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Biology Chapter 11
Introduction to Genetics: Mendel and
Meiosis
IQ #1
1. How many chromosomes would a sperm or an egg
contain if either one resulted from the process of
mitosis?
2. If a sperm containing 46 chromosomes fused with an
egg containing 46 chromosomes, how many
chromosomes would the resulting fertilized egg
contain? Do you think this would create any problems in
the developing embryo?
3. In order to produce a fertilized egg with the appropriate
number of chromosomes (46), how many chromosomes
should each sperm and egg have?
Section 11-4: Meiosis
I. MEIOSIS
A. Meiosis= process of
_________________________
in which the number of
Reduction Division
chromosomes per cell is cut in 1/2
and the homologous chromosomes that exist in a diploid cell
are separated. (and produce haploid cells)
B. Purpose=Form gametes (egg and sperm)
II. DIPLOID AND HAPLOID CHROMOSOME NUMBER
A. During ________________
the genetic material
fertilization
from one parent combines with genetic material from
another
Example: A fruit fly has 8 chromosomes
A set of 4 came from the female fly
A set of 4 came from the male fly
B. The two sets of chromosomes are said to be
homologous = a female chromosome has a
corresponding male chromosome.
C. Diploid (2n)=contain both sets of
homologous chromosomes
D. Haploid (n)= contain 1 set only
Male gamete Sperm (n) = 23 chromosomes
Female gamete Egg (n) = 23 chromosomes
Question: If we start with a diploid cell, how do we get an
organism that produces haploid gametes?
Answer:Meiosis (aka: reduction division)
1 replication; 2 divisions
Example:
46
Human
what if:
16
92
46
8
Fruit fly
Duplicated
8
46
Duplicated
chromosomes
8
chromosomes
23
23
23
23
4
4
4
4
III.
PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES:
MEIOSIS I & II
INTERPHASE: growth, DNA synthesis, protein production,
organelle production
A.
Meiosis I
prophase I
chromosomes
tetrads)
2n
1. homologous
pair up (Form
2. nucleoli disappear
3. nucleus disappears
4. crossing-over occurs:
portions of chromatids
exchange genetic material
(diagram 277)
Crossing-Over
Crossing Over:
exchange of genetic material between
homologous chromosomes
Go to
Section:
Crossing Over
Go to
Section:
Crossing-Over
Crossing
Over
Go to
Section:
metaphase I
1. homologous pairs (tetrads) line up at the
equator
2. spindles attach to chromosomes
independent assortment occurs
anaphase I
1. spindles pull the homologous
chromosomes toward opposite ends of the
cell
Key point: homologous pairs separate, cell
now haploid
Telophase I
1. Nuclear membranes reform
n
n
2. cell begins to separate into two
new haploid cells
3. 2 haploid daughter cells
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Interphase I
Prophase I
chromosome pairs with
Cells undergo Each
its corresponding
a round of DNAhomologous chromosome to
form a tetrad.
replication,
forming
duplicate
Chromosomes.
Go to
Section:
Metaphase I
Anaphase I
Spindle fibers attach to the
chromosomes.
The fibers pull the
homologous chromosomes
toward the opposite ends of
the cell.
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo
a round of DNA
replication,
forming
duplicate
Chromosomes.
Each
chromosome
pairs with its
corresponding
homologous
chromosome to
form a tetrad.
Spindle fibers attach to the
chromosomes.
The fibers pull the
homologous chromosomes
toward the opposite ends of
the cell.
Go to
Section:
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo
a round of DNA
replication,
forming
duplicate
Chromosomes.
Each
chromosome
pairs with its
corresponding
homologous
chromosome to
form a tetrad.
Spindle fibers
attach to the
chromosomes.
The fibers pull the
homologous chromosomes
toward the opposite ends of
the cell.
Go to
Section:
Figure 11-15 Meiosis
Meiosis I
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo
a round of DNA
replication,
forming
duplicate
Chromosomes.
Each
chromosome
pairs with its
corresponding
homologous
chromosome to
form a tetrad.
Spindle fibers
attach to the
chromosomes.
The fibers pull the
homologous
chromosomes
toward the
opposite ends of
the cell.
Go to
Section:
B. Meiosis II (similar process as mitosis; no replication)
Prophase II
Metaphase II
Anaphase II
Telophase II/
Cytokinesis
n
n
n
***RESULT: 4 haploid daughters that are genetically different!!
n
Figure 11-17 Meiosis II
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Meiosis II
Section 11-4
Prophase II
Go to
Section:
Meiosis I results
in two haploid (N)
daughter cells,
each with half the
number of
chromosomes as
the original.
Metaphase II
The
chromosomes line
up in a similar
way to the
metaphase stage
of mitosis.
Anaphase II
Telophase II
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Meiosis II
Prophase II
Meiosis I results
in two haploid (N)
daughter cells,
each with half the
number of
Go to chromosomes as
Section:the original.
Metaphase II
Anaphase II
The chromosomes line up in a The sister chromatids
similar way to the metaphase separate and move toward
stage of mitosis.
opposite ends of the cell.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Meiosis II
Section 11-4
Prophase II
Meiosis I results
in two haploid (N)
daughter cells,
each with half the
number of
Go to chromosomes as
Section:the original.
Metaphase II
The
chromosomes line
up in a similar
way to the
metaphase stage
of mitosis.
Anaphase II
The sister
chromatids
separate and
move toward
opposite ends of
the cell.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Meiosis II
Section 11-4
Prophase II
Meiosis I results
in two haploid (N)
daughter cells,
each with half the
number of
Go to chromosomes as
Section:the original.
http://www.sumanasinc.com/webcontent/anisampl
es/majorsbiology/meiosis.html
Metaphase II
The
chromosomes line
up in a similar
way to the
metaphase stage
of mitosis.
Anaphase II
The sister
chromatids
separate and
move toward
opposite ends of
the cell.
Telophase II
Meiosis II results
in four haploid (N)
daughter cells.
IV. GAMETE FORMATION (refer to page 278)
A. Males
The 4 haploid cells (gametes) = sperm
1.
2. male gametes produced by a process called
_________________
spermatogenesis
B. Females
1. 4 haploid cells are produced but only
viable egg
1-haploid cell is a
3-producepolar bodies caused by uneven cytoplasmic
division
2. female gametes produced by a process called
_______________
oogenesis
(a) In the male, all four haploid products of meiosis are retained and differentiate into
sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg
cell and three (in some cases, only two) small cells called polar bodies that do not give
rise to functional gametes. Although not indicated here, the mature egg cell has usually
grown much larger than the oocyte from which it arose.
V. COMPARING MITOSIS AND MEIOSIS
A. Mitosis results in the production of two genetically
identical diploid cells, whereas meiosis produces four
genetically different haploid cells.
http://biologyinmotion.com/cell_division/
Mitosis
Number of daughter
cells
Type of cells produced
Number of divisions
Number of replications
Purpose of division
2 diploid cells
Body cells
Meiosis
4 haploid cells
gametes
1
2
1
1
Sexual
Growth, replacement, repair,
asexual reproduction
reproduction
Section 11-1
Standards addressed: CA 3.b. Students know the genetic basis for
Mendel’s laws of segregation and independent assortment.
National 7 2.c. Students know an inherited trait can be determined by
one or more genes. 7.2.d. Students know plant and animal cells contain
many thousands of different genes and typically have two copies of
every gene. The two copies (or alleles) of the gene may or may not be
identical, and one may be dominant in determining phenotype while the
other is recessive. B1. 2.d. Students know new combinations of alleles
may be generated in a zygote through the fusion of male and female
gametes (fertilization).
Key Ideas: What is the principle of dominance?
What happens during segregation?
INTRODUCTION TO GENETICS
I. The work of Gregor Mendel
A. Genetics : the scientific study of heredity
B. Heredity: Passing genes from generation to generation
II. Gregor Mendel's Peas
A. In the 1800's, _____________________________
(an
Gregor Mendel
Austrian Monk) conducted the first scientific study of heredity
using pea plants.
B. Pea plants contain both
male (pollen:sperm) and female (eggs)
reproductive parts.
Flowering Plant Structures: Pea Plant
C. _______________
Fertilization
= Joining of male and female reproductive cells
D. _________________=
a pea plant whose pollen
Self-pollination
fertilizes the egg cells in the very same flower.
1. Mendel discovered that some
plants ___________
“Bred True” for certain traits
2. Trait= Specific Characteristics
Example: seed color, plant height
3.True breeding (a.k.a. pure)=
Peas that are allowed to self-pollinate produce
offspring identical to themselves
Example: Short plants that self pollinate for
generations always produce offspring that were pure for
shortness.
Cross Pollination
Self pollination
E. Cross-pollination
_______________= male sex cells from one
flower pollinate a female sex cell on a different
flower.
F. Mendel manually cross pollinated pea plants,
removing the male parts to ensure no selfpollination would occur. Through a series of
experiments, Mendel was able to make
discoveries of basic principles of heredity.
1. principle of Dominance
2. principle of Segregation
3. principle of Independent Assortment
III. Experiments Mendel performed
A. Mendel studied7 __ different traits in pea
plants each with 2 contrasting characters. (refer
to page 264)
B. Each trait Mendel studied was controlled by
one gene.
C. Different forms of a gene (trait) Alleles
=
Example: Gene for plant height has 2 alleles
Dominant: T = tall
Recessive: t = short
Figure 11-3 Mendel’s Seven F1
Crosses on Pea Plants
Mendel’s Seven Crosses on Pea Plants
Section 11-1
Go to
Section:
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
Mendel Experiment #1:
Parent
Offspring
pure bred tall x pure bred tall
TT X TT
All plants are
TALL
pure bred short x pure bred
short
tt X tt
Pure bred tall x pure bred
short
TT X tt
All plants are
SHORT
All plants are
TALL
Conclusion:
·
individual factors (now known as genes
_________)
·
the factors
did not blend
________________________________=
some alleles
Principle of Dominance
are dominant (expressed trait;written as a capital letter;
ex. T) some are recessive (hidden/masked trait; written
as a lower case letter; ex. t)
From these conclusions, Mendel wanted to continue his
experiments to see what happened to the recessive trait
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Principles of Dominance
Section 11-1
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
3 tall : 1 short
Go to
Section:
Short
Conclusion:
·
___________________________:
The
Principle
of Segregation
reappearance of the recessive allele indicated
that at some point the allele for shortness
separated from the allele for tallness. Mendel
suggested that the alleles separated during the
formation of the sex cells (gametes)….During
meiosis.
IV. PROBABILITY AND PUNNETT
SQUARES
The likelihood that a particular
A. Probability =
event will occur
# of times a particular event occurs
B. Probability=
# of opportunities for the event to occur
(# of trials)
Example #1: If you flip a coin, what is the probability
of landing on heads?
Probability=1
(side that has a head on it)
2 2( opportunities on a coin; head or
tails)
Example #2: If you flip a coin 3 times what is the
x ½ x ½ = 1/8
probability of landing on heads? ½Probability=
A. Each flip is
independent of the next. Past
outcomes do not affect future ones.
Similar to alleles that segregate
randomly, like a coin flip.
B. Thelarger the number of trials the closer you get
to the expected outcomes
C. The principles of probability can be used to
predict the outcomes of genetic crosses.
IV. PUNNETT SQUARES
Use of Punnett squares help determine the
probable outcomes of genetic crosses.
·
New vocabulary to help with Punnett squares
-Homozygous =Having 2 identical alleles (TT,
tt)
Having 2 different alleles
-Heterozygous=
(Tt)
Genetic makeup of an organism (TT, tt,
-Genotype=
Tt)
Physical appearance (tall or
-Phenotype=
short)
The offspring resulting from a cross
-Hybrids=
between parents of contrasting traits
Example of a Punnett square:
Parent (P) cross
homozygous tall( TT) x homozygous short( tt )
·
t
T
Tt
T
Tt
t
Tt
Tt
F1
offspring
Probability of producing homozygous tall
offspring? 0/4
Probability of producing hybrid? 4/4
IV. PROBABILITY AND SEGREGATION
A. For fun, lets cross F1’s to see if Mendel’s assumption
about segregation are correct:
Tt x Tt
T
t
T
TT
Tt
t
Tt
tt
If the alleles segregate during meiosis, then the
probable outcomes will be:
TT= 1/4
Tall= 3
Tt= 2/4
Short= 1
tt= 1/4
Ratio tall:short= 3:1
Conclusion:
Mendel was correct in his assumptions
about Segregration
IV. PROBABILITY AND INDEPENDENT
ASSORTMENT
A. Mendel wondered if one pair of alleles affected
the segregation of another pair of alleles.
Do round seeds have to be yellow?
B.The two factor cross: Mendel crossed RRYY x
rryy (P)(aka:two trait cross)
All offspring are
Hybrid (RrYy) (F1)
A. Then he crossed the hybrids (F1):
RrYy x RrYy
·
Punnett square formatting rules for 2 trait
crosses
1. Determine the possible gametes produced by
the parents. 2 methods:
irst two
(RY)
a. F-utside two
RrYy
(Ry)
(rY)
Onside
two
(ry)
I-ast two
L-
a. Use a punnett square. One trait on top and the
other trait on the side.
Parent 1: RrYy
y
Y
Parent 2: RrYy
Y
y
R
RY
Ry
R
RY
Ry
r
rY
ry
r
rY
ry
Possible gametes
Possible gametes
2. Place one parent’s gametes at the top of a 16Punnett square and the other parent’s gametes
on the side of the 16-Punnett square.
RY
Ry
rY
ry
RY RRYY RRYy
RrYY
RrYy
Ry RRYy RRyy
RrYy
Rryy
rY RrYY
RrYy
rrYY
rrYy
ry RrYy
Rryy
rrYy
rryy
Section 11-3
Probability:
RY (round and yellow)= 9/16
Ry (round and green = 3/16
rY (wrinkled and yellow)= 3/16
ry (wrinkled and green)= 1/16
Phenotype Ratio= 9:3:3:1
Conclusion=
Alleles for seed shape
independently assort.
Go to
Section:
Independent assortment
Genes for different traits can segregate
independently during the formation of gametes
****This is true if the traits you are studying
are located on different chromosomes
Just by chance all 7 of Mendel’s traits were on
different chromosomes.
**Summary of Mendel’s Principles**
1. The inheritance of biological characteristics is
determined by individual units known as genes.
Genes are passed from parents to their offspring.
2. In cases in which two or more forms (alleles) of
the gene for a single trait exist, some forms of the
gene may be dominant and others may be
recessive.
3. In most sexually reproducing organisms, each
adult has two copies of each gene – one from each
parent. These genes are segregated from each
other when gametes are formed.
4. The alleles for different genes usually segregate
Summary of Gregor Mendel’s Work
Gregor
Mendel
concluded
that
experimented
with
Pea
plants
“Factors”
determine
traits
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
Beyond Dominant and Recessive Alleles
Key idea: Some alleles are neither dominant
nor recessive, and many traits are controlled
by multiple alleles or multiple genes.
Ex. Four O’clock flowers (see next slide)
Incomplete Dominance in Four O’clock
Flowers
Incomplete Dominance:
One allele is
not completely
_______________
dominant over another.
Therefore the phenotype
in the heterozygous is
in between
somewhere __________
the two homozygous
phenotypes.
Incomplete Dominance in Four O’clock
Flowers
equally
Codominance: both alleles contribute _________
to the phenotype.
Ex. Cholesterol
more than two
Mutliple Alleles: Genes that have _____________
alleles.
This does not mean an individual can have more
than two alleles, but that there are more than two
alleles in the _______________
for a given trait.
population
Ex. Rabbit coat color, blood type
Multiple Alleles and Codominance
3 Alleles:
iA, iB, I
iA and iB are
codominant
iA, iB both
dominate over
i
Blood
Type/Phenotype
BO
BB
Polygenic Inheritance: The interaction of many
genes controls one trait.
It is usually recognized in traits that show a
____________________
such as skin color, height,
range of phenotypes
and body weight.
Applying Mendel’s Principles.
Mendel’s principles do not apply only to plants.
Thomas Hunt Morgan
1. In the early 1900’s
________, Morgan (a nobel prize
winning geneticist) decided to look for a model
organism to advance the study of genetics.
2. He studied the _____________,
Drosophila
fruit fly
melanogaster.
3. This specimen was a good choice because:
 _______
and can be kept in a small place
tiny
 produce ___________
of offspring
hundreds
 has only _________
of chromosomes
4 pairs
 they can produce a new _______________
every
generation
4 weeks
Fruit Flies
(Drosophila melanogaster)
Genetics and the environment
Genes alone ______________________
do not determine
the
characteristics of an organism. The interaction
environment
between genes and the ________________are
necessary.
Ex. Consider the height of a sunflower. Genes
provide a plan for the development of a sunflower
but the condition of the soil, climate, and water
availability will also influence the height of the
sunflower.
11-5: Gene Linkage and Gene Maps
Standards addressed: CA B1 3.b students know
the genetic basis forMendel’s laws of segregation
and independent assortment. *B1 3.d. Students
know how to use data on frequency of
recombination at meiosis to estimate genetic
distances between loci and to interpret genetic
maps of chromosomes.
Key concept: What structures actually assort
independently?
Actually ________________________
do assort
the chromosomes
independently just as Mendel had suggested but the
_______
linked together
genes on the chromosomes can be ____________.
A. Linked genes
1. Genes located on the _________
same
chromosome
together
2. Inherited _____________
3. Do not undergo independent
___________________;
assortment
they don't follow Mendel's law (Just by
chance all the traits Mendel studied were
located on separate chromosomes...none
were linked.)
B. Linkage group= all the genes on a
_____________
chromosome
* If there are ___
4 pairs of chromosomes then there are
4 linkage groups. Humans have ____
23 pairs of
____
chromosomes therefore ____
23 linkage groups
III. Crossing Over
A. If two genes are found on the same
chromosome, does it mean that they are linked
forever? NO!
recombinants.
Crossing over produces ___________________
B.new
Recombinants=
combinations individuals with
_________________ of genes
IV. Gene Mapping
A. Sturtevant stated that:
 crossing over occurs ________________
along
randomly
the linkage groups.
 the _______________
the genes are from each
further
other the ______________
they will cross over
more likely
of recombination (how often
 using thefrequency
_______________________
crossing over occurs), a gene _______
can be made
map
for each chromosome
B. Gene map= the __________________
positions of genes on a
chromosome
Example: gene a and gene b cross over 20%
gene a and gene c cross over 5%
gene b and gene c cross over 75%
chromosome:
C
A
B
Figure 11-19 Gene Map
of the Fruit Fly
Exact location on chromosomes
Chromosome 2