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TEST CROSSES
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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 !
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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
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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
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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
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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.
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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
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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.