Genetics, Heredity, DNA
Objectives:
• Define Genetics, heredity, and genes.
• Explain the relationship between traits and
heredity.
• Explain Gregor Mendel's contribution to
the development and understanding of
genetics.
1. What do we call different forms a gene may have for a
trait?
2. What height of pea plant (tall or short) did Mendel find
to be dominant?
3. How are dominant and recessive traits represented?
(upper or lower case)
Give an example!
• 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
o He performed cross-pollination
o He became the pollinator himself
o He controlled 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.
Genetics
Part II
Traits and Inheritance
Objectives:
• Explain the relationship between dominant
and recessive traits
• Compare and contrast homozygous and
heterozygous alleles.
• Explain the relationship between genotype
and phenotype.
• Compare and contrast homozygous and
heterozygous alleles.
WHAT ARE ALLELES?
o Alleles 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: (CAPITAL LETTERS)
will always be expressed and will “mask” a
recessive trait
o A recessive trait (lowercase letters)
can only be expressed if there are no
dominant alleles present.
Example:
Eye color—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 is
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
Mom has blue eyes
(bb)
Dad has brown
eyes (BB or Bb)
Therefore, Dad must have the Bb
genotype, because he must have given her
the “b” allele. His “b” allele is masked by
his “B”/dominant allele.
Daughter has blue eyes
(bb)
Genetics
Part III
Punnett Square
Objectives:
• Predict and analyze the genetic (genotype) and physical
(phenotype) characteristics of offspring using Punnett
Squares and pedigrees.
• Differentiate between genotype and phenotype.
• Predict possible parental genotype based on observable
phenotype of offspring.
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
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:
¼ offspring to be BB, or Brown Eyes
2/4 or 1/2 to be Bb, or Brown Eyes
and ¼ to be bb or Blue eyes
B
b
B
BB
Bb
b
Bb
bb
So, if Miss Carnigan had children
with her husband to be …what
color eyes would they have?
b
b
b
b
bb
bb
bb
bb
Mr. Ellinger
Miss Carnigan
Blue eyes (bb)
Blue eyes (bb)
All of their kids would have blue eyes!
Using a Punnett Square Clip
Let’s try some practice problems…
PUNNETT SQUARE
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
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