Growth and Development

• Species


  A group of closely related organisms that share certain characteristics and can produce new individuals through reproduction
• For any species to survive past a single generation, reproduction is essential
• Asexual reproduction


  Involves just one parent and results in one or more offspring that are genetically identical to that parent
• Sexual reproduction


  Involves two parents and results in offspring that have some genetic material (DNA) from each parent
• Organisms produced by asexual reproduction have only one parent, and they have the same genetic information (in the form of DNA) as the parent
• In sexual reproduction, offspring receive half of their genes from one parent and half from the other
• Offspring produced by sexual reproduction combine genes inherited from each parent's gametes
• Offspring gets a unique combination of genes from its parents, so it will differ from its siblings
• Cloning


  A technique that makes identical genetic copies
• Cloning involves inserting a nucleus from a "parent" organism's cell into an egg cell from which the nucleus has been removed
• The resulting offspring from cloning is a clone of the individual that donated the original cell nucleus
• Mitosis


  • Produces two cells that each have a full set of identical genes and chromosomes
  • Distributes one copy of the genetic information to each new cell
• Meiosis


  • Divides the genetic material in a way that results in the production of the sex cells required by organisms that reproduce sexually
  • Each sex cell has only half the genetic material needed for a cell to function properly
• Mitotic cell division


  1. DNA replication makes an identical copy of all the genetic information

  2. The replicated strand carries the instructions for the same proteins as in the original strand

  3. The double-stranded chromosome then has a duplicate set of instructions to pass on to each of two cells
• Meiotic cell division


  1. The two chromosomes of each pair (still double-stranded) separate, moving to opposite ends of the cell

  2. The strands separate and move to opposite ends of each of the dividing cells

  3. Four cells are formed, each having half the number of chromosomes of the organism's body cells
• When sperm and egg combine during fertilization, all of the newly paired chromosomes and all of the required genetic information are present in the fertilized egg
• Meiotic division begins with a body cell that has the full number of chromosomes typical of the species
• During meiotic division, the two chromosomes of each pair can be arranged in two ways when they pair up at the start, which helps increase genetic variation
• When chromosomes line up in pairs during meiosis, their strands may connect or cross over and then separate in a way that parts are exchanged, resulting in different combinations of information
• Meiotic cell division


  • Divides chromosomes into smaller sets and forms smaller cells
  • Responsible for much of the genetic variation among the sex cells of each individual
• When chromosomes line up in pairs during meiosis


  Their strands may connect or cross over and then separate in a way that parts are exchanged
• There are no two sperm or egg cells, even from the same parent, that are alike
• Summary of Mitotic and Meiotic Cell Division

  • Number of cell divisions
  • Exchange of genetic material between chromosomes
  • Number of functioning cells produced from original
  • Genetic makeup of final cells produced
  • Function of cells produced in multicellular organisms
• Mitotic cell division


  An exact duplication of the complete set of chromosomes of a cell, followed by the separation of these duplicate sets into two new cells
• Zygote


  A cell that contains all of the genetic information needed by the offspring
• Fertilization, zygote formation, and early development

  1. Fertilization

  2. Zygote formation

  3. Mitotic divisions
• Differentiation


  Cells becoming different from one another, leading to the formation of specialized cells, tissues, and organs
• Gene expression


  When a gene is actively producing its protein
• Gene expression can be modified through interaction with the environment

  For example, fruit flies developing straight wings instead of curly wings when raised in a cooler environment, or a plant growing white instead of green without sunlight
• In human females, gametes are produced in the ovaries
• Zygote


  A single cell formed by the union of a sperm and an egg during fertilization
• Essential parts of the human female reproductive system

  • Ovary
  • Oviduct
  • Uterus
  • Birth canal (vagina)
• Early events of pregnancy

  1. Egg released by ovary travels down oviduct where fertilization occurs

  2. Mitotic divisions of zygote begin as it continues to uterus

  3. Developing embryo sinks into uterine wall, placenta forms
• Functions of parts of the human female reproductive system

  • Ovary: Produces egg cells, releases hormones
  • Oviduct: Site of fertilization, carries egg to uterus
  • Uterus: Site where embryo and fetus develop
  • Birth canal (vagina): Passage for birth
• Birth


  1. Muscular uterus undergoes a series of contractions

  2. Contractions push the baby out of the mother's body
• The early events of pregnancy are shown in Figure 4-12
• Testes


  • Organs that produce sperm cells
  • Produce the hormone testosterone, which is associated with male sexual development and reproduction
• Essential parts of the human male reproductive system

  • Reproductive glands
  • Penis
  • Testes
  • Urinary bladder
• Functions of parts of the human female reproductive system

  • Ovary: Produces egg cells; releases hormones estrogen and progesterone
  • Oviduct: Site of fertilization; carries egg to uterus
  • Uterus: Site where embryo and fetus develop
  • Birth canal (vagina): Site where sperm enter and swim to egg; passageway for birth of baby
• The male reproductive system and other male characteristics are influenced by several hormones, including testosterone from the testes