Download Chapter 10 Notes (Overhead Version)

Chapter 10: Genetics
Meiosis (Reduction Division)
MEIOSIS is the way many organisms produce gametes through a type of cell division where
the chromosome number is halved (HAPLOID)
Only occurs in eukaryotic cells in phases similar to the phases of mitosis.
I. Chromosome Number
A. In most organisms, gamete (sex cells) can either be EGG OR SPERM
B. Humans have 46 chromosomes or 23 PAIRS of chromosomes.
1. Egg cell would carry 23 chromosomes
2. Sperm cell would carry 23 chromosomes
C. Genes are located on chromosomes in the cell nucleus.
D. Mendel's principles of genetics require at least two things:
1. Each organism must inherit a single copy of every gene from both its
“parents.” Because each organism has two “parents,” each organism must
carry two complete sets of genes.
2. When an organism produces its own gametes, those two sets of genes
must be separated from each other so that each gamete contains just one
set of genes.
D. Diploid cells (Body cells)
1. Homologous: chromosomes that came from the male parent has a
corresponding chromosome from the female parent.
2. Diploid: A cell that contains both sets of homologous chromosomes. The
number of chromosomes in a diploid cell is sometimes represented by the
symbol 2N. Diploid cells contain two complete sets of chromosomes and
two complete sets of genes.
E. Haploid cells
1. The gametes of sexually reproducing organisms, including fruit flies and
peas, contain only a single set of chromosomes, and therefore only a single
set of genes. These are haploid (one set) and represented by N.
F. How are haploid (N) gamete cells produced from diploid (2N) cells? Meiosis must
occur
II. Phases of meiosis
Meiosis: Meiosis is 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.
Meiosis usually involves two distinct divisions called meiosis I and meiosis II.
A. Meiosis I: Homologous chromosomes are separated and crossing over occurs
B. Meiosis II:
1. Sister Chromatids of each chromosomes are separated.
2. By the end of meiosis II, the diploid cell that entered meiosis has become
4 haploid cells.
Interphase I  Meiosis I (Prophase I Metaphase I Anaphase I  Telophase I)
Meiosis II (Prophase II Metaphase II Anaphase II  Telophase II)
A. Meiosis I: In Meiosis I, the division of the cell is very similar to mitosis. The
end result is the splitting of the chromosomes from their homologous pair.
1. Prophase 1:Each chromosome pairs with its corresponding homologous
chromosome. This creates a TETRAD.
a. There are 4 chromatids in a tetrad.
b. Crossing-Over: During meiosis I, while paired up with their sister
chromatids, alleles can exchange material between homologous
chromosomes to form new combinations of alleles.
1. Creates Genetic Variation!!
Synapse
Tetrad
MEIOSIS I
Interphase
Prophase I
Cell doubles in size, DNA and
organelles replicate (G1, S, G2)
Chromosomes condense and
spindle forms.
Chromosomes come together
=SYNAPSE
Chromosomes line up in tetrads
Crossing over occurs *GENETIC
VARIATION
Metaphase I
Anaphase I
Telophase I/ Cytokinesis
Homologous pairs (tetrads) line
up in the middle of the cell
Homologous pairs of
chromosomes pulled toward
opposite sides of the cell
Law of segregation
Chromosomes uncoil, cells
separate cells divide. Each new
cell is haploid
B. Meiosis II:
1. At this point, each of the cells has a haploid number of chromosomes
and each chromosome has 2 chromatids (a copy of the original).
2. At the end of Meiosis II, you get four haploid (N) daughter cells.
Meiosis II
Prophase II
NO REPLICATION
NO CROSSING OVER
Metaphase II
Condensing again
Chromosomes line up just as the
Anaphase II
Telophase II/Cytokinesis
line up in mitosis – in the middle
The sister chromatid are pulled to
opposite ends (poles)
The end product are four haploid
cells that may develop into
gametes
C. Meiosis vs. Mitosis: Mitosis results in two genetically identical diploid cells.
Meiosis produces four genetically different haploid cells.
MITOSIS
DAUGHTER CELLS WITH FULL
SET
DIPLOID
MEIOSIS
DAUGHTER CELLS WITH
HAPLOID
N
2N
2 CELLS
1 CELL DIVISION
GENETICALLY IDENTICAL
4 CELLS
2 CELLS DIVISION
GENETICALLY DIFFERENT
III. FORMATION OF GAMETES
A. Meiosis occurs within the Reproductive Organs,
1. Reproductive organs
a. TESTES (Boys)
b. OVARIES. (Girls)
B. Development of Sperm Cells
1. Each cell produces FOUR Haploid Cells called SPERMATIDS
2. Spermatids develop into sperm in a process of SPERMATOGENESIS
C. Development of Egg Cells
1. Each cell produces ONE Haploid egg and three non-functional polar bodies
because during each division – most of the cytoplasm and nutrients goes to one
cell (egg)
2. Mature egg cells or ova develop in a process called OOGENESIS
The work of Gregor Mendel
I. The experiments of Gregor Mendel
A. Genetics: the study of heredity
B. Gregor Mendel:
1. An Austrian Monk who was born in 1822.
2. He was educated in Math and Science.
3. worked as a high school teacher.
4. Worked in the monastery garden and took a particular interest in the pea
plants.
`
a. Pea plants reproduce quickly
b. Small
c. Self pollinating
C. Fertilization: Process in sexual reproduction in which male and female
reproductive cells (gametes) join to form a new cell
D. Self-pollination: The sperm cells in pollen fertilize the egg cells in the same
flower. The seeds that are produced by self-pollination
inherit all of their characteristics from the single plant.
E. True Breeding: that if they were allowed to self-pollinate, they would produce
offspring identical to themselves
F. Cross-pollination: Taking the sperm from one plant to fertilize the egg of
another plant. This produces seeds that have two different
plants as parents.
G. Trait: a specific characteristic, such as seed color or plant height, that varies
from one individual to another.
F. Hybrid: The offspring of crosses between parents with different traits.
II. Genes and Alleles
When conducting genetic crosses the following terms are important.
A. P generation: (Parental Generation) the original pair of crossed plants.
B. F1 generation: (First Filial Generation) Filius and filia are the Latin words for
“son” and “daughter.”
C. Hybrid: The offspring of crosses between parents with different traits.
D. Genes: Factors that are passed down from parent to offspring
E. Alleles: Different form of a gene.
1. Seed color: yellow, green. Each color is an allele, a different form of
the gene.
F. Mendel’s Conclusions:
1. Biological inheritance is determined by factors that are passed from one
generation to the next.
2. We now know the factors Mendel was referring to are genes. Each
gene is made up of two alleles (one of a number of different forms of a
gene).
3. Some alleles are dominant and some are recessive.
a. Dominant: An organism with a dominant allele for a particular form
of a trait will always exhibit that form of the trait.
1. (Denoted with a CAPITAL LETTER)
b. Recessive: An organism with a recessive allele for a particular
form of a trait will exhibit that form only when the
dominant allele for the trait is not present.
1. (Denoted with a lower case letter)
G. Segregation: The separation of alleles during gamete formation.
1. Gamete: Specialized cells involved in sexual reproduction
a. egg or sperm cells.
b.The alleles for the gene that controls plant height segregate from
each other so that each gamete carries only a single allele of each
gene.
c. Each F1 plant produces two types of gametes—those with the
allele for tallness and those with the allele for shortness.
Applying Mendel’s Principles
The principles of probability can be used to predict the outcomes of genetic crosses
I. Probability and Punnett Squares
A. Probability: the mathematic likelihood an event will occur
1. (flipping a coin : 50% heads, 50% tails)
B. Punnett squares: can be used to predict and compare the genetic variations
that will result from a cross.
C. Homozygous: Organisms that have two identical alleles for a particular trait
1. TT or tt
D. Heterozygous: Organisms that have two different alleles for the same trait
1. Tt
E. Phenotype: The physical appearance of a trait (Tall or short). **not always
visible (can’t see colorblindness)
F. Genotype: The genetic make up (alleles) of an organism (Tt, TT or tt).
I. Independent Assortment
A. After Mendel showed that alleles segregate during gamete formation he
wondered if the segregation of one pair of alleles (such as plant height)
affected the segregation of another set of alleles (such as seed color)
B. Two-Factor Cross F1
1. Mendel crossed true breeding round and yellow seeded plants (RRYY)
with true breeding wrinkled and green seeded plants (rryy)
RRYY x rryy
RY
RY
RY
RY
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
2. Results
a. All plants were heterozygous RrYy and all are round and yellow
b. Provided hybrid plants to breed for F2 generation
C. Two-Factor Cross: F2
1. Mendel crossed the F1 plants to produce F2 offspring
RrYy x RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
2. Results
a. A 9:3:3:1 ratio was found
b. Law of independent assortment was discovered.
1. Different traits can segregate independently, one trait does
not influence each other.
III. Summary
A. Inheritance of biological factors is determined by genes that are passed down
from parent to offspring
B. Two or more forms of an allele can exist and can be dominant or recessive.
C. In most sexually reproducing organisms, each adult has two copies of a gene.
One from each parent
D. Alleles for different genes sort independently
Other Patterns of Inheritance
There are some exceptions to Mendel’s principles.
Genetics is complicated.
A majority of genes have more than one allele
Many traits are controlled by more than one gene. (skin color, height, eye color,
fingerprint patterns)
Some alleles are neither dominant nor recessive, and many traits are controlled by
multiple alleles or multiple genes.
I. Incomplete dominance. (Think—Intermediate)
A. One allele is not completely dominant over another allele
B. The heterozygous phenotype lies somewhere between the two homozygous
phenotypes.
C. Example in flowers: Cross between two four o’clock plants show one of these
complications.
1. When you cross the red and white plant the offspring is pink in the F1
generation
a. It “seems” that it is simply a blending of the dominant (red) and
recessive (white),
2. BUT when you get the F2 generation, red, white and pink show up. The
hybrid is a phenotypic mix between dominant and recessive.
D. Example in humans: hypercholesterolemia (high blood cholesterol levels)
1. Causes:
a. Total cholesterol - all the cholesterols combined
b. High density lipoprotein (HDL) cholesterol
1. often called "good" cholesterol
c. Low density lipoprotein (LDL) cholesterol
1. often called "bad" cholesterol
1. The LDL cholesterol needs to be broken down, the only way
this can be done is with the help of LDL receptors to help
mediate the endocytosis of the “bad cholesterol”
d. Homozygous dominant (HH) person does not have
hypercholesterolemia,
e. Heterozygous Hh have a mild case of this disease,
f. Homozygous recessive person (hh) has a severe cholesterol
problem.
II. Codominance—(Think Cooperate
A. Both alleles (dominant and recessive) contribute to the phenotype of the
organism. B. Example: Feather color certain varieties of chicken
a. The allele for black feathers is codominant with the allele for white feathers
1.Heterozygous offspring are described as erminette or “speckled.
2. Cross a black feathered chicken with a white feathered chicken
a. FBFB = Black feathers
b. FwFw = White feathers
c. FBFw =Speckled feathers
FB
FB
Fw
FB Fw
FB Fw
Fw
FB Fw
FB Fwolyg
III.Multiple Alleles
A. Many genes have more than two alleles.
B. Blood type is an example of this.
1. The alleles that make up all blood types are A, B or i
2. Type A and B are codominant to each other, both are dominant to type O
Polygenic Traits – poly = many genic = genes. Some traits are controlled by the interaction of
two or more genes. Different combinations of these alleles produce very different traits. Eye
color is an example, as is height.
o
Height  AABBCC = 6 ft tall
o aabbcc = 5 ft tall
o
AaBbCc = 5 ft 6 inches
AS DOES AABbcc
IV Genes and the Environment
Characteristics of an organism are not solely determined by genes, environment plays a role.
A. Western White Butterfly (Ponita occidentalis)
1. Butterflies that hatched in summer had a different color pattern than those that
hatched in spring.
a. Those that hatched in spring had greater levels of pigment in their wings.
b. ENVIRONMENT in which butterflies developed influenced expression of
genes.
1. The change in pigment influenced the temperature of the butterfly.
The darker pigment helped increase the temp, which is important
for flight effectiveness.
Meiosis
MEIOSIS is the way many organisms produce gametes through a type of cell division where
the chromosome number is halved (HAPLOID)
Only occurs in eukaryotic cells in phases similar to the phases of mitosis.
I. Chromosome Number
A. In most organisms, gamete (sex cells) can either be EGG OR SPERM
B. Humans have 46 chromosomes or 23 PAIRS of chromosomes.
1. Egg cell would carry 23 chromosomes
2. Sperm cell would carry 23 chromosomes
C. Genes are located on chromosomes in the cell nucleus.
D. Mendel's principles of genetics require at least two things:
1. Each organism must inherit a single copy of every gene from both its
“parents.” Because each organism has two “parents,” each organism must
carry two complete sets of genes.
2. When an organism produces its own gametes, those two sets of genes
must be separated from each other so that each gamete contains just one
set of genes.
D. Diploid cells
1. Homologous: chromosomes that came from the male parent has a
corresponding chromosome from the female parent.
2. Diploid: A cell that contains both sets of homologous chromosomes. The
number of chromosomes in a diploid cell is sometimes represented by the
symbol 2N. Diploid cells contain two complete sets of chromosomes and
two complete sets of genes.
E. Haploid cells
1. The gametes of sexually reproducing organisms, including fruit flies and
peas, contain only a single set of chromosomes, and therefore only a single
set of genes. These are haploid (one set) and represented by N.
F. How are haploid (N) gamete cells produced from diploid (2N) cells?
II. Phases of meiosis
Meiosis: Meiosis is 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.
Meiosis usually involves two distinct divisions called meiosis I and meiosis II.
A. Meiosis I: Homologous chromosomes are separated and crossing over occurs
B. Meiosis II:
1. Sister Chromatids of each chromosomes are separated.
2. By the end of meiosis II, the diploid cell that entered meiosis has become
4 haploid cells.
Interphase I  Meiosis I (Prophase I Metaphase I Anaphase I  Telophase I)
Meiosis II (Prophase II Metaphase II Anaphase II  Telophase II)
A. Meiosis I: In Meiosis I, the division of the cell is very similar to mitosis. The
end result is the splitting of the chromosomes from their homologous pair.
1. Prophase 1:Each chromosome pairs with its corresponding homologous
chromosome. This creates a TETRAD.
a. There are 4 chromatids in a tetrad.
b. Crossing-Over: During meiosis I, while paired up with their sister
chromatids, alleles can exchange material between homologous
chromosomes to form new combinations of alleles.
1. Creates Genetic Variation!!
MEIOSIS I
Interphase
Prophase I
Cell doubles in size, DNA and
organelles (G1, S, G2)
Chromosomes condense and
spindle forms.
Chromosomes come together
=SYNAPSE
Chromosomes line up in tetrads
Crossing over occurs *GENETIC
VARIATION
Metaphase I
Anaphase I
Telophase I/ Cytokinesis
Homologous pairs (tetrads) line
up in the middle of the cell
Homologous pairs of
chromosomes pulled toward
opposite sides of the cell
Independent Assortment
Chromosomes uncoil, cells
separate cells divide. Each new
cell is haploid
B. Meiosis II:
1. At this point, each of the cells has a haploid number of chromosomes
and each chromosome has 2 chromatids (a copy of the original).
2. At the end of Meiosis II, you get four haploid (N) daughter cells.
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II/Cytokinesis
NO REPLICATION
Condensing again
Chromosomes line up just as the
line up in mitosis – in the middle
The sister chromatid are pulled to
opposite ends (poles)
The end product are four haploid
cells that may develop into
gametes
C. Meiosis vs. Mitosis: Mitosis results in two genetically identical diploid cells.
Meiosis produces four genetically different haploid cells.
MITOSIS
DAUGHTER CELLS WITH FULL
SET
MEIOSIS
DAUGHTER CELLS WITH
HAPLOID
2N
N
2 CELLS
1 CELL DIVISION
GENETICALLY IDENTICAL
4 CELLS
2 CELLS DIVISION
GENETICALLY DIFFERENT
III. FORMATION OF GAMETES
A. Meiosis occurs within the Reproductive Organs,
1. Reproductive organs
a. TESTES
b. OVARIES.
B. Development of Sperm Cells
1. Each cell produces FOUR Haploid Cells called SPERMATIDS
2. Spermatids develop into sperm in a process of SPERMATOGENESIS
C. Development of Egg Cells
1. Each cell produces ONE Haploid egg and three non-functional polar bodies
because during each division – most of the cytoplasm and nutrients goes to one
cell (egg)
2. Mature egg cells or ova develop in a process called OOGENESIS
FORMATION OF GAMETES
Meiosis occurs within the Reproductive Organs, in the TESTES or OVARIES.
In the development of Sperm Cells, each cell produces FOUR Haploid Cells called
SPERMATIDS which develop into sperm in a process of SPERMATOGENESIS
OOGENESIS is the production of Mature Egg Cells or OVA.
In the development of eggs, each cell produces ONE Haploid egg and three non-functional
polar bodies because during each division – most of the cytoplasm and nutrients goes to one cell
(egg)
11-5 Linkage and Gene Maps
The Law of Independent Assortment states that chromosomes assort independently during
gamete formation (not individual genes)
HOWEVER – if genes are on the same chromosome they are inherited together. – ie. All of the
chromosomes on chromosome 1 are inherited together because they are all on the same
chromosome.
Gene Maps
If genes are found on the same chromosome – they can be mapped out. This shows the relative
positions of the genes on the chromosomes.
Linkage and Gene Maps: Thomos Hunt Morgan realized, in working with fruit flies, that it is the chromosomes
that assort independently of one another rather than the genes (as Mendel thought)

Gene Linkage: genes for different traits are located on the same chromosome

Gene Map: Shows the relative locations of each known gene on one chromosome. These maps can
be constructed by measuring the frequencies of crossing-over between genes.