1. SINGLE TRAIT PUNNETT SQUARE
GENETICS
SINGLE TRAIT PUNNETT SQUARE

2. STUDENT EXPECTATION
7-2.6 STUDENTS WILL MAKE PREDICTIONS ABOUT POSSIBLE OUTCOMES OF VARIOUS GENETIC COMBINATIONS OF INHERITED CHARACTERISTICS T t TT Tt T T

3. HIGHLIGHT OF OBJECTIVE 2
SINGLE-TRAIT PUNNETT SQUARES MAY BE USED, AND STUDENTS WILL BE EXPECTED TO PREDICT GENETIC OUTCOMES.
75%
3:1

4. Gregor Mendel
The basic laws of heredity were first formed during the mid-1800’s by an Austrian botanist monk named Gregor Mendel. Because his work laid the foundation to the study of heredity, Mendel is referred to as “The Father of Genetics.”

5. Mendel’ Pea Plants
Mendel based his laws on his studies of garden pea plants. Mendel was able to observe differences in multiple traits over many generations because pea plants reproduce rapidly, and have many visible traits such as:
Pod color
Seed Color
Plant Height
Green
Yellow
Green
Yellow
Seed Shape
Short
Pod Shape
Tall
Wrinkled
Round
Smooth
Pinched

6. Mendel’s Experiments
Mendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring. X
Short Offspring
Purebred Short Parents X
Purebred Tall Parents
Tall Offspring

7. Mendel’s First Experiment
Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants. X
Parent Short P generation
Parent Tall P generation
Offspring Tall F1 generation
Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

8. Mendel’s Second Experiment
Mendel then crossed two of the offspring tall plants produced from his first experiment.
Parent Plants
Offspring X
Tall F1 generation
3⁄4 Tall & 1⁄4 Short F2 generation
Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

9. TOOLS TO KNOW
PARENT’S GENES
A PUNNET SQUARE IS A TOOL USED TO PREDICT THE POSSIBLE GENOTYPES FOR THE OFFSPRING OF TWO KNOWN PARENTS.
PARENT’S GENES

10. T,t TT, tt Tt, Gg TERMS TO KNOW ALLELES HOMOZYGOUS HETEROZYGOUS
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

11. Tt, Gg T OR G t or g TERMS TO KNOW HYBRID DOMINANT RECESSIVE
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

12. TERMS TO KNOW PHENOTYPE TALL, SHORT, GREEN, WRINKLED GENOTYPE
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
3:1, 2:2, 1:2:1

13. 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

14. 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

15. HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
WHAT DO THE RESULTS SHOW?
RESULTS: B B
PHENOTYPIC: 100% BLACK
4:0 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
4:0 ALL Bb b Bb Bb
THEN WE CAN MAKE PREDICTIONS ABOUT THE OUTCOMES

16. HOW TO USE A PUNNETT SQUARE
WHAT ARE THE RESULTS?
LET’S LOOK AT ANOTHER PUNNETT SQUARE AND PREDICT THE OUTCOME T t
PHENOTYPIC:
75% TALL % SHORT
3 TO 1 RATIO: TALL TO SHORT T T T T t
T IS THE DOMINANT ALLELE FOR TALLNESS
GENOTYPIC:
1TT: 2Tt: 1tt :2:1 RATIO
25 %TT, % Tt, 25% tt t T t t t
t IS THE RECESSIVE ALLELE FOR SHORTNESS

17. 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?

18. 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?

19. PRACTICAL APPLICATION OF PUNNETT SQUARESD D
IF THE DOG IS PUREBRED (DD), IT DOESN’T 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 DD d Dd Dd d d Dd Dd Dd Dd

20. 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 DD Dd d Dd dd d d Dd dd Dd dd

21. PRACTICAL APPLICATION OF PUNNETT SQUARESD d D d D DD Dd d Dd dd d Dd dd d 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.

22. TAKS FORMATTED ITEMS ANSWER: 50%
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%

23. TAKS FORMATTED ITEMS H h H 4 1 h 3 2
WHICH OF THE FOLLOWING HAS THE hh GENOTYPE?
1 & 3 2 4
NONE H 4 1 h 3 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

24. TAKS FORMATTED ITEMS B b B BB Bb b Bb bb
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 b Bb bb
4. WHAT FRACTION IS HOMOZYGOUS DOMINANT IN THE ABOVE CROSS?
1/2
1/4
1/3
3/4

25. TAKS FORMATTED ITEMS B B B BB BB b Bb Bb
5. IN THIS CROSS, WHAT IS THE RATIO OF BB TO Bb?
3 : 1
4 : 1
2 : 2
0 : 4 B BB BB b Bb Bb