Understanding Growth & Development

1. Understanding Growth & Development

2. Reproduction Strategies • One characteristic of all living things is the ability to reproduce • It allows genes for common traits to pass from one generation to the next • This ensures the survival of the species

3. Reproduction Strategies, cont. • Two main categories of reproductive strategies: • Asexual • Sexual • Many species use only one strategy • Some species are able to use both strategies depending on availability of partners or environmental conditions

4. Reproduction Strategies, cont. • Methods of asexual reproduction: • Binary fission – bacteria • Budding – yeast & hydra • Mitosis – single celled eukaryotes • Advantages: • One organism can increase a population • Energy is not used making sex cells • No need to search for mates • Disadvantage: No genetic diversity; one dies, they all die!!!

5. Reproduction Strategies, cont. • Methods of sexual reproduction: • External fertilization (sperm and egg have to make contact in body of water) – fish & frogs • Internal fertilization (implantation of male gamete in moist environment of female) – plants, birds, reptiles & most mammals • Advantage: genetic diversity • Disadvantage: requires a mate

6. Formation of Gametes • Gametes – sex cells; sperm or egg (ovum) • Diploid (2n) cell – cell with complete set of chromosomes - All body cells are diploid • Haploid (n) – cell with half the genetic material of parent cell - Gametes are haploid - Meiosis: creation of haploid cells from diploid cells

7. Meiosis • The creation of haploid cells requires 2 cycles of division: • Meiosis I – genetic recombination • Meiosis II – reduction division • Somatic (body) cells do not undergo meiosis • As in mitosis, meiosis is preceded by interphase and DNA replication

8. Meiosis I • Prophase 1: Step 1- Matching (homologous) chromosomes pair up with each other to form a tetrad

9. Meiosis I, cont. • Prophase I: Step 2- Homologous chromosomes exchange genetic information with each other – this is called “crossing over”

10. Meiosis I, cont. • The cell goes through Metaphase, Anaphase and Telophase I • At the end of Telophase I/Cytokinesis I, there are two new cells that are still diploid (2n) • The geneticmaterial has been recombined, so the new cells are no longer identical to the parent cell

12. Meiosis II • From Cytokinesis I, the cells immediately go through P M A T (II) • At the end of Cytokinesis II, there are four new daughter cells that are haploid (n) • These are the gametes

14. Importance of Meiosis • Allows for sexual reproduction which is the basis of genetic variation in offspring • This variation allows the offspring a diversity that could be the difference between living or dying • This gives the species as a whole a greater chance of surviving in a changing ecosystem • Genetic variation is the foundation of evolution by natural selection

16. Comparison of Mitosis/Meiosis

17. The Human Reproductive System

18. Species that reproduce sexually have specialized structures that produce gametes • In humans, this process is influenced by the endocrine system • This system produces hormones that play an important role in the development and management of reproductive capacity

19. Male Reproduction • During childhood the body grows but does not change much • Puberty begins between the ages of 11 & 16 • This process is started when the brain sends signals to the hypothalamus that it is time

20. Male Reproduction, cont. • Role of the Pituitary gland: • Releases FSH (follicle stimulating hormone) into bloodstream • Once at the testes, FSH triggers specialized cells to make testosterone • Testosterone triggers: • Sperm production • Development of external organs • Facial/body hair • Deepening of voice • Increase in muscle/bone mass

21. Male Reproduction, cont. • In human males (and many other organisms) gametes are called spermatozoa or sperm • Formation of sperm from stem cells (called follicles) is called spermatogenesis • 1 follicle produces 4 sperm • Length of meiosis: 65 to 75 days

22. Male Reproduction, cont. • Approximate number of stem cells that go through process each day: 3 million • There are 300-500 million sperm that exit the body upon ejaculation • Sperm are able to remain viable up to 48 hours inside the female reproductive system

24. Did You Know? • The shape of the head of a sperm varies from rounded to more oblong or pointed depending on the species? Rat Human Fly

25. Female Reproduction • Oogenesis – production of female gametes (ovum/ova) • Begins as female fetus develops within the uterus of her mother • As the fetus develops, follicles go through Prophase I of Meiosis and then lie dormant within the ovaries • Each follicle will produce one egg and 3 non-viable polar bodies

27. Female Reproduction, cont. • Puberty begins around 10-14 years old: • Role of the pituitary gland: • Releases FSH into the bloodstream • Once at ovaries, FSH triggers the completion of meiosis in one follicle • Estrogen and progesterone are also secreted to support growth of uterine lining • If the ovum is not fertilized, it and the uterine lining are shed; this is menstruation

28. Female Reproduction, cont. • Estrogen production is the beginning of puberty; also triggers: • Breast development • Broadening of hips • Growth of body hair • Slight deepening of voice

29. Female Reproduction, cont. • Once the egg is fertilized, it becomes a zygote • The zygote secretes a hormone that allows it to implant in the uterine wall • Estrogen and progesterone keep the zygote implanted and the uterine wall becomes a structure called the placenta

30. Female Reproduction, cont. • The zygote goes through rapid mitosis to become an embryo • During mitosis, genes switch on and off that control the production of certain chemicals • These chemicals initiate differentiation in cells • This allows cells to become tissues, organs, organ systems and organisms