Human reproduction by teacher Francesca De Marzi

1. HUMAN
REPRODUCTION
Teacher Francesca De Marzi

2. WHAT IS REPRODUCTION?
• It’s the ability of an organism to GENERATE OFFSPRING (figli, prole)
WITH SIMILAR CHARACTERISTICS to their parents
ASEXUAL REPRODUCTION SEXUAL REPRODUCTION
Ex. Bacteria, fungi…
Involves a SINGLE INDIVIDUAL
No fusion of two gametes
Ex. Vertebrates
Involves TWO INDIVIDUALS of
2 opposite sexes of the same species
Fusion of two gametes

3. WHAT IS REPRODUCTION?
• It’s the ability of an organism to GENERATE OFFSPRING (figli, prole)
WITH SIMILAR CHARACTERISTICS to their parents
ASEXUAL REPRODUCTION SEXUAL REPRODUCTION
Ex. Bacteria, fungi…
Involves a SINGLE INDIVIDUAL
No fusion of two gametes
Ex. Vertebrates
Involves TWO INDIVIDUALS of
2 opposite sexes of the same species
Fusion of two gametes

4. OPPOSITE SEXES are recognisable by:
• PRIMARY SEX CHARACTERISTICS
Reproductive organs (also called genital organs)
• SECONDARY SEX CHARACTERISTICS
Change of appearance which happens during puberty
(ex. Breast and wider hips in females, deep voice and
body hair in males etc.)

5. CHROMOSOMES
• Chromosomes are molecules of DNA in the nucleus of the cell

6. GENES
• a GENE is a SEGMENT OF DNA
• Each GENE carries specific
information about us
(for example:
- Gene 1 of the picture could carry
information about color of our eyes
- Gene 2 could carry susceptibility to a
particular disease (=malattia)

7. HUMANS HAVE 46 CHROMOSOMES
• We say that we have 23 PAIRS OF
HOMOLOGUE CHROMOSOMES
(coppie di cromosomi omologhi)
in the nucleus of each cell
• In each pair, the 2 chromosomes
have SAME SHAPE AND
FUNCTION
• Therefore, EVERY GENE IS
DUPLICATED

8. HUMANS HAVE 46 CHROMOSOMES
• We say that we have 23 PAIRS OF
HOMOLOGUE CHROMOSOMES
(coppie di cromosomi omologhi)
in the nucleus of each cell
• In each pair, the 2 chromosomes
have SAME SHAPE AND
FUNCTION
• Therefore, EVERY GENE IS
DUPLICATED
…ACTUALLY, NOT IN ALL CELLS,
BECAUSE…

9. TWO KINDS OF CELLS
SOMATIC CELLS:
ANY CELL FORMING
THE BODY OF AN ORGANISM
23 pairs of chromosomes
23 x 2 = 46
they are then called
DIPLOID CELLS
(diplo= double)
GERMS CELLS or
GAMETES:
THEY WILL GIVE ORIGIN TO A
NEW ORGANISM IF FERTILIZED
23 chromosomes
23 x 1 = 23
They are then called
HAPLOID CELLS
(aplo= single)

10. MALE GAMETES
SPERM cell (Ancient Greek: σπέρμα, "seed“)
• HEAD
(nucleus with 23 chromosomes +
little cytoplasm with substances that dissolve the egg
cell membrane)
• NECK
(with a lot of mithocondria because it needs a lot of
energy to move)
• TAIL / FLAGELLUM (to move)

11. FEMALE GAMETES
EGG cell or OOCYTE
• CYTOPLASM
(rich in nutritious substances)
• NUCLEUS
(with 23 chromosomes)
• CELL MEMBRANE
• PROTECTIVE LAYERS

12. CREATING NEW CELLS:
MITOSIS and MEIOSIS

13. CREATING NEW CELLS:
MITOSIS and MEIOSIS
Both are processes of cell division (they give origin to new cells)
• MITOSIS INVOLVES ALL THE CELLS OF THE BODY
• MEIOSIS INVOLVES ONLY SOME CELLS WHICH WILL FORM
THE GAMETES

14. CREATING NEW CELLS:
MITOSIS and MEIOSIS
Both are processes of cell division (they give origin to new cells)
• MITOSIS INVOLVES ALL THE CELLS OF THE BODY
• MEIOSIS INVOLVES ONLY SOME CELLS WHICH WILL FORM
THE GAMETES

15. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE

16. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE
“PRO”:
BEFORE/ AT FIRST

17. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE
“META”:
IN THE MIDDLE

18. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE
“ANA”:
TO THE OPPOSITE SIDE

19. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE
“TELOS”:
AT THE END

20. MITOSIS
IT DOES NOT MODIFY THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 2 cells with 23 pairs (46)
of chromosomes of chromosomes each
4 PHASES called
PROPHASE - METAPHASE – ANAPHASE - TELOPHASE
Tip: italian word PoMATe

21. MITOSIS

22. MITOSISCENTRIOLES
MITOTIC SPINDLE
(fuso mitotico)

23. CHROMOSOMES
• Chromosomes are molecules of DNA in the nucleus of the cell

24. MITOSIS

25. MITOSIS
• The nucleus dissolves, all the
CHROMOSOMES double
themselves creating two
CHROMATIDES (like an ‘X’)
• The CENTRIOLES go to the
two poles of the cell
• Then the CENTRIOLES develop
the MITOTIC SPINDLE

26. MITOSIS
• The nucleus dissolves, all the
CHROMOSOMES double
themselves creating two
CHROMATIDES (like an ‘X’)
• The CENTRIOLES go to the
two poles of the cell
• Then the CENTRIOLES develop
the MITOTIC SPINDLE
• The 46
CHROMOSOMES
align themselves on
the equator of the
cell
• …And they CONNECT
TO THE SPINDLE at
their center

27. MITOSIS
• The nucleus dissolves, all the
CHROMOSOMES double
themselves creating two
CHROMATIDES (like an ‘X’)
• The CENTRIOLES go to the
two poles of the cell
• Then the CENTRIOLES develop
the MITOTIC SPINDLE
• The 46
CHROMOSOMES
align themselves on
the equator of the
cell
• …And they CONNECT
TO THE SPINDLE at
their center
• The 46 CHROMATIDS
separate from each
other
• The MITOTIC SPINDLE
shortens (si accorcia)
making the
CHROMATIDS MIGRATE
towards the POLES
(poli) of the cell

28. MITOSIS
• The nucleus dissolves, all the
CHROMOSOMES double
themselves creating two
CHROMATIDES (like an ‘X’)
• The CENTRIOLES go to the
two poles of the cell
• Then the CENTRIOLES develop
the MITOTIC SPINDLE
• The 46
CHROMOSOMES
align themselves on
the equator of the
cell
• …And they CONNECT
TO THE SPINDLE at
their center
• The 46 CHROMATIDS
separate from each
other
• The MITOTIC SPINDLE
shortens (si accorcia)
making the
CHROMATIDS MIGRATE
towards the POLES
(poli) of the cell
• The 46 CHROMATIDS
(single chromosomes) are
on the two opposite sides
of the cell
• The SPINDLE dissolves
• The nucleus forms again
• THE CELL DIVIDES IN TWO

30. GUESS THE PHASE

32. CREATING NEW CELLS:
MITOSIS and MEIOSIS
Both are processes of cell division (they give origin to new cells)
• MITOSIS INVOLVES ALL THE CELLS OF THE BODY
• MEIOSIS INVOLVES ONLY SOME CELLS WHICH WILL FORM
THE GAMETES

33. MEIOSIS
IT HALVES THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 4 cells with 23
of chromosomes chromosomes each
8 PHASES called
PROPHASE 1 – METAPHASE 1 – ANAPHASE 1- TELOPHASE 1
PROPHASE 2 – METAPHASE 2– ANAPHASE 2 - TELOPHASE 2

34. MEIOSIS
IT HALVES THE NUMBER OF CHROMOSOMES IN A CELL
1 cell with 23 pairs (46) 4 cells with 23
of chromosomes chromosomes each
8 PHASES called
PROPHASE 1 – METAPHASE 1 – ANAPHASE 1- TELOPHASE 1
PROPHASE 2 – METAPHASE 2– ANAPHASE 2 - TELOPHASE 2
Yes, it seems like
TWO CONSECUTIVE MITOSIS
But with some differences…

35. HUMANS HAVE 46 CHROMOSOMES
• We say that we have 23 PAIRS OF
HOMOLOGUE CHROMOSOMES
(coppie di cromosomi omologhi)
in the nucleus of each cell
• In each pair, the 2 chromosomes
have SAME SHAPE AND
FUNCTION
• Therefore, EVERY GENE IS
DUPLICATED

36. MEIOSIS
• In the first cell division (P1, M1, A1, T1) what binds to the SPINDLE are THE PAIRS OF CHROMOSOMES
(homologous chromosomes) not every single chromosome
• When the spindle shortens, EACH CROMOSOME GOES TO THE POLE OF THE CELL
THEREFORE IN THE FIRST DIVISION, WE END UP WITH TWO CELLS
WITH 23 CHROMOSOMES EACH -> HAPLOID CELLS

37. MEIOSIS
• In the first cell division (P1, M1, A1, T1) what binds to the SPINDLE are THE PAIRS OF CHROMOSOMES
(homologous chromosomes) not every single chromosome
• When the spindle shortens, EACH CROMOSOME GOES TO THE POLE OF THE CELL
THEREFORE IN THE FIRST DIVISION, WE END UP WITH TWO CELLS
WITH 23 CHROMOSOMES EACH -> HAPLOID CELLS

38. MEIOSIS
• In the first cell division (P1, M1, A1, T1) what binds to the SPINDLE are THE PAIRS OF CHROMOSOMES
(homologous chromosomes) not every single chromosome
• When the spindle shortens, EACH CROMOSOME GOES TO THE POLE OF THE CELL
THEREFORE IN THE FIRST DIVISION, WE END UP WITH TWO CELLS
WITH 23 CHROMOSOMES EACH -> HAPLOID CELLS

39. MEIOSIS
• Each cell goes through another cell division similar to a mitosis
• Chromosomes attach to the SPINDLE and their chromatides divides in
two different cells. Chromatides give origin to chromosomes again.

40. TWO KINDS OF CELLS
SOMATIC CELLS:
ANY CELL FORMING
THE BODY OF AN ORGANISM
23 pairs of chromosomes
23 x 2 = 46
they are then called
DIPLOID CELLS
(diplo= double)
GERMS CELLS or
GAMETES:
THEY WILL GIVE ORIGIN TO A
NEW ORGANISM IF FERTILIZED
23 chromosomes
23 x 1 = 23
They are then called
HAPLOID CELLS
(aplo= single)

41. GAMETOGENESIS
• MEIOSIS creates 4 haploid cells, which are the GAMETES
• This process of creating GAMETES with meiosis is called
GAMETOGENESIS
• In MALES: from one starting cell, we have 4 spermatozoa at the end
• In FEMALES: from one starting cell, we have 4 cells: only one of them
will become the egg cell, the other 3 degenerate and die

42. HUMANS HAVE 46 CHROMOSOMES
• We say that we have 23 PAIRS OF
HOMOLOGUE CHROMOSOMES
(coppie di cromosomi omologhi)
in the nucleus of each cell
• In each pair, the 2 chromosomes
have SAME SHAPE AND
FUNCTION
• Therefore, EVERY GENE IS
DUPLICATED

43. HUMANS HAVE 46 CHROMOSOMES
• We say that we have 23 PAIRS OF
HOMOLOGUE CHROMOSOMES
(coppie di cromosomi omologhi)
in the nucleus of each cell
• In each pair, the 2 chromosomes
have SAME SHAPE AND
FUNCTION
• Therefore, EVERY GENE IS
DUPLICATED (ex. Gene «Color of the
eye».
• Those two genes can carry, anyway,
different information: one
chromosome has the gene «Color of
the eye: BLUE» and the other
chromosome «Colour of the eye:
BROWN»)

44. MEIOSIS

45. CROSSING OVER
• In PROPHASE 1, before being divided, the homologue chromosomes are
one beside the other
THE HOMOLOGUE CHROMOSOMES ARE
SO CLOSE TO EACHOTHER,
THAT THEY EXCHANGE DNA FRAGMENTS

46. CROSSING OVER
THEY EXCHANGE RANDOM SEGMENTS
It will SHUFFLE all the information in the two
homologue chromosomes

47. CROSSING OVER
THIS EXCHANGE IS TOTALLY RANDOM
THIS WILL LEAD TO
MORE THAN 8 BILLIONS NEW POSSIBLE
COMBINATIONS OF CHROMOSOMES

48. CROSSING OVER
THIS EXCHANGE IS TOTALLY RANDOM
THE CHROMOSOMES THAT COME FROM THE PARENTS
WILL NOT, ANYWAY, BE EXACTLY LIKE THE ONES OF
THE PARENTS.
THEIR INFORMATION WILL BE MORE MIXED

49. CROSSING OVER
CROSSING OVER INCREASES
THE VARIABILITY OF THE TRAITS
(aumenta la variabilità dei tratti somatici)
THAT’S WHY BROTHERS ARE ALWAYS DIFFERENT
THEREFORE, TRAITS COME FROM THE PARENTS, BUT THEY
ALSO SHUFFLE IN MANY DIFFERENT COMBINATIONS

50. • The process in which male and female gametes unite
FERTILISATION (fecondazione)
23 + 23 = 46
chromosomes

51. • In mammals, fertilization is INTERNAL
Male gametes are released directly in the female’s apparatus
LOW ENERGY WASTE, HIGH PROBABILITY OF SUCCESS
(minimal waste of gametes; greater chance of individual egg fertilisation,
longer time period of egg protection)
…Success in reproduction is the main goal for every species.
INTERNAL FERTILISATION

52. • In many aquatic animals (fishes,
amphibians etc.) the fertilisation is
external
• Less chance of success, they must
produce more gametes
(external fertilisation)

53. FUNCTIONS OF REPRODUCTIVE SYSTEM:
• PRODUCTION and PRESERVATION of the male/female GAMETES
• FERTILISATION via SEXUAL INTERCOURSE: to make oocytes and
spermatozoa come in contact
INTERNAL FERTILISATION

54. FERTILISATION
23 (haploid) + 23 (haploid) = 46 (diploid)

55. ZYGOTE
The new diploid cell is called ZYGOTE
and has 23 chromosomes from the father
and 23 chromosomes from the mother

56. ZYGOTE
The ZYGOTE cell starts doing mitosis
At the end, it will be composed of millions of new cells, forming
the embryo, which will become a foetus

57. ZYGOTE
The ZYGOTE cell starts doing mitosis
At the end, it will be composed of millions of new cells, forming
the EMBRYO (which will become a FOETUS)