Transcript Chapter 11: Introduction to Genetics

Chapter 11:
Introduction to Genetics
By: Riley Thomas
11-1 The Work of Gregor
Mendel

Genetics is the scientific study of
heredity. Genetics, explain every living
thing and how it has a set of
characteristics inherited from its parent
or parents.
Gregor Mendel, the
“Father of Genetics”
Gregor Mendel was very important,
because he understood biological
inheritance.
 Mendel was a so own as the "Father of
Genetics " He was born in 1822 in what is
now the Czech Republic. Mendel was a
teacher and also took charge of the
garden duties at the monastery. Mendel
worked with garden peas.

*Pea plants use part of their flowers to
reproduce. The male part produces
pollen; pollen is the male sex cell. The
female part produces eggs, which are the
female sex cell*
When Mendel took the part as
monastery gardener, he had several
stocks of pea plants. These peas were
true breeding. True breeding is a term
used to describe organisms that produce
offspring identical to themselves if
allowed to self-pollinate.
 The true-breeding plants were the basis
of Mendel's experiment.
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However, pea plants can also crosspollinate. In cross-pollination, male sex
cells in pollen from the flower on one
plant fertilize the egg cells of a flower on
another plant. The seeds produced from
cross-pollination have two plants as
parents.
To perform his experiment, Mendel had
to select the pea plants that he would
mate with each other.
 He had to prevent the pea flowers from
self-pollinating and control their crosspollination.
 Mendel accomplished this task by
cutting away the male parts of a flower
and then dusting the flower with pollen
from a second flower.

Mendel studied seven different pea
plants traits.
 A trait is a specific characteristic.
 Mendel studied crossed plants with each
of the seven contrasting characters and
studied their offspring.
 Mendel called each original pair of
plants the P(parental) generation. He
called the offspring the F1, or “first filial'“
generation.
 The offspring of crosses between parents
with different traits are called hybrids.
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Below is a chart of the different crosses
Mendel did.
From his first experiments Mendel drew
two conclusions:
 1. Biological inheritance is determined
by factors that are passed from one
generation to the next.
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2. The principle of dominance, which
states that some alleles are dominant
and others are recessive.
Alleles are the different forms of a gene .
 Mendel also had a question he wanted
to, answer:
 Had the recessive alleles disappeared, or
were they still present in the F1 plant?
 To answer this question, he allowed all
seven kinds of F1 hybrid plants to
produce an F2 (second filial) generation
by self-pollination.
 The traits controlled by the recessive
alleles appeared.
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Segregation means separation.

Gametes are sex cells
Ex: Pollen is a male sex cell
Eggs are a feminine sex cell
Magnified
Image of
flower
pollen.
11-2 Probability and Punnett
Squares
The likelihood that a particular event will
occur is called probability.
 The principles of probability can predict
the outcomes of genetic crosses.
 Probabilities predict the average
outcome of a large number of events.
But cannot predict the precise outcome
of an individual event.

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A Punnett square is a diagram that shows
the different gene combinations that
might result from a genetic cross.
Below is an example:
Tt*Tt

The letters in the Punnett square
represent alleles:

Capital letters for dominant alleles and
lowercase letters for recessive alleles.

In this example, T represents tallness and
t represent the recessive allele for
shortness.
Organisms that have two. identical
alleles for a particular trait TT or tt (for this
example) are said to be homozygous
 Organisms that have 2 different alleles
for the same trait are heterozygous.
 Homozygous organisms are true
breeding for a particular trait.
 Heterozygous organisms are hybrid for a
particular trait.
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Phenotype means physical
characteristics.

Genotype means genetic makeup.
A human’s
genetic
makeup.
11-3 Exploring Mendelian

The principle of independent
assortment, states that genes for
different traits can segregate
independent during the formation of
gametes.
Mendel's principles form the base on
which the modern science of genetics
has been built.
 These principles can be summarized as
follows:
 Individual units known as genes
determine the inheritance of biological
characteristics.
 In organisms that reproduce sexually,
genes are passed from parents to their
offspring

In cases in which two or more forms of
the gene for a single trait exists, some
forms of the gene may be dominant and
others may be recessive.
 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.
 The alleles from different genes usually
segregate independently of one
another.

*Some alleles are neither dominant nor
recessive, and multiple alleles or multiple
genes control many traits. *
 Incomplete Dominance
 Cases in which one allele is not
completely dominant over another are
called incomplete phenotype is
incomplete dominance. In incomplete
dominance, the heterozygous
phenotype is somewhere in between the
two homozygous phenotypes.
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An example of Incomplete Dominance is
when:

RED Flower x WHITE Flower PINK Flower
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Codominance is a similar situation (as
Incomplete Dominance) in which both
alleles contribute to the phenotype of
the organisms.
Example:
 red x white ---> red & white spotted

Multiple Alleles
 Many genes have more than two alleles
and are therefore said to have multiple
alleles.
 This does not mean that an individual
can have more than two alleles.
 It onlymeans that more than two possible
alleles exist in a population.

Polygenic Traits
 Many traits are produced by the
interaction of several genes.
 Traits controlled by two or more genes
are said to be polygenic traits which
means, "having many genes".

11-4 Meiosis
Homologous is a term used to refer to
chromosomes that each have a
corresponding chromosome from the
opposite sex parent.
 A cell that contains both sets of
homologous chromosomes is said to be
diploid, which means, "two sets".
 Haploid is a term used to refer to a cell
that contains only a single set of
chromosomes and therefore only a
single set of genes.

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
stages: the first meiotic division, called
meiosis I, and the second meiotic
division, meiosis II.
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Below are the various phases of meiosis and
what happens during them:
MEIOSIS 1
Interphase 1: Cells undergo a round of DNA
replication, forming duplicate
chromosomes.
Prophase 1: Each chromosome pairs with its
corresponding homologous chromosome
to form a tetrad.
Metaphase 1: Spindle fibers attach to the
chromosomes.
Anaphase 1: The fibers pull the homologous
chromosomes toward opposite ends of the
cell.
MEIOSIS II
 Prophase ll: Meiosis I result in two haploid
daughter cells, each with half the
number of chromosomes, as the original
cell.
 Metaphase ll: The chromosomes line up
in a similar way to the metaphase stage
of mitosis.
 Anaphase ll: The sister chromatids
separate and move toward opposite
ends of the cell.
 Telophase II: Meiosis II results in four
haploid daughter cells.
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*Mitosis results in the production of two
genetically identical diploid cells.
whereas meiosis produces four
genetically different haploid cells. *
11-5 Linkage and Gene
Maps
Thomas Hunt Morgan did research on fruit
flies, which led him to the principle of
linkage.
 Morgan and his associates observed so
many genes that were inherited together
that before long they could group all of the
fly's genes into four linkage groups.
 The linkage groups assorted independently,
but all of the genes in one group were
inherited together.

Drosophila has four chromosomes, which
led to two remarkable conclusions:
 1. Each chromosome is actually a group
of linked genes
 2. Mendel's principle of independent
assortment still hold true.
 (It is the. chromosomes, however, that
assort independently, not individual
genes.)
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This has been an R-Thom Production.