REPRODUCATION

WHY ARE THEY NECESSARY?SPECIALIZED SEX CELLSWhy do diploid organisms need to have specialized sex cells?Sex cells (gametes: sperm or egg) allow traits to be combined from two organisms2n (46)2n (46)+4n = 92too many

2Sexual ReproductionGametes have only one of each chromosomeRequires special cell division: Meiosis 2n = 46+n (23)n (23)Diploid cells (2n) Gametes (n) Takes place in gonads (testis, ovary)

3Mitosis Cells divide 1x

MeiosisCells divide 2x

How is Meiosis different from Mitosis?2n2n2n2nnnnnnnDiploid CellsHaploid Cells4MitosisMeiosisIdentical cellsDifferent cells5MitosisMeiosisCell division is overCells divide again; sister chromatids line up Done6How many unique gametes can a cell with two pairs of chromosomes make?7Why bother?For humans with 23 pairs of chromosomes?(2)23 > 8 million different possible gametesFor a couple possible unique offspring (8 million) x (8 million) = (64,000,000,000,000)But wait! Theres more!8Crossing over enables even greater varietyExchange of equivalent sections between homologous chromosomes.Occurs at random locations along chromosome.Creates new versions of chromosomes.9CQ#1: The cell to the right shows a diploid organism with two chromosomes (2n=2). The pictures below show some of the steps this cell may go through during mitosis or meiosis. A. B. C.D.E. F. G. H.Place the appropriate steps in order for a cell going through mitosis. (Note: you may use just some or all of the steps.) 10CQ#2: The cell to the right shows a diploid organism with two chromosomes (2n=2). The pictures below show some of the steps this cell may go through during mitosis or meiosis. A. B. C.D.E. F. G. H.Place the appropriate steps in order for a cell going through meiosis. (Note: you may use just some or all of the steps.) 11CQ#3: The different copies of chromosome 21 in John and Jane are shown to the right. Parent #1Parent #2Which of the following is a normal gamete that might be produced by either John or Jane?A B C D E12KING HENRY VIIIKing Henry married six times in hopes of producing a strong line with male heirs. Katherine of AragonAnne BoleynJane SeymourAnne of ClevesKatherine HowardKatherine Parr

CHILDRENKatherine of Aragon had six pregnancies: 3 sons, 3 daughters, only one daughter survivedAnne Boleyn had three pregnancies: 1 son, 1 daughter, and 1 unknown, only 1 daughter survived.Jane Seymour had one pregnancy: 1 son, who survivedNone of Henrys remaining wives had pregnancies

WHO WAS AT FAULT?Henry divorced Katherine, and beheaded Anne due to his belief that his wives were denying him male heirs.

CQ#4: Was it in fact the fault of his wives?

YESNO

WHY?Females can provide only Xs to their childrenMales can provide either an X or a Y Gamete Formation SpermThis process is called spermatogenesisTakes place in the testes of the maleThe process begins with a diploid cell called the spermatogonium

The spermatogonium enlarges and undergoes meiosis I and II.The final product is 4 haploid sperm cellsEach sperm cell has the same number of chromosomes and the same amount of cytoplasmEach sperm cell also has a long, tail-like flagellum used for movement

Gamete Formation - EggsThis process is called oogenesisTakes place in the ovary of the femaleThe process begins with a diploid cell called the oogonium

The oogonium enlarges and undergoes meiosis I and IIAt the end of meiosis one, however, the cytoplasm is not equally divided between the two daughter cells.The cell that receives most of the cytoplasm is called the primary oocyte, the other cell is called the polar body

The polar body is not a viable gameteAs the primary oocyte undergoes meiosis II, the cytoplasm again divides unevenly.The cell that receives most of the cytoplasm is called the Ovum or egg.

Why the unequal division?The unequal division of the cytoplasm during oogenesis is to provide the ovum with enough nutrients to support the developing zygote for a few days after fertilization

What is the zygote?The zygote is the new cell formed through the process of fertilization.