1. Ch 13 Sexual Life Cycles and Meiosis

2. Reproduction and the Transmission of Traits
Living organisms
Have ability to reproduce
Heredity
Transmission of traits from one generation to the next
Variation
Offspring often differ in appearance from parents and siblings
Environmental and genetic influences
Genetics
Scientific study of heredity and variation

3. Progeny (or offspring)
-Inherit chromosomes from parents
-DNA in chromosomes encode the genes that
specify characteristics
For example
eye color, blood type, predisposition to disease

4. What are the mechanisms by which chromosomes are passed onto (eukaryotic) offspring?
Asexual reproduction
Sexual reproduction

5. Bud forms by mitosis of parent cells
LE 13-2
Asexual reproduction
Bud forms by mitosis of parent cells
Bud genetically identical to parent
Parent
Bud
0.5 mm

6. Sexual Reproduction
Meiosis: formation of haploid gametes (eggs, sperm) in
parents
2. Fertilization: fusion of gametes from opposite parents--> diploid zygote-->mitotic growth-->embryo-->adult

7. Human Sexual Reproduction
LE 13-5
Human Sexual Reproduction
Key
Haploid gametes (n = 23)
Haploid (n)
Ovum (n)
Diploid (2n)
Sperm
cell (n)
MEIOSIS
FERTILIZATION
Ovary
Testis
Diploid
zygote
(2n = 46)
Offspring
genetically unique
from parents
Mitosis and
development
Multicellular diploid
adults (2n = 46)

8. How many chromosomes are inherited by human zygotes?or
2n= 46
n= the number of chromosomes in a set
23 from mother, maternal chromosomes
23 from father, paternal “

9. Human Karyotype 5 µm Stained metaphase chromosomes from human
LE 13-3
Human Karyotype
5 µm
Stained metaphase
chromosomes
from human
somatic cell
Why stain metaphase
chromosomes?
Compact &
easier to see com-
pared to interphase

10. Pair of homologous 5 µm chromosomes Centromere Sister chromatids
LE 13-3
Pair of homologous
chromosomes
5 µm
Centromere
Sister
chromatids

11. Can you tell the difference between a human male and female by the karyotype?
Humans have
22 pairs of autosomes (non-sex chromosomes)
1 pair of sex chromosomes
Female sex ch.: XX
Male sex ch.: XY

12. LE 13-3
Human Karyotype
5 µm
Male or female?

13. If somatic cells have two sets of chromosomes (diploid), how do gametes end up with only one set (haploid)?
Diploid precursors to the egg and sperm undergo meiosis in the testis and ovary.

14. Overview of meiosis aka tetrad Diploid Haploid LE 13-7 Interphase
Homologous pair
of chromosomes
in diploid parent cell
Diploid
Chromosomes
replicate
aka tetrad
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
Haploid
Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Meiosis II
Sister chromatids
separate
Haploid cells with unreplicated chromosomes

15. Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of
LE 13-4
Key
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosomes
Centromere
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)

16. MEIOSIS I: Separates homologous chromosomes
LE 13-8ab
MEIOSIS I: Separates homologous chromosomes
PROPHASE I
METAPHASE I
ANAPHASE I
Centromere
(with kinetochore)
Sister chromatids
remain attached
Sister
chromatids
Chiasmata
Metaphase
plate
Spindle
Tetrad
Microtubule
attached to
kinetochore
Homologous
chromosomes
separate
Homologous chromosomes
(red and blue) pair and
exchange segments
Homologous recombination (crossing-over)
Tetrads line up
Pairs of homologous
chromosomes split up

17. MEIOSIS II: Separates sister chromatids
LE 13-8b
MEIOSIS II: Separates sister chromatids
TELOPHASE I AND
CYTOKINESIS
TELOPHASE II AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
Cleavage
furrow
Haploid daughter cells
forming
Sister chromatids
separate
Two haploid cells
form; chromosomes
are still double
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes

18. (before chromosome replication)
LE 13-9
MITOSIS
MEIOSIS
Parent cell
(before chromosome replication)
Chiasma (site of
crossing over)
MEIOSIS I
Prophase
Prophase I
Chromosome
replication
Chromosome
replication
Tetrad formed by
synapsis of homologous
chromosomes
Duplicated chromosome
(two sister chromatids)
2n = 6
Chromosomes
positioned at the
metaphase plate
Tetrads
positioned at the
metaphase plate
Metaphase
Metaphase I
Anaphase
Sister chromatids
separate during
anaphase
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Anaphase I
Telophase
Cytokinesis
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
Sister chromatids separate during anaphase II

19. Mitosis produces
two genetically identical diploid cells
Meiosis produces
four genetically distinct haploid cells

20. Mechanisms of Genetic Variation Among Offspring Caused by Sexual Reproduction
Crossing over (homologous recombination)
(Prophase I)
2. Independent assortment of chromosomes
(Metaphase I & II)
3. Random fertilization (post-meiosis)

21. Recombination Chiasmata, pl Prophase I of meiosis LE 13-11 Nonsister
chromatids
Recombination
Prophase I
of meiosis
Tetrad
Chiasma,
site of
crossing
over
Chiasmata, pl
Metaphase I
Metaphase II
Daughter
cells
Recombinant
chromosomes

22. Independent Assortment
LE 13-10
Independent Assortment
Key
Maternal set of
chromosomes
Possibility 1
Possibility 2
Paternal set of
chromosomes
Metaphase I
Two equally probable
arrangements of
chromosomes at
Metaphase II
Daughter
cells
Combination 1
Combination 2
Combination 3
Combination 4

23. Any sperm can fuse with any ovum (unfertilized egg)
Random Fertilization
Any sperm can fuse with any ovum (unfertilized egg)
a (human) zygote has about 64 trillion diploid combinations
Each zygote has unique genetic identity

24. I think they were talking
about us. I hope they had
it right!
If not maybe we can
answer questions.

25. See meiosis animation
What is missing?