Human Biology Sylvia S. Mader Michael Windelspecht Chapter 18 Patterns of Chromosome Inheritance Lecture Outline Part 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18.4 Meiosis What is crossing-over? Crossing-over is the exchange of genetic information between ______________ sister chromatids during synapsis. This occurs during ___________ of meiosis and increases genetic variation.

c. resulting chromatids 18.4 Meiosis What is crossing-over? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sister chromatids of a chromosome sister chromatids of its homologue A a A A a a B b B b B b crossing-over between chromatids 1 and 3 C c C c C c D d D D d d 1 2 3 4 1 2 3 4 1 2 3 4 a. synapsis b. crossing-over c. resulting chromatids Figure 18.11 Synapsis and crossing-over increase variability. 3

What is independent alignment? 18.4 Meiosis What is independent alignment? In metaphase I, homologous pairs align independently at the equator. Maternal or paternal member may be oriented toward either pole. It gives rise to various possible combinations of maternal and paternal chromosomes in gametes descended from this cell.

Independent alignment 18.4 Meiosis Independent alignment Figure 18.12 Independent alignment at metaphase I increases variability.

Meiosis II Prophase II Chromosomes _________ again. Metaphase II Chromosomes align at the equator. Anaphase II Sister chromatids separate to opposite poles. Telophase II 4 daughter cells result, each with 23 _________________ chromosomes.

Cells have one chromosome from each homologous pair. 18.4 Meiosis Meiosis II Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prophase II Cells have one chromosome from each homologous pair. Figure 18.10 The phases of meiosis.

Cells have one chromosome from each homologous pair. 18.4 Meiosis Meiosis II Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. haploid with paired sister chromatids haploid with paired sister chromatids Prophase II Cells have one chromosome from each homologous pair. Metaphase II Chromosomes align at the equator. Figure 18.10 The phases of meiosis. 8

Meiosis II 18.4 Meiosis Figure 18.10 The phases of meiosis. 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. haploid with paired sister chromatids haploid with paired sister chromatids Prophase II Cells have one chromosome from each homologous pair. Metaphase II Chromosomes align at the equator. Anaphase II Sister chromatids separate and become daughter chromosomes. Figure 18.10 The phases of meiosis. 9

Meiosis II 18.4 Meiosis Figure 18.10 The phases of meiosis. 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. haploid with paired sister chromatids haploid with paired sister chromatids Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Prophase II Cells have one chromosome from each homologous pair. Metaphase II Chromosomes align at the equator. Anaphase II Sister chromatids separate and become daughter chromosomes. Figure 18.10 The phases of meiosis. 10

Meiosis II 18.4 Meiosis Figure 18.10 The phases of meiosis. 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. haploid haploid with paired sister chromatids haploid with paired sister chromatids haploid Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Daughter cells Meiosis results in four haploid daughter cells. Prophase II Cells have one chromosome from each homologous pair. Metaphase II Chromosomes align at the equator. Anaphase II Sister chromatids separate and become daughter chromosomes. Figure 18.10 The phases of meiosis. 11

The production of sperm and eggs 18.4 Meiosis The production of sperm and eggs ___________________ The process of making sperm in males. A continual process after puberty. About 400 million sperm are produced per day.

The production of sperm and eggs 18.4 Meiosis The production of sperm and eggs ______________ The process of making eggs in females. During meiosis, 1 egg and 3 ___________ are formed. Polar bodies act to hold discarded chromosomes and thus disintegrate. Normally, 1 egg per month is produced, and ____ are produced during the entire reproductive cycle. 13

The production of sperm and eggs 18.4 Meiosis The production of sperm and eggs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SPERMATOGENESIS primary spermatocyte 2 n Meiosis I secondary spermatocytes n Meiosis II spermatids n Metamorphosis and maturation sperm n OOGENESIS primary oocyte 2n Meiosis I first polar body n secondary oocyte n Meiosis II Meiosis II is completed after entry of sperm. second polar body n Fertilization cont'd egg n sperm nucleus n Figure 18.13 A comparison of spermatogenesis and oogenesis in mammals. fusion of sperm nucleus and egg nucleus zygote 2n