

- COULD HAVE _____

- COULD HAVE _____

TTTt

http://mac122.icu.ac.jp/BIOBK/BioBookgenintro.html

BOTH LOOK ALIKE !

TESTCROSSused to tell what genes an organism has

Cross an UNKNOWN parent with a ____________________________

and see results

Offspring give a clue about the

unknown parent’s genes

HOMOZYGOUS RECESSIVE

TESTCROSS

t

t

T T T t

t

t

Tt Tt

Tt Tt

Tt tt

Tt tt

All offspring will be TALL

50% will be TALL50% will be SHORT

DEAF DOGSDeafness in dogs is caused by a

recessive allele. Deaf dogs have the genotype dd.

A HEARING dog could have 2 possible GENOTYPES

______ ______

How do we tell which one it is?

DD Dd

TESTCROSS HEARING PARENT WITH DEAF PARENT

d

d

D D D d

d

d

Hear Hear

Hear Hear

Hear Deaf

Hear Deaf

If you get some deaf puppies, you know parent genotype was Dd NOT DD.

DRAGONSFirebreathing (F) in dragon

is a dominant trait

NON-firebreathing (f) is recessive.

A firebreathing dragon could have 2 possible GENOTYPES

______ ______

How do we tell which one it is?

FF Ff

http://www.webweaver.nu/clipart/dragons3.shtml

TESTCROSSFIREBREATHING PARENT WITH NON-FIREBREATHER

f

f

F F F f

f

f

Fire Fire

Fire Fire

Fire NO

Fire NO

If you get some NON-fire breathing dragons you know parent genotype was Ff NOT FF.