1. In eukaryotes, heritable information is passed to the next generation via processes that include meiosis plus fertilization

2. Genes are the units of heredity, and are made up of segments of DNA
Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs)
Each gene has a specific location called a locus on a certain chromosome
Most DNA is packaged into chromosomes
One set of chromosomes is inherited from each parent
Inheritance of Genes

3. Sets of Human Chromosomes
Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes
A karyotype is an ordered display of the pairs of chromosomes from a cell
The two chromosomes in each pair are called homologous chromosomes, or homologs
Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characters
Sets of Human Chromosomes

4. TECHNIQUE 5 µm Pair of homologous replicated chromosomes Centromere
Fig. 13-3b
TECHNIQUE
5 µm
Pair of homologous
replicated chromosomes
Centromere
Figure 13.3 Preparing a karyotype
Sister
chromatids
Metaphase
chromosome

5. The sex chromosomes are called X and Y
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome
The 22 pairs of chromosomes that do not determine sex are called autosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

6. A diploid cell (2n) has two sets of chromosomes
Each pair of homologous chromosomes includes one chromosome from each parent
The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father
A diploid cell (2n) has two sets of chromosomes
For humans, the diploid number is 46 (2n = 46)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

7. Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of
Fig. 13-4
Key
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Figure 13.4 Describing chromosomes
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)

8. For humans, the haploid number is 23 (n = 23)
A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n)
For humans, the haploid number is 23 (n = 23)
Each set of 23 consists of 22 autosomes and a single sex chromosome
In an unfertilized egg (ovum), the sex chromosome is X
In a sperm cell, the sex chromosome may be either X or Y
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

9. Fertilization is the union of gametes (the sperm and the egg)
The fertilized egg is called a zygote and has one set of chromosomes from each parent
The zygote produces somatic cells by mitosis and develops into an adult
Chromosome Life Cycle

10. At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are the only types of human cells produced by meiosis, rather than mitosis
Meiosis results in one set of chromosomes in each gamete
Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

11. Multicellular diploid adults (2n = 46)
Fig. 13-5
Key
Haploid gametes (n = 23)
Haploid (n)
Egg (n)
Diploid (2n)
Sperm (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n = 46)
Figure 13.5 The human life cycle
Mitosis and
development
Multicellular diploid
adults (2n = 46)

12. Different Life Cycle Fig. 13-6
Key
Haploid (n)
Haploid unicellular or
multicellular organism
Diploid (2n)
Haploid multi-
cellular organism
(gametophyte) n
Gametes n n
Mitosis n
Mitosis
Mitosis n
Mitosis n n n n n
MEIOSIS
FERTILIZATION
Spores n
Gametes n
Gametes n
MEIOSIS
FERTILIZATION
Zygote
MEIOSIS
FERTILIZATION 2n 2n 2n 2n
Diploid
multicellular
organism
Zygote
Diploid
multicellular
organism
(sporophyte)
Figure 13.6 Three types of sexual life cycles 2n
Mitosis
Mitosis
Zygote
(a) Animals
(b) Plants and some algae
(c) Most fungi and some protists

13. Reduction division followed by fertilization ensures genetic diversity in sexually reproducing organisms
Meiosis ensures that each gamete receives one complete haploid (1N) set of chromosomes
During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent. Orientation of the chromosome pairs is random with respect to the cell poles
Meiosis

14. Separation of the homologous chromosomes ensures each gamete receives a haploid (1N) set of chromosomes composed of both maternal and paternal chromosomes
Meiosis

15. Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number 1
Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Meiosis II 2
Sister chromatids
separate
Haploid cells with unreplicated chromosomes

16. Prophase I Metaphase I Anaphase I Centrosome (with centriole pair)
Fig. 13-8a
Telophase I and
Cytokinesis
Prophase I
Metaphase I
Anaphase I
Centrosome
(with centriole pair)
Sister chromatids
remain attached
Centromere
(with kinetochore)
Sister
chromatids
Chiasmata
Spindle
Metaphase
plate
Figure 13.8 The meiotic division of an animal cell
Cleavage
furrow
Homologous
chromosomes
Homologous
chromosomes
separate
Fragments
of nuclear
envelope
Microtubule
attached to
kinetochore

17. During meiosis (prophase I), homologous chromosomes exchange genetic material via a process called “crossing over” which increases genetic variation in resultant gametes
Area of cross over is called chiasmata
Crossing Over

18. Telophase II and Cytokinesis
Fig. 13-8d
Telophase II and
Cytokinesis
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Haploid daughter cells
forming
Figure 13.8 The meiotic division of an animal cell

19. At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes
Each daughter cell is genetically distinct from the others and from the parent cell
Meiosis End Products

20. Replicated chromosome
Fig. 13-9a
MITOSIS
MEIOSIS
MEIOSIS I
Parent cell
Chiasma
Chromosome
replication
Chromosome
replication
Prophase
Prophase I
Homologous
chromosome
pair
2n = 6
Replicated chromosome
Metaphase
Metaphase I
Anaphase
Telophase
Anaphase I
Figure 13.9 A comparison of mitosis and meiosis in diploid cells
Telophase I
Haploid
n = 3
Daughter
cells of
meiosis I 2n 2n
MEIOSIS II
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II

21. Figure 13.9 A comparison of mitosis and meiosis in diploid cells
Fig. 13-9b
SUMMARY
Property
Mitosis
Meiosis
DNA
replication
Occurs during interphase before
mitosis begins
Occurs during interphase before meiosis I begins
Number of
divisions
One, including prophase, metaphase,
anaphase, and telophase
Two, each including prophase, metaphase, anaphase,
And telophase
Synapsis of
homologous
chromosomes
Does not occur
Occurs during prophase I along with crossing over
between nonsister chromatids; resulting chiasmata
hold pairs together due to sister chromatid cohesion
Number of
daughter cells
and genetic
composition
Two, each diploid (2n) and genetically
identical to the parent cell
Four, each haploid (n), containing half as many
Chromosomes as the parent cell; genetically different
from the parent cell and from each other
Figure 13.9 A comparison of mitosis and meiosis in diploid cells
Role in the
animal body
Enables multicellular adult to arise from
zygote; produces cells for growth, repair,
and, in some species, asexual reproduction
Produces gametes; reduces number of chromosomes by half
and introduces genetic variability among the gametes

22. 3 events unique to meiosis
all three occur in meiosis l:
– Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information
– At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes
– At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate
3 events unique to meiosis

23. Fertilization Involves the fusion of two gametes
Increases genetic variation by providing for new combinations of genetic information in the zygote
Restores the diploid number of chromosomes
Fertilization