Transcript colored contact lenses

Fundamentals of Genetics
Genetics
• The field of Biology devoted to
understanding how characteristics are
transmitted from parents to offspring.
Gene
• A segment of DNA that contains coding
for a polypeptide or protein
• A unit of hereditary information.
Heredity
• The transmission of characteristics
from parents to offspring.
Discussion-Mendel’s Data WS
• How are traits inherited?
• Where does a person get their eye
color, hair color, and so on?
• What if one parent has brown hair and
the other one is blond? What hair color
will their children have?
Gregor Mendel
• Austrian monk who experimented with
garden peas
• Used knowledge of statistics and
studied heredity
• Known as the father
• of genetics
Pollination
• Self -Pollination
• Cross-Pollination
• Web Link
A Brief History
In the past, people did not understand
how traits were inherited, but there
were many guesses based on things
that could be observed.
Two theories emerged….
Theories
Blending Theory - offspring are a straight
mix
Particulate Theory - traits are inherited as
"particles", offspring receive a "piece"
from each parent, some pieces may
hide the others
Tall x Short = Hybrid
Mendel Video 3 min
On Mendel’s Data WS Read
Introduction
Bozeman Science 0-3:42
One Monk’s Boredom
• Part 1 – Story Time!!
– read pp 75-76 In “What’s in Your Genes?”
book.
Mendel’s First (P1 to F1)
• In the first set of experiments, Mendel conducted
cross-pollination between a pure breeding tall
plant and a pure breeding dwarf plant. He
collected the seeds from this cross pollination
and allowed them to germinate. All the resulting
plants were found to be tall.
• P1 to F1
generation
Next he…
• In a similar pollination between a pure breeding
plant with purple flowers and a pure breeding
plant with white flowers, all the resulting plants of
the next generation produced only purple
flowers.
• F1 generation
Probability
• Probability: the likelihood that a
specific event will occur.
• May be expressed as a decimal, %,
fraction, or ratio
• Probability= # of actual times
# of opportunities
Punnett Squares Practice
• Punnett Squares Practice
Principle of Dominance
• Based on these results, Mendel came to the
conclusion that in a cross-involving two
contrasting characters, only one character
expresses itself in the next generation.
• Mendel called the character, which expressed
as dominant character and the character, which
failed to express, as recessive character. This
idea came to be known as the principle of
dominance (first law).
F2 Generation
• At this stage, Mendel wanted to know whether
the tall plants resulting from a cross between tall
and dwarf plants, were similar to the tall plants of
the P1 generation. Hence, he allowed the tall
plants of the F1 generation to undergo selfpollination. In the next generation, Mendel found
both tall plants and dwarf plants.
• The results were most surprising since the
recessive character dwarfness had reappeared
in the next generation. (F2 generation)
Mendel discovered that each trait is
controlled by two factors (alleles)
Genes – factors that
determine your
traits
Genes are located on
chromosomes
Locus – the location
of a single gene on
a chromosome
• Dominant factor: masks the other
factor for a specific characteristic
• Recessive factor: has no observable
effect on an organism’s appearance
when paired with a dominant factor.
The hidden factor.
Genotype and Phenotype
• Genotype: the genetic makeup of an
organism. Consists of the alleles that
the organism inherits from its parents
– Purple flowered plants PP or Pp
– White flowered plants pp
• Phenotype: the appearance of an
organism as a result of its genotype.
– PP or Pp = purple flowers
– pp = white flowers
GENOTYPE - what genes, letters, the
organism has (TT, Tt, tt)
• Homozygous: same Letters (TT or tt)
• Heterozygous: different letters (Tt)
PHENOTYPE - what it looks like (tall or
short)
Mendel’s Garden Peas
• Observed 7 characteristics of pea
plants. Each characteristic occurred in
2 contrasting traits.
WS
Characteristic
Trait
Plant height
long/short stems
Flower position
axial/terminal
Pod color
green/yellow
Flower Color
purple/white
Pea Shape
round/wrinkled
Pod shape
inflated/constricted
Pea Color
yellow/green
• Example: Mendel’s experiments – the
dominant trait of yellow seed color in F2
generation occurred 6022 times, the
recessive trait of green seed color
appeared 2001 times. Total # of
individuals = 8023
• Probability of Dominant trait
6022 / 8023 = 0.75 or 75%, ¾, 3:4
• Probability of Recessive trait
2001 / 8023 = 0.25 or 25%, ¼, 1:4
• P= Parent
• F1=first Filial cross
• F2 =second Filial Cross
• Mendel’s monohybrid
• 3:1 ratio
Mendel’s Results and
Conclusions
• Crossed green pods with
yellow pods (P1)
• All green pods produced
(F1)
• ¾ green pods and ¼ yellow
pods (F2)
• Finish Mendel’s WS
Mendel’s Results and
Conclusions
• Hypothesized that something within the
pea plants controlled the
characteristics he observed – called
these “factors”
• Said that each trait was inherited by the
means of a separate factor. Reasoned
that there must be a pair of factors
controlling each trait because the
characteristics he studied had 2
alternative forms.
Recessive and Dominant
Traits
• When Mendel crossed strains, one of
the P1 traits failed to appear in the F1
plants but reappeared in a 3:1 ratio in
the F2 generation.
• Mendel concluded that one factor in a
pair may prevent the other from having
an effect.
• Human phenotypes can appear to be
altered: hair dye, colored contact
lenses, surgery, etc but they do not
alter the individual’s true phenotypes
or genotype.
Colored Contact Lenses
• Homozygous: when both alleles of a
pair are alike.
– PP= homozygous dominant
– pp= homozygous recessive
• Heterozygous: when the two alleles in
the pair are different.
– Pp= heterozygous for flower color.
– Video (1.5 minutes)
Test Cross
• An individual of unknown genotype is
crossed with a homozygous recessive
individual (bb).
• Can be used to determine the genotype
of any individual whose phenotype is
dominant. If one of the offspring turns
up with the recessive trait, then you
know the unknown parent is
heterozygous (Bb).
The Law of Segregation
• States that a pair of factors
segregate or separate
during formation of gametes
(reproductive cells).
• Each gamete receives only
one factor of each pair
• When two gametes combine
during fertilization, the
offspring have two factors
controlling a specific trait
The Law of Independent
Assortment
• States that factors for different
characteristics are distributed to
gametes independently.
The Law of Independent
Assortment
• Mendel crossed plants that differed in
two characteristics such as flower
color and seed color.
– Data showed that traits from dominant
factors do not necessarily appear
together.
– Factors for different characteristics are not
connected.
• Most of Mendel’s findings agree with
what biologists now know about
molecular genetics.