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Genetics
Unit 6
What is genetics?
Genetics: Is the science of heredity
• Genetics began with Mendel
• Mendel is considered the “Father of Genetics”
• Mendel was a monk who experimented with
pea plants to study heredity
What is a trait?
Trait: Is a notable feature or characteristic in an
organism
• Physical traits
– Examples - Hair color, eye color, & height
• Behavioral traits
– Example – Sheepdog has herding instincts
• Medical conditions
– Examples – Cancer, Sickle cell, cystic fibrosis
Why did Mendel study peas?
• Peas reproduce and grow quickly
• They had easy to observe traits
• Can reproduce using 2 different plants or using 1 plant
– True-Breeding: Can produce offspring with only 1 parent
Cross Pollination – 2 parents
self-fertilizing/true-breeding
What are alleles?
Allele: Alternative form that a single gene may have for
a particular trait. (huh?)
A gene in a particular place on a particular chromosome will
express a particular trait….like flower color
Purple is an Allele coming from mom
Chromosome from MOM
Chromosome from DAD
But what color
will the
offspring show?
White is an Allele coming from dad
How do alleles determine what traits will show?
Some alleles are dominant and others are recessive
Do
you
have
to
remember
which
Dominant: A trait that will appear (show)
* traits
Represented
a CAPITALand
letter which are
are with
dominant
Example: Tall (T), Black (B), Brown (B)
recessive?...
NO…
Recessive: A trait that
is masked (hidden) if a
dominant allele is present, but will show if both
Punnett
Square questions will give
alleles
are recessive
* Represented
with
lower
letter
you clues
orawill
tellcase
you in
the
Example:
blond TO
(b), READ!
blue (b)
question!short
You(t),
HAVE
I do you know a trait will show or not?
Rule #1: If there is a dominant trait present, it will
always show that trait.
Tall is dominant over short
Capital “T” bosses the little “t”
TT
Tt
Dominant
Dominant
Dominant
Shows Tall
Recessive
Shows Tall
I do you know a trait will show or not?
Rule #2: If there is NOT a dominant trait present,
then the recessive trait will always show.
Tall is dominant over short
tt
Recessive
Recessive
Shows Short
Clicker Question #1
Who is considered the
“Father of Genetics”?
a. Darwin
b. Hooke
c. Mendel
d. Paquin
Clicker Question #2
These plants were used in Mendel’s
experiments because they grow
& reproduce quickly:
a.
b.
c.
d.
Peas
Corn
Wheat
Roses
Clicker Question #3
What is true-breeding?
a. 2 parents reproduce offspring
b. 2 offspring with three parents
c. Self fertilizing plants
d. Cross pollinating plants
Clicker Question #4
Tall is dominant over short
If a girl has Tt, she will show:
a. Short
b. Tall
c. Both (a) & (b)
d. None of the above
Before we start Punnett
Squares, we have a few more
things to learn…
What are some terms that will help with
understanding Punnett Squares?
Homozygous: Organism with 2 of the same
alleles for a particular trait. Also called “pure”.
Examples
–
TT
tt
DD
dd
Same sized
Same
letters!
sized
Same
letters!
sized
Same
letters!
sized letters!
Homo means: ________
Same
Think: Same SIZED letters
What are some terms that will help with
understanding Punnett Squares?
Heterozygous: Organism with 2 different alleles
for a particular trait. Also called “hybrid”.
Examples
–
Tt
Dd
Gg
Bb
Different sized
Different
letters!
sized
Different
letters!
Different
sized letters!
sized letters!
Hetero means: __________
Different
Think: Different SIZED letters
What are some terms that will help with
understanding Punnett Squares?
Phenotype: The observable characteristic or
outward expression of an allele pair
Characteristics you can see with your eyes!
Think: Phenotype -- Physical
Blond Hair
Black Hair
Red Hair
Brown Hair
What are some terms that will help with
understanding Punnett Squares?
Phenotype
Characteristics you can see with your eyes!
Multi color
Butterfly
Blue
Butterfly
White
Butterfly
Orange
Butterfly
What are some terms that will help with
understanding Punnett Squares?
Genotype: The organism’s allele pairs
Characteristics you can NOT see with your eyes!
Think: Genotype – Genetic Code
bb HH
GG
Gg
Bb
gg BB
Hh
hh
Clicker Question #5
Another term for
heterozygous is:
a. Allele
b. Same
c. Hybrid
d. Pure
Clicker Question #6
tt is an example of:
a. homozygous
b. heterozygous
c. hybrid
d. all of the above
Clicker Question #7
tt is an example of:
a. phenotype
b. heterozygous
c. hybrid
d. genotype
Clicker Question #8
Tall is dominant over short
If a boy has tt, he will show:
a. tall
b. short
c. both (a) & (b)
d. none of the above
Clicker Question #9
Tall is an example of:
a. phenotype
b. Heterozygous
c. pure
d. genotype
What is Mendel’s Law of Segregation?
Law of Segregation: States that the two alleles
for each trait separate during meiosis.
During meiosis, the alleles separate
During fertilization, the
alleles unite into a pair again
What’s the difference between monohybrid ?&
dihybrid crosses?
Punnett Square: A diagram used to predict the possible
outcomes (offspring) of a particular cross or breeding.
Monohybrid Cross: The use of Punnett Square for 1 trait
(will have 4 boxes)
Punnett Square Video
What’s the difference between monohybrid ?&
dihybrid crosses?
Dihybrid Cross: The
use of Punnett
Square for 2 traits
(will have 16 boxes)
What’s the difference between monohybrid ?&
dihybrid crosses?
Law of Independent Assortment: Mendelian law
stating that two alleles for each trait separate
during meiosis
During Dihybrid crosses: The random assortment
of alleles results in four possible gametes…each
of which is equally likely to occur
I will show you this when I show
dihybrid crosses
Sometimes two traits can be
dominant at the same time
What’s the difference between incomplete
dominance and co-dominance?
Incomplete Dominance: Complex inheritance pattern
in which the heterozygous phenotype is intermediate
between those of the two homozygous parent
organisms…huh?
Mixes like paint!
R
R
W
RW
RW
W
RW
RW
What’s the difference between incomplete
dominance and co-dominance?
Co-Dominance: Complex inheritance pattern that
occurs when neither allele is dominant and both
alleles are expressed.
B
W
W
B
BW
BW
BW
BW
Clicker Question #10
Each gamete has only one
allele for a trait because of:
a. recessive
b. Law of segregation
c. dominance
d. phenotype
Clicker Question #11
When a white flower & a red
flower have pink offspring,
this is because of:
a.
b.
c.
d.
Co-dominance
Law of segregation
Law of Independent assortment
Incomplete dominance
Clicker Question #12
In speckled chickens, both
alleles are express
because of:
a. Co-dominance
b. Law of segregation
c. Law of Independent assortment
d. Incomplete dominance
Clicker Question #13
The cross with one trait is
called:
a. Dihybrid
b. Trihybrid
c. Monohybrid
d. All of the above
Clicker Question #14
A dihybrid cross will have
how many squares?
a. 4
b. 16
c. 18
d. 20
When a woman is about 25 weeks
pregnant… she can go to the doctor to
determine the sex of her unborn child.
What determines the sex of the child?
All eggs that female carries contain a X sex
chromosome
Sperm can either have a X or Y sex
chromosome
To be a girl…. She has two x chromosomes.
• To be a boy….. He has a X and Y sex
chromosome.
There is 50% chance that you get either
be a boy or girl. Its all depends on which
sperm is the first to reach the egg.
Sex-linked Inheritance
• Definition: A gene carried on either the X
or Y chromosome
– X-linked – only found on the X
• Colorblindness - recessive
• Hemophilia - recessive
– Y-linked – only found on the Y
• Hair on ears
• Can a female be born with this trait?
Man with hairy ears!
http://www.ucm.es/info/genetica/grupod/mendelismo/Hairy%20ear01.jpg
Hemophilia
• Definition: disorder in which the blood
does not clot
• Not fatal – just lots of treatments to keep
blood volume levels appropriate
Xh = hemophilia allele
XX or XY = normal
XhX = carrier – only females
XhXh or XhY = hemophilia
Why do men get hemophilia more
than women?
Because women will have to have both Xh
gene in order to get hemophilia.
Pedigree Chart
• Pedigrees shows how a specific gene trait
is passed down from one generation to the
next.
Pedigree Chart
How many female carriers for hemophilia are there?
Can a male be a carrier?
Could a male with hemophilia have a child who is not
affected by or a carrier of hemophilia? How?
Karyotype
Definition: Picture of the
chromosomes from a
person’s cell.
How many pairs of
chromosomes are there?
What is the gender of the
person in this karyotype?
How can karyotypes be
useful to doctors?
http://www.contexo.info/DNA_Basics/images/karyotype1.gif
Normal Karyotype vs. Down Syndrome
Karyotype. Which one is which?
http://www.blackwellpublishing.com/korfgenetics/jpg/300_96dpi/Fig6-15.jpg
http://sps.k12.ar.us/massengale/karyotype_male.jpg
Genetic Disorders
• Down’s Syndrome – extra chromosome on Pair 21 –
happens because of Non-disjunction in Meiosis
• Turner Syndrome – Female – has only 1 X Chromosome –
tend to be sterile, may not reach full sexual maturity
• Cystic Fibrosis – Recessive disorder – lungs and digestive
system don’t work properly and thick mucous builds up in
respiratory tract
• Kleinfelter’s Disease – male who is XXY – may have
feminine-type characteristics
– Does not mean they are gay!
• Hemophilia – blood disorder
• Huntington’s Disease – Autosomal Dominant –
Neurological Breakdown - fatal
• Sickle Cell Anemia – Autosomal Recessive – sickle-shaped
blood cells – can’t move through bloodstream as easily – not
fatal – typically found in African Americans
Genetic Disorders
• Tay-Sachs disease is a rare fatal inherited disorder that
progressively destroys nerve cells (neurons) in the brain and
spinal cord. Tay-Sachs disease becomes apparent in infancy.
Infants with this disorder typically appear normal until the age of
3 to 6 months, when their development slows and muscles
used for movement weaken.
• Albinism – a genetic disorder characterized by the complete
or partial absence of pigment in the skin, hair, and eyes. This is
due to a lack of melanin production.
• Achondroplasia – an autosomal dominant genetic disorder
that causes dwarfism
• Galactosemia – an autosomal recessive genetic disorder in
which a person cannot digest the sugar galactose properly. Life
threatening complications appear after birth such as lethargy,
jaundice, liver damage, bleeding, cataracts, mental retardation..