1. Will S., Will C., Esther P. , Nia M.

2.  Fertilization and Meiosis alternate in sexual life
cycles
A Life Cycle:
 the generation-to-generation sequence of stages
in the reproductive history of an organism

3.  In humans
 Each somatic cell has 46 chromosomes, made up of two
sets
 One set of chromosomes comes from each parent
 When chromosomes are arranged in pairs starting
with the longest are called a karyotype.
 Homologous chromosomes are two chromosome
that are the same in length, centromere position
and staining pattern.
 Females XX Males XY Small parts of XY are
homologous.
 They are called sex chromosome.

4. Pair of homologous
5 µm
chromosomes
Centromere
Figure 13.3

5.  We inherit one set of chromosomes from each
parent. One set is 23 chromosomes in humans.
 One set is represented by the letter "n“.
 Any cell with 2 sets of chromosome is called a
diploid cell, which has ‘2n’ so a normal human
would have 46 chromosomes.
 Gametes contain only one set so they are called
haploid cells.
 This set contains 22 autosomes and 1 gender
chromosome.
 A unfertilized egg only has a X chromosome but
sperm cells can have X or Y chromosomes.

7.  -The life cycle begins with a haploid sperm cell
specifically from the father fuses with a haploid
ovum from the mother. (sperm + egg = life)


8.  -The process of gametes, culminating in fusion
of their nuclei, is called fertilization.
 -The resulting fertilized egg, or zygote, is
diploid because it contains 2 haploid sets of
chromosomes bearing genes representing the
maternal and paternal family lines.
 -As the human develops from a zygote to a
sexually mature adult, mitosis generates all the
somatic cells of the body. Both chromosomes
sets in the zygote and all the genes they carry
are passed with precision to our somatic cells.

9.  -The only cells of the human body not produced by
mitosis are the gametes, which develop in the gonads-
ovaries in the females and testes in the males.
 -Then in fertilization once 2 gametes fuse, the normal
chromosomes number of 46 would 2x to 96 and
continual sequence.
 -Meiosis is a type of cell division reduce the number of
sets of chromosomes from tow to one in the gametes,
compensating for the doubling that occurs at
fertilization.
 -Fertilization restores the diploid condition by
combining 2 haploid sets of chromosomes and the
human life cycle is repeated, generation after
generation

10.  The human life cycle
Key
Haploid gametes (n = 23)
Haploid (n)
Ovum (n)
Diploid (2n)
Sperm
Cell (n)
MEIOSIS FERTILIZATION
Ovary Testis Diploid
zygote
(2n = 46)
Mitosis and
development
Multicellular diploid
Figure 13.5 adults (2n = 46)

11.  Alternation of Generations- The second life
cycle exhibited by plants and algae
 Sporophyte- the multicellular diploid stage in
alternation of generations.
 Spores- haploid cells produced in the
sporophyte.
 Gametophye- the multicellular haploid stage in
alternation of generations.

12.  In animals
 Meiosis occurs during gamete formation
 Gametes are the only haploid cells
Key
Haploid
Diploid
n n
Gametes
n
MEIOSIS FERTILIZATION
Zygote
2n 2n
Diploid Mitosis
multicellular
organism
Figure 13.6 A (a) Animals

13.  Plants and some algae
 Exhibit an alternation of generations
 The life cycle includes both diploid and haploid
multicellular stages
Haploid multicellular
organism (gametophyte)
Mitosis n Mitosis
n n
n n
Spores
Gametes
MEIOSIS FERTILIZATION
Diploid
2n
multicellular 2n
organism Zygote
(sporophyte) Mitosis
Figure 13.6 B (b) Plants and some algae

14.  In most fungi and some protists
 Meiosis produces haploid cells that give rise to a
haploid multicellular adult organism
 The haploid adult carries out mitosis, producing cells
that will become gametes
Haploid multicellular
organism
n
Mitosis Mitosis
n
n n
Gametes n
MEIOSIS FERTILIZATION
2n
Zygote
Figure 13.6 C (c) Most fungi and some protists