TEST CROSSES

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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 _____

TT
Tt
BOTH LOOK ALIKE !
http//mac122.icu.ac.jp/BIOBK/BioBookgenintro.html
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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 parents genes

HOMOZYGOUS RECESSIVE
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TESTCROSS
T t
T T
t t
Tt tt Tt tt
t t
Tt Tt Tt Tt
50 will be TALL 50 will be SHORT
All offspring will be TALL
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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
• ______ ______
• 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
Hear Hear Hear Hear
Hear Deaf Hear Deaf
d d
If you get some deaf puppies, you know parent
genotype was Dd NOT DD.
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DRAGONS
http//www.webweaver.nu/clipart/dragons3.shtml

• Firebreathing (F) in dragonis 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
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TESTCROSSFIREBREATHING PARENT WITH
NON-FIREBREATHER
F f
F F
f f
Fire Fire Fire Fire
Fire NO Fire NO
f f
If you get some NON-fire breathing dragons you
know parent genotype was Ff NOT FF.