Transcript genetics

GENETICS
Gregor Mendel: “Father of Genetics"
Gregor Mendel:
“Father of Genetics"
• parents were farmers
• he became ordained as a priest
• studied science and mathematics at the
University of Vienna
Mendel's Experiments:
• Mendel chose pea plants as his
experimental subjects, mainly because
they were easy to cross and showed a
variety of traits
• (purple vs. white flowers, tall vs. short
stems, round vs. wrinkled seeds)
Mendel’s Experiment
1. Mendel chose true-breeding lines of each
plant/trait. (true breeding lines always produced
offspring of the same type)
2. He crossed a true breeding plant with a plant of
the opposite trait (purple x white). He called this
the Parent (P) generation.
3. He recorded data on the offspring of this cross
First Filial (F1) generation.
4. He self-pollinated the F1 offspring
5. He recorded data on the offspring of the second
generation as the Second Filial or (F2)
generation.
Cross showing Parent, F1 and F2 Generations for
Flower Color
Analysis of Mendel’s Experiment
• The F1 generation always displayed one trait
(he later called this the dominant trait)
• The F1 generation must have within it the trait
from the original parents - the white trait
• The F2 generation displayed the “hidden” trait,
1/4 of the F2 generation had it (he later called
this hidden trait the recessive trait)
• Each individual has two "factors" that determine
what external appearance the offspring will
have. (We now call these factors genes or
alleles).
Mendel established three principles
(or Laws) from his research
1. The Law of Dominance and Recessiveness one trait is masked or covered up by another
trait
2. Law of Segregation - the two factors (alleles)
for a trait separate during gamete formation.
3. Law of Independent Assortment - factors of a
trait separate independently of one another
during gamete formation.
Ex. A flower being purple has nothing to do
with the length of the plants stems - each
trait is independently inherited.
MODERN GENETICS
• Mendel's factors are now called alleles.
• Alleles are variations of a gene.
• For every trait a person has, two alleles
determine how that trait is expressed.
• We use letters to represent alleles, since
every gene has two alleles, all genes can
be represented by a pair of letters.
PP = purple, Pp = purple, pp = white
(P = purple p = white)
Homozygous:
• Homozygous when the alleles are the same SIZE,
the individual is said to be homozygous, or true
breeding.
• Letters can be capital or lowercase, as long
as they are the same.
– Ex. AA, bb, EE, dd
Heterozygous:
Heterozygous: when the alleles are different
SIZES, in this case the DOMINANT allele is
expressed.
• Ex. Pp, Aa
Genotype:
• What the GENES are.
• Genotype: gene is represented by alleles
(letters)!
– Ex. BB, Pp, etc…
Phenotype:
• PHOTO
• Phenotype: what an organism physically
looks like
– tall, purple..
Punnett Square:
• Punnett Square: used to determine the
PROBABILITY of having a certain type of
offspring given the alleles in the gametes
of the parents
How to Solve a Punnett Square
1. Determine the genotypes (letters) of the
parents. Bb x Bb
2. Set up the punnett square with one
parent on each side.
3. Fill out the Punnett square
middle.
B
b
4. Analyze the number of B
offspring of each type.
b
Solve the following:
• In pea plants, round seeds are dominant to
wrinkled seeds.
Genotype Phenotype
RR
= round
Rr
= round
rr
= wrinkled
Cross two plants, one that is homozygous
round and one that is recessive.
Monohybrid cross:
What you have done is called a Monohybrid
cross:
• a cross involving one pair of contrasting
traits.
• The genotypic ratio would be ___:___:___
HD
He
The phenotypic ratio would be ____;____
hr
Dihybrid cross:
• Dihybrid cross: a cross involving two
pairs of contrasting traits. Ex. PpTt x PpTt
• For these crosses your punnett square
needs to be 4x4
• In any case where the parents are
heterozygous for both traits (AaBb x
AaBb) you will get a 9:3:3:1 ratio.
• If you cross other combinations, you will
need to do a square. Try RrYy x rryy.
Incomplete Dominance
• There is no dominant or recessive, the
heterozygous condition results in a
“BLEND" of the two traits. Example:
Snapdragons can be red, white, or pink
(heterozygous)
Codominance
BOTH traits are dominant and therefore
both traits show.
Example: A cross between a white
rabbit and a brown rabbit produces
offspring with brown AND white spots.
Sex-Linked Traits
• The genes for these traits are on the X
chromosome, because boys only receive
one X chromosome they are more likely to
inherit disorders passed to them from their
mother who would be
a carrier.
• Ex. Hemophilia
Colorblindness
Colorblindness tests
• What number do you see?
The punnett square below shows
how a woman who is a carrier
passes the trait to her son, but not
her daughters.
Multiple Allele Traits
• Traits that are
controlled by more
than two alleles.
EX: Blood type in
humans is controlled
by three alleles: A, B,
and O.
Phenotype
Genotype
A
AA or AO
B
BB or BO
AB
AB only
O
OO only
Examples of Blood-type crosses
Blood Transfusions
• Blood can only be transferred to the body of a
person who's immune system will "recognize"
the blood. A and B are antigens (flags) on the
blood that will be recognized. If the antigen is
unfamiliar to the body, your body will attack and
destroy the transfused blood as if it were a
hostile invader (which can cause death).
• O is like a blank, it has no antigens. O is called
the universal donor because a person can
receive a transfusion from O blood without
having an immune response.
• AB is the universal acceptor, because a
person with AB blood has both the A and B
antigens already in the body, A and B blood can
be transfused to the person (as well as O) and
the body will recognize it and not attack.
Polygenic Traits
• Traits controlled by many genes:
hair color, height, weight, intelligence
Sex Influenced Traits
• Traits that are influenced by gender.
Pattern baldness affects men because
testosterone activates the genes.
Human Genetics
• Human genetics is studied using
PEDIGREES, which diagram how a trait is
inherited in a family. It helps us determine
genotypes of the family members.
This pedigree is for the recessive allele that causes
albinism. Albinos are humans that have no
pigment, their skin is very pale and all of their hair is
white, including their eyebrows and eyelashes.
Label each part of the pedigree below. How would you designate a carrier?
This pedigree shows how albinism can be inherited over 2 generations.
Human genetics can also be studied by looking at identical twins, which
help establish whether NATURE or NURTURE influences our traits.
Human Genetic Diseases
Albinism • Albinism: inability to produce pigment,
white hair and skin, autosomal recessive
Huntingtons • symptoms of mental illness appear late in
life
Huntington’s Disease effects
the brain’s basal Ganglia
• autosomal dominant
Sickle Cell Disease
• blood cells are
shaped abnormally
so can’t properly
carry oxygen
molecules.
*autosomal recessive
Tay Sachs • fat builds up in the brain of infants and
causes degeneration and early death,
autosomal recessive
Hemophilia
• “Bleeder's Disease”, inability of the blood
to clot, sex linked recessive
Cystic Fibrosis
• - mucus builds up in lungs causing
respiratory problems, autosomal
recessive