1. Exam II Lectures and Text Pages
I. Cell Cycles
Mitosis (218 – 228)
Meiosis (238 – 249)
II. Mendelian Genetics
III. Chromosomal Genetics
IV. Molecular Genetics
Replication
Transcription and Translation
V. Microbial Models
VI. DNA Technology

2. The Meiotic Cell Cycle A reduction division
Allows for sexual reproduction
Two parents
Creates genetic variation

3. Hereditary Similarity and Variation
Living organisms
Are distinguished by their ability to reproduce their own kind
100 µm
Figure 12.2 A
Figure 13.2
Parent
Bud
0.5 mm
Figure 13.1

4. Reproduction and Genetic Variation
Asexual reproduction produces genetic clones
Requires only mitosis
Only one parent
Sexual reproduction produces offspring of the same species as the parents, but with genetic variation
Requires meiotic cell division at some time in the lifecycle
Two parents

5. Terms Heredity Variation Genetics
Is the transmission of traits from one generation to the next
Variation
Inherited differences among individuals of the same species.
Shows that offspring differ somewhat in appearance from parents and siblings
Figure 13.1
Genetics
Is the scientific study of heredity and hereditary variation

6. Inheritance of Genes Genes Are the units of heredity
Are specific linear sequences of nucleotides on a DNA molecule
Are packaged on and transmitted by chromosomes

7. Inheritance of Genes Each gene in an organism’s DNA We inherit
Has a specific locus on a certain chromosome
We inherit
One set of chromosomes from our mother and one set from our father
Most genes program the cell to make a specific protein; the action of proteins produce inherited traits.

8. Comparison of Asexual and Sexual Reproduction
In asexual reproduction
One parent produces genetically identical offspring by mitosis
Figure 13.2
Parent
Bud
0.5 mm

9. Comparison of Asexual and Sexual Reproduction
In sexual reproduction
Two parents give rise to offspring that have unique combinations of genes inherited from the two parents
Figure 13.1

10. Life Cycles Fertilization and meiosis alternate in sexual life cycles
A life cycle
Sequence of stages from conception to reproduction in an organism’s life.

11. Sets of Chromosomes in Human Cells
In humans
Each somatic cell has 46 chromosomes, made up of two sets
One set of chromosomes comes from each parent (in the gamete)

12. Karyotyping A karyotype
Is an ordered (standard sequence), visual representation of the chromosomes in a somatic cell
5 µm
Pair of homologous
chromosomes
Centromere
Sister
chromatids
Figure 13.3

13. Homologous Chromosomes (Homologues)
Are the two chromosomes composing a pair
Have the same characteristics (size, centromere, staining pattern)
Have the same loci at the same locations on the chromosome
Are inherited as one member of each pair from each parent

14. Chromosomes Autosome: A chromosome that is not a sex chromosome.
Sex chromosomes
Are distinct from each other in their characteristics
Are represented as X and Y
Determine the sex of the individual, XX being female, XY being male

15. Sets of Chromosomes A haploid cell Has one set of chromosomes
A human gamete is haploid and has 23 chromosomes (n = 23)
A diploid cell
Has two haploid sets of each of its chromosomes
In a human has 46 chromosomes (2n = 46)

16. Human Life Cycle At sexual maturity During fertilization The zygote
Ovaries and testes produce haploid gametes by meiosis
During fertilization
Gametes fuse, forming a diploid zygote
The zygote
Develops into an adult by mitotic cell division
Figure 13.5
Key
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
Sperm
Cell (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n = 46)
Mitosis and
development
Multicellular diploid
adults (2n = 46)

17. The Variety of Sexual Life Cycles
The three main types of sexual life cycles differ in the timing of meiosis and fertilization
1. Diploid adult produces haploid gametes by meiosis, all other stages are diploid
2. Two adult life stages, one diploid (produce spores by meiosis) and one haploid (produce gametes by mitosis)
3. Haploid adult produces gametes by mitosis, diploid zygote produces haploid spores by meiosis. All stages except zygote are haploid

18. Animal Life Cycle Meiosis occurs during gamete formation
Gametes are the only haploid cells
Gametes
Figure 13.6 A
Diploid
multicellular
organism
Key
MEIOSIS
FERTILIZATION n 2n
Zygote
Haploid
Mitosis
(a) Animals

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

20. Most Fungi and Some Protists Life Cycle
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
Zygote is only diploid stage
MEIOSIS
FERTILIZATION n 2n
Haploid multicellular
organism
Mitosis
Gametes
Zygote
(c) Most fungi and some protists
Figure 13.6 C

21. Chromosome Duplication
Precedes either type of cell division
All the chromosomes are duplicated and thus each consists of two identical sister chromatids
Figure 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
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)

22. Meiosis – A Reduction Division
Meiosis reduces the number of chromosome sets from diploid to haploid
Meiosis
Takes place in two divisions, meiosis I and meiosis II

23. Stages of the Meiotic Cell Cycle
Interphase
Chromosomes and centrosomes replicate
Meiosis I
Separates each homologous pair and reduces the number of chromosomes from diploid to haploid
Meiosis II
Separates sister chromatids and produces four haploid daughter cells
Figure 13.7
Interphase
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes 1 2
Homologous
separate
Haploid cells with
replicated chromosomes
Sister chromatids
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II

24. Interphase and Meiosis I
Synapsis and crossing over occur. Pairs of homologous chromosomes are separated
Centrosomes
(with centriole pairs)
Sister
chromatids
Chiasmata
Spindle
Tetrad
Nuclear
envelope
Chromatin
Centromere
(with kinetochore)
Microtubule
attached to
kinetochore
Tertads line up
Metaphase
plate
Homologous
chromosomes
separate
Sister chromatids
remain attached
Pairs of homologous
chromosomes split up
Chromosomes duplicate
Homologous chromosomes
(red and blue) pair and exchange
segments; 2n = 6 in this example
INTERPHASE
MEIOSIS I: Separates homologous chromosomes
PROPHASE I
METAPHASE I
ANAPHASE I
Figure 13.8

25. Telophase I and Cytokinesis
Meiosis I is the reduction division – yields two haploid cells
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II AND
MEIOSIS II: Separates sister chromatids
Cleavage
furrow
Sister chromatids
separate
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes
Two haploid cells
form; chromosomes
are still double
Figure 13.8

26. Interkinesis
In some species: After telophase I and cytokinesis, nuclear membranes and nucleoli reappear, and the cell enters a period of interkinesis before meiosis II. In other species, the daughter cells immediately prepare for meiosis II.
With or without interkinesis, no DNA replication occurs.

27. Meiosis II Meiosis II separates sister chromatids (similar to mitosis)
Figure 13.8