Sexual Reproduction

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Sexual Reproduction

• The process of sexual reproduction involves two
  parents.  
• Both parents normally contribute one gamete or
  sex cell to the process.  
• This process assures that the genetic information
  given to the offspring will be obtained equally
  from each parent. 
• The female gamete is called the egg or the ovum
  and the male gamete is called a sperm. 
• These gametes are formed in specialized
  reproductive structures called gonads.  
• The sperm is much smaller than the egg, but is
  capable of moving on its own power using a
  whip-like tail called a flagellum.

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• MeiosisThe process of meiosis produces gametes
  or sex cells. 
• Mitosis produces other cell types.  
• The process of meiosis halves the chromosome
  number from the original parent cell in the four
  cells it forms. 
•   It does this by having two cell divisions
  forming four cells, where mitosis has only one
  cell division forming two cells.   
• Both processes start out with one doubling or
  replication of the chromosome material.  

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• Another important way that meiosis differs from
  mitosis is the exchange of chromosome pieces
  which occurs in the first division of this
  process.   This exchange of chromosome pieces is
  called crossing over.  
• Crossing over assures that the cells produced as
  a result of meiosis will be different from and
  exhibit variations from the parent cell that
  produced them.    This process is chiefly
  responsible for the variations seen in members of
  the same species of sexually reproducing
  organisms.    These variations are the driving
  force for the process of natural selection.
• The process of crossing over and how it produces
  variation when these chromosomes are recombined
  in the process of fertilization is illustrated in
  the graphic below.

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Tetrad
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• Another important way that meiosis differs from
  mitosis is the exchange of chromosome pieces
  which occurs in the first division of this
  process.   This exchange of chromosome pieces is
  called crossing over.  
• Crossing over assures that the cells produced as
  a result of meiosis will be different from and
  exhibit variations from the parent cell that
  produced them.    This process is chiefly
  responsible for the variations seen in members of
  the same species of sexually reproducing
  organisms.    These variations are the driving
  force for the process of natural selection.
• The process of crossing over produces variation
  when these chromosomes are recombined.

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Reproductive system
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• Male reproductive SystemThe structure and
  function of the human male reproductive system,
  is very similar to that of many other mammals.  
• The male system is designed to make sperm or
  male gamete, make sex hormones, and is adapted to
  provide for the delivery of these gametes to the
  female to allow for fertilization.

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• Male Reproductive System Structures
• 1.   testes -- produces sperm and the hormone
  testosterone
• 2.  scrotum -- pouch enclosing the testes keeping
  the sperm at an optimum temperature for
  development 
• 3.  vas deferens -- tube carrying sperm away from
  the testes
• 4.  prostate gland -- the largest of several
  glands which add lubricating and other fluids to
  the sperm 
• -- this combination of sperm and fluids is called
  semen
• 5.  urethra -- tube through the penis carrying
  sperm to the outside of the body
• 6.  penis -- adaptation for internal
  fertilization of the female

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• Male Reproductive System Structures
• 1.   testes -- produces sperm and the hormone
  testosterone
• 2.  scrotum -- pouch enclosing the testes keeping
  the sperm at an optimum temperature for
  development 
• Epididymis A coiled tube
• 3.  vas deferens -- tube carrying sperm away from
  the testes
• 4.  prostate gland -- the largest of several
  glands which add lubricating and other fluids to
  the sperm 
• -- this combination of sperm and fluids is called
  semen
• 5.  urethra -- tube through the penis carrying
  sperm to the outside of the body
• 6.  penis -- adaptation for internal
  fertilization of the female

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Male Reproductive System

•  

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Male Reproductive system
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Female Reproductive system

• Ovaries Make eggs, female sex hormones estrogen
  and progesterone
• Oviduct/Fallopian tubes passage for egg to the
  uterus
• Uterus/Womb where embryo develops
• Cervix opening of uterus into the muscular tube
  called vagina
• Vagina Birth canal entry passage for the penis
  to deposit semen

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• Female Reproductive System Structures
• 1.  ovary -- (females have two of these) --
  produce female gametes or eggs and the hormone
  estrogen
• 2.  oviduct (fallopian tube) -- carries the egg
  away from the ovary
•  -- internal fertilization normally occurs here
• 3.  uterus -- implantation and development of the
  embryo and fetus before birth occurs here
• 4.  vagina or birth canal -- entry point for
  sperm from the male and exit tube for the baby
  when it is born

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Menstrual cycle
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When does the cycle start?

• At puberty when an individual becomes capable of
  reproduction
• Ends/ceases at menopause
• Interrupted during pregnancy/or some illnesses

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Menstrual cycle

• Is a series of events (last for 28 days) that
  prepares the uterus for pregnancy
• Starts with the maturation of egg in a FOLLICLE
  inside the OVARY
• And then thickening/vascularization of the lining
  of the uterine wall, and if fertilization (union
  of egg and sperm) does not happen, ends with the
  breakdown of the uterine lining (causing the
  periods/menstruation)

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Who are the main players that regulate this cycle?

• Hormones
• FSH (follicle stimulated hormones) and LH
  (luteinizing hormone) made by PITUITARY gland
• Estrogen and progesterone made by the ovaries

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4 stages of menstrual cycle

• Follicle stage (1-14 days)
• Ovulation (Day 15)
• Luteal stage (10-12 days)
• Menstruation (last 4-5 days)

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Four Stages of menstrual cycle

• 1 Follicle stage (1-14 days) Egg in an ovary
  matures inside a sac called follicle and
  follicle secretes estrogen which stimulates the
  follicle maturation and the thickening of uterine
  lining

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• Ovulation mature ovarian follicle ruptures and
  discharges an ovum

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How does the egg develop? (First, it matures
and then is released)
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Stage 3 Luteal stage(10-12 days)

• Left over follicle (minus egg) becomes corpus
  luteum
• Which now makes progesterone that finishes up the
  thickening of uterus

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Stage 4 Menstruation

• If fertilization doesnt happen, the uterus
  lining breaks down in the next 4-5 days
• That is menstruation
• If fertilization happens

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• First, hypothalamus signals Pituitary to make FSH
  
• FSH signals ovaries to make Estrogen(made by
  follicle)
• High Estrogen levels signal Pituitary to stop
  making FSH!
• Now, pituitary makes Luteinizing Hormone which
  signals corpus luteum to make progesterone..

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• Follicle stage
• Egg maturesfollicle secretes estrogen
• How?.. the pituitary gland releases follicle
  stimulating hormoneFSH, that stimulates follicle
  to make estrogen
• estrogen makes Uterine wall thick by
  vascularization
• Lasts 14 days Ovulation happens
• Now estrogen inhibits the FSH made by pituitary
  glandpituitary now starts to make Luteinizing
  HormoneLH
• Luteal phase
• LH stimulates the formation of Corpus luteum
• CL makes progesterone which increases the
  vascularization of the uterine liningendometrium

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• First, hypothalamus signals Pituitary to make FSH
  
• FSH signals ovaries to make Estrogen(made by
  follicle)
• High Estrogen levels signal Pituitary to stop
  making FSH!
• Now, pituitary makes Luteinizing Hormone which
  signals corpus luteum to make progesterone..

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4 Stages of the Menstrual cycle

• Follicle stage
• Ovulation
• Corpus Luteum stage
• Menstruation

1.Estrogen
2. Progesterone
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• Ovulation is the process in the menstrual cycle
  by which a mature ovarian follicle ruptures and
  discharges an ovum (also known as an oocyte,
  female gamete, or casually, an egg) that
  participates in reproduction

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What is fertilization?
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Fertilization

• The union of male and female gametes to form a
  zygote

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Why doesnt cleavage result in an increase in the
size of the zygote?
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• The first few divisions of the zygote are called
  cleavage.
• Cleavage is mitotic divisions
• Different stages of development of zygote after
  cleavage
• 1) Holow ball of cellsblastula
• 2) Invagination of blastula makes
  gastrulaprocess is called gastrulation

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Where does fertilization occur in humans?

• Inside the body
• Where does the development of baby happen?
• Inside the female body
• Fertilization and development, both are INTERNAL
• It happens in most mammals

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Placenta
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Organisms with EXTERNAL fertilization and
development?

•  Organisms which spend their lives or a large
  proportion of their lives in the water tend to
  lay their eggs in great numbers (thousands) in
  the water and wait for the male of the species to
  release sperm near them to fertilize them.   The
  fertilization which occurs outside the body of
  the organism is called external fertilization. 
  These young organisms then develop outside the
  mother in the water once this has occurred, which
  is called external development.  A disadvantage
  of this process is that the eggs have lesser
  probability of getting fertilized (hence large
  numbers) and developing young have little or no
  parental protection.    Many fish and amphibians
  like frogs undergo fertilization and development
  in this manner.

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• Reptiles and birds use the process of internal
  fertilization to fertilize their eggs.  In this
  situation, the male of the species inserts his
  sperm inside the female, who then lays her
  fertilized eggs outside her body.   
• The process of development is external.  Reptiles
  and especially birds tend to lay fewer eggs and
  provide much more parental protection for their
  developing young.    

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4 Stages of the Menstrual cycle

• Follicle stage
• Ovulation
• Corpus Luteum stage
• Menstruation

1.Estrogen
2. Progesterone
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• First, hypothalamus signals Pituitary to make FSH
  
• FSH signals ovaries to make Estrogen(made by
  follicle)
• High Estrogen levels signal Pituitary to stop
  making FSH!
• Now, pituitary makes Luteinizing Hormone which
  signals corpus luteum to make progesterone..

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• Follicle stage
• Egg maturesfollicle secretes estrogen
• How?.. the pituitary gland releases follicle
  stimulating hormoneFSH, that stimulates follicle
  to make estrogen
• estrogen makes Uterine wall thick by
  vascularization
• Lasts 14 days Ovulation happens
• Now estrogen inhibits the FSH made by pituitary
  glandpituitary now starts to make Luteinizing
  HormoneLH
• Luteal phase
• LH stimulates the formation of Corpus luteum
  which makes progesterone that increases the
  vascularization of the uterine liningendometrium

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