Genetics
Think abouT This….
• “My parents have brown eyes,
why are mine blue?”
• “My broTher is
short?”
tall.
Why am I
• “Why does My sisTer have
blonde hair while mine is
brown?”
Are these
inherited traits?
Your eye color
Your hair color and texture
Your height
Are these inherited traits?
Your personality
Your musical,
athletic, and
artistic abilities
Gregor Mendel
• Born in 1822 in
Austria
• Studied the garden
pea plant to
determine genetics
Father of Genetics
Gregor Mendel
• Heredity – the passing on of
characteristics from parents to
offspring
• Characteristics that are
inherited are called traits
Gregor Mendel
• Mendel studied only 1 trait at a time to
control the variable
• The tall plants that he worked with had
been tall for many generation and had
always produced tall offspring
– This is called true breeding
Mendel’s Monohybrid
Crosses
• Mono = one
• A hybrid is the offspring of parents that
have different forms of a trait
– Such as tall and short
Mendel’s Monohybrid Crosses
• P generation - parents
• The F1 generation
(hybrids) were all purple –
self pollinated
• F2 generation had a ratio
of 3:1
– 3 purple
– 1 white
• F stands for filial – son or
daughter
The rule of dominance
• The dominant
trait is the trait that is
observed
• The recessive trait is
the trait that
‘disappears’
• What trait is
dominant?
The rule of dominance
•
Which is dominant and which is
recessive?
1)
2)
3)
4)
TT Tt
tt
BB bb Bb
ww WW Ww
HH hh Hh
Phenotypes and Genotypes
• The way an organism looks or behaves is
called its phenotype
Phenotypes and Genotypes
• The allele
combination an
organism contains is
its genotype
– represented as TT for
tallness
– Any plant that is tall
has a genotype either
TT of Tt
Homozygous
• Homo: same
• Two alleles for
the trait are the
same
(TT or tt)
• Which ones
are homozygous?
Heterozygous
• Hetero = different
• Two alleles differ
from one another
(Tt)
Monohybrid crosses
• a cross that shows the possible offspring for one trait
Punnett Square
A
a
A
AA
Aa
a
Aa
aa
Aa x Aa
A: White fur
a: Brown fur
Genotypic Ratio: 1:2:1
Phenotype: 3 white:1 brown
Practice!
Cross a HOMOZYGOUS dominant female rabbit with a
HETEROZYGOUS male rabbit using the same trait.
A: White fur
a: Brown Fur
What is the
genotypic ratio?
What is the
phenotypic ratio?
A
A
a
A
Practice!
Cross a HOMOZYGOUS dominant female rabbit with a
HETEROZYGOUS male rabbit using the same trait.
What is the
genotypic ratio?
2 = AA
2 = Aa
A
A
A
AA
AA
a
Aa
Aa
2:2 or
50%
What is the
phenotypic ratio?
4 white fur
Practice!!
• Cross a female (Tt) with a male (Tt) using
the traits:
T
t
T: tall
t: short
T
t
Practice!!
• Cross a female (Tt) with a male (Tt) using
the traits:
T
t
T: tall
t: short
T
t
TT
Tt
Tt
tt
Now its time for more
practice…
Dihybrid
crosses
• two traits calculated :RrYy x RrYy
Dihybrid Crosses:
a cross that shows the possible offspring for two traits
BbRr x BbRr
BR
Br
bR
br
Fur Color:
B: Black
b: White
BR
BBRR
BBRr
BbRR
BbRr
Coat Texture:
R: Rough
r: Smooth
Br
BBRr
BBrr
BbRr
Bbrr
BbRr x BbRr
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
Phenotypic Ratio:
9:3:3:1
More Complex Patterns
of Heredity
• Codominance/ Incomplete
dominance
• Multiple Alleles
• Sex-Linked Traits
Codominance:
two dominant alleles are
expressed at
the same time
CRCR
CWCW
CRCW
Codominance
• Sickle-Cell
Anemia is
another
codominant S
N
trait.
NA
NA
NSNA
NSNA
NANA
NANA
NA=Normal RBC
NS=Sickle Cell RBC
NA
Multiple Alleles:
traits with more than 2 alleles
• Blood type has 3 alleles: A, B, O
• A and B are codominant over O
• O is recessive
Phenotype
Genotype
Can Receive
From
Can Donate To
A
AA, AO
A, O
A, AB
B
BB, BO
B, O
B, AB
AB
AB
A, B, AB,O
AB
O
OO
O
A, B, AB, O
What are Sex-Linked Traits?
Traits that are located on one of
the sex chromosomes (XY)
Hemophilia: Failure of
blood to clot
Alix and Nicholas II
Muscular Dystrophy:
wasting away of
muscles
Can I inherit a sex-linked
disease?
Fathers (XY) can
only pass
disorders to
daughters (XX)
Mothers (XX) can
pass disorders to
both sons (XY) and
daughters (XX)
Most disorders are carried
on the X chromosome, so
males are more likely to
inherit them.
How can I tell if I have
a genetic disorder?
• Karyotypes are a “map” of all 46 (23 pair)
of chromosomes.
What’s wrong with this
Karyotype?
Is this a male or a female?
What’s wrong with this
Karyotype?
Is this a male or a female?
Down Syndrome
Down syndrome occurs because of the
presence of an extra 21st chromosome.
Down syndrome is also called trisomy 21
Physical Traits
• Short stature. A child often grows slowly
and, as an adult, is shorter than average.
• A short, wide neck with excess fat and skin
• Small, low-set ears.
Klinefelter Syndrome
• chromosome abnormality
that affects only men
• born with at least one
extra X chromosome.
• The male with Klinefelter
Syndrome will be born
with 47 chromosomes in
each cell, rather than the
normal number of 46.
• Klinefelter Syndrome is
also called 47 X-X-Y
syndrome.
• An infant with
Kleinnfelter's Syndrome
appears normal at birth,
but the defect usually
becomes apparent in
puberty when secondary
sexual characteristics fail
to develop, and testicular
changes occur that
eventually result in
infertility in the majority of
those affected.
Patau syndrome
• Trisomy 13
• Most cases of Patau
syndrome are not
inherited, but occur as
random events during
the formation of
reproductive cells
(eggs and sperm).
Symptoms:
• Mental & motor
challenged
• polydactyly (extra
digits)
• Heart defects
• Cleft palate
• Spinal defects