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GENETICS & HEREDITY
Chapters 9.1 & 9.2
REMEMBER…
• If it is in RED it goes in your notes
• If it is in BLACK it is important, so pay attention
KEEP AN EYE OUT FOR HOOTIE!!
• If you see him RAISE YOUR HAND!!
• You will receive 5 ROCKS cards
• IF you are correct
• HINT: He won’t be this big :)
MENDEL
• What did Mendel study?
MENDEL
•He found that the plants had
offspring.
•What does Purebred mean?
•Many generations have same traits
without a change.
•EX. TT or tt
MENDEL
•What does hybrid mean?
•There have been changes over
the generations
•Ex. Tt or Pp or Bb
ALLELES
• Alleles are the different forms of genes
• TYPES
• Dominant-ALWAYS SHOWS THROUGH. Labeled
with a capital letter
• Recessive-HIDDEN traits. Labeled with a lower
case letter.
Pp
Dominant Allele Recessive Allele
T-Pink
t-Blue
What trait will show through in this
example?
T-Pink
t-Blue
What trait will show through in this
example?
T-Pink
t-Blue
What trait will show through in this
example?
T-Pink
t-Blue
Is the purebred or Hybrid?
T-Pink
t-Blue
Is the purebred or Hybrid?
T-Pink
t-Blue
Is the purebred or Hybrid?
DEFINITIONS
•Genotype- the genes of an organism
for one specific trait
•Phenotype- the physical appearance of
a trait in an organism
HUGE TO KNOW!!!!
•Homozygous= two alleles
that are the same for a trait
(Pure) EX. TT, tt, BB or bb
•Heterozygous= two different
alleles for a trait (Hybrid)
•EX. Tt, Bb
HINT:::::
HETEROZYGOUS
ALWAYS MEAN
DOMINANT!!!!!!!!!!!!!
PRACTICE
•We use two letters to represent the genotype.
• A capital letter represents the dominant form of a gene
(allele)
•lowercase letter represents a recessive form of the gene
(allele).
•Example below: P=dominant purple and p= recessive
white
The phenotype for this
flower is violet while
its genotype (if
homozygous) is PP.
The phenotype for this
flower is white while
its genotype is pp (to
be white the flower
must have two of the
recessive copies of the
allele).
PUNNETT SQUARES
The Punnett square is
the standard way of
working out what the
possible offspring of
two parents will be.
• It is a helpful tool to
show allelic
combinations and
predict offspring
ratios.
BEFORE WE GO FURTHER LETS REVIEW
HOW TO SET UP A PUNNETT SQUARE…
We begin by constructing a grid of two
perpendicular lines.
Next, put the genotype of one parent across
the top and the other along the left side.
For this example lets consider a genotype of
BB crossed with bb.
B
b
b
B
• Notice only one
letter goes above
each box
• It does not matter
which parent’s
genotype goes on
either side.
Next, fill in the boxes by copying the
column and row head-letters down and
across into the empty spaces.
B
B
b
Bb
Bb
b
Bb
Bb
PUNNETT SQUARES
• Now that we have learned the
basics of genetics lets walk
through some examples using
Punnett Squares.
Usually write the
capital letter first
Lets say:
W- dominant white
w- recessive violet
Cross 2 parents are heterozygous (Ww).
What percentage of the offspring will have violet
flowers?
ANSWER: 25% (homozygous recessive)
Red hair (R) is dominant over blond hair (r). Make a
cross between a heterozygous red head and a blond.
R
r
r
r
What percentage of the offspring will have red hair?
50%
Let’s try some more…
In pea plants, tall pea plants (T) are
dominant over short pea plants (t).
Construct a Punnett
Cross a heterozygous tall pea plant
and a short pea plant.
T
t
t
What are the
percentage of
phenotypes?
t
50% tall
50% short
Black eyes (R) is dominant over red eyes (r)
in rats. Make a cross between a homozygous rat with
black eyes and a rat with red eyes.
r
R
Rr
r
Rr
R
Rr
What is the possibility
of a red eye off
springs?
Rr
0%

CLASSWORK:
LET’S TRY THIS TOGETHER