B B - Net Start Class

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Transcript B B - Net Start Class

Chapter 11
Introduction to Genetics
• Gregor Mendel and his work
(Section 11-1)
– Peas and Genetics
– Genes and Dominance
• Probability and Punnett
Squares (Section 11-2)
• Exploring Mendelian Genetics
(Section 11-3)
– Independent Assortment
– Mendel’s principles
• Beyond Mendelian Genetics
X
First Generation (F1)
X
100% pink!!!
Second Generation (F2)
3 pink, 1 blue - ¾ pink (75%), ¼ blue (25%)
How did this
happen?
Section 11-1
Genetics!!!
• Patterns of Inheritance
Box 1
• You inherit traits (physical characteristics)
from your parents- Heredity!Box
2
• Heredity is what makes you unique
– Examples of Traits:
•
•
•
•
•
Blue, Green, Brown, Black, Hazel Eye color
Red, Brown, Black, Blonde hair color
Pale, Olive, Dark skin color
Box 1
Tall, short, average heights
Or, pink and blue fur!
• Genetics = the scientific study of heredity
Box 3
and its importance in biology
Am I in
heaven?
Gregor Mendel
• Gregor Mendel (1822), an Austrian
monk who studied inheritance patterns
in pea plants, his work is now consideredBox 4
the foundation of modern genetics
– He worked with ordinary garden peas, planted
in the garden at his monastery.
– His love of plants and science allowed him to
spend a lifetime devoted to both.
• In 1866, he published a groundbreaking
work that later became known as Mendel’s
Laws on Heredity, but NO ONE
BELIEVED HIM!!!
• Years later, his work was rediscovered,
and modern genetics was born
Yet another
lovely flower! I
am truly in
heaven!
Ah! What a
lovely
flower!
What Mendel Did
Let’s cross
you with the
white flower.
• Background:
– Fertilization = when the female’s egg and
the male’s sperm (flower sperm = pollen)
Box 5
unite to produce an embryo
• Plants, animals, and most living things,
sexually reproduce
Box 6
• Sexual reproduction = combination of egg
and sperm to create a new cell, or embryo
• Mendel’s peas were True-Breeding, meaning if Box 7
they were allowed to self-pollinate, they would
produce baby pea plants (offspring) identical
to themselves
– Mendel knew what to expect from his pea plantsthey should look exactly like their parent plant!
• He Cross-pollinated his pea plants, mixed up
the parents, to see what the resulting plants
Hmm, what
would look like
have we here?
Box 7
P x
P
F1
What Mendel Found
X F1
Box 11
F2
Box 8
• Mendel studied 7 different pea plant traits
that varied from one individual plant to the
next (like human traits!)
• These traits had 2 forms, such as either
green seeds or yellow seeds, smooth pods
or wrinkled pods
– He crossed plants with each of the 7
contrasting characteristics and studied their
offspring
Box 9
• P = represents the parent generation
• F (from the Latin word fillius and filia- son
and daughter)
• F1 = first generation
• F2 = second generation
Box 9
• Hybrids = offspring of crosses between
Box 10
Are you an
F1 or F2?
Mendel’s Experiment
P generation
tall
short
Mendel’s Experiment
P generation
tall
short
F1 generation
tall
tall
Mendel’s Results
Box 12
All the F1 plants expressed only the dominant trait!
Seed
Shape
Seed
Color
Seed
Coat Color
Pod
Shape
wrinkled
green
white
constricted
Yellow dominant
Pod
Color
Flower
Position
Flower
Height
yellow
terminal
short
Smooth dominant
Axial dominant
Tall dominant
round
Round dominant
yellow
gray
Gray dominant
smooth
green
Green dominant
axial
Ha! Those are
MY peas!
tall
Mendel’s Principles of Heredity
Hello!
•
Mendel learned 2 principles from these
experiments:
1. Biological inheritance is determined
Box 13
by factors (we call them genes) that
are passed from one generation to
the next,
Box 14
Genes = chemical factors that
determine traits – each trait is
controlled by 1 gene that occurs in 2
contrasting forms or alleles
Box 13
Box 15
Allele = a
different form
of a gene
2. Principle of Dominance: some alleles are
dominant and others are recessive
Brown eyes = BB or Bb
Blue eyes = bb
Principle of Dominance
Box 16
• An organism with a dominant allele for
a particular form of a trait will always
exhibit that form of the trait
• In other words, if you have the dominant
allele, you will express that dominant
trait
• An organism with a recessive allele for
a particular form of a trait will exhibit
that form only when the dominant allele
is not present
Short = tt
Box 17
• In other words, you must
have 2 recessive alleles
to express the recessive trait
Eeek!
Tall = TT or Tt
I’m
Dominant!!
I’m so
proud!
Where did the recessive
traits go?
• Mendel wanted to know why all
his F1 plants expressed only
dominant traits ?????
• He wondered, “Had all the
recessive traits disappeared? Or
were they still present in the F1
plants?”
• To answer this question, he Box 18
allowed his F1 plants to selfF1 X F1
• pollinate
F2
Naughty!
Naughty!
Mendel’s Experiment
Tall, short,
tall, tall
P generation
tall
short
F1 generation
tall
tall
Mendel’s Experiment
Tall, short, tall,
tall, tall, tall, tall,
tall, SHORT!
Ha!
P generation
tall
short
F1 generation
tall
tall
F2 generation
tall
tall
tall
short
F1 Cross
All in Box 18
• Mendel thought the results for his
F1 cross were amazing!
• All the recessive traits reappeared
in the F2 offspring!
• This was due to segregation
(separation) of alleles
• Segregation of the alleles happens
when gametes (sex cells) are
formed
• One trait comes from the father,
one trait comes from the mother
I’m good!
Man
of the
Year
Segregation
F1
Tt
Tt
X
Tall
Tall
Segregation
Gametes
F2
T
t
T
t
TT
Tt
Tt
tt
Tall
Tall
Tall
Short
3 Tall, 1 Short
3 :1 Ratio
Gametes
Hmmm…
.
Section 11-2
Genetics and Probability
• Probability = the likelihood that a
particular event will occur Box 19
• For example, tossing a coin
• Probability of heads = ½ or 50%
• Probability of tails = ½ or 50%
• If you flip a coin 3 times in a row, what is the
probability of heads each time?
• Each coin toss is independent of the previous
toss, so ½ x ½ x ½ = 1/8 or 13% chance of all
heads
Box 20
• The way alleles segregate is completely
random, like a coin toss (50% chance for each
allele)
Box 20
• We can use the principles of probability to
PREDICT the outcome of genetic crosses
Yeah, I
look
good.
Punnett Squares
• Punnett
Punnett Squares = tool used to
predict and compare the genetic
Squares
variations that may result from a
cross
X
T
Tall = Tt
Box 21
T
t
TT
Tt
Box 22
Genotype = genetic makeup
(Geno = genes)
Box 23
Tall = Tt
t
Tt
tt
Fill in the Punnet Square
Genotype = TT, Tt, tt
Phenotype = physical
characteristics
(Pheno = physical)
Phenotype = Tall, short
Box 24
Heterozygous =
Tt = Heterozygous2 different alleles for the same
trait
Homozygous =
TT or tt = Homozygous2 identical alleles for the same
trait
Box 25
Why didn’t
I think of
that?
Punnett Squares
X
Phenotype = Brown eyes
Phenotype = Blue eyes
Genotype = BB or Bb
Genotype = bb
B
B
b
Bb
Bb
b
Bb
Bb
Genotype offspring = 100% Bb
Phenotype offspring =
100% brown eyes
B
B
b
b
b
Bb
bb
B
BB
Bb
b
Bb
bb
b
Bb
bb
Genotype offspring = 50% Bb,
Genotype offspring = 25% BB,
50% bb
50% Bb,
Phenotype offspring = 50% brown,
25% bb
50% blue eyes
Phenotype offspring = 75% brown,
25% blue eyes
Section 11-3
Mendelian Genetics
• Mendel wondered if the traits
segregated independently, or were they
somehow linked together
• His experiment = 2 factor Test Cross for
F1 and F2
Round Yellow peas
Genotype: RRYY
Box 26
X
Wrinkled Green peas
Genotype: rryy
100% RrYy, Round Yellow peas
‘Tis my peas
against
yours!
I won!
2 Factor Cross: F2
• Mendel’s F1 plants were RrYy, or all
heterozygous for seed shape and
color genes
• Mendel asked himself, “Would
these alleles segregate
independently? Or would they stay
together?”
• To find out, Mendel crossed his F1
plants to create the F2 generation:
To segregate or not
RrYy
x
RrYy
to segregate, that
Box 27
X
‘tis question.
2 Factor Cross: F2
Box 27
F2 plants :
556 seeds
315 round and yellow (parental)
32 wrinkled and green
(parental)
209 combination of phenotypes
(combo of alleles)
Alleles for seed shape and color
segregated independently
Ah, my beautiful
peas!
Mendel’s Principles
Therefore, thou
must write all my
Principles!
Thou must
remember my
Principles!
And, stop
whining- start
writing!!!
Box 28
1. Genes, passed from parents to
offspring, determine the inheritance of
biological characteristics.
2. When 2 or more forms (alleles) of a
gene exist, some forms may be
dominant and some recessive.
3. In sexual reproduction, each adult
has 2 copies of each gene (one from
each parent), and these genes
segregate from each other when
gametes are formed.
4. The alleles for different genes usually
segregate independently of one
another.
Box 29
Principle of
Independent
Assortment
• Principle of Independent
Assortment: genes for different traits can
segregate independently during the
formation of gametes
– This helps to account for the many genetic
variations observed in plants, animals and other
organisms
– Seed color isn’t tied to seed shape or plant
height
– Just like having red hair doesn’t mean you have
blue eyes, or being tall doesn’t mean you have
a big nose
• Genes for different traits are
independently assorted into the sex
cells (eggs and sperm)
Did you know
pollen is flower
sperm?
Section 11-4
Exceptions to Mendel’s Rules
• Some alleles are neither dominant
or recessive – what????
• Some traits are controlled by
multiple alleles or multiple genes
Box 30
• Incomplete Dominance = cases
when one allele is not completely
dominant over another
What??? Say it
‘tisn’t so
Incomplete Dominance
Red should be dominant over white, or vise
versa, but neither is completely dominant,
thus, incomplete dominance.
Four o’clock
plants
Box 31
When you cross Red and
White Four O’clock Flowers,
you get PINK flowers!!!!
Pink
Flowers!
Codominance
Box 32
• Codominance = both alleles
contribute equally to the phenotype
• The offspring is a mixture of both
alleles
Le Moo.
Red cow
X
White cow
Box 33
Roan cow
Neither white or red
Red fur and white fur
A pink cow? I
don’t think so.
Multiple Alleles
Box 34
• Multiple Alleles = when a gene
has more than two alleles
– Does NOT mean a person can have more
than two alleles for a single trait
(still 1 gene from mom, 1 from dad)
– The trait itself has more than 2 forms
(alleles)
– Ex. Blood types, A, B, AB, O
• All are a type of human blood
• But, humans can be either blood type
Box 35
Blood type A = AA or AO
Blood type B = BB or BO
Blood type AB = AB
Blood type O = OO
Blood? I don’t do
blood. Where are
my peas?
Polygenic Traits
Box 36
If you see a graph like this on my test,
or the TAKS test, then you know one
gene can’t control the trait! Polygenic!
Poly = many, Genic = genes
• Polygenic traits = traits
controlled by more than one
gene
Box 37
This range of heights and skin colors tells us more
than 2 genes control both traits.
If 2 genes controlled height and 2 genes controlled
skin color, we would see either tall or short people,
light or dark skin, and nothing in between. Is that
what we see?
I’m
tall.
Drosophila melanogaster
Box 38
• Thomas Hunt Morgan (1900s)worked with Drosophila melanogaster
(fruit fly) to study Mendel’s principles
• Why study fruit flies?
– Produce lots of offspring (don’t we know it)
– Short life span (can do lots of tests)
– Has variations we can cross
Box 38
So, Mendel’s principles apply to all
organisms, not just plants!
I prefer flowers.
Especially peas.
Genes and the Environment
• Genetics is only part of what determines the
physical characteristics of an organism
• Our environment also plays a big roleBox 39
– Your behavior is partially determined by genes
inherited from your parents, but also by the
environment in which you were/are raised
• Twin studies
– Plants are dependent on weather
– Domesticated animals vs. wild animals
Wonder twin
powers,
Activate!
Form of..
Pea soup?
So, don’t blame
your genes
totally for your behavior that’s mostly learned at home!
Form of..
A pea
plant!
Section 11-5
Linkage and Gene Maps
• Genes are found on chromosomes,
and we inherit whole chromosomes
from our parents
Box 40
• Therefore, it’s actually chromosomes
that assort independently, not
individual genes
• So, some genes are “linked” together
by virtue of being on the same
chromosome
Gene for curly hair
Gene for hair length
Box 40
I have curly hair,
and I’m tall.
Genetic Diversity
• Even if 2 genes are found on the same
chromosome, they may not be linked
forever
• Crossing Over during Prophase I of Box 41
Meiosis leads to a genetic “mixing” up
• This generates Genetic Diversity
Stop that. It’s
wrong! Or is it?
Crossing over
Gene Maps
• The further apart two genes are on a
chromosome, the more likely they
are to be separated during meiosis
• The rate at which genes were
separated and recombined is used to
make Gene Maps Box 42
Gene Map = shows the location of
a variety of genes on a
chromosome and how far apart the
genes are
That doesn’t look
like a pea plant.
Chromosome 19
End of Ch. 11
I wonder if anyone
will miss me? Will
they forget about
me and my
research?
I hope thou
hast enjoyed
learning about
my work!
Go plant some
peas!
Save the peas!
Hmm…pea soup
sounds good, I
wonder if I have any
peas left over?