42 - zygote • After implantation in the uterus a...

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These haploid cells, or gametes, are produced by gametogenesis , involving meiotic cell divisions. Two events in meiosis contribute to genetic diversity: crossing over of homologous chromosomes and independent assortment of the chromosomes. The gonads ( testes and ovaries ) are the sites of gametogenesis. The gametes are formed by germ cells which originate very early in the developing embryo. Oogenesis produces eggs through two meiotic divisions. External fertilization requires an aquatic habitat in which the gametes are released for transport. Internal fertilization was an important evolutionary step in the colonization of land by animals. To enable internal fertilization, many accessory sex organs have developed, such as the penis (a tube for depositing sperm in the female reproductive tract). The physical joining of the male and female accessory sex organs is called copulation . Fertilization is the union of haploid sperm and haploid egg to produce a single diploid cell, the
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Unformatted text preview: zygote • After implantation in the uterus, a blastocyst begins to secrete human chorionic gonadotropin ( hCG ), which keeps the corpus luteum functional. • The female reproductive cycle actually consists of two linked cycles: an ovarian cycle (28 days) that produces eggs and hormones and a uterine cycle that prepares the endometrium for the arrival of a blastocyst. FSH first but LH peaks Estrogen first then peaks and goes down while progestron increases and flattens out Hypothalamus GnRH anterior pituitary fsh/lh ovaries estrogen progesterone uterus cut vans deferens in males and fallopian tubes in females Using IVF and genetic analysis, a procedure called preimplantation genetic diagnosis ( PGD ) can eliminate the risk that adults who are carriers of genetic diseases will produce affected children...
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This note was uploaded on 04/24/2008 for the course BIOLOGY 020.152 taught by Professor Pearlman during the Spring '08 term at Johns Hopkins.

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