Lecture 11

Spermatogenesis
I) Spermatocytogenesis:
Spermatogonium → Spermatid
(2N, 4C)
(1N, 1C)
“Genetic”
II) Spermiogenesis:
Spermatid → Spermatozoan
(1N, 1C)
(1N, 1C)
“Metamorphic”
- loss of cytoplasm
- addition of flagellum
- addition of acrosome
SPERMATOGENESIS
ANAPHASE I
ANAPHASE II
OÖGENESIS
SPERMATOGENESIS
OÖGENESIS
ANAPHASE I
ANAPHASE II
OOGENESIS (MAMMALIAN)
Fetus
1.
2.
Oogonium (lx) (2n) undergoes cell growth and mitotic
division to produce oogonia (nx) (2n).
Start of Meiosis I (Prophase I).
Transformation of oogonium (1x) (2n) to 1º (primary)
oocyte (1x) (2n) by passage through Prophase I up to
zygotene/pachytene and cell growth.
Birth
3.
4.
1º oocyte (2n) arrested in Prophase I (zygotene/pachytene).
Growth of follicle, 1º oocyte (2n), and zona pellucida.
Puberty
5.
6.
7.
8.
Pre-ovulatory surge of luteinizing hormone (LH).
Resumption of Meiosis I.
1º oocyte (lx) (2n) transformed to 2º oocyte (1x) (1n) and
first polar body (1x) (1n) after completion of Meiosis I.
2º oocyte arrested in Meiosis II (Metaphase II).
Fertilization
9.
10.
11.
12.
13.
Sperm (ln) penetration.
Meiosis II resumes.
Formation of zygote (2n).
Formation of second polar body (1n).
First polar body (1n) completes mitotic division to
produce two more polar bodies (1n).
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Fetus and
after birth
(before
puberty)
Oogonium
1° oocyte (Zygotene/Pachytene of Prophase I)
1
* LH surge - puberty
Immature 2° oocyte (Prophase II)–ovulation and 1st polar body
Movement of 2° oocyte to reproductive tract
After
puberty
Mature 2° oocyte (Metaphase II)
2
*
Fertilization (sperm penetration)
Ootid (completion of Meiosis II; Metaphase II → end of
Telophase II) and 2nd polar body
Ootid → Ovum
differentiation
THEORIES OF SEX DETERMINATION
1. Sex is dependent upon genes on the chromosomes.
2. Sex is dependent upon the environment.
1) Examples of sex determination dependent upon genes on the
chromosomes:
A. Chromosomes
Autosomes - all chromosomes other than sex
chromosomes (same in diploid males
and females).
Sex chromosomes - Chromosomes particularly
concerned with the determination of sex
(X and Y and Z & W)
B. Normal chromosome compliment in some organisms.
Organisms
Sex chromosomes Autosomes
Male Female
Protenor
X
XX
6 pairs
Humans
XY
XX
22 pairs
Drosophila melanogaster
XY XX
3 pairs
Chickens
XX
XY
38 pairs
Honey bee
Male 16 Female 32
N
2N
C. Sex chromosome types:
Female Male
XX and XO Male 1 less than female
XX and XY Female has like sex chromosomes (homogametic)
Male has unlike sex chromosomes
(heterogametic) (i.e., mammals)
XY and XX Male has like sex chromosomes (homogametic)
(ZW) (ZZ) Female has unlike sex chromosomes
(heterogametic) (i.e., chickens)
D. Some abnormalities:
Drosophila Female
Normal
XX
Abnormal XXY
Humans
Normal
Abnormal
Fertile
Yes
Yes
Male
XY
X
Female
Fertile
XX
Yes
X
No
Turner's
Syndrome
Fertile
Yes
No
Male
Fertile
XY
Yes
XXY
No
Klinefelter's
Syndrome
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E. Method of sex determination:
Protenor:
1X = male, 2X = female
Humans:
presence of Y = male (XY, XXY)
absence of Y = female (X, XX, XXX )
Honey bee: male produced from an unfertilized egg
(Parthenogenesis). Female produced from fertilized egg
Chicken:
male 2X, female XY
Drosophila melanogaster
a) Genetic balance theory:
It is the ratio of the genes in the X
chromosome(s) (which are female
determining) to the genes in the
autosomes (which are male determining)
that determines sex in Drosophila
melanogaster.
b) The Y chromosome is necessary for fertility in
Drosophila melanogater males.
Sex Determination
Environmental:
External Stimuli – Ex. light, moisture, temperature,
chemical.
Internal Stimuli – Ex. hormonal
Genetic:
Autosomes
Gonosomes (sex chromosomes)
Terms:
i) Homogametic sex: produces one kind of gamete in reference
to the sex chromosomes.
ii) Heterogametic sex: produces two kinds of gametes in reference
to the sex chromosomes.
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