Genetics…
it’s all about
YOU!
Have you ever heard someone say…
“You have your father’s eyes.”
or
“You’ve got your mother’s smile.” or
physical
characteristics
“You look just like your grandfather.”
We all know that we get certain traits
from our parents or grandparents.
But have you ever wondered HOW it happens?
How you got your dad’s eyes or your mom’s smile?
The answer to “How does it happen?” is…
GENETICS!
Heredity is
the passing of traits from
parents to offspring.
Genetics is the study of heredity.
Traits are physical characteristics, like
eye color, hair color, freckles,
or blood-type.
Who was the first person to study genetics?
An Austrian priest and
science teacher named
Gregor Mendel
Some Human Traits
Dimples
mid-digit hair
cleft chin
Tongue-roller
Mendel was an Austrian monk
and science teacher who was
also responsible for the
monastery’s garden.
During the years 1856-1863, he
conducted experiments with
over 28,000 pea plants.
His experiments were the first
large-scale, long-term scientific
study of heredity ever done.
His work, published in 1865, was ignored at the time,
because other scientists did not understand its importance.
However, Mendel’s experiments with pea plants
were rediscovered in 1900. He is now known as
the “Father of Genetics” for his discoveries of
inheritance patterns in pea plants.
Mend
el
flower bed
staircase & flower bed
Photos of Brno
monastery in Austria
Photos of Brno
monastery in Austria
northern wall of the monastery’s garden
beehives and apiary
Mendel’s choice of pea plants for his
experiments was a good choice, for 2 reasons:
1. They reproduce quickly & have many offspring
2. They have many simple, either-or traits
Mendel tested 7 pea plant traits:
 seed shape
 pod color
 seed color
 pod shape
Inflated
Pinched
 flower color
 stem height
Short
 flower
position
Side
End
Pea
Plants
In order to control
which plants
pollinated which
plants, Mendel had
to hand-pollinate
every flower in the
pea plants he was
experimenting on.
purebred
purebred means that all the offspring have
the same trait as the parents.
Short
X
Short
X
Short
Short
Short
In his first experiment, Mendel crossed
(mated) a purebred tall pea plant with a
purebred short pea plant.
Short
X
What do you think happened?
You would predict that half the offspring would
be tall and half would be short, wouldn’t you?
Or maybe you would predict that the
offspring would all be medium height.
Mendel’s first
experiment
Both predictions are WRONG!!!
In every single experiment, Mendel found
that ALL the offspring were… tall!!!
Short
P generation
(parents)
X
purebred tall
purebred short
F1 generation
(children)
offspring are all tall
So what happened to the “short” trait? Did it
disappear?
Here’s where Mendel showed true genius!
What he did next was… he crossed (mated)
the tall offspring from the first experiment
with each other.
X
Mendel’s second
experiment
He was trying to find out if the “short” trait
had really disappeared, or if it was still
present in the tall pea plants, but was
covered up somehow.
The results from his second cross were truly
amazing. What do you think happened?
In EVERY SINGLE EXPERIMENT, the
offspring in the second cross were:
offspring of
first cross
(F1 generation)
X
Short
offspring of
second cross
(F2 generation)
3/4 (75%) tall & 1/4 (25%) short
P1
generation
Here’s a summary of Mendel’s experiments
X
“Parents”
Here’s a
(purebred
plants)
summary of
Mendel’s
experiments
X
F1
generation
“Children”
(hybrid tall
plants)
F2
generation
“Grandchildren”
75% tall
25% short
Mendel tested his experiment again and
again, and got the same results every time.
Then he tested 6 other traits in the same way, and
he got the exact same results with those traits.
“Parents”
P
“Children”
F1
“Grandchildren”
F2
The F1 generation
plants were always
100% the dominant
trait.
The F2 generation
plants were always
75% the dominant
trait, and 25% the
recessive trait.
Mendel’s
actual
experimental
results
So, what’s going on here?
Mendel drew several conclusions:
1. The inheritance of each trait is determined
by "factors" (now called genes) that are passed
on from parents to offspring unchanged.
2. An organism inherits two factors, one from
each parent, for each trait.
3. One factor can “mask” or cover up another
factor.
4. A trait may not show up in an individual but
can still be passed on to the next generation.
Genes
Mendel realized that one factor in a pair was
masking, or hiding, the other factor. For
instance, in his first experiment, when he
crossed a purebred tall plant with a purebred
short plant, all offspring were tall. Although the
F1 offspring all had both tall and short factors,
they only displayed the tall factor. He
concluded that the tallness factor masked, or
“covered up”, the shortness factor.
Today, scientists refer to the “factors” that
control traits as genes.
Genes
A gene is a section of a chromosome,
which contains the instructions for a trait
(Examples: plant height or flower color in
pea plants, or hair color and blood type in
humans)
Genes
All chromosomes come in
pairs that are the same size,
and have the same genes in
the same locations. This is
because an organism inherits
2 sets of chromosomes, one
from the father and one from
the mother.
Since the chromosomes come in
pairs, the genes come in pairs too.
Every organism has 2 of every gene
in their chromosomes. These genes
are called gene pairs.
Alleles
• different forms of a gene
For example:
 If the gene is for tail color
 If the gene is for flower
in critters, the 2 alleles
would be “blue tail” or
“orange tail”.
color in pea plants, the 2
alleles would be “purple”
or “white”.
Chr.
Gene for
tail color
Blue allele
Gene for
flower color
Orange allele
Alleles
• different forms of a particular gene
What are some possible alleles for:
~ handedness?
~ hair color?
~ eye color?
~ hair texture?
~ dimples?
Dominant and Recessive
Dominant and Recessive Alleles
Alleles
Dominant: Alleles that cover up or
hide recessive alleles.
Recessive: alleles that are hidden or
covered up by a dominant allele.
Which of the 2 tail color alleles
in critters was dominant?
Homozygous and Heterozygous
 homozygous: has 2 identical
alleles for a trait (purebred)
 heterozygous: has 2 different
alleles for a trait (hybrid)
Homozygous
or
Heterozygous?
Homozygous or Heterozygous?
TT
bb
Rr
SS
Gg
tt
YY
Alleles
Homozygous or Heterozygous?
A
b
a
c
D
e
c
d
e
F
F
G
h
I
G
B
H
I
Genetic Notation
Geneticists assign a letter to each allele for a
trait. They use the first letter in the dominant
trait. So, for the trait stem height, since tall is
dominant, the letter “T” would be used. The
dominant allele (tall) is abbreviated “T” and the
recessive allele (short) is abbreviated “t”.
A purebred tall plant would be TT, and
a purebred short plant would be tt.
A hybrid pea plant (like the tall plants
in the F1 generation) would be Tt,
because it has one dominant tall allele,
and one recessive short allele.
Genetic Notation
Genotype and Phenotype
 An organism’s genotype is its
genetic make-up. (Examples: TT, Tt, tt)
 An organism’s phenotype is its
physical appearance. (Examples: tall
plant, round seed, purple flower)
Genotype
Phenotype
TT
tall plant
Tt
tall plant
tt
short plant
What would be the phenotype for the following
genotypes?
Genotype
Gg
gg
Phenotype
green pod
GG
yellow pod
green pod
pp
white flower
Pp
purple flower
PP
purple flower
Yy
yellow seed
RR
round seed
rr
wrinkled seed
SS
side flower
What are the possible genotypes for the
following phenotypes?
Phenotype
end flower
Possible Genotypes
ss
side flower
SS, Ss
green seed
yy
yellow seed
YY, Yy
round seed
RR, Rr
wrinkled seed
tall plant
short plant
rr
TT, Tt
tt
Probability…
• is the likelihood (chance) that an event
will happen.
• is expressed as a percentage or fraction.
Everyday examples of probability:
• weather! Lots of times we hear predictions like
“80% chance of rain,” or “20% chance of snow.”
• the lottery “There’s a 1 in 10 million chance
your ticket will be a winner.”
• genetics is all about probability
Calculating Probability
Probability is calculated using this formula:
Actual outcomes
x 100 = Probability %
Possible outcomes
Example A: If I flip a coin, the probability that it will
show heads is 1 out of 2, or 50%.
Example B: If I roll a die, the probability that I will roll a
3 is 1 out of 6, or 16.7%.
Example C: If I roll a die, the probability that I will roll an
even number is 3 out of 6, or 50%.
Multiple Probabilities
In multiple probabilities (likelihood of 2 or
more events happening at the same time),
you multiply the probability of one event
times the probability of the second event.
Prob of Event 1 x Prob. of Event 2 = Multiple Probability
For example: the probability of flipping
two coins and getting 2 heads is:
1 x 1= 1
2
2
4
or 25%
Probability Practice
1. What is the probability that, if I roll a pair of dice,
I will get 2 sixes?
1 out of 36, or 2.8%
2. What is the probability that, if I flip a penny 10
times, I will get heads all 10 times?
1 ÷ 210, or 1/1024
3. If I’m a pea plant, and my father is hybrid tall, what
is the probability that I got a t gene from him? 1/2
4. If I’m a pea plant, and my mother is hybrid tall, what
is the probability that I got a t gene from her?
1/2
5. If I’m a pea plant, and both my parents are hybrid
tall, what is the probability that I will get a t gene
from both of them?
1/2 x 1/2 = 1/4, or 25%
Probability
When flipping 2 pennies, there are 4
possible outcomes:
H-H
H-T
T-H
T-T
Same thing
Probability Probability Probability Probability
1/4 or 25% 1/4 or 25% 1/4 or 25% 1/4 or 25%
25% + 25% = 50%
How does this relate to genetics?
In hybrid (heterozygous) crosses, the
probabilities are the same as when flipping
pennies!
Punnett Squares
Punnett squares are diagrams that show the
probability that offspring will inherit a certain
trait.
For example: this is a Punnett square for a cross
between two purebred (homozygous) tall pea plants.
Genotype of offspring:
T
T
T
TT
TT
T
TT
TT
100% TT
Phenotype of offspring:
100% tall
Two purebred tall plants can only have
purebred tall offspring.
How To Make Punnett Squares
How about a cross between two purebred
short pea plants?
Short
t
Short
t
Genotype of offspring:
100% tt
t
tt
tt
t
tt
tt
Phenotype of offspring:
100% short
Two purebred short plants can only
have purebred short offspring.
How about a cross between a purebred tall
and a purebred short pea plant?
t
t
T
T
Tt
Tt
Tt
Tt
Genotype: 100% Tt
Phenotype: 100% tall
This is a Punnett square of Mendel’s first
experiment. The result is all hybrid tall
offspring.
Cross between 2 Hybrid (Heterozygous)
tall plants
T
t
T
TT
Tt
t
Tt
tt
Genotype:
TT 25%
Tt 50%
tt 25 %
Phenotype:
Tall 75%
Short 25%
Look familiar? This is Mendel’s second cross…
Okay…how about a cross between a
purebred tall and a hybrid tall plant?
T
T
T
TT
TT
t
Tt
Tt
Genotype:
50% TT, 50% Tt
Phenotype:
100% tall
How about a cross between a purebred short
and a hybrid tall plant?
Genotype:
t
t
T
Tt
Tt
t
t t
t t
50% Tt, 50% tt
Phenotype:
50% tall, 50% short
Punnett Square for Albinism in Humans
In the cross Nn x Nn, where N is a dominant allele for
Normal pigmentation and n is a recessive allele for no
pigmentation (albinism), there is a¾_ probability the
offspring will be normal pigmentation and ¼_ probability
they will be albino.
N
n
N NN Nn
n
Albino
child,
USA
Nn
nn
Albino
child,
Tanzania
Dirk brings his family tree to
class
Family Tree
Exploring a Pedigree
Pedigree: diagram that shows the presence of a trait in a family.
A carrier is a person who does not have the recessive
trait, but does have the recessive gene. (They’re hybrid)
Pedigree of Queen Victoria of England
for the trait of hemophilia
How many children did Victoria and Albert have?
How many were daughters, and how many were sons?
How many of Victoria’s daughters were carriers of the hemophilia gene?
How many of Victoria’s sons were hemophiliacs?
How many of her grandsons were hemophiliacs? How many of her great-grandsons?
Mermaid Tails
Pedigree Analysis is a Key Tool in Human
Genetics
Analyzing a pedigree is like puzzle-building – you try things
(assigning potential genotypes) until the pieces fit, and
you’re as certain as you can be about genotypes and
inheritance patterns (autosomal vs. X-linked; dominant vs.
recessive; complete, incomplete or co-dominance).
Pedigree Analysis
Shea Family PedigreeBlue/non-blue eyes
Shea Family PedigreeADD/non-ADD
A Pedigree of a Dominant Human Trait
A Pedigree of a Recessive Human Trait
Note that the trait can
appear in offspring of
parents without the trait.
Heterozygotes
(hybrids) who do not
show the trait are
termed carriers.
How many possible
carriers are there on
this pedigree?
7
Co-Dominance
One exception to the dominant / recessive pattern
is co-dominance. In this pattern, both alleles are
dominant, and both traits are expressed.
A capital letter represents one of the co-dominant alleles.
A different capital letter represents the other co-dominant
allele.
In cattle, red and white coats are co-dominant. The hybrid
offspring is called roan; it has both red and white hairs in its
coat.
RR
red
roan steer
X
RW
roan
WW
white
Co-Dominance
In horses, gray horses (GG) are codominant to white
horses (WW). The heterozygous horse (GW) is an
appaloosa horse (a white horse with gray spots).
Gray (GG)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
X
White (WW)
Appaloosa (GW)
BLOOD TYPE: an example of codominance in humans
There are 4 blood types: A, B, AB, O
 Blood type is determined by 2 factors in the blood:
factors A and B.
•If factor A is present, you are Type A.
•If factor B is present, you are Type B.
•If A and B factors are present, you are Type AB.
•If neither factor is present, you are Type O.
• The A and B factors are co-dominant; when both are
present, both are expressed.
• Type O is recessive (needs two O genes to be present).
Blood Type Genotypes & Phenotypes
Phenotype
Type A blood
Genotype
AA
or
AO
Type B blood
BB
BO
Type AB blood
AB
Type O blood
OO
or
1) What are the genotype and phenotype probabilities
for the children of a man with Type A blood
(homozygous) and a woman with type B blood
(homozygous)?
2) What are the genotype and phenotype probabilities for
the children of a man with Type O blood and a woman with
Type AB blood?
1) What are the genotype and
phenotype probabilities for the
children of a man with Type A
blood (homozygous) and a
woman with Type B blood
(homozygous)?
2) What are the genotype and
phenotype probabilities for the
children of a man with Type O
blood and a woman with Type
AB blood?
Incomplete Dominance
One thing Mendel didn’t realize was that there are some
exceptions to the dominant / recessive pattern of
inheritance that he observed in his pea plants.
One exception is: incomplete dominance. In this
pattern, one allele/trait does not completely dominate
the other allele/trait. The result: the traits are blended.
F1 generation:
offspring of red
and white
flowers are all
pink (a blend of
the 2 parents’
colors).
Incomplete dominance
F2 generation:
offspring of
pink plants are
25% red, 25%
white, and 50%
pink
Incomplete Dominance
Here’s what’s happening:
R
R
W
RW
RW
W
RW
RW
Red crossed with white
makes pink offspring.
R
W
RR
RW
W RW
WW
R
Pink crossed with
pink makes:
25% red
25% white
50% pink
Incomplete Dominance
A capital letter (P) represents one of the incompletely
dominant alleles.
 The same capital letter prime (P1) represents the other
incompletely dominant allele, so that the two do not get
mixed up.
In humans, curly hair (HH)
A heterozygous
human has wavy hair
(HH1).
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
is incompletely dominant
to straight hair (H1H1).
Cross a person with
curly hair with a person
who has wavy hair.
Polygenic Inheritance
When a single trait is determined by more than
one gene, we say that it is polygenic.
Also:
• eye color
• hair color
• blood type
Height is a
polygenic trait
Multiple Alleles
• Eye color is determined by more
than one gene
• Thus eye color appears to vary on
an almost continuous scale from
brown to green to gray to blue
• Eye color is determined by three
genes: one controls texture of the iris
which refracts light to make blue, and
a second which determines the amount
of pigment, called melanin. When a
small amount of melanin is present,
blue or green eyes result, while brown
& black eyes result from increasing
amounts of melanin
Eye Color
Eye colors can range from the most common color,
brown, to the least common, green. Rare genetic
specialties can even lead to unusual eye colors:
black, red, and violet. Eye color is an inherited trait
influenced by more than one gene (polygenic).
There are 3 genes that control
eye color. One gene has Brown
(B) and blue (b) alleles (Brown
is dominant over blue). The 2nd
gene also has 2 alleles: Green /
hazel (G) and lighter color (g).
Green is dominant over the
lighter-color allele.
Heterochromia (eyes that
are different colors)
Eye Color Calculator
activity
Hair color
• Hair color is determined by
more than one gene
• Thus hair color appears to
vary on an almost
continuous scale from
black to brown to blond to
red
• The brown and black
pigment is melanin
• The red pigment is an ironcontaining molecule
Hair color
It is thought that hair color is controlled by
two genes.
Brown hair
Black hair
Dark brown hair
Red hair
Auburn hair
Grey (gray) hair
Blonde hair
White hair
One gene has 2 alleles: Brown (B) and blonde (b).
The 2nd gene has 2 alleles: Non-red (N) and red (n).
The combination of these two genes, plus
environmental factors (and age), contributes to the
many different shades of hair color in humans.
Skin Color
Skin color is determined by the amount and
type of melanin, the pigment in the skin. Skin
color is determined by 6 different genes, which
accounts for the vast range of different skin
colors in human beings.
link
Chromosomes, Genes and DNA
The structure and an actual
picture of a chromosome.
Human chromosome set from a
skin cell.
Chromosomes are long strands of DNA, wrapped
around proteins. Humans have 46 chromosomes in every
cell.
Genes are sections of chromosomes. Humans
have 20,000 - 25,000 genes in every cell.
karyotype
Karyotype: a picture of all 46 of a person’s
chromosomes, arranged in 23 pairs.
Note that 22 of the 23
pairs of chromosomes
are the same size, and
have the same
banding patterns.
However, the 23rd pair
of chromosomes do not
look alike at all.
The 23rd pair of
chromosomes are
called the “sex”
chromosomes, or “X
and Y” chromosomes.
The first 22 pairs of
chromosomes are
called “autosomal.”
Make a karyotype
How scientists read chromosomes
Human Chromosome 1
False-color photograph shows human chromosomes,
with the Chromosome 1 pair highlighted in blue.
Chromosome 1 contains nearly twice as many genes as the
average chromosome and makes up eight percent of the
human genetic code. It is packed with 3,141 genes and
linked to 350 illnesses including cancer, Alzheimer’s,
Parkinson’s disease, and a gene for a common form of cleft
lip and palate.
X and Y Chromosomes
The 23rd pair of chromosomes in
humans determines a person’s
gender.
A female has two X chromosomes;
a male has 1 X and 1 Y chromosome.
Female: XX
Male:
XY
X chromosome is much larger than the Y chromosome.
B
Which of these
karyotypes shows a
male, and which
shows a female?
A
Gender Determination
egg
girl
X
X
boy
Y
Genetic abnormalities of the XY Chromosomes
Klinefelter
Syndrome
XYY syndrome
Triple X
syndrome
Turner
Syndrome
Fragile X Syndrome
Fragile X Syndrome
Fragile X syndrome is caused by a mutation in
the FMR1 gene, located on the X chromosome.
The mutated gene cannot produce enough of a
protein that is needed by the body's cells,
especially brain cells, to develop and function
normally.
There are a variety of symptoms, including:
Mental retardation, Hyperactivity, Short
attention span, and Autism.
Click here to learn
more about FXS
Down Syndrome
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are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Down Syndrome, or Trisomy 21,
occurs when a person has 3
copies of Chromosome 21,
instead of the normal 2 copies.
Other Genetic Abnormalities
Who’s Got the Most Chromosomes?
Who’s Got the Most Chromosomes?
Plants
Animals
Apple
34
Dog
78
Peas
14
Frog
26
Onion
16
Goldfish
94
Potato
48
Horse
66
Rice
24
Housefly
12
Tomato
24
Human
46
Corn
20
Mosquito
Click here to find out how
many chromosomes
other species have.
6
Mouse
40
Chicken
78
GENES BY THE NUMBERS
Even though all
the cells
the body
contain the exact same
GENES
BYinTHE
NUMBERS
genes, the genes that are “turned on” in each cell vary
depending on the cell’s function. These are the numbers of
working genes in different parts of the body.
Brain
3195
White blood cell
2164
Liver
2091
Heart
1195
Pancreas
1094
Bone
904
Colon
879
Skeletal muscle
735
Kidney
712
Skin
629
Thyroid Gland
584
Eye
547
Small Intestine
297
Smooth muscle
127
Esophagus
76
Red blood cell
8
Some Genetics Numbers
Some Genetics Numbers
3 billion base pairs
1 billion codons
in one human cell
there are…
25, 000 genes
46 chromosomes
6.5 feet of DNA
Number of people on Earth: 7 billion
Number of people with exactly your DNA ….1
YOU !!!
Asexual Reproduction
Asexual Reproduction
 organism divides and produces an exact
replica (clone) of itself.
Examples: bacteria, amoeba, yeast, algae
• no genetic material (DNA) is exchanged.
• no genetic diversity in the species
(except for mutations)
algae
amoeba
paramecium
hydra (budding)
Sexual Reproduction
Sexual
 involves the
mixingReproduction
of DNA, usually from the union
of an egg cell and a sperm cell.
Examples: humans, flowers, fish, frogs, birds, snakes
 half the genetic material comes from the mother,
and half from the father.
 offspring is unique (no other organism on
Earth has exactly the same DNA it has)
 there is genetic diversity in the species, which
helps ensure that a species will survive a
widespread disease or environmental disaster.
frogs
sperm fertilizing egg
paramecia
hoverflies
Twins and Multiple Births
Twins and Multiple Births
There are two types of twins, and they
occur in two different ways…
Fraternal twins
• not identical
• two eggs are
fertilized at the
same time
Click here to
learn more
about twins
Identical twins
• identical
• formed when
one fertilized
egg divides
Chances of multiple births
Twins: 1 in 90
Triplets: 1 in 8100
Quadruplets: 1 in 729,000
Multiple Births
Multiple Births
first set of
octuplets born
alive, in Houston
TX, in 1998
triplets
identical quadruplets
van Tol
quintuplets
Gosselin
twins &
sextuplets
McCaughey septuplets
news on multiple births
Homologous chromosomes
• Two chromosomes which contain the same
genes but may contain different alleles*
*Alleles are
different forms
of the same
gene.
For example: the
gene for eye
color has many
alleles: blue,
green, brown,
hazel, black,
gray, etc.
What’s Where?
What’s Where?
cell
nucleus
chromosome
gene
Chromosomes are made out of… DNA.