Download For instance: BB or bb.

• Heredity :
the passing of traits from
parent to offspring
Traits are controlled by genes,
SO what is GENETICS?
Genetics: The study of how
traits are inherited.
GREGOR MENDEL
o First known geneticist and
“father of genetics”
o Was an Austrian monk and was
born in 1822
o Did most of his genetic studies on
pea plants
WHAT ARE ALLELES?
o Are ONE FORM of a gene (there can be
more than one form)
o Sex cells have one form of a gene on their
chromosomes
o Body cells have two forms or ALLELES for
a single gene (you got one from Mom and
one from Dad)
o One may be dominant over another. If this
happens, the dominant gene is the one expressed.
If not, the recessive trait is expressed.
DOMINANT AND RECESSIVE
o A Dominant trait:
will always be expressed and will “mask” a
recessive trait
o A recessive trait
can only be expressed if there are no
dominant alleles present.
Example:
Eyecolor—Brown color is dominant
and blue is recessive.
A person can have a brown allele and
a blue allele but still have brown eyes
because the brown allele is dominant
and “hides” the blue allele.
• Generally, dominant alleles are
represented with a capital letter, and
recessive alleles are represented with
a lower case letter.
Example:
R= dominant r = recessive
Each
organism is
represented
by TWO
letters, one
for each
allele.
o “Purebred” species have two alleles of the
same trait
o Represented by two of the same letters. This
is called homozygous. For instance: BB or bb.
o Species with two different alleles or two
different forms of the gene would be
“hybrid”
o Represented by two different “letters” and by
called “heterozygous”. For instance: Bb
o The alleles present in the organism are
referred to as its genotype. For instance,
BB, Bb, or bb.
o The PHYSICAL trait that shows,
regardless of genotype is called a
PHENOTYPE.
o For instance, Blue or Brown Eyes.
PROBABILITY
o Helps predict the chance that
something will happen
o Example: the probability of throwing
heads or tails on a coin is 50% (1/2
chances)
o Your predictions become more
accurate with the more trials you run!
Using a Punnett Square…
o Used to help predict Mendelian
genetics
Steps for using the Punnett square:
1) One parent’s alleles (genotype) go
along the top
2) The other parent’s alleles go down
the side.
3) You fill in the squares like doing the
communicative property of
B
b
multiplication.
B
b
BB
Bb
Bb
bb
Let’s try some practice problems…
Practice Problem #1
• Predict the fur color of the offspring
of a brown heterozygous hamsters and a
white homozygous hamster. Brown is
dominant. White is recessive.
• Use any letter you like.
Practice Problem #1
b
b
B
b
Bb
Bb
bb
bb
Practice Problem #2
• Predict the offspring of 2 white
homozygous cows. Black is dominant
over white.
• Use any letter you like.
Practice Problem #2
b
b
b
b
bb
bb
bb
bb
Practice Problem #3
• Predict the offspring of 2 Grey
Heterozygous rats. Gray is dominant
over white, which is recessive.
• Use any letter you like.
Practice Problem #3
G
g
G
g
GG
Gg
Gg
gg
Practice Problem #4
• Predict the pea shape of the
offspring of one Heterozygous Round
Pea plant and one homozygous
wrinkled pea plant. Round is dominant
over wrinkled.
• Use any letter you like.
Practice Problem #4
r
r
R
r
Rr
Rr
rr
rr
Practice Problem #5
you don’t have to write this one down…
• What are the chances of having a boy
or a girl?
• How would you solve this one?
Practice Problem #5
X
X
X
Y
XX
XX
XY
XY