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Sex Cells: The Biology of Sex • The Nature vs. Nurture Debate – Biology supports that this is a complex issue – Men and Women are more similar than different • Male and Female are not necessarily adequate as labels for people Humans • Being bodies that learn language thereby becoming wordlings humans are the symbol-making, symbol-using, symbolmisusing animal inventor of the negative separated from our natural condition by instruments of our own making goaded by the spirit of hierarchy acquiring foreknowledge of death and rotten with perfection Human • hu·man n. 1.A member of the genus Homo and especially of the species H. sapiens. 2.A person: the extraordinary humans who explored Antarctica. --adj. • • • • • Of, relating to, or characteristic of humans: the course of human events; the human race. Having or showing those positive aspects of nature and character regarded as distinguishing humans from other animals: an act of human kindness. Subject to or indicative of the weaknesses, imperfections, and fragility associated with humans: a mistake that shows he's only human; human frailty. Having the form of a human. Made up of humans: formed a human bridge across the ice. From WebMD • human • \Hu"man\, a. [L. humanus; akin to homo man: cf. F. humain. See Homage, and cf. Humane, Omber.] Belonging to man or mankind; having the qualities or attributes of a man; of or pertaining to man or to the race of man; as, a human voice; human shape; human nature; human sacrifices. To err is human; to forgive, divine. --Pope Human • Species of sentient being originating from/on the planet Earth in the Milky Way galaxy, is distinguished from other species in several ways: – Anthropologically: Differentiation through evolution – Biologically: DNA sequence comprised in 23 chromosomal pairs – Sociologically: Social, hierarchical, dominate environment and other species, use tools and language DNA DNA n. • A nucleic acid that carries the genetic information in the cell and is capable of self-replication and synthesis of RNA. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine. The sequence of nucleotides determines individual hereditary characteristics. • d(eoxyribo)n(ucleic) a(cid). Chromosome chro·mo·some n. 1. A threadlike linear strand of DNA and associated proteins in the nucleus of eukaryotic cells that carries the genes and functions in the transmission of hereditary information. 2. A circular strand of DNA in bacteria that contains the hereditary information necessary for cell life. Unraveling DNA to see a chromosome Gene gene n. • A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism. Genes undergo mutation when their DNA sequence changes. • A self-replicating protein molecule that occupies a fixed place on a chromosome; a unit of heredity Mitosis • When most cells in the body reproduce, which they need to do to grow or replace old cells, they do so through a process called mitosis. • In mitosis, the chromosomes pair up and split, creating two new cells, which are in theory identical to each other. Human Cells • Each cell in the human body contains a set of chromosomes from a mother (her egg) and a father (his sperm). When you look at human chromosomes, they are X-shaped, except for the male Y chromosome. – Every human cell, except for the sex cells, contains 46 chromosomes. • When a body produces sex cells (sperm or egg, depending on whether one is a male or female), the body must reduce the number of chromosomes by half. – Sex cells contain only 23 chromosomes Meiosis • To do this, it randomly sorts chromosomes from both sets in one cell division and then reduces them by half in another. Therefore, each sperm or egg that the body produces is unique and different -- it contains a different mix of the mother's and father's genes. – This is why two brothers in the same family can look and act totally different from one another even though they come from the same parents -- it all depends on which genes (chromosomes) were randomly chosen when producing the sex cells of the mother and father. Comparison of Mitosis and Meiosis Spermatogenesis Spermatogenesis n: development of spermatozoa and Oogenesis n: development of the ova Types of Chromosomal Mutations Fertilization • When semen is deposited at the base of the uterus, the sperm must first cross the barrier of the cervix and then up the lining of the uterus into the Fallopian tubes to reach the egg. – Only one of the Fallopian tubes contains an egg, so many sperm travel in the wrong direction. – This process must be completed within 12 to 48 hours, before the sperm die. – Fewer than 1,000 sperm out of the millions in the semen actually reach the Fallopian tubes.