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Mendel and
Meiosis
Basic Genetics
Gregor Mendel’s Peas
Gregor Mendel’s Peas
Genetics is the scientific study of
heredity.
Gregor Mendel was an Austrian monk.
His work was important to the
understanding of heredity.
Considered to be “Father of Genetics”
Mendel carried out his work with
ordinary garden peas.
Copyright Pearson Prentice Hall

Mendel observed the phenomenon
of inheritance

Heredity is the transmission of
traits from parents to offspring.

Mendel knew that
the male part of each
flower produces pollen,
(containing sperm).
the female part of the
flower produces egg cells.
Characteristics Mendel
Studied

Seed texture

Seed color

Seed coat color

Pod appearance

Pod color

Position of flowers along stem

Stem length
A trait is a specific characteristic
that varies from one individual to
another
Pollination

The transfer of pollen is known as pollination

The transfer of pollen within a single plant OR
fertilization that occurs with a single plant is
known as self-pollination

An organism that has the same genes for a
particular trait is known as pure-bred

The transfer of pollen from one plant to
another OR fertilization that occurs between
two individual plants is known as cross
pollination

Each original pair of plants is the P
(parental) generation.

The offspring are called the F1, or “first
filial,” generation - Offspring of our
parents

The offspring of crosses between parents
with different traits are called hybrids.

Mendel crossed the F1 generation with
itself to produce the F2 (second filial)
generation. – Our children
Mendel's first conclusion

was that biological inheritance is
determined by factors that are
passed from one generation to the
next.

Today, scientists call the factors
that determine traits genes.

Each of the traits Mendel studied
was controlled by one gene that
occurred in two contrasting forms
that produced different characters
for each trait.

The different forms of a gene are
called alleles.
Mendel’s second conclusion

is called the principle of
dominance.

The principle of dominance states
that some alleles are dominant and
others are recessive.
Meiosis – 2 nuclear divisions

Definition – cell division

Occurs in the Sex cells – gametes

4 Daughter Cells are formed with
HALF of the number of
chromosomes

Humans have 46 Chromosomes; 23
in egg and 23 in sperm

2 Stages of Meiosis
Meiosis I – 1St Stage

4 Stages – Prophase I, Metaphase I,
Anaphase I, Telophase I

Prophase I - Homologous chromosomes
pair to form tetrads – “crossing over” may
occur

Metaphase I – Tetrads line up at the
equator

Anaphase I – Separation occurs and each
homologous chromosome goes to a pole

Telophase I – Original cell divides into two
and each cell has one of the homologous
chromosomes
Meiosis II – 2nd Stage- NO DNA
replication

Prophase II, Metaphase II, Anaphase II,
Telophase II

Prophase II – nuclear membrane disappears

Metaphase II – Chromosomes line up at equator

Anaphase II – Separation occurs however, this
time sister chromatids separate at the
centromere

Telophase II – Original cell is divided into 4
haploid cells, each containing HALF the number
of chromosomes
More About Meiosis
Sexual reproduction – 2 cells unite to
form 1st cell of an organism
Zygote – fertilized egg
Haploid – (N); ½ number of
chromosomes (sex cell number) ex:
N=23 chromosomes
Diploid – (2N) Original number of
chromosomes (body cell number) ex:
2N=46
Gametes – sex cells
Advantages and Disadvantages of
Sexual and Asexual Reproduction
Asexual
Reproduction
Sexual
Reproduction
Advantages
Disadvantages
It produces a large number
of offspring quickly, which
may increase chances of
survival in a favorable and
stable environment.
Offspring are genetically
identical to parent
organism, which may limit
their ability to survive a
changing environment.
It requires only one parent
organism.
Offspring are genetically
different from each parent,
which may help the
organism to adapt and
survive a changing
environment.
It produces a smaller
number of offspring more
slowly, so fewer offspring
may survive.
It usually requires two
parents, one male and one
female.