Transcript 10-2 & 11-2 Mendel Genetics 2010

Georgia Standards:
SB2d. Explain the relationship between
changes in DNA and the appearance of new
traits.
SB2c. Using Mendel’s Laws, explain the role of
meiosis in reproductive variability
Essential Questions:
•How is the study of genetics related to the
characteristics of life?
•How do you predict the probability of various
genotypes inherited and the expressed phenotypes?
•How does meiosis generate variation in offspring?
Warm-up
• What is Genetics?
• What do you think of when you hear the
word genetics????
11-1 Warm-up: Analyzing Inheritance
Section 11-1
• Offspring resemble their parents.
• Offspring inherit genes for characteristics
from their parents.
• To learn about inheritance, scientists have
experimented with breeding various plants
and animals.
• In each experiment shown in the table on the
next slide, two pea plants with different
characteristics were bred. Then, the offspring
produced were bred to produce a second
generation of offspring. Consider the data and
answer the questions that follow.
Go to
Section:
11-1 Warm-up: Analyzing Inheritance
Parents (P)
First Generation (F1) Second Generation (F2)
Long stems  short stems
All long
787 long: 277 short
Red flowers  white flowers
All red
705 red: 224 white
Green pods  yellow pods
All green
428 green: 152 yellow
Round seeds  wrinkled seeds
All round
5474 round: 1850 wrinkled
Yellow seeds  green seeds
All yellow
6022 yellow: 2001 green
1. In the first generation of each experiment, how do the
characteristics of the offspring compare to the parents’
characteristics?
2. How do the characteristics of the second generation compare to
Go tothe characteristics of the first generation?
Section:
Gregor Mendel: Father of Genetics
•Gregor Mendel (1860’s) an Austrian Monk
•Gregor Mendel used pea plants and a quantitative approach
to collect data.
•Mendel studied seven different pea plant traits. A trait is a
specific characteristic, such as seed color or plant height, that
varies from one individual to another.
Important terms
• Genotype- genetic make-up of an
organism (allele combinations= AA or Aa)
• Phenotype- physical trait that is visible.
• Allele- different forms of a gene
Ex. Aa- A and a
Gregor Mendel’s Experiment:
• Mendel crossed plants with each of the 7 contrasting
traits and studied their offspring.
• Mendel called each original pair of plants the P
(parental) generation.
• He called the offspring of the P generation, the F1, or
“first filial,” generation. Filius is the Latin word for
“son.”
– These pea plants were cross pollinated.
– The offspring of crosses between parents with different traits
are called hybrids.
Gregor Mendel’s Experiment:
cross-pollination, male sex cells in pollen from the flower on
one plant fertilize the egg cells of a flower on another plant.
Self-pollination- male sex cells in pollen are used to fertilize the
egg of the same flower.
Gregor Mendel’s Conclusions:
• Genes and Dominance
– Mendel’s first conclusion was that biological
inheritance is determined by factors (genes)
that are passed from one generation to the
next.
• Each of the traits Mendel studied was controlled by
one gene that occurred in two contrasting forms.
• The different forms of a gene are called alleles
Gregor Mendel’s Conclusions:
• Mendel’s second conclusion is called the
principle of dominance, which states that
some alleles are dominant and others are
recessive.
– An organism with a dominant allele for a particular
form of a trait will always have that form.
– An organism with a recessive allele for a particular
form of a trait will have that form only when the
dominant allele for the trait is not present.
Segregation of Alleles:
•
During gamete
formation, alleles are
segregated from each
other so that each
gamete carries only a
single copy of each
gene.
– Each F1 plant produces
two types of gametes—
those with the allele for
tallness and those with the
allele for shortness.
– The alleles are paired up
again when gametes fuse
during fertilization.
Checkpoint Questions:
1. What are dominant and recessive alleles?
2. What is segregation? What happens to alleles
during segregation?
3. What did Mendel conclude determines
biological inheritance?
4. Describe how Mendel cross-pollinated pea
plants.
5. Why were true-breeding pea plants important
for Mendel’s experiments?
Warm-up
• Height in pea plants is
controlled by one of two
alleles; the allele for a tall
plant is the dominant
allele, while the allele for
a short plant is the
recessive one.
• What about people? Are
the factors that determine
height more complicated
in humans?
1. Make a list of 10 adults
whom you know. Next to the
name of each adult, write
his or her approximate
height in feet and inches.
2. What can you observe
about the heights of the ten
people?
3. Do you think height in
humans is controlled by 2
alleles, as it is in pea
plants? Explain your
answer.
11-2 Warm-up: Tossing Coins
Section 11-2
• If you toss a coin, what is the probability of
getting heads? Tails? If you toss a coin 10 times,
how many heads and how many tails would you
expect to get? Working with a partner, have one
person toss a coin
• ten times while the other person tallies the
results on a sheet of paper. Then, switch tasks
to produce a separate tally of the second set of
10 tosses.
Go to
Section:
Interest Grabber continued
11-2 Warm-up: Tossing Coins
Section 11-2
1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do
the results of your tosses compare? How about the results of your
partner’s tosses? How close was each set of results to what was
expected?
2. Add your results to those of your partner to produce a total of 20
tosses.
Assuming that you expect 10 heads and 10 tails in 20 tosses, how
close are these results to what was expected?
3. If you compiled the results for the whole class, what results would
you expect?
4. How do the expected results differ from the observed results?
Go to
Section:
11-2: Probability and Punnett Squares
• The principles of probability can be used
to predict the outcomes of genetic
crosses.
• The gene combinations that might result
from a genetic cross can be determined by
drawing a diagram known as a Punnett
square. (See note sheet)
Punnett square
• This Punnett square
shows the probability of
each possible outcome of
a cross between hybrid
tall (Tt) pea plants.
• Genotype: 25% TT, 50%
Tt, 25%tt (1:2:1)
• Phenotype: 75% Tall,
25% short (3:1)
Punnett Squares
• Organisms that have two identical alleles for a
particular trait—TT or tt in this example—are
said to be homozygous
• Organisms that have two different alleles for the
same trait are heterozygous (Ex: Tt)
• Homozygous organisms are true-breeding for a
particular trait. Heterozygous organisms are
hybrid for a particular trait.
Punnett Squares
• All of the tall plants have the same
phenotype, or physical characteristics.
• They do not, however, have the same
genotype, or genetic makeup.
A Dihybrid Cross: F1
• Dihybrid Cross:
– Shows inheritences of two
traits at once
• F1 Mendel crossed plants that
were homozygous dominant
for round yellow peas with
plants that were homozygous
recessive for wrinkled green
peas. All of the F1 offspring
were heterozygous dominant
for round yellow peas.
• The cross did not indicate
whether genes assort, or
segregate, independently.
Did this mean that the two dominant alleles would
always stay together? Or would they “segregate
independently.”
• A combination of alleles
were produced that were
not found in either parent
– This means that genes for
different traits can
segregate independently
during the formation of
gametes. (Independent
Assortment)
Concept Map
Gregor
Mendel
experimented
with
concluded that
Pea
plants
genes for different
traits can segregate
independently during
the formation of
gametes
which is
called the
Go to
Section:
“Factors”
determine
traits
Law of
Independent
Assortment
Some alleles
are dominant,
and some alleles
are recessive
which is
called the
Law of
Dominance
Alleles are
separated during
gamete formation
which is
called the
Law of
Segregation
A Summary of Mendel’s Principles
• Genes determine
inheritance of biological
characteristics.
• Genes are passed from
parents to offspring
• In most sexually reproducing
organisms, each adult has
two copies of each gene—
one from each parent.
These genes are
segregated from each
during gamete formation.
• Some forms of the gene
may be dominant and
• The alleles for different
others may be
genes usually segregate
recessive.
independently of one
another.
Exceptions to Simple Dominance
Does the segregation of one pair of alleles
affect the segregation of another pair of
alleles?
• For example, does the gene that
determines whether a seed is round or
wrinkled in shape have anything to do with
the gene for seed color? Must a round seed
also be yellow?
Exceptions to the Laws:
• Some alleles are neither dominant nor
recessive, and many traits are controlled by
multiple alleles or multiple genes.
• incomplete dominance occurs when one
allele is not completely dominant over
another
• In incomplete dominance, the heterozygous
phenotype is somewhere in between the two
homozygous phenotypes.
Incomplete Dominance
• Some alleles are neither
dominant nor recessive.
• In four o’clock plants, for
example, the alleles for
red and white flowers
show incomplete
dominance.
• Heterozygous (RW)
plants have pink
flowers—a mix of red and
white coloring
Codominance
• In codominace, both • In certain varieties of
alleles contribute to
chickens, the allele
the phenotype of the
for black feathers is
organism.
codominant with the
allele for white
• For example, in cattle
the allele for red hair
feathers.
is codominant with
– Heterozygous
the allele for white
chickens appear
hair.
speckled with black
– Cattle with both alleles
are roan, or pinkish
brown, because their
coats are a mixture of
both red and white hairs.
and white feathers.
Multiple Alleles
• Many genes have
more than two alleles
and are therefore said
to have multiple
alleles.
• This does not mean
that an individual can
have more than two
alleles. It only means
that more than two
possible alleles exist
in a population.
• One of the best-known
examples is coat color
in rabbits.
• A rabbit’s coat color is
determined by a single
gene that has at least
four different alleles.
• Many other genes have
multiple alleles
– human genes for
blood type
Polygenic Traits
• Many traits are produced
by the interaction of
several genes.
• Traits controlled by
two or more genes
are said to be
polygenic traits,
which means
“having many
genes.”
• Different combinations of
alleles for these genes
produce very different
eye colors.
• Polygenic traits often
show a wide range of
phenotypes.
– Ex: skin color, eye
color for fruit flies,
height (humans)
Polygenic Traits:
• Most traits are controlled by
two or more genes and are,
therefore, called polygenic
traits.
• Each gene of a polygenic
trait often has two or more
alleles.
• As a result, one polygenic
trait can have many possible
genotypes and even more
possible phenotypes.
EX: height (A bell-shaped curve is
also called a normal distribution)
Checkpoint Point Questions:
1. Explain what independent assortment
means.
2. Describe two inheritance patterns besides
simple dominance.
3. What is the difference between
incomplete dominance and codominance?
Genetics Webquest
• See WS