1	Life Cycles and Meiosis The life cycle of most individuals begins at fertilization. Fertilization is the union of two cells each with half as many chromosomes as body cells.
2	Reading Assignment Chapter 12 discusses our understanding of the reasons why starting a life by uniting games from two individuals is believed to be advantageous (compared to cloning). Focus on the KEY CONCEPTS, don’t worry about the names of the meiosis stages. Read ‘Seedless Fruits’ Essay (p.266).
3	Cycles Patterns in biology that end back where they start are called cycles. Cell Division Cycle Cultural Growth Cycle (colonization of patch with abundant resources for growth) Life Cycle also referred to as Clonal Life Cycle (CLC) because it begins at fertilization. (CLC ends in death, but it returns to fertilization via meiosis.)
4	Stages of Drosophila Life Cycle
5	Timing of events Timing of actions (especially sex) in the life of an individual are normally affected by: Time of day (circadian rhythms) Season (time of year) AGE (time since birth)
6	Eukaryotic Life as a Cycle
7	Eukaryotic Life Cycle as a line
8	Fertilization For multicellular organisms fertilization (=sex) is union of two cells called gametes. All the chromosome from both gametes remain in the zygote. The gametes have only half as many chromosomes as are in normal body cells. The cell divisions halving the number of chromosomes is called meiosis.
9	Meiosis There is a special type of cell division that occurs in diploid cells called meiosis. Meiosis reduces the two complete sets of information in the diploid cell into cells that have only one complete set. The haploid cells resulting from meiosis are gametes or sex cells.
10	Gamete Types Male gametes are sperm in animals and pollen in plants. Females gametes are eggs in animals and ovules in plants.
11	Individuals from Fertilization Union of sperm and egg results in a diploid cell with 2 complete sets of chromosomes. The fertilized egg is call a zygote. The zygote cell divides and the clone of cells adheres together to form an individual. Each individual is a clone (population) of diploid cells.
12	Sexes, Animals vs. Plants Most animal species have individuals divided into two sexes, males that produce small, active gametes (small, active gametes are called sperm) and females that produce large gametes (eggs). Most flowering plants have both anthers (male) and ovules (female) in each flower. Such individuals do not have a ‘gender’.
13	Distinguishing sex, sexes and gender The union of two gametes to form a zygote is biological sex. Sexes, male and female, are attributes of individuals, particularly the kind of gametes they can produce but also associated with behavioural differences. Gender is a word acknowledging social and cultural associations of sexes.
14	Sex and Reproduction Individually and collectively humans have a high level interest in sexuality. Suppression of exposure of juveniles to sexually explicit material is a common, if not universal, pattern of human culture. Sexual behavior and sex ‘appropriate’ appearance is something most individuals feel strongly about.
15	Plant Life Cycles Annual lives less than a year and individual dies after setting seed. Biennial lives two years, sets seed in second year and then individual dies. Perennial lives more than 2 years Short lived – a few to a dozen years only. Long lived – some plants have been clonally propagated for hundreds of years. All woody plants are perennials.
16	Asexual Reproduction Does NOT involve meiosis and union of gametes. Cloning (forming a new individual from a small piece of another one) has been done in plants for a long time. Cloning does not result in a genetically new individual (fertilization does).
17	Cloning in agriculture Many woody plants, especially fruit trees, are propagated (another word for reproduce) by grafting cuttings onto roots. All Jonathon apples are clonal descendants of a single tree born in Ontario in 18th century.
18	Uniparental Reproduction Uniparental means a single individual can produce progeny without a partner. If via meiosis, process is called selfing. The individual is source of both the male and female gametes used in fertilization. Many crop plants reproduce by selfing. Peas and corn both normally have most ovules fertilized by pollen from the same plant.
19	LINES, preserve desired traits In selfing species it is easy to establish and maintain varieties (also called lines) with characteristic traits. Varieties differ in time to maturity, flavor, hardiness or other traits. In species that require two parents to reproduce establishing a line (=breed) takes a longer time, but allows the breeder to pick existing traits and mix them.
20	Breeds Most domestic animals have many different breeds. Breed membership is determined by a registry – if both parents are members then offspring are members. Organizations maintain pedigrees and registration to evaluate breed membership.
21	The Garden Pea Variety A Annual Propagated as a true-breeding line by selfing. GREEN seeds WRINKLED seeds Variety B Annual Propagated as a true-breeding line by selfing. YELLOW seeds ROUND seeds
22	Problem
23	VOCABULARY Breed Clonal life cycle Diploid Fertilization Gametes Haploid Line Meiosis Selfing Sex Sexes Zygote