Reproduction and molecular genetics

• Deoxyribonucleic acid (DNA)


  A molecule that carries genetic information which is important for cellular functions such as cell division and cell differentiation
• Nucleotide


  The basic unit of DNA, containing sugar, phosphate group and nitrogenous base
• Nitrogenous bases


  • Adenine (A)
  • Cytosine (C)
  • Guanine (G)
  • Thymine (T)
• Formation of nucleotides


  Each of the four bases combines with a sugar and a phosphate group to form four different nucleotide molecules - adenine nucleotide, thymine nucleotide, guanine nucleotide, cytosine nucleotide
• Polynucleotide


  Long chains of joined nucleotides
• Sugar-phosphate backbone


  The structure that makes up the outside of the DNA molecule
• Gene


  A sequence of nucleotides that controls the formation of a single polypeptide
• DNA molecule


  Made up of two polynucleotide chains that twist around each other to form a double helix
• Complementary base pairing


  Adenine(A) always bonds with Thymine(T), Cytosine(C) always bonds with guanine (G)
• The ratios of adenine to thymine and cytosine to guanine are always in a 1:1 molecule
• Chromosome


  The DNA molecule is wrapped around proteins to form a single chromosome, found in the nucleus
• Gene


  The basic units of inheritance in a living organism, made up of a sequence of nucleotides that controls the formation of a single polypeptide
• Polypeptide synthesis from a gene

  1. The message in the gene is copied into a molecule called mRNA

  2. mRNA travels from the nucleus to the cytoplasm and attaches to a ribosome

  3. the ribosome moves along the mRNA, synthesizing a polypeptide
• Flow of genetic information

  gene → mRNA → polypeptide
• Sexual reproduction


  A process that results in genetically dissimilar offspring through the fusion of two gametes to form a zygote
• Gametes


  Reproductive cells produced in reproductive organs, the male gamete is the sperm and the female gamete is the egg or ovum
• Human cells contain 46 chromosomes, gametes contain half that number, 23 chromosomes
• Zygote


  The cell formed by the fusion of a male and female gamete, which undergoes cell division to produce normal body cells and form an offspring
• Male reproductive system


  • Testes, scrotum, sperm ducts, prostate gland, urethra and penis
• Testes


  Two oval-shaped structures in the scrotum that produce sperm and male sex hormones (testosterone), and are responsible for the development and maintenance of secondary sexual characteristics in males
• Scrotum


  A pair of pouch like sacs that contain the testes, they lie outside the main body cavity at a lower temperature for proper sperm development
• Sperm ducts


  Loop over the ureter and open into the urethra, transporting sperm from testes to urethra
• Prostate gland


  Lies at the base of the urinary bladder where the two sperm ducts join the urethra, secretes a fluid that mixes with sperms to form semen
• Penis


  An erectile organ that contains spongy tissue that fill with blood during arousal, causing the penis to become erect and stiff. It enters the vagina when erect during sexual intercourse to deposit semen containing sperm
• Sperm


  The male gamete, produced throughout the life of a male human after he reaches physical maturity. It contains a head with a nucleus, a middle piece with mitochondria, and a tail that propels it
• Female reproductive system


  • Ovaries, oviducts, uterus, cervix and vagina
• Ovaries


  Small almond shaped structures located on each side of the uterus that produce ova/eggs and female sex hormones (oestrogen and progesterone)
• Oviduct


  A narrow muscular tube with a funnel like opening close to the ovary, that connects the ovary to the uterus and has a lining of cilia to move the egg along
• Uterus


  Has elastic muscular walls shaped like an upside down pear, where the fetus develops during pregnancy
• Uterine lining


  The smooth inner lining of the uterus that is shed during menstruation and rebuilt after
• Cervix


  The circular ring of muscles in lower part of the uterus that opens into the vagina
• Vagina


  Leads from the cervix to the outside of the body, where semen is deposited during sexual intercourse and menstrual blood flows out
• Ovum (egg)


  The female gamete, a female is born with all the potential eggs she will ever have, only about 500 will mature
• Differences between male and female gametes

  • Structure: Male-has a head, middle piece and tail. Nucleus contains either an X or Y chromosome. Female-spherical shape. Nucleus has one X chromosomes
  • Motility: Male-has a tail that enables it to swim to the oviduct. Female-is moved along the oviduct by cilia and peristalsis
  • Numbers: Male-a large number is released during ejaculation. Female-only one egg is released per month
• Menstrual cycle


  The monthly discharge of blood from the uterus via the vagina, the first sign of puberty
• Menstruation


  The uterine lining breaks down and is shed with some blood
• Menstrual cycle


  1. Day 1-5 Uterine lining is shed, menstruation

  2. Day 6-9 Uterine lining is repaired

  3. Day 10-15 Uterine lining thickens - fertile period (Ovulation, day 14)

  4. Day 16-28 Uterine lining continues to thickening, becoming well-supplied with blood capillaries
• Menstrual cycle details


  • ovulation usually occurs on day 14
  • fertilization is possible from day 10-15 (fertile period)
  • the egg can survive 1-2 days in the female reproductive system
  • sperm can survive 3-5 days in the female reproductive system
  • The rest of the days make up the infertile period
• If no fertilization occurs

  1. egg breaks down

  2. secretion of progesterone decreases

  3. on the 28th day, without progesterone, the thickened uterine lining breaks down

  4. menstruation begins and the cycle repeats
• If fertilization occurs


  1. fertilized egg becomes a zygote which develops into an embryo

  2. ovary secretes progesterone and oestrogen to thicken and maintain the uterine lining for implantation

  3. embryo embeds itself in the uterine lining until the placenta is formed

  4. placenta takes over the production of progesterone and oestrogen to maintain the uterine lining