MIDDLE SCHOOL GENETICS

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MIDDLE SCHOOL GENETICS
T
T
Tt
t
t

• SINGLE TRAIT PUNNETT SQUARE

¼
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TOOLS TO KNOW
PARENTS GENES
A PUNNET SQUARE IS A TOOL USED TO PREDICT THE
POSSIBLE GENOTYPES FOR THE OFFSPRING OF TWO KNOWN
PARENTS.
PARENTS GENES
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TERMS TO KNOW
ALLELES DIFFERENT FORMS OF A TRAIT THAT A GENE MAY HAVE T,t
HOMOZYGOUS AN ORGANISM WITH TWO ALLELES THAT ARE THE SAME TT, tt
HETEROZYGOUS AN ORGANISM WITH TWO DIFFERENT ALLELES FOR A TRAIT Tt, Gg
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TERMS TO KNOW
HYBRID SAME AS HETEROZYGOUS Tt, Gg
DOMINANT A TRAIT THAT DOMINATES OR COVERS UP THE OTHER FORM OF THE TRAIT REPRESENTED BY AN UPPERCASE LETTER T OR G
RECESSIVE THE TRAIT BEING DOMINATED OR COVERED UP BY THE DOMINATE TRAIT REPRESENTED BY A LOWER CASE LETTER t or g
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TERMS TO KNOW
PHENOTYPE THE PHYSICAL APPEARANCE OF AN ORGANISM (WHAT IT LOOKS LIKE) TALL, SHORT, GREEN, WRINKLED
GENOTYPE THE GENE ORDER OF AN ORGANISM (WHAT ITS GENES LOOK LIKE) TT, GG, Tt, gg Gg, tt
RATIO THE RELATIONSHIP IN NUMBERS BETWEEN TWO OR MORE THINGS 31, 22, 121
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HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
THE PARENTS ALLELES GO ON THE OUTSIDE OF THE
SQUARE
B
B
BB X bb
b
b
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HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
THE PARENTS ALLELES GO ON THE OUTSIDE OF THE
SQUARE
DROP THE LETTERS ON THE TOP, INTO EACH SQUARE
B
B
b
B
B
b
b
MOVE EACH LETTER ON THE SIDE, INTO EACH SQUARE
b
THE ORDER DOES NOT MATTER IN THE BOXES, BUT
UPPERCASE FIRST IS A GOOD RULE
B
B
b
b
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HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
WHAT DO THE RESULTS SHOW?
RESULTS
B
B
PHENOTYPIC 100 BLACK 40 RATIO, BLACK TO
BROWN
IF B IS THE DOMINANT ALLELE FOR BLACK
b
Bb
Bb
AND b IS THE RECESSIVE ALLELE FOR BROWN
GENOTYPIC 100 Bb 40 ALL Bb
b
Bb
Bb
THEN WE CAN MAKE PREDICTIONS ABOUT THE OUTCOMES
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HOW TO USE A PUNNETT SQUARE
WHAT ARE THE RESULTS?
LETS LOOK AT ANOTHER PUNNETT SQUARE AND PREDICT
THE OUTCOME
T
t
PHENOTYPIC 75 TALL 25 SHORT 3 TO 1
RATIO TALL TO SHORT
T
T
T
T
t
T IS THE DOMINANT ALLELE FOR TALLNESS
GENOTYPIC 1TT 2Tt 1tt 121 RATIO 25
TT, 50 Tt, 25 tt
t
T
t
t
t
t IS THE RECESSIVE ALLELE FOR SHORTNESS
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PRACTICAL APPLICATION OF PUNNETT SQUARES
THE ALLELES OF A PARTICULAR SPECIES OF DOG CAN BE
EITHER D (NORMAL HEIGHTH) OR d (DWARF). THE
HETEROZYGOUS (Dd) AND HOMOZYGOUS DOMINANT (DD)
FORM OF THIS DOG LOOK THE SAME (TALL). IF YOU
FOUND A STRAY DOG OF THIS BREED, HOW COULD YOU
DETERMINE ITS GENOTYPE?
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PRACTICAL APPLICATION OF PUNNETT SQUARES
COULD A DOG BE CROSSED WITH ANOTHER DOG TO
DETERMINE IF HE WAS PUREBRED FOR TALLNESS?
WHAT GENOTYPE SHOULD THE DOG HAVE THAT IS BEING
USED FOR THE CROSS?
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PRACTICAL APPLICATION OF PUNNETT SQUARES
D
D
IF THE DOG IS PUREBRED (DD), IT DOESNT MATTER
WHAT YOU CROSS IT WITH, THE OFFSPRING WILL ALWAYS
LOOK LIKE THE DOMINANT.
DD
DD
D
D
DD
DD
D
D
D
D
D
DD
d
DD
Dd
Dd
d
Dd
Dd
d
Dd
Dd
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PRACTICAL APPLICATION OF PUNNETT SQUARES
WHAT WOULD BE THE MOST EFFECTIVE CROSS FOR
DETERMINING IF THE DOG IS HETEROZYGOUS (Dd) ?
CROSSING IT WITH A PUREBRED (DD) WILL NOT HELP.
WHAT WOULD THE RESULTS BE IF YOU CROSSED IT WITH
ANOTHER HETEROZYGOUS?
WHAT WOULD THE RESULTS BE IF YOU CROSSED IT WITH
A HOMOZYGOUS RECESSIVE (dd)?
d
D
d
D
D
d
Dd
DD
Dd
dd
d
d
dd
Dd
dd
Dd
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PRACTICAL APPLICATION OF PUNNETT SQUARES
d
D
D
d
D
Dd
DD
d
Dd
dd
d
d
Dd
dd
dd
Dd
THE HETEROZYGOUS CROSS WOULD ONLY GIVE YOU A 25
CHANCE OF THE RECESSIVE TRAIT APPEARING.
THE MOST EFFECTIVE CROSS WAS USING THE HOMOZYGOUS
RECESSIVE. THIS WOULD GIVE A 50 CHANCE OF THE
RECESSIVE TRAIT APPEARING.
THIS PROCESS IS CALLED A TEST CROSS. IN A LITTER
OF DOGS, IF A RECESSIVE DOG APPEARS, THEN YOU
KNOW THAT THE ORIGINAL DOG WAS NOT A PUREBRED.
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TAKS FORMATTED ITEMS
IN DROSOPHILA MELANOGASTER (FRUIT FLIES), RED EYE
COLOR (R) IS DOMINANT OVER BROWN EYE COLOR (r).
IF THE FLIES IN THE PICTURE WERE CROSSED, WHAT
PERCENT OF THEIR OFFSPRING WOULD BE EXPECTED TO
HAVE BROWN EYES?
ANSWER 50
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TAKS FORMATTED ITEMS
H h

• WHICH OF THE FOLLOWING HAS THE hh GENOTYPE?
• 1 3
• 2
• 4
• NONE

H
1
4
3
h
2

• 2. WHICH OF THE FOLLOWING IS A TRUE STATEMENT?
• INDIVIDUAL 4 IS RECESSIVE
• INDIVIDUALS 1 3 ARE HETEROZYGOUS
• INDIVIDUAL 2 IS DOMINANT
• ALL INDIVIDUALS ARE FEMALE

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TAKS FORMATTED ITEMS
B b

• 3. IF B IS THE ALLELE FOR BLACK FUR AND b IS THE
  ALLELE FOR WHITE FUR, WHAT PERCENT WOULD BE
  BLACK?
• 25
• 50
• 100
• 75

B
Bb
BB
Bb
b
bb

• 4. WHAT FRACTION IS HOMOZYGOUS DOMINANT IN THE
  ABOVE CROSS?
• 1/2
• 1/4
• 1/3
• 3/4

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TAKS FORMATTED ITEMS
B B

• 5. IN THIS CROSS, WHAT IS THE RATIO OF BB TO Bb?
• 3 1
• 4 1
• 2 2
• 0 4

B
BB
BB
Bb
b
Bb
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• BIBLIOGRAPHY
• Mendel picture provided by wikipedia.com
• Dog and tree pictures provided by Microsoft
  ClipArt
• Graphics from TEA/ TAKS information booklet
  Middle School Science Grade 8
• Dice graphic from Microsoft Clipart