Introduction to Genetics
-Genetics is the study of heredity.
-Heredity is how different genes are passed down from
parents to children.
PHENOTYPE
 A phenotype is the expression of an observable
physical trait or characteristic of an organism,
such as stature or blood type, based on genetic
and environmental influences.
Examples vs Non-examples
Hair PHENOTYPE
Twins born with
blonde and red hair
Hair-do: not a phenotype
A weird girl who fros-out
her hair
Phenotypes
 Can you think of some
examples of
phenotypes?
 Write down at least 2
examples of phenotypes
(traits) in your notes
How good are you at judging
chimpanzee phenotype?
Which chimps are related?
Phenotypes? Yes or no?
Polydactyl
Phenotypes? Yes or no?
 NO!
 Flamingos get their pink color from the food they
eat, not their genes!
HOMOZYGOUS organism
with two identical alleles for
the same trait
**root word “homo” = same
HETEROZYGOUS organism
with two different alleles for
the same trait
**root word “hetero” = different
Homozygous vs. Heterozygous
Two alleles for the “height gene” might be
TALL (T) and SHORT (t)
A homozygous individual would be TT or
tt –two of the same alleles
A heterozygous individual would be Tt –
two DIFFERENT alleles
DOMINANT
allele that is expressed when at least
one allele is present (TT or Tt = tall)
“cover up”
RECESSIVE
allele that is expressed only when
homozygous (no dominant allele)
(tt = short)
Recessive
aa
Dominant
AA or Aa
Dominant
WW or Ww
Recessive
ww
Dimples (D)
No dimples (d)
dd
What could AC Slater’s
genotype be? Zach’s?
DD or Dd
SNOWFLAKE –rare albino gorilla
Albinism
•combination of recessive alleles
passed from both parents of an
individual
•prevents
the body from
My
PHENOTYPE
is making
the usual(or
amounts
of the pigment
Albino
no color).
melanin
NN = Normal pigmentation
(dominant)
My GENOTYPE is nn.
Nn = Normal pigmentation
nn = Albinism
About 1 in 17,000 people have
some type of albinism, although
up to 1 in 75 are carriers.
TRAIT
a characteristic
Examples:
Plant size, seed color, pod shape
GENE
(a segment of DNA
that controls traits)
Above you see chromosomes. The circled
area is a gene on chromosome #22. The
absence of this gene causes velocardio-facial syndrome (VCFS)
which may cause ADD and mental illness
Breast Cancer and Genes
ALLELES
Each gene comes in different
forms called alleles, so the
gene that controls flower color
may come in two alleles: purple
and white.
ALLELES
different forms
of a gene
Genotype
The combination of
the two alleles for
a given gene
MENDEL’S
EXPERIMENTS
GREGOR MENDEL
 The “father” of Genetics
 Lived from 1822-1884
 Austrian Monk
 Published his work in
1866, but no one took
him seriously until 1900.
 Studied Pea Plants!
Mendel experimented with 7
different characteristics
GENES
Each feature of the pea plants is
controlled by a gene. It may
have a gene that controls its
color, another size for and
another for shape.
Monohybrid cross.
 First, Mendel kept all the traits the same
except for _one___. This is a called a
__monohybrid___cross___ ________
 One trait disappeared in the _F1_______
 It reappear in the F2 in a ratio of 3:1_____
Dihybrid Cross
 Next, Mendel
controlled all traits
except for __2__. He
called this a
_dihybrid cross_____
 Again, two traits
disappeared in the F1
 They reappeared in the
F2 in a ratio of 9:3:3:1
Mendel’s Principles of Inheritance
 Inherited traits are transmitted by genes which
occur in alternate forms called alleles
 Principle of Dominance - when 2 forms of the
same gene are present the dominant allele is
expressed
 Principle of Segregation - in meiosis two alleles
separate so that each gamete receives only one
form of the gene
 Principle of Independent Assortment - each trait
is inherited independent of other traits (chance)
If we saw an organism that
had round seeds (round is
dominant), how could we
figure out what its genotype
is?
Test Cross
A cross between an
unknown and a
homozygous recessive
Example of a Test Cross
Unknow
n
Incomplete
Dominance
When a combination of the
dominant and recessive creates a
new phenotype. RR = red, rr =
white, and Rr = pink
Incomplete Dominance
RR
Rr
rr
Co-dominance
When both traits are expressed
equally. Example: AB blood type
Sex Linked Trait
a trait that is found on
either the X or Y
chromosome
Hemophilia is an
example of a sex
linked trait.
Hemophilia
a disease where your
blood doesn’t clot.
Hemophilia only occurs
when all of the X
chromosomes have a copy
of the recessive gene.
SICKLE CELL ANEMIA
PEDIGREE
chart that shows the
relationships within a
family
Pedigree Basics
 Males are squares, females are circles, and
unborn babies are triangles or octagons
 Shaded figures represent individuals with
the trait, a carrier could be 1/2 shaded
 Generations are numbered with roman
numerals (I, II, II, IV) from top to bottom
 People within generations are numbered
(1,2,3) from left to right
ANTIBODY
a protein produced by white blood
cells in the body in response to the
presence of an antigen, for
example, a bacterium or virus
ANTIGEN
a substance, usually a protein,
on the surface of a cell or
bacterium that stimulates the
production of an antibody
Blood Groups
Blood group A
You have A antigens on the
surface of your red blood cells
and B antibodies in your blood
plasma.
Blood group B
You have B antigens on the
surface of your red blood
cells and A antibodies in
your blood plasma.
Blood Groups
Blood group AB
You have both A and B antigens
on the surface of your red blood
cells and no A or B antibodies at
all in your blood plasma.
Blood group 0
You have neither A or B
antigens on the surface of your
red blood cells but you have
both A and B antibodies in your
blood plasma.
AMNIOCENTESIS
A technique used to
determine the genetic
traits of a baby before it
is born
Klinefelter Syndrome
 Have male genitalia and internal ducts, but




underdeveloped testes
Do not produce sperm
Slight enlargement of the breasts
47,XXY
1 out of every 500 male births
Turner Syndrome
 Has female external genitalia
 Underdeveloped ovaries
 Short (under 5 feet)
 Webbed Neck
 Broad, Shield-like chest
 45,X
 1 out of every 3000 female births
Cri-du-Chat Syndrome
 Partial monosomy (part of 1 chromosome is lost)
 Loss of about 1/3 of the short arm of chromosome
5
 Anatomical malfomrations (gastrointestinal and
cardiac complications)
 Mentally retarded
 Abnormal development of the larynx which makes
the baby’s cry sound like a cat’s cry
 1 in 50,000 live births
Down Syndrome









BKA trisomy 21 (47, 21+); 3 copies of the 21st chromosome
Short
Small round heads
Protruding, furrowed tongues which cause mouth to remain partially
open
Mentally challenged (IQ below 70)
Shortened life expectancy (<50)
Prone to reparatory disease and heart malformations
Have 15x higher chance of getting leukemia
Chance of having a baby with Down syndrome goes up as the mother
gets older