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Using the worksheet received today complete the first page. Use your HW to Label the steps of MEIOSIS, quite Using the worksheet received today complete the first page. Assessment of Teaching SkillsUse your (ATS-P) HW to Label the steps Performance of MEIOSIS, quite Chapter 23 Meiosis and Sexual Reproduction Replication Asexual Reproduction (review) • Single parent gives rise to new offspring by mitotic cell division • Each new individual receives a set of chromosomes identical to the parent chromosomes • No variation of hereditary information (I) Sexual Reproduction • Two parents give rise to new offspring by the fusion of nuclear materials from two different cells • Offspring are not identical to the parent • Variations exist, which increases the species ability to adapt to the changing environment (A) Reproductive System • Gonads- specialized organs that produce gametes a) ovaries - female gonad - produce ova (egg) b) testes - male gonad - produce sperm cell Draw a Cell: 2n=6 1. AS it carries out Meiosis 2. Provide 2 KEY characteristics for each stage Gametes • Sex cells 1. Males – sperm 2. Females – ovum •BOTH ARE MONOPLOID!!!!!! Comparison of Ova and Sperm • Egg cells contain stored food in the form of yolk • Egg cells are larger than sperm • Sperm are motile, egg cells are not • BOTH ARE MONOPLOID!!!!!! (Remember) Diploid • Contain the full number (set) of chromosomes • Represented by: 2n (C) Haploid • Also known as monoploid • Represented by: n • The gametes contain half the number of chromosomes • Remember, gametes are sex cells that combine to form new offspring. Therefore gametes are haploid and once they fuse (combine), they form a zygote that is diploid Homologous Chromosomes • Pairs of similar chromosomes • Humans have 46 chromosomes: 22 pairs of homologous chromosomes 1 pair of sex chromosomes Homologous Chromosomes Diploid 2n = 46 Monoploid n=23 (Sperm/Egg) Fertilization • The fusion of the nuclei of one sperm with one ova (egg) to produce a zygote The above image is from (II) Meiosis • Known as Reduction Division • Meiosis is a type of cell division in which the daughter cell receives only half the number of chromosomes present in the parent cell 23 Pairs of chromosomes of a human cell • The chromosomes labeled X and Y are the sex chromosomes • XX = female • XY = male Replication (III) Stages of Meiosis • In meiosis, each cell divides twice: 1. The first stage is very similar to mitosis 2. The second stage is also like mitosis with the exception that there is NO replication of chromosomes Phases of Meiosis First Division Second Division Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II Meiosis Meiosis 23 Pairs of chromosomes of a human cell • The chromosomes labeled X and Y are the sex chromosomes • XX = female • XY = male Replication Key SS = single-stranded DS = double-stranded First Meiotic Division Prophase I • Replication of SS chromosomes into DS chromosomes • This is known as synapsis Metaphase I • Alignment of the DS chromosomes in the middle of the cell Anaphase I • DS chromosome separates • This is known as disjunction Telophase I • Cytokinesis occurs and the nuclear membrane reappears around the nuclei of the two newly formed daughter cells • At this point, the daughter cells are exact replicas of the parent cell Second Meiotic Division Prophase II • Chromosomes DO NOT replicate Metaphase II • Same as metaphase I Anaphase II • Same as anaphase I Telophase II • Both daughter cells undergo cytokinesis forming four haploid cells • Therefore: As a result of meiosis, diploid (2n) cells divide and form haploid (n) cells which mature into specialized reproductive cells (sperm and egg) • Each daughter cell contains half the number of chromosomes of the original cell Using complete sentences, describe what do YOU FEEL are the major goals of MITOSIS and MEIOSIS. I need to see all of the water quality group, for tomorrow's trip. Tuesday: Read and outline pages 307-315 You will need your textbook tomorrow!!!!!! I’m growing The above image is from 23 Pairs of chromosomes of a human cell • The chromosomes labeled X and Y are the sex chromosomes • XX = female • XY = male Normal somatic cell 2n = 46 Sperm cell n=23 Replication Meiosis Crossing Over Crossing Over With Mr. Rizzo Crossing over Crossing Over: Two different strands of DNA exchange information Recombination: result from crossing over, forms ”recombinate chromatids” Illustration of crossing-over and recombination during the formation of gametes or meiosis. homologous pair In meiosis, the Primary sex cells of the sperm or ova must replicate, then reduce the number of chromosomes in half. During the early stages of cell division in meiosis, two chromosomes of a homologous pair may exchange segments in the manner shown above, producing genetic variations in the sex cells. Meiosis: Stage Meiosis I Meiosis 1 Synapsis: like chromosomes match up and align during Meiosis chiasma The site where the exchange of chromosome segments between homologous chromosomes takes place (crossing-over) NON DISJUNCTION Part Two: Meiosis II begins In ALL FOUR CELLS n=2 Meiosis for real !!!!! Meiosis 1 Animation (360 kb) Meiosis 2 Animation (360 kb) Meiosis for real !!!!! (III) Sexual Reproduction in Animals Asexual Reproduction (review) • Single parent gives rise to new offspring by mitotic cell division • Each new individual receives a set of chromosomes identical to the parent chromosomes • No variation of hereditary information Normal somatic cell 2n = 46 Sperm cell n=23 Replication (I) Sexual Reproduction • Two parents give rise to new offspring by the fusion of nuclear materials from two different cells • Offspring are not identical to the parent • Variations exist, which increases the species ability to adapt to the changing environment (A) Reproductive System • Gonads- specialized organs that produce gametes a) ovaries - female gonad - produce ova (egg) b) testes - male gonad - produce sperm cell (B) Hermaphrodite • Contain both male and female reproductive structures (C) Gametogenesis • Process by which gametes are produced in the gonads • Two types: - Spermatogenesis - Oogenesis Oogenesis • The primary oocyte goes through first meiotic division and the cytoplasm of the cell is divided unequally • The larger daughter cell is called the secondary oocyte and the smaller daughter cell is called the polar body • During second meiotic division, 1 mature ovum is produced and 3 polar bodies Spermatogenesis • Primary spermatocyte goes through first meiotic division and form two daughter cells of equal size • Each daughter cell (secondary spermatocyte) goes through the second meiotic division forming four motile sperm cells of equal size Comparison of Ova and Sperm • Egg cells contain stored food in the form of yolk • Egg cells are larger than sperm • Sperm are motile, egg cells are not (A) Gametes • Sex cells 1. Males – sperm 2. Females – ovum (B) Fertilization • The fusion of the nuclei of one sperm with one ova (egg) to produce a zygote • Sperm (n) + Ovum (n) =2n • Sperm (23) + Ovum (23) = 46 Parthenogenesis •An embryo develops from an unfertilized egg •typically involves the development of eggs into viable offspring from females without fertilization by sperm.. • Parthenogenesis is no longer only for lower invertebrates, such as aphids, mites and nematode worms--it's also been found in fish, bees, birds and lizards. the second polar body -- the daughter cell produced along with the egg in the second stage of meiosis -- acts like a sperm and re-enters the egg. Essentially the egg fertilizes itself! As this polar body contains identical genetic material to the egg, having been produced by normal division of an already haploid cell, the resulting diploid cell has only half the genetic diversity of the female's original cells. Thus fewer bands appear in the DNA fingerprint of the offspring. Parthenogenesis Parthenogenesis but wrong!!!!! Fertilization • Union of a haploid sperm nucleus with a haploid egg nucleus – This results in a diploid zygote with the full number of chromosomes n n 2n Fertilization • Union of a haploid sperm nucleus with a haploid egg nucleus • This results in a diploid zygote with the full number of chromosomes Fertilization and the Stages of Mitosis Two types of Fertilization External Fertilization Internal Fertilization **Parthenogenesis** External Fertilization •Eggs are fertilized outside the body of the female •Large number of eggs are required •This type of fertilization is found in an aquatic environment Ex: fish and frogs External Fertilization External Fertilization External Fertilization External Fertilization What are some differences between External and Internal Fertilization? Provide examples!!! External Fertilization External Fertilization Happy Earth Day External Fertilization External Fertilization External Fertilization Internal Fertilization • Takes place inside the body of the female • Less eggs are required Ex: mammals, birds and reptiles Internal Fertilization