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SINGLE TRAIT PUNNETT SQUARE
Tt
T
t
T
t
¼
Punnett Squares
Genetics
• Genetics is the study of genes and inheritance
• Inheritance is how traits are passed on from generation to generation.
• Chromosomes are made
up of genes, which are made up of DNA.
Gregor Mendel
• Austrian monk
• Experimented with pea plants
• He discovered that traits were carried from one generation to the next.
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
TERMS TO KNOW
HYBRID ONE OF EACH TRAIT (SAME AS HETEROZYGOUS) Tt, Gg
DOMINANT A TRAIT THAT DOMINATES THE OTHER FORM OF THE TRAIT
THE TRAIT THAT IS VISIBLE
REPRESENTED BY AN UPPERCASE LETTER
T OR GRECESSIVE THE TRAIT BEING
DOMINATED OR COVERED UP BY THE DOMINATE TRAIT
THE TRAIT IS NOT VISIBLE
REPRESENTED BY A LOWER CASE LETTER
t or g
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
(SAME AS MATH)
3:1, 2:2, 1:2:1
Mendel’s Experiment
He chose to work with pea plants because
– Readily available– Reproduced quickly– Traits were distinct
Mendel’s Experiment
Mendel crossed true breeding plants that had two distinct and contrasting traits, like purple and white flowers. After the first cross, the plants self-fertilized.
Mendel’s ExperimentP generation is parental generation.
F1 generation is the first generation.
F2 generation is the second generation.
Mendel’s Experiment
He studied these seven traits
Mendel’s Phenotypic Conclusions
In the F1 generation, all plants had the same trait.
In the F2 generation, there was always a 3:1 ratio of a single trait.
Mendel’s Genotypic Conclusions
In the F2 generation,
The genotypic ratiois different.
Remember P is dominant so the plants will be purple even with Pp.
TOOLS TO KNOW
A PUNNET SQUARE IS A TOOL USED TO PREDICT THE POSSIBLE GENOTYPES FOR THE OFFSPRING OF TWO KNOWN PARENTS.
PARENT’S GENES
PA
RE
NT
’S G
EN
ES
HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
THE PARENTS’ ALLELES GO ON THE OUTSIDE OF THE SQUARE B B
b
b
BB X bb
HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
THE PARENTS’ ALLELES GO ON THE OUTSIDE OF THE SQUARE B B
b
b
B B
B BUPPERCASELETTERS SHOULDGO FIRST
b b
b b
HOW TO USE A MONOHYBRID (ONE TRAIT) PUNNETT SQUARE
B B
b
b
Bb Bb
Bb Bb
WHAT DO THE RESULTS SHOW?
B IS THE DOMINANT ALLELE FOR BLACK
b IS THE RECESSIVE ALLELE FOR BROWN
RESULTS:
PHENOTYPIC: 100% BLACK
4:0 RATIO, BLACK TO BROWN
GENOTYPIC:
100% Bb
4:0 ALL Bb
Bb Bb Bb Bb
HOW TO USE A PUNNETT SQUARE
T t
T
t
RESULTS:
TT, Tt, Tt, tt
PHENOTYPIC:
75% TALL 25% SHORT
3 TO 1 RATIO: TALL TO SHORT
GENOTYPIC:
1TT: 2Tt: 1tt 1:2:1 RATIO
25 %TT, 50% Tt, 25% tt
LET’S LOOK AT ANOTHER PUNNETT SQUARE AND PREDICT THE OUTCOME T T
T t
T t
t t
T IS THE DOMINANT ALLELE FOR TALLNESS
t IS THE RECESSIVE ALLELE FOR SHORTNESS
Probability and Punnett Squares
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