Download Can 2 Brown-Eyed Parents have a Blue

Can 2 Brown-Eyed Parents
have a Blue-Eyed Baby?
+
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UNDERSTANDING HEREDITY
Copy WHITE
??
Before we begin, we need to
understand how babies are made!


Egg and sperm come together to
make a zygote…
The DNA in the egg & sperm
determines what DNA goes in the
zygote.
Zygote: Cell
made when egg
& sperm join
 Chromosomes come in
HOMOLOGOUS PAIRS
matching
Gender
Half the chromosomes
comes from the
FATHER.
The other matching
half comes from the
MOTHER.
In genetics, there are
2 ways to describe
individuals…
In genetics, there are 2 ways to describe individuals…
(1)

Phenotype:
The physical traits that an organism has.
Can you list 3
traits of my
phenotype?
(PHENOtype --> type of PHYSICAL features)
More practice…
List 2 differences in their
Phenotype:
A)
B)
and
and
In genetics, there are 2 ways to describe individuals…
(2)

Genotype:
The genes that an organism has.
 Represented by letters.
(GENotype --> type of GENES)
More practice…
Do these have the same
Genotype?
Hint: DNA (genes)  RNA  PROTEIN TRAIT
A)
B)
and
and
There can different versions of the same gene…
Genotype (cont.)

There are different versions of the same gene,
called alleles.

For every trait, you have 2 alleles.
- One version from your father (through sperm)
- One version from your mother (through egg)
Mom’s
version
Dad’s
version
Normal Human Karyotype
1
2
3
4
5
6
7
8
Eye color
9
10
11
17
18
19
12
20
13
14
21
22
15
16
X X
We will only be looking at 2 types of
alleles for now:
DOMINANT
ALLELES
and
recessive alleles
The 2 types of alleles we are looking at…
(1)
Dominant Allele:
 Its trait is expressed all the time.
 Represented by a capital letter.
(Example: B = brown eyes)
The 2 types of alleles we are looking at…
(2)
Recessive Allele:
 Its trait is expressed ONLY if there is no dominant
allele.
 Represented by a lowercase letter.
(Example: b= blue eyes)
Dominant vs. Recessive
Ssh! I’ll speak
for both of us!
Let’s look at zygosity – the 2
alleles the zygote has.
Allele from
sperm
Gene for Eye Color
Allele from
egg
“Zygosity”– Looking at the 2 alleles that the zygote has…
Homozygous:
 Homo = “Same”
 Homozygous = Having 2 of the same
alleles for the same gene
“Homozygous Dominant”
Recessive”
Dominant
Recessive
Recessive
Dominan
t
“Zygosity”– Looking at the 2 alleles that the zygote has…
Heterozygous:
 Hetero = “Different”
 Heterozygous = Having 2 different alleles
for the same gene
Dominant
(R)
Recessive
(r)
So how do we use this information??
What are the possible genotypes for eye color for the children of
…a dad that is homozygous recessive and
…a mom that is heterozygous?
Dad’s
Body cell
rr
Rr
meiosis
Mom’s
Body cell
meiosis
Possible SPERMS made by Dad
Possible EGGS made by Mom
As you see, there are
many combinations…
A Punnett Square
will make this easier!
Zygote
Four Easy Steps to
Solve PUNNETT SQUARES!
1. Make a square with 4 boxes
2. Put Mom’s genotype in 2 eggs (left)
3. Put Dad’s genotype in 2 sperms (top)
4. Drop the top, Drag the left
From Mom
From Dad
Homozygous
Dominant Mom
×
Homozygous
Dominant Dad
Genotypic Ratio=
Phenotypic Ratio=
Heterozygous
Mom
×
Homozygous
Dominant Dad
Genotypic Ratio=
Phenotypic Ratio=
Heterozygous
Mom
×
Heterozygous
Dad
Genotypic Ratio=
Phenotypic Ratio=
B
b
b
Bb
bb
b
Bb
bb
bb
Bb
?
What color eyes do
you think the younger
brother has?
B
bb
b
b
Bb
bb
b
Bb
bb
bb
?
bb
?
bb
?
NOTE: The probability resets for every baby!
Vocabulary Squares
Textbook Definition
Definition in Your Own Words
Describes an individual that
has identical alleles for a
trait on both homologous
chromosomes.
When someone has two of
the same version for a gene.
Homozygous
I’ll speak for
both of us!
No! I’ll speak
too!
Picture
Jack has BB, so he is
homozygous dominant.
Example – or – In a Sentence
Possible other Vocabulary for your squares:
 Punnett Square
 Probability
 Zygote
 Trait
 Heredity
 Dihybrid cross
 Polygenic