Download Biology_1_&_2_files/8 Genetics ACADEMIC

Make of list of at least three organisms that reproduce
asexually and three organisms that reproduce sexually.
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In asexual reproduction, how does the offspring
compare to the parent?
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In sexual reproduction, how does the offspring
compare to the parent?
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Why are chromosomes important to an organism?
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In asexual reproduction, a single parent passes a
complete copy of its genetic information to each of its
offspring.
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An individual formed by asexual reproduction is
genetically identical to its parent.
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Prokaryotes reproduce asexually by a kind of cell
division called binary fission.
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Many unicellular eukaryotes also reproduce asexually.
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Some multicellular eukaryotes, such as starfish, go
through fragmentation.
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Fragmentation is a kind of reproduction in which the
body breaks into several pieces. Some or all of these
fragments regrow missing parts and develop into
complete adults.
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Other animals, such as the hydra, go through
budding. In budding, new individuals split off from
existing ones.
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Some plants, such as potatoes, can form whole new
plants from parts of stems.
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Other plants can reproduce from roots or leaves.
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Some crustaceans, such as water fleas, reproduce
by parthenogenesis. Parthenogenesis is a process in
which a female makes a viable egg that grows into
an adult without being fertilized by a male.
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Most eukaryotic organisms
reproduce sexually.
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In sexual reproduction, two
parents give genetic material to
produce offspring that are
genetically different from their
parents.
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Each parent produces a
reproductive cell, called a
gamete. A gamete from one
parent fuses with a gamete
from the other.
Visual Concept: Sexual
Reproduction
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The resulting cell, called a zygote, has a combination
of genetic material from both parents. This process is
called fertilization.
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Because both parents give genetic material, the
offspring has traits of both parents but is not exactly
like either parent.
Visual Concept: Fertilization
Germ Cells and Somatic Cells
► The cells of a multicellular organism are often
specialized for certain functions.
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Cells that are specialized for sexual reproduction are
called germ cells. Only germ cells can produce
gametes.
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Other body cells are called somatic cells. Somatic cells
do not participate in sexual reproduction.
Advantages of Sexual Reproduction
► Asexual reproduction is the simplest, most efficient
method of reproduction.
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Asexual reproduction allows organisms to produce
many offspring in a short period of time without using
energy to make gametes or to find a mate.
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But the genetic material of these organisms varies
little between individuals, so they may be at a
disadvantage in a changing environment.
Advantages of Sexual Reproduction
► Sexual reproduction, in contrast, produces genetically
diverse individuals.
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A population of diverse organisms is more likely to
have some individuals that survive a major
environmental change.
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Each chromosome has thousands of genes that play
an important role in determining how an organism
develops and functions.
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Each species has a characteristic number of
chromosomes.
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An organism must have exactly the right number of
chromosomes. If an organism has too many or too
few chromosomes, the organism may not develop and
function properly.
Visual Concepts: Chromosome
Number
Click above to play the video.
Haploid and Diploid Cells
► A cell, such as a somatic cell, that has two sets of
chromosomes is diploid.
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A cell is haploid if it has one set of chromosomes.
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Gametes are haploid cells.
Haploid and Diploid Cells
► The symbol n is used to represent the number of
chromosomes in one set.
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Human gametes have 23 chromosomes, so n = 23.
The diploid number in somatic cells is written as 2n.
Human somatic cells have 46 chromosomes (2n = 46).
Click above to play the video.
Homologous Chromosomes
► Each diploid cell has pairs of
chromosomes made up of two
homologous chromosomes.
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Homologous chromosomes are
chromosomes that are similar in
size, in shape, and in kinds of
genes.
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Each chromosome in a homologous
pair comes from one of the two
parents.
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Homologous chromosomes can
carry different forms of genes.
Visual Concept: Homologous
Chromosomes
Click above to play the video.
Autosomes and Sex Chromosomes
► Autosomes are chromosomes with genes that do not
determine the sex of an individual.
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Sex chromosomes have genes that determine the sex
of an individual.
Visual Concept: Sex
Chromosomes and Autosomes
Autosomes and Sex Chromosomes
► In humans and many other organisms,
the two sex chromosomes are referred
to as the X and Y chromosomes.
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The genes that cause a zygote to
develop into a male are located on the Y
chromosome.
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Human males have one X chromosome
and one Y chromosome (XY), and
human females have two X
chromosomes (XX).
Visual Concept: The Role of Sex
Chromosomes in Sex Determination
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An individual formed by asexual reproduction is
genetically identical to its parent.
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In sexual reproduction, two parents give genetic
material to produce offspring that are genetically
different from their parents.
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Each chromosome has thousands of genes that play
an important role in determining how an organism
develops and functions.
If a human sperm and egg each had 46 chromosomes,
how many chromosomes would a fertilized egg have?
Explain why increasing the number of chromosomes a
human cell might cause problems.
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What occurs during the stages of meiosis?
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How does the function of mitosis differ from the
function of meiosis?
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What are three mechanisms of genetic variation?
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Meiosis is a form of cell division that produces
daughter cells with half the number of chromosomes
that are in the parent cell.
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During meiosis, a diploid cell goes through two
divisions to form four haploid cells.
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In meiosis I, homologous chromosomes are separated.
In meiosis II, the sister chromatids of each homologue
are separated.
Visual Concept: Meiosis
Click above to play the video.
Meiosis I
► Meiosis begins with a diploid cell that has copied its
chromosomes.
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During prophase I, the chromosomes condense, and
the nuclear envelope breaks down. Homologous
chromosomes pair. Chromatids exchange genetic
material in a process called crossing-over.
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In metaphase I, the spindle moves the pairs of
homologous chromosomes to the equator of the cell.
The homologous chromosomes remain together.
Meiosis I
► In anaphase I, the homologous chromosomes
separate. The spindle fibers pull the chromosomes of
each pair to opposite poles of the cell. But the
chromatids do not separate at their centromeres. Each
chromosome is still made of two chromatids. The
genetic material, however, has recombined.
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During telophase I, the cytoplasm divides
(cytokinesis), and two new cells are formed. Both cells
have one chromosome from each pair of homologous
chromosomes.
Meiosis II
► Meiosis II begins with the two cells formed at the
end of telophase I of meiosis I.
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The chromosomes are not copied between meiosis I
and meiosis II.
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In prophase II, new spindles form.
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During metaphase II, the chromosomes line up
along the equators and are attached at their
centromeres to spindle fibers.
Meiosis II
► In anaphase II, the centromeres divide. The
chromatids, which are now called chromosomes, move
to opposite poles of the cell.
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During telophase II, a nuclear envelope forms around
each set of chromosomes. The spindle breaks down,
and the cell goes through cytokinesis.
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The result of meiosis is four haploid cells.
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The processes of mitosis and meiosis are similar but
meet different needs and have different results.
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Mitosis makes new cells that are used during growth,
development, repair, and asexual reproduction.
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Meiosis makes cells that enable an organism to
reproduce sexually and happens only in reproductive
structures.
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Mitosis produces two genetically identical diploid cells.
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Meiosis produces four genetically different haploid
cells. The haploid cells produced by meiosis contain
half the genetic information of the parent cell.
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If you compare meiosis and mitosis, they may appear
similar but they are very different.
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In prophase I of meiosis, every chromosome pairs
with its homologue. A pair of homologous
chromosomes is called a tetrad.
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As the tetrads form, different homologues exchange
parts of their chromatids in the process of crossingover. The pairing of homologous chromosomes and
the crossing-over do not happen in mitosis.
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Therefore, a main difference between meiosis and
mitosis is that in meiosis, genetic information is
rearranged leading to genetic variation in offspring.
Visual Concept: Comparing
Meiosis and Mitosis
Visual Concept: Comparing the
Results of Meiosis and Mitosis
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Genetic variation is advantageous for a population.
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Genetic variation can help a population survive a
major environmental change.
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Genetic variation is made possible by sexual
reproduction.
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In sexual reproduction, existing genes are rearranged.
Meiosis is the process that makes the rearranging of
genes possible.
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Fusion of haploid cells from two different individuals
adds further variation.
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Three key contributions to genetic variation are
crossing-over, independent assortment, and random
fertilization.
Crossing-Over
► During prophase I, homologous chromosomes line up
next to each other.
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Each homologous chromosome is made of two sister
chromatids attached at the centromere.
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Crossing-over happens when one arm of a chromatid
crosses over the arm of the other chromatid.
Crossing-Over
► The chromosomes break at the
point of the crossover, and
each chromatid re-forms its full
length with the piece from the
other chromosome.
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Thus, the sister chromatids of
a homologous chromosome no
longer have identical genetic
information.
Visual Concept: Tetrads and
Crossing-Over of Genetic Material
Independent Assortment
► During metaphase I, homologous pairs of
chromosomes line up at the equator of the cell.
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The two pairs of chromosomes can line up in either of
two equally probable ways.
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This random distribution of homologous chromosomes
during meiosis is called independent assortment.
Visual Concept: Independent
Assortment
Random Fertilization
► Fertilization is a random process that adds genetic
variation.
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The zygote that forms is made by the random joining
of two gametes.
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Because fertilization of an egg by a sperm is random,
the number of possible outcomes is squared.
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During meiosis, a diploid cell goes through two
divisions to form four haploid cells.
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Mitosis produces cells that are used during growth,
development, repair, and asexual reproduction. Meiosis
makes cells that enable an organism to reproduce
sexually and it only happens in reproductive
structures.
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Three key contributions to genetic variation are
crossing-over, independent assortment, and random
fertilization.
Write a sentence using each one of the following terms:
haploid, diploid, zygote.
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What is a diploid life cycle?
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What is a haploid life cycle?
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What is alternation of generations?
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Most animals have a diploid life cycle.
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Most of the life cycle is spent in the diploid state.
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All of the cells except the gametes are diploid.
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A diploid germ cell in a reproductive organ goes
through meiosis and forms gametes.
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The gametes, the sperm and the egg, join during
fertilization. The result is a diploid zygote.
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This single diploid cell goes through mitosis and
eventually gives rise to all of the cells of the adult,
which are also diploid.
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In diploid life cycles, meiosis in germ cells of a
multicellular diploid organism results in the formation
of haploid gametes.
Meiosis and Gamete Formation
► Male animals produce gametes called sperm.
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A diploid germ cell goes through meiosis I. Two cells
are formed, each of which goes through meiosis II.
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The result is four haploid cells.
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The four cells change in form and develop a tail to
form four sperm.
Visual Concept: Formation of
Sperm
Click above to play the video.
Meiosis and Gamete Formation
► Female animals produce gametes called eggs, or ova
(singular, ovum).
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A diploid germ cell begins to divide by meiosis. Meiosis
I results in the formation of two haploid cells that have
unequal amounts of cytoplasm.
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One of the cells has nearly all of the cytoplasm. The
other cell, called a polar body, is very small and has a
small amount of cytoplasm.
Meiosis and Gamete Formation
► The polar body may divide again, but its offspring cells
will not survive.
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The larger cell goes through meiosis II, and the
division of the cell’s cytoplasm is again unequal.
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The larger cell develops into an ovum. The smaller
cell, the second polar body, dies.
Meiosis and Gamete Formation
► Because of its larger share of cytoplasm, the mature
ovum has a rich storehouse of nutrients.
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These nutrients nourish the young organism that
develops if the ovum is fertilized.
Visual Concept: Formation of the
Egg Cell
Click above to play the video.
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The haploid life cycle happens in most fungi and some
protists.
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Haploid stages make up the major part of this life
cycle.
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The zygote, the only diploid structure, goes through
meiosis immediately after it is formed and makes new
haploid cells.
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The haploid cells divide by mitosis and give rise to
multicellular haploid individuals.
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In haploid life cycles, meiosis in a diploid zygote
results in the formation of the first cell of a
multicellular haploid individual.
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Plants and most multicellular protists have a life cycle
that alternates between a haploid phase and a diploid
phase called alternation of generations.
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In plants, the multicellular diploid phase in the life
cycle is called a sporophyte.
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Spore-forming cells in the sporophyte undergo meiosis
and produce spores.
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A spore forms a multicellular gametophyte.
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The gametophyte is the haploid phase that produces
gametes by mitosis.
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The gametes fuse and give rise to the diploid phase.
Visual Concept: Alternation of
Generations
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In diploid life cycles, meiosis in germ cells of a
multicellular diploid organism results in the formation
of haploid gametes.
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In haploid life cycles, meiosis in a diploid zygote
results in the formation of the first cell of a
multicellular haploid individual.
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Plants and most multicellular protists have a life cycle
that alternates between a haploid phase and a diploid
phase called alternation of generations.
List five characteristics that are passed on in families.
Name one characteristic that is inherited but that may
also be influenced by behavior or environment.
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Why was Gregor Mendel important for modern
genetics?
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Why did Mendel conduct experiments with garden
peas?
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What were the important steps in Mendel’s first
experiments?
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What were the important results of Mendel’s first
experiments?
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the study of heredity
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A monk named Gregor Mendel did
breeding experiments in the 1800s with
the garden pea plant.
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The science of heredity and the
mechanism by which traits are passed
from parents to offspring is called
genetics.
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Modern genetics is based on Mendel’s
explanations for the patterns of heredity
in garden pea plants.
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Most of Mendel’s experiments involved
crossing different types of pea plants. In
this case, the word cross means “to
mate or breed two individuals.”
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The garden pea plant is a good subject
for studying heredity because the plant
has contrasting traits, usually selfpollinates, and grows easily.
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In the study of heredity, physical
features that are inherited are called
characters.
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A trait is one of several possible forms
of a character.
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The offspring of a cross between
parents that have contrasting traits is
called a hybrid.
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In garden pea plants, each flower
contains both male and female
reproductive parts. This arrangement
allows the plant to self-pollinate, or
fertilize itself.
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Cross-pollination occurs when pollen
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Mendel cross-pollinated pea plants
by removing the male parts from
some of the flowers then dusting the
female parts with pollen from
another plant.
from the flower of one plant is
carried by insects or by other means
to the flower of another plant.
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
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The garden pea is a good subject for studying heredity
because it matures quickly and produces many
offspring.
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Thus, Mendel was able to compare several results for
each type of cross and collect repeated data.
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Collecting repeated data is an important scientific
method.
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A monohybrid cross is a cross that is done to study
one pair of contrasting traits. Crossing a plant that has
purple flowers with a plant that has white flowers is an
example of a monohybrid cross.
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Mendel’s first experiments used monohybrid crosses
and were carried out in three steps.
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Each step involved a new generation of plants. A
generation is a group of offspring from a given group
of parents.
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Plants that self-pollinate for several generations
produce offspring of the same type. Such a plant is
said to be true-breeding for a given trait.
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The first group of parents that are crossed in a
breeding experiment are called the parental
generation or P generation. The offspring of the P
generation is called the first filial generation, or F1
generation.
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Mendel allowed the F1 generation to self-pollinate
and produce new plants. He called this offspring the
second filial generation, or F2 generation.
Visual Concept: Mendel’s
Experiments
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All of Mendel’s F1 plants expressed the same trait for a given character.
The contrasting trait seemed to have disappeared.
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The contrasting trait reappeared, however, in some of the F2 plants
when the F1 plants were allowed to
self-pollinate.
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For each of the seven characters that Mendel studied, he found a
similar 3-to-1 ratio of contrasting traits in the F2 generation.
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Modern genetics is based on Mendel’s explanations for
the patterns of heredity that he studied in garden pea
plants.
►
The garden pea plant is a good subject for studying
heredity because the plant has contrasting traits,
usually self-pollinates, and grows easily.
►
Mendel’s first experiments used monohybrid crosses
and were carried out in three steps.
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For each of the seven characters that Mendel studied,
he found a similar 3-to-1 ratio of contrasting traits in
the F2 generation.
A gardener noticed that some of the flowers on her
plants were white. In previous years, they had been
purple.
Write down a possible explanation for this difference.
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What patterns of heredity were explained by Mendel’s
hypotheses?
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What is the law of segregation?
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How does genotype relate to phenotype?
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What is the law of independent assortment?
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Mendel developed several hypotheses to explain the
results of his experiments.
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These hypotheses are collectively called the
Mendelian theory of heredity and form the
foundation of modern genetics.
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Mendelian theory explains simple patterns of
inheritance. In these patterns, two of several
versions of a gene combine and result in one of
several possible traits.
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Different traits result from different versions of
genes. Each version of a gene is called an allele.
Visual Concept: Allele
Click above to play the video.
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Each allele can lead to a unique trait.
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Traits can come from either parent because each
pair of alleles is separated when gametes form
during meiosis.
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Only one of the pair is passed on to offspring.
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An allele that is fully expressed whenever it is
present is called dominant.
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An allele that is not expressed when a dominant
allele is present is called recessive.
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A recessive allele is expressed only when there is no
dominant allele present.
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Traits may also be called dominant or recessive.
Visual Concept: Comparing
Dominant and Recessive Traits
Click above to play the video.
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Because chromosome pairs split randomly during
meiosis, either one of a pair of homologous
chromosomes might end up in any one gamete.
Chance decides which alleles will be passed on.
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In modern terms, the law of segregation holds that
when an organism produces gametes, each pair of
alleles is separated and each gamete has an equal
chance of receiving either one of the alleles.
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Scientists use a code of letters to represent the
function of alleles.
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A dominant allele is shown as a capital letter. This
letter usually corresponds to the first letter of the
word for the trait.
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A recessive allele is shown as a lowercase letter.
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Offspring do not show a trait for every allele that they
receive. Instead, combinations of alleles determine
traits.
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The set of specific
combinations of alleles that an
individual has for a character is
called the genotype.
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The detectable trait that results
from the genotype’s set of
alleles is called the
phenotype.
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Thus, genotype determines
phenotype.
Visual Concept: Genotype
Click above to play the video.
Visual Concept: Comparing
Genotype and Phenotype
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If an individual has two
identical alleles of a certain
gene, the individual is
homozygous for the
related character.
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If an individual has two
different alleles of a certain
gene, the individual is
heterozygous for the
related character.
Visual Concept: Comparing
Homozygous and Heterozygous
Genotypes and Resulting
Phenotypes
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A dihybrid cross involves two characters, such as
seed color and seed shape.
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Mendel used dihybrid crosses in his second
experiments and found that the inheritance of one
character did not affect the inheritance of another
character.
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In modern terms, the law of independent
assortment holds that during gamete formation, the
alleles of each gene segregate independently.
Independent Assortment in Peas
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Genes are said to be linked when they are close
together on chromosomes.
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Scientists now know that many genes are linked to
each other as parts of chromosomes.
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Genes that are located close together on the same
chromosome will rarely separate independently.
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The only genes that follow Mendel’s law of
independent assortment are those that are far apart.
►
Mendelian theory explains simple patterns of
inheritance. In these patterns, two of several
versions of a gene combine and result in one of
several possible traits.
►
In modern terms, the law of segregation holds that
when an organism produces gametes, each pair of
alleles is separated and each gamete has an equal
chance of receiving either one of the alleles.
►
Genotype determines phenotype.
►
In modern terms, the law of independent assortment
holds that during gamete formation, the alleles of
each gene segregate independently.
Since the dawn of agriculture, people have used
selective breeding to improve crops and domestic
animals. Modern applications of Mendelian genetics
and gene technology have resulted in major changes
in crops and animals.
List some examples of selective breeding in domestic
animals or crops that you know of.
Explain how you might go about selecting for a
particular trait.
►
How can a Punnett square be used in genetics?
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How can mathematical probability be used in
genetics?
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What information does a pedigree show?
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A Punnett square is a model that predicts the likely
outcomes of a genetic cross.
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A Punnett square shows all of the genotypes that
could result from a given cross.
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The simplest Punnett square consists of a square
divided into four boxes.
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The combination of letters in each box represents one
possible genotype in the offspring.
Visual Concept: Punnett Square
with Heterozygous Cross
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In a monohybrid homozygous cross, all of the
offspring will be heterozygous (Yy) and will express
the dominant trait.
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In a monohybrid heterozygous cross the genotypic
ratio will be 1 YY : 2 Yy : 1 yy. The phenotypic ratio
will
be 3 : 1.
►
A Punnett square shows the possible outcomes of a
cross, but it can also be used to calculate the
probability of each outcome.
►
Probability is the likelihood that a specific event will
occur.
►
Probability can be calculated and expressed in many
ways.
►
Probability can be expressed in words, as a decimal,
as a percentage, or as a fraction.
 devised by R. C. Punnett
 used to predict results of
a cross
 assign the traits letters
 dominant alleles are
capitalized
 recessive alleles are lower
case
► W=
purple
► w = white
Tt X Tt Cross
Tt X Tt Cross
►
Homozygous Parents
►
WW x ww
►
all are Ww - genotype
which is heterozygous
►
purple - phenotype
►
Heterozygous Parents
►
Ww x Ww
25% WW = purple
► 50% Ww = purple
► 25% ww = white
►
Is there a way to determine
genotypes of organisms?
 If recessive, it is homozygous.
►
Testcross
 unknown genotype crossed with
known genotype (recessive trait)
► white with purple
► genotype HAS to be either
WW or Ww
► resulting generation will
answer the question
Visual Concept: Calculating
Probability
►
Probability formulas can be used to predict the
probabilities that specific alleles will be passed on to
offspring.
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The possible results of a heterozygous cross are
similar to those of flipping two coins at once.
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A pedigree is a diagram that shows how a trait is
inherited over several generations of a family.
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Pedigrees can be used to help a family understand a
genetic disorder.
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A genetic disorder is a disease or disorder that can
be inherited.
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A pedigree can help answer questions about three
aspects of inheritance: sex linkage, dominance, and
heterozygosity.
A horizontal
line
connecting a
male and
female
represents a
marriage.
A half-shaded
circle or square
indicates that a
person is a
carrier of the
trait.
A completely
shaded circle
or square
indicates that
a person
expresses the
trait.
A Pedigree
A circle
represents
a female.
A square
represents a
male.
A vertical line
and a bracket
connect the
parents to their
children.
A diagram that shows how a
trait is inherited in a family
A circle or
square that
is not
shaded
indicates
that a
person
neither
expresses
the trait nor
is a carrier
of the trait.
Visual Concept: Pedigree
►
The sex chromosomes, X and Y, carry genes for many
characters other than gender.
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A sex-linked gene is located on either an X or a Y
chromosome.
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Traits that are not expressed equally in both sexes are
commonly sex-linked traits.
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Colorblindness is an example of a sex-linked trait that
is expressed more in males than in females.
Visual Concept: Sex Linkage
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If a person has a trait that is autosomal and dominant
and has even one dominant allele, he or she will show
the trait.
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If a person has a recessive trait and only one recessive
allele, he or she will not show the trait but may pass it
on.
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If a person is either heterozygous or homozygous
dominant for an autosomal gene, his or her phenotype
will show the dominant trait.
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If a person is homozygous recessive, his or her
phenotype will show the recessive trait.
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A recessive trait in a child shows that both parents
were heterozygous carriers of that recessive allele.
►
A Punnett square shows all of the genotypes that
could result from a given cross.
►
Probability formulas can be used to predict the
probabilities that specific alleles will be passed on to
offspring.
►
A pedigree can help answer questions about three
aspects of inheritance: sex linkage, dominance, and
heterozygosity.
Study the animals shown in Figure 11.
List possible mechanisms that allow the arctic fox to
change its fur color with changing seasons.
►
Are there exceptions to the simple Mendelian pattern
of inheritance?
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How do heredity and the environment interact to
influence phenotype?
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How do linked genes affect chromosome assortment
and crossover during meiosis?
A) Complete
Dominance
► like
we have seen,
where one trait is
completely dominant
heterozygous traits that appear
to be an intermediate of the
homozygous parental traits
four o’clocks
red x white ----> pink
RR
WW
RW
Neither allele is dominant and the
trait is somewhere in the middle.
Incomplete Dominance in
Four O’Clock Flowers
Incomplete Dominance in
Four O’Clock Flowers
C) Codominance
► when
both genes of a
heterozygote are both
fully expressed
► neither allele is dominant
over the other
►
horse coat color
 red and white -----> roan
does not mean that an
organism can have more
than two alleles
means that more than
two alleles exist
C = full color – dominant
cch = chinchila
dominant to ch and c
ch = Himalayan
dominant to c
c = albino
Blood Groups
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
E) Polygenism
► controlled
by more than
1 pair of genes and
have a wide range of
phenotypes
► either
on same
chromosome or
different chromosomes
► height,
weight, hair,
skin color
temperature
warmth darkens pigments
cool lightens pigments
diet
Visual Concept: Comparing
Complete, Incomplete, and
Codominance
►
Phenotype can be affected by conditions in the
environment, such as nutrients and temperature.
►
In humans, many characters that are partly
determined by heredity, such as height, are also
affected by the environment.
►
Many aspects of human personality and behavior are
strongly affected by the environment, but genes also
play an important role.
►
Many traits do not follow Mendel’s laws because he
studied the simplest kinds of heredity where
characters are determined by independent genes.
►
During meiosis, genes that are close together on the
same chromosome are less likely to be separated than
genes that are far apart.
►
Genes that are close together, as well as the traits
they determine, are said to be linked.
►
Linked genes tend to be inherited together.
►
The Mendelian inheritance pattern is rare in nature;
other patterns include polygenic inheritance,
incomplete dominance, multiple alleles, and
codominance.
►
Phenotype can be affected by conditions in the
environment, such as nutrients and temperature.
►
During meiosis, genes that are close together on the
same chromosome are less likely to be separated than
genes that are far apart.