Download Chapter 11 Genetic and Meiosis

MEIOSIS
Chapter 11
REVIEW

Cell has issues when it grows larger in size
Not enough DNA
 Nutrients and wastes cannot pass the cell membrane



Cell solves these problems through the process of
cell division
Mitosis – the portion of cell
division where the nucleus divides
MITOSIS

Almost every cell of the body uses mitosis to
divide the nucleus

Somatic cells – cells that are not sex cells/gametes

Exs) liver cell, bone cell, brain cell etc.
AS LONG AS IT IS NOT SPERM OR EGGS IT
USES MITOSIS

Cell grows (G1), synthesizes
DNA (S), makes molecules
and organelles (G2) and then
is ready for cell division
(mitosis and cytokinesis)
STAGES OF MITOSIS
1.
Prophase – chromatin
condenses into chromosomes
and nuclear envelope breaks
down, centrioles move and
spindle fibers form
2.
Metaphase – chromosomes
line up in middle of cell and
spindle fibers attach to
centromere
PROPHASE
STAGES OF MITOSIS
3.
Anaphase – spindle fibers
pull at centromere and
separate sister chromatids
pulling them to opposite
ends of the cell
4.
Telophase – chromosomes
break down into chromatin
and nuclear envelope
reforms
THE END OF MITOSIS


After telophase, the cells cytoplasm splits by the
process of cytokinesis
As a result we are left with…
2 IDENTICAL DAUGHTER CELLS
THE NEW STUFF…



There are many studies into the
process that makes each one of us
different
Gregor Mendel – a monk born in
1822 who did many studies in the
field of genetics
Genetics – the study of heredity

Why is it that we have traits (eye
color, hair color, etc.) similar to our
parents, yet we are not all alike?
GENETICS



Mendel recognized that the offspring of “parents”
were similar and began to investigate why this
happens
He came to the conclusion that the parent
organisms must pass on traits in their genetic
material
These traits are located on
their genes (DNA)
MENDEL’S PREDICTIONS


Mendel was correct about the passing of traits
and the idea of genes
He wasn’t sure how these events happened but
knew
1.
2.
An organism must inherit a single copy of every
gene from both its “parents”
When and organism produces its own cells to pass
to offspring, there are 2 sets that must separate
from each other so that each cell contains just 1 set
of genes
STOP! WHAT DOES THIS MEAN?!?!

Gametes – the sex cells of an organism
Sperm and eggs
 Mitosis deals with non-gametes (somatic cells)



Remember, in mitosis we result in genetically
identical cells
WE DO NOT WANT GENETICALLY
IDENTICAL OFFSPRING!!!
TRANSLATION OF MENDEL’S IDEA #2
When and organism produces its own cells to pass to
offspring, there are 2 sets that must separate from
each other so that each cell contains just 1 set of
genes


Every cell of the human body contains a specific
number of chromosomes (46)
In order for offspring to maintain that number of 46
and not end up with duplicate (92), the parent gamete
(sex cell) must half their number of chromosomes
 End
result > 23 (mom) + 23 (dad) = 46 offspring
chromosomes
TRANSLATION OF MENDEL’S IDEA #1
An organism must inherit a single copy of every gene from
both its “parents”


Remember, each of the 46 chromosomes needs to
halved by the parents (to make 23)
Parents will only contribute each of those 23 genes
one time to their offspring
 (parents
do not want to give multiple copies of the same
gene)
 So,
again 23 + 23 = 46 chromosomes total
CHROMOSOMES AND GAMETES
Remember…


Chromosomes – the structures in the cell that
carry the genetic material (genes) from the
parent cell to the daughter cell
Gametes – sex cells or germ cells (sperm and egg)
CHROMOSOMES

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There are many chromosomes in the body that
carry information for many different “things”
Examples – eye color, hair color, height, 2nd toe
length, etc… (everything that makes you, you!)
When 2 cells come together from 2 parents, the
matching chromosomes must come in contact
These matching chromosomes are called
homologus

Homologous Chromosomes – same chromosome types
between mother and father cells
CHROMOSOME NUMBERS

Haploid – a cell that contains a single set of
chromosomes
Remember “hap” sounds like half
 Is usually represented as N


Diploid – a cell that contains both sets of
homologous chromosomes
Remember “di” means 2 (kinda like “bi” – bicycle)
 Is usually represented as 2N


Since the somatic cells of the body are diploid we
need the sex cells to be haploid so offspring do
not have more chromosomes than necessary
WHAT DO DIPLOID/HAPLOID NUMBERS MEAN?
Diploid Barbie
2N = 46
chromosomes
Diploid Ken
2N = 46
chromosomes
Haploid Ken Cell
N = 23
chromosomes
Haploid Barbie Cell
N = 23
+
chromosomes
Sperm cell
Egg cell
Equals
Diploid Baby
2N = 46
chromosomes
HOW ARE HAPLOID GAMETES PRODUCED?

Meiosis

a process of reduction division in which the number
of chromosomes per cell is cut in half through the
separation of homologous chromosomes in a diploid
cell

Involves 2 distinct divisions
1.
2.

Meiosis 1
Meiosis 2
Starts with 1 diploid cell and results in 4
haploid daughter cells that are
GENETICALLY DIFFERENT from the
parent cell
MEIOSIS 1

Prior to meiosis 1, each chromosome is replicated


Same as S phase of interphase prior to mitosis
Meiosis 1 starts with the cell beginning to divide
very similarly to mitosis

Unlike mitosis, meiosis 1 has homologous pairing in
each step

Homologous Pairing – the same chromosome types
from mom and dad come together (eye color, hair
color, etc.)
PROPHASE 1

Homologous chromosomes pair and form a tetrad


Since 1 chromosome is made of 2 chromatids, there
are 4 chromatids in a tetrad
While in their tetrad, homologous chromosomes
are able to trade/swap information in a process
called crossing over
this process results in the exchange of traits (alleles)
between the same chromosomes therefore creating
new trait combinations
 One reason why you are
different from your parents!

REMAINDER OF MEIOSIS 1


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Meiosis utilizes the remainder of the cycles as
mitosis did separating homologous chromosomes
instead of sister chromatids
Metaphase 1 – spindle fibers attach to homologous
chromosomes
Anaphase 1 – spindle fibers separate homologous
chromosomes
REMAINDER OF MEIOSIS 1


Telophase 1/Cytokinesis – the nuclear envelope
reforms around chromosomes and the cytoplasm
splits
As a result of Meiosis 1, 2 daughter cells are
produced tat have half the number of genetically
different chromosomes
MEIOSIS 2

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After Meiosis 1, the 2 cells produced proceed to
meiosis 2 (there is no chromosome replication)
Each of the daughter cells move through Meiosis
2 much in the same way Mitosis occurs
Prophase 2 – the centriole move
to opposite ends of the cell, the
nuclear envelope breaks down
Metaphase 2 – chromosomes
line up in the middle of the
cell and spindle fibers attach
to the centromere
MEIOSIS 2


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Anaphase 2 – the spindle fibers pull on the
centromere and split the sister chromatids
Telophase 2 & Cytokinesis – the nuclear envelope
forms and the cell cytoplasm splits
4 genetically DIFFERENT cells result
GAMETE FORMATION

The male gamete that is produced is called a
sperm (spermatocyte)


There are 4 sperm cells that are produced as a result
of meiosis
The female gamete that is produced is called an
egg (oocyte)
There is 1 egg cell produced as a result of meiosis
 The 3 other cells produced are called polar bodies

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Polar Bodies are not used in reproduction and are
considered to be the trash bags of the egg, but can be useful
in genetic testing
COMPARING MITOSIS AND MEIOSIS

Sloppy Copy

Mitosis/Meiosis Picture
Fold paper down middle
 Draw Mitosis on left side starting with interphase
and ending with cytokinesis beginning with 4
chromosomes (X’s)
 Draw Meiosis on right side starting with interphase
and ending with cytokinesis 2 beginning with 4
chromosomes (X’s)


Mitosis/Meiosis Compare/Contrast Graphic
Organizer
3 ways they are similar
 3 ways they are different
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THE WORK OF GREGOR MENDEL
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
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Every living thing has a set of
characteristics inherited from its
parent(s)
Genetics – study of heredity
The father of genetics was Gregor
Mendel

Was an Austrian monk that studies
the passing of traits in pea plants
GREGOR MENDEL’S PEA PLANTS
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
He was put in charge of the gardens at the
monastery
He knew how the process of fertilization occurred
When the male and female cells join during sexual
reproduction
 In plants fertilization happens because of pollination

CREATING PLANTS

Pea plants are able to self-pollinate
The sperm in the pollen can fertilize the egg cell of
the same plant
 As a result, a plant can be created from only 1
“parent” and therefore have the same characteristics
of that 1 parent


Since plants were self-pollinating, they would
also be considered true-breeding

They would produce offspring identical to themselves
Ex) tall plants would make more tall plants
 Ex) green seeded plants would make more green seeded
plants

MENDEL’S GETS STARTED


Even though true-breeding plants are good,
Mendel was interested in what would happen if
different traits were “crossed”
Mendel manipulated flowers so they could not
self-pollinate and then began to cross breed
plants with different characteristics
Ex) cross a tall plant with a short plant
 Ex) cross a yellow seed plant with a green seed plant

GENES AND DOMINANCE

Mendel studied contrasting pea plant traits


Trait – a specific characteristic (such as color or
height) that varies from one individual to another
Mendel looked at the offspring that he created by
crossing parents with different traits

These offspring were called hybrids
P – symbol for the parental generation
F1 – symbol for the 1st generation
WHAT DID THE 1ST GENERATION LOOK
LIKE?


To Mendel’s surprise, the offspring were not a
combination of the 2 different traits
One of the traits did not even appear
MENDEL’S CONCLUSIONS
1.
Biological inheritance is determined by factors
that are passed from one generation to the next
We know that this is because of genes – chemical
factors that determine traits
 The different forms of a gene is an allele


2.
Ex)
alleles of height – tall & short
alleles of color – yellow & green
Some alleles are dominant and others are
recessive (principal of dominance)
Dominant traits will be exhibited whenever present
 Recessive traits will only be exhibited when it’s the
only trait present

SEGREGATION


Mendel wanted to know if the recessive trait had
completely disappeared in the F1 generation
He allowed the F1 generation plants to cross by
self-pollination, creating a F2 generation
F1 CROSS RESULTS


Mendel discovered the recessive traits
reappeared
Mendel concludes that the dominant allele had
only masked the recessive allele and that
recessive alleles never disappeared
The alleles must separate or segregate from each
other
 Gametes pick up one allele or another during the
segregation process

HOW DID SEGREGATION WORK?

Mendel concludes:

When each of the F1 plant
flowers produces gametes, the
two alleles segregate from each
other so that each gamete
carries only a single copy of
each gene

Therefore, each F1 plant
produces 2 types of gametes –
those with the allele for tallness
and those with the allele for
shortness
MENDEL’S RESULTS


Mendel repeated his experiments many times to
see what would happen
He realized that for each cross, he got the same
basic results


Ex) whenever he crossed Tt for height, ¾ of offspring
were tall and ¼ of offspring were short
Mendel realized that he could apply the
principals of probability to explain the results of
genetic crosses
GENETICS AND PROBABILITY


Probability – the likelihood that a particular
event will occur
Example – Coin Flip
The chances that a coin will come up heads is 50% (1/2
or 1:2)
 The chances that a coin will come up tails is 50% (1/2
or 1:2)


If you flipped a coin and it came up heads, what are
the chances that it will come up heads the next time?
The next time?

Each event is independent of each other, so each time is a
50% chance
COIN TOSS ACTIVITY


Hypothesis: If I toss a coin 2 times, I would
expect to get _______ Heads and ________ Tails.
Toss your coin 2 times and record results

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Toss 1 ____ H
_____ T
Toss 2 ____ H
_____ T
Toss your coin 8 more times and record results
Toss 3
Toss 7
Toss 4
Toss 8
Toss 5
Toss 9
Toss 6
Toss 10
ACTUAL COIN TOSS RESULTS

For first 2 tosses:

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Total Results
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Number Heads ______ Number Tails ______
Number Heads ______ Number Tails ______
Did the actual results for the entire class come
closer to your hypothesis of 50/50 chance for
heads and tails?
HOW IS COIN FLIPPING RELEVANT TO
GENETICS?


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When we are dealing with probabilities of an
event, past outcomes DO NOT affect future ones
Each event is completely separate and therefore
has just as equal chances for an outcome as the
one before
The segregation of alleles is completely random,
just like a coin toss

You randomly get what you get, every single time
PUNNETT SQUARES

Punnett Square – is a diagram that shows the gene
combinations that can result from a genetic cross
Dominant traits are expressed by capital letters (T)
 Recessive traits are expressed by lower case letters (t)


Homozygous – organisms that have identical alleles
for a particular trait (TT or tt)

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Are true breeding (pure-bred) organisms for a trait
Heterozygous – organisms that have different
alleles for a particular trait (Tt)

Are hybrid organisms for a particular trait
PUNNETT SQUARE RESULTS
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
The outcomes of a punnett square can be described by
both their “letters” and their “appearances”
Phenotype – the physical characteristics of an
organism (the appearance)


Genotype – the genetic makeup of an organism (the
letters)


Ex) tall, short, yellow, green
Ex) TT, Tt, tt
Organisms can have the same phenotype even though
they have different genotypes

TT – tall & Tt – tall
PROBABILITY AND SEGREGATION

Was Mendel’s model for segregation correct when
looking at alleles for height?

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Are we able to determine the same results by looking
at probabilities for height?


YES! (branching tree example)
YES (punnett square example)
The results are the same no matter how you look at it
PROBABILITIES PREDICT AVERAGES


Probabilities can predict the average outcome of
a large number of events (remb. the coin tossing)
They cannot predict the precise outcome of an
individual event


The predictions are based on chances for each
individual event
When dealing with genetics, the larger the
number of offspring, the closer your results will
be to the predicted number
INDEPENDENT ASSORTMENT



Mendel said that alleles segregate during the
formation of gametes
When Mendel was doing his experiments he
wanted to know if alleles segregated on their own
(independently) or if one allele can affect another
allele
Mendel goes back to the pea plant to find the
answer
2 FACTOR CROSSES – F1


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Mendel performed his pea plant experiments now
looking at 2 different traits at once
Mendel crossed purebred plants round yellow
(RRYY) and wrinkled green (rryy) [P] and looked
at their offspring [F1]
All offspring were heterozygous round yellow
(RrYy)

We are not able to see if the alleles
segregate independently with these
results…
2 FACTOR CROSS – F2



Mendel crossed 2 of the F1 offspring to
create a F2 generation
Mendel wanted to know if
dominant/recessive alleles stay together
(RY/ry)
Mendel looked at the F2 results and
saw…




9/16 were round yellow
3/16 were round green
3/16 were wrinkled yellow
1/16 was wrinkled green
Remember our P
generation genotypes…
RRYY – round yellow
rryy – wrinkled green
F2 RESULTS

Mendel saw in the F2 generation the presence of
offspring that did not exist in any parent



Round green and wrinkled yellow
This fact means that alleles are capable of
segregate independently
Independent Assortment – genes for different
traits are able to separate on their own and do
not influence each others inheritance

the alleles for seed shape and color did not influence
each other since they were capable of separation
PRINCIPAL OF INDEPENDENT
ASSORTMENT

This states…


Genes for different traits can segregate
independently during the formation of gametes
Along with crossing over, independent
assortment is the other process that accounts for
genetic variation
SUMMARY OF MENDEL’S PRINCIPALS


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The inheritance of biological characteristics is
determined by individual units known as genes.
Genes are passes from parents to offspring
In cases in which 2 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.
In most sexually reproducing organisms, each adult
has 2 copies of each gene – one from each parent.
These genes are segregated from each other when
gametes are formed
The alleles for different genes usually segregate
independently of one another.
BEYOND DOMINANT AND RECESSIVE



There are some exceptions to
some of Mendel’s principals
Since many genes have more
than 2 alleles and many traits are
controlled by more than 1 gene,
genetics can be very complicated
Genetics deals with more than
just dominance and recessiveness
PATTERNS OF INHERITANCE
(HOW GENES ARE INHERITED)

Incomplete Dominance – when one
allele is not completely dominant and
another completely recessive
The offspring will be a mixture of 2 phenotypes
 Ex) some flowers with red and white parents
will result with a pink phenotype


Codominance – both alleles contribute to
the phenotype of an organism
The offspring will show more than 1 phenotype
 Ex) a white chicken and a black chicken have
offspring that are black and white “speckled”

PATTERNS OF INHERITANCE
(HOW GENES ARE INHERITED)

Multiple Alleles – when genes have
more than one allele possibility
The individual will not have more than 2
allele, there are just more than 2
possibilities in the population
 Ex) coat color in rabbits


Polygenic Traits – traits that are
controlled by 2 or more genes
Traits can be produced by the interaction
of genes
 Ex) fly eye color, skin color, coat color in
labs

APPLYING MENDEL’S PRINCIPALS


There are many scientists that tried to test
Mendel’s principals
Thomas Hunt Morgan – a scientist from the early
1900’s that performed genetic tests on fruit flies




Why Fruit Flies?
Small organism (easy to care for and doesn’t take up
much room)
Reproduces quickly
Inexpensive to get and keep
Fruit flies will prove to be very important to the
study of genetics!!
GENETIC AND THE ENVIRONMENT


Characteristics of organisms are not
determined by genetics alone
The interaction of organisms and the
environment can play a role in genetics
Height of plants determined by the sun
 Evolution of organisms based on surroundings
 The development of disease based on contact
with different substances in environment


“genes provide a plan, how plan unfolds
depends on environment”
GENE LINKAGE


We have been able to look at how genes
located on different chromosomes assort
independently
What happens to genes on same
chromosomes
Do they assort?
 Must they be inherited together?


These questions were tested by Thomas
Hunt Morgan with his fruit fly research
GENE LINKAGE IN DROSOPHILA
MELANOGASTER


Morgan was able to identify more
than 50 genes
He saw that many genes were
inherited together



Ex) many times reddish-orange eyes
and small wings were almost always
inherited together and were rarely
separated
Does this mean independent
assortment doesn’t occur?
Through much research, Morgan
discovered 4 linkage groups
GENE LINKAGE IN DROSOPHILA
MELANOGASTER

When Morgan crossed the linkage groups,
he realized…
that the linkage groups assorted independently
 all of the genes that were involved with the
linkage group were inherited together


This information leads to 2 conclusions
1.
2.

Each chromosome is actually a group of linked
genes
It is the chromosome that assorts
independently, not the gene
Mendel didn’t see gene linkage because the
genes he was looking at were on different
chromosomes
GENE MAPS

Just because genes are found on the same
chromosome, does not mean that they are
linked forever



Crossing-over can separated genes on same
chromosomes producing new alleles
Researchers of Morgan’s looked at the
rate at which linked genes were separated
and used their findings to produce gene
maps
Gene map – shows the relative locations
of each gene on a chromosome

Crossing-over rates were used to construct
the drosophila and human genome map