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6.1 Meiosis
CHAPTER 6 NOTES
GENERAL INFO
__________________– requires two parents and
produces offspring that are genetically different
from each other
GENERAL INFO
Sexual reproduction – requires two parents and
produces offspring that are genetically different
from each other
______________– variation, or inherited genetic
differences, in a species
Genetic diversity – variation, or inherited genetic
differences, in a species
Genetic diversity – variation, or inherited genetic
differences, in a species
In eukaryotic organisms, the chromosome number is
referred to as the ______________(2n) since there
are two sets of chromosomes
Genetic diversity – variation, or inherited genetic
differences, in a species
In eukaryotic organisms, the chromosome number is
referred to as the diploid number (2n) since there
are two sets of chromosomes
Genetic diversity – variation, or inherited genetic
differences, in a species
In eukaryotic organisms, the chromosome number is
referred to as the diploid number (2n) since there
are two sets of chromosomes
Humans inherit one set of chromosomes, the ______
_______(1n), from each parent
In eukaryotic organisms, the chromosome number is
referred to as the diploid number (2n) since there
are two sets of chromosomes
Humans inherit one set of chromosomes, the haploid
number (1n), from each parent
MORE GENERAL INFO
Haploid chromosomes are carried in gametes
(sex cells), specialized cells necessary for
reproduction
 Male gametes are called _____ and female
gametes are called _____

MORE GENERAL INFO
Haploid chromosomes are carried in gametes
(sex cells), specialized cells necessary for
reproduction
 Male gametes are called sperm and female
gametes are called eggs


During fertilization, an egg cell joins a sperm cell
and the genetic information is combined, resulting
in a diploid cell called a ______

The zygote undergoes mitosis and cell division and
develops into an embryo

During fertilization, an egg cell joins a sperm cell
and the genetic information is combined, resulting
in a diploid cell called a zygote

The zygote undergoes mitosis and cell division and
develops into an embryo
STAGES OF MEIOSIS

Process that produces four gametes with half
the number of chromosomes
MEIOSIS I
A.
Prophase I – homologous chromosomes pair up
(one from each parent) and non sister chromatids
exchange genetic material (called crossing over)
A.
Metaphase I – homologous chromosomes pair up
at the equator
A.
Anaphase I – homologous chromosomes separate
and are pulled to opposite poles by the spindle
fibres
A.
Telophase I – one chromosomes from each
homologous pair is at each pole of the cell

Interkinesis – 2 cells result and each cell grows and
makes proteins but unlike mitosis, DNA does not
replicate
MEIOSIS II
A.
Prophase II – there is one chromosome of the
homologous pair in each cell
A.
Metaphase II – the X-shaped chromosomes form
a single line across the middle of the cell
A.
Anaphase II – sister chromatids move to opposite
poles of the cell (each one is now considered a
chromosome)
A.
Telophase II – spindle fibres begin to disappear
and a nuclear membrane forms around each set
of chromosomes

Cytokinesis – the two daughter cells are separated
CROSSING OVER

In crossing over, parts of non-sister chromatids
exchange segments of DNA to create an infinite
amount of genetic variation

Independent assortment is when homologous pairs of
chromosomes separate at the equator and move
towards opposite ends... you never know which one
will go which way

In sperm cell, all four cells may develop into
mature sperm but in egg cell there is an
unequal division of cytoplasm and organelles
so three cells disintegrate and only one large
egg cell remains
CHROMOSOME MUTATION
During meiosis, pieces of chromosomes can be
lost, duplicated or moved within a chromosome
or moved to another chromosome
 Mutations occur when cells are exposed to
mutagens
 Large chromosome errors are usually
prevented from being passed along because
the offspring will die before birth or fail to reach
reproductive age


A karyotype is a picture of all our chromosomes
arranged in a particular order

Karyotypes are studied to help physicians diagnose
and treat patients with genetic disorders (syndromes)
like Down syndrome