SEXUAL REPRODUCTION
Chapter 4 lesson 1
Part 1
Reproduction of Organisms
Why do living things
reproduce?
Sexual Reproduction and Meiosis
• What is sexual reproduction,
and why is it beneficial?
• What is the order of the
phases of meiosis, and what
happens during each phase?
• Why is meiosis important?
sexual reproduction
a type of reproduction in which the genetic
materials from two different cells combine,
producing an offspring.
Gamete
•The cells that combines to
form offspring
•A reproductive cell
•A sex cell
•Formed by meiosis
•In most organisms meiosis
produces 1 of 2 types of
gametes
2 types of gametes
•Ova (singular-ovum) female gametes; female sex
cell(book calls them eggs)
•Sperm - male gametes; male
sex cell
2 types of gametes
ovum
sperm
Where are gametes formed?
In reproductive organs
• Testes – male reproductive organs
• Ovaries – female reproductive organs
The female sex cell, an ovum, forms in an
ovary.
The male sex cell, a sperm, forms in the testis.
Fertilization
the formation
of a zygote
from the
union of 2
gametes
The process when a sperm and an ovum join togther.
What is sexual reproduction? (cont.)
During a process
called
fertilization, an
ovum cell and a
sperm cell join
together to create
a zygote.
Zygote
The new cell
that forms
from
fertilization
Diploid cells
• Organisms that reproduce sexually form
somatic (body) cells and germ (gametes; sex)
cells.
• In somatic cells of most organisms, similar
chromosomes occur in pairs.
• Diploid cells are cells that have pairs of
chromosomes.
Diploid cells
Diploid cells
• Pairs of chromosomes that have genes
for the same traits arranged in the
same order are called homologous
chromosomes.
• Because one chromosome is inherited
from each parent, the chromosomes
are not identical.
• Different organisms have different
numbers of chromosomes.
Homologous chromosomes
Haploid cells
Haploid cells are cells that have only
one chromosome from each pair of
chromosomes.
haploid
from Greek haploeides, means
“single”
Haploid vs Diploid
Normal human cells have
23 pairs of chromosomes
which is a total of 46
chromosomes.
Human diploid number is 46
Human haploid number is 23
Diploid & Haploid Examples
Haploid
Diploid
Honey bee
16
32
Crayfish
100
200
Rabbit
22
44
Watermelon
11
22
Corn
10
20