Download BB or bb.

Heredity & Genetics
• Heredity = the passing of
traits from parent to
offspring
o Traits are controlled by genes,
so therefore, GENETICS is
the study of how traits are
inherited through the action
of alleles
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
o He made careful observations,
and strictly adhered to the
scientific method
o He performed cross-pollination by
becoming the pollinator himself, and
controlling which plants mixed.
o Some traits Mendel worked with were
shape of pea and it’s pod, color and
shape of seeds, plant height, flower
position and flower color.
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.
o 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, and therefore would be
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 have
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.
Genetics by Brainpop
My Dad
has
brown
eyes (BB
or Bb)
My Mom has
blue eyes
(bb)
Miss Hemphill
has blue eyes (bb)
Therefore, my dad must have
the Bb genotype, because he
must have given me the “b”
allele. His “b” allele is
masked by his “B”/dominant
allele.
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!
Why is it that if a couple has 2
children, they don’t always have
one boy and one girl?
2 is a really small trial #…so won’t
always “see” the ratio!
…we will investigate this more later on!
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
multiplication.
4) See Below:
Steps for using the Punnett square:
Let’s say the parents are Bb and Bb
(the same genotype).
What would be their phenotype?
Brown Eyes
So you would predict:
1/4 offspring to be BB, or Brown Eyes
2/4 or 1/2 to be Bb, or Brown Eyes
and 1/4 to be bb or Blue eyes
b
B
B
b
BB
Bb
Bb
bb
So, if Miss Hemphill had children
with her husband to be …what
color eyes would they have?
b
b
b
b
bb
bb
bb
bb
Mr. Ellinger
Miss Hemphill
Blue eyes (bb)
Blue eyes (bb)
All of our kids would have blue eyes!
Using a Punnett Square Clip
Heredity by Brainpop
Heredity by Brainpop
1What do we call different forms a gene may have for a trait?
2What height of pea plant (tall or short) did Mendel find to be
dominant?
3Which kind of trait can’t be passed from parent to child?
a)Eye color
b) height
c) broken arm
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
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