Transcript Asexual reproduction

Inheritance of Traits
Sexual reproduction
In organisms that reproduce
sexually, traits are inherited
through gametes.
Gametes (sperm and eggs)
are produced by meiosis.
Asexual reproduction
Genetically identical clones
of the parent.
In some exceptions, genetic
material can be exchanged
between clones.
Example: antibiotic resistance
in bacteria can be
transferred via plasmid DNA.
In sexual reproduction, haploid sperm
and egg unite to form a diploid zygote.
Bacteria reproduce asexually by binary fission.
Binary Fission and Budding
Asexual reproduction: binary
fission.
A single parent cell dividing
into two daughter cells.
Binary fission in the
bacterium Staphylococcus
Asexual reproduction: budding.
Part of the parent body is
‘pinched off’ to produce a
small individual exactly like the
parent.
Budding in Hydra
New individual
Sexual vs Asexual Reproduction
Sexual Reproduction
Asexual Reproduction
Produces genetic variation.
Quick.
Usually takes longer than asexual
reproduction.
No variation, so are more
vulnerable when environment
changes.
Daphnia with eggs.
These diploid eggs are
produced mitotically
and hatch into clones
of the adult.
Some organisms, e.g. aphids and water
fleas (Daphnia), reproduce asexually most
of the time, but also go through sexual
reproduction as well.
Introduction to Meiosis
The purpose of meiosis is to produce haploid sex cells
(gametes).
They have one copy of each chromosome.
In humans the haploid number is 23.
Meiosis only occurs only in the ovaries and testes.
Sperm surround an egg prior to fertilization
Meiosis I
Interphase
DNA replication
2N
One chromosome from each
homologous pair is donated to
each intermediate cell.
In prophase 1, homologues
pair up to form tetrads in a
process called synapsis. The
sister chromatids can
exchange genetic information
during crossing over.
Prophase 1
Synapsis and
crossing over
2N
Metaphase 1
Anaphase 1 separates
homologous chromosomes.
Tetrads line up on
the equator of the
cell.
2N
Anaphase 1
Telophase 1
1N
Intermediate cell
Intermediate cell
Homologues separate
Meiosis II
1N
Intermediate cell
The second division of
meiosis is similar
to mitosis.
Prophase 2
There is no chromosome
duplication in meiosis II.
1N
Sister chomatids (now
separate chromosomes) are
pulled apart and are
donated to each gamete
cell.
Metaphase 2
1N
The gametes are haploid
(1N).
Anaphase 2
Telophase 2
1N
Gamete
(egg or sperm)
Individual
chromosomes separate
Cell Division: An Overview
Spermatogenesis
Male
embryo
Mitosis
Male
adult
2N
2N
Meiosis
Sperm
1N
Fertilization
Zygote
Mitosis
2N
Mitosis
Embryo
2N
Somatic cell
production
Mitosis
Female
embryo
Female
adult
2N
2N
Meiosis
Egg
1N
Oogenesis
Adult
2N
Somatic cell
production
Aneuploidy
Nondisjunction during
meiosis can lead to an
abnormal chromosome
number.
These chromosomal
defects
are known as
aneuploidy.
XY
XX
XY
XY
XXY
X
XY
X
XO
X
X
XXY
X
X
XO
Aneuploidy in Sex
Chromosomes
Aneuploidy can result in an
abnormal number of sex
chromosomes.
Turner syndrome affects
females.
X
Klinefelter syndrome affects
males.
XXY
Turner Syndrome karyotype
Aneuploidy in Autosomes
Aneuploidy can also affect
autosomes (non-sex
chromosomes).
In trisomy, the nucleus of the
cells have one extra chromosome
(2N+1).
Three forms of trisomy survive to
birth:
Down syndrome (trisosmy 21)
Edward syndrome (trisomy 18)
Patau syndrome (trisomy 13)
Down Syndrome karyotype