Meiosis PPT PDF

Sexual Reproduction Somatic cells = all cells other than sex cells ○ Mitosis: division of a cell into two genetically identical...

Sexual Reproduction Somatic cells = all cells other than sex cells ○ Mitosis: division of a cell into two genetically identical daughter cells ○ Diploid (2n): cells with two versions of each set of chromosomes Sex cells = gametes = eggs and sperm Meiosis: formation of reproductive cells with half the Meiosis ○ number of chromosomes ○ Haploid (n): cells with a single set of each chromosome Chapter 6 ○ Zygote (2n): sperm and egg fused together Chromosomes Haploid and Diploid Normal human karyotype Human have 23 pairs of chromosomes ○ 22 Autosomes Non-sex chromosomes ○ 1 pair sex chromosomes XX = Female XY = Male  DNA Replication DNA Replication Homologous = chromosomes that are the same in function and size ○ Diploid organisms have a pair of homologous chromosomes Tetrad = Pair of homologous chromosomes after replication ○ Occurs during metaphase I in Meiosis I ○ Sister chromatids = 1 chromosome Chromosome Before and After Replication Summary of Meiosis Two processes of cell division Meiosis I: homologous chromosomes separate Meiosis II: sister chromatids separate  Mitosis Meiosis I 1. Diploid cells with two pairs of Somatic Gamete cell precursor homologous chromosomes (one pair from father and one pair from mother) 2. Chromosomes duplicate to form two sister chromatids 3. Chromosomes line up on metaphase plate, one sister 3. Homologous chromosomes line up chromatid on each side of the plate on opposite sides of metaphase plate 4. Sister chromatids separate 4. Homologous pairs of chromosomes separate, sister chromatids still intact Meiosis II 5. Chromosomes line up on metaphase plate, one sister chromatid on each side of the plate 6. Sister chromatids separate 7. Cells divide again, 4 haploid cells Meiosis vs. Mitosis Steps of Meiosis Mitosis Meiosis Produces 2 identical daughter Produces 4 non-identical daughter cells cells Daughter cells 2n (diploid) Daughter cells n (haploid) One cell division Two cell divisions (Meiosis I and Occurs in somatic cells for II) growth/development, and to Occurs in production of egg and replace damaged or dead cells sperm cells (gametes) Does not increase genetic Increases genetic diversity diversity  Sources of Genetic Variation Crossing over = process in which homologous chromosomes exchange reciprocal portions of themselves during Prophase I Chromosomes form. Nuclear membrane breaks down. Centrosomes duplicate and move poleward. Sources of Genetic Variation Sources of Genetic Variation Independent assortment = random distribution of homologous chromosome pairs during metaphase I of meiosis I  Location of Genes within Chromosomes Independent Assortment During meiosis I, tetrads can line up two different ways before the Gene = section of DNA that chromosomes separate. codes for a specific trait Ex: Hair color Allele = different versions of a gene Ex. Black hair or red hair Check Your Understanding 1. True or False: Sex cells are diploid 2. True or False: Humans have a total of 46 chromosomes 3. True or False: The purpose of meiosis is to create genetically identical daughter cells  Check Your Understanding Check Your Understanding 4. Crossing over occurs during which of the following phases of 5. Sister chromatids pull apart during which of the following meiosis? phases? a. Metaphase II a. Anaphase of Mitosis b. Prophase I b. Metaphase of Meiosis I c. Anaphase I c. Anaphase of Meiosis II d. Metaphase I d. Metaphase of Mitosis I e. Prophase II e. More than one of the above Genetic Diversity Genetic Diversity Crossing over and independent assortment are the reason we look a little like each of our parents “To them, we all look the same” – Dr. Horn Meiosis: Creates genetic diversity through the formation of gametes. Involves two rounds of division, resulting in four unique daughter cells with half the chromosome number. Essential for sexual reproduction, contributing to variation in offspring. Mitosis: Produces two identical daughter cells, maintaining genetic consistency. Involves one round of division, essential for growth, repair, and asexual reproduction. Significance of Variation: Key Point Variation is present in all living organisms and is the foundation of evolution. It arises from the differential survival and reproduction of individuals with specific traits, driving natural selection.  Boys and Girls Biological Boys and Girls Individuals have two copies of Sperm carrying an X sex chromosomes in every cell chromosome results in a female Females = Two X chromosomes offspring Males = One X and one Y chromosome Sperm with a Y chromosome produces a male. Males determine the sex of the child Each egg gets one Half the sperm cells get an X chromosome X chromosome, and half get a Y chromosome Sex of the Child Spermatogenesis Half of the sperm produced Sperm cells develop in have X chromosome and the seminiferous half have Y chromosome tubules of the testes. Mitosis ○ 50% chance of having either a boy or a girl They mature in the Meiosis 1 epididymis. Meiosis 11 During ejaculation, sperm are transported Maturation through the vas deferens. Image modified from What is Life? A Guide to Biology, Third Edition © 2015 W. H. Freeman and Company  Male Reproductive Organs Birth Control- Men Condoms are a popular and effective method of birth control for men. Barrier Method: ○ Prevents sperm from reaching the egg. Protection Against STIs ○ Reduces the risk of sexually transmitted infections. Easy to Use ○ Widely available and can be used at any time. No Hormonal Side Effects: ○ Unlike hormonal methods, condoms do not affect hormone levels. Variety: ○ Available in different materials, sizes, and textures for comfort and pleasure. Image modified from What is Life? A Guide to Biology, Third Edition Image modified from What is Life? A Guide to Biology, Third Edition © 2015 W. H. Freeman and Company © 2015 W. H. Freeman and Company Female Reproductive Organs Oogenesis and the Release of an Egg 1. Oogonia multiply during fetal development. 2. Each oogonium begins meiosis but stops at Prophase I, becoming a primary oocyte in a follicle. 3. After puberty, FSH stimulates primary oocytes to finish meiosis I, producing a secondary oocyte and a polar body that disintegrates. 4. During ovulation, the follicle releases the secondary oocyte, which hasn’t completed meiosis II. If fertilized, it finishes meiosis II, creating a polar body and an egg with most of the cytoplasm. Image modified from What is Life? A Guide to Biology, Third Edition Image modified from What is Life? A Guide to Biology, Third Edition © 2015 W. H. Freeman and Company © 2015 W. H. Freeman and Company  Female Reproductive Cycle Female Reproductive Cycle The ovarian cycle (egg development) and Follicle-Stimulating Hormone (FSH): menstrual cycle (endometrium Stimulates primary oocytes to complete meiosis. development and release) are regulated by female hormone levels. Progesterone: Thickens the uterine lining for potential implantation; produced by the corpus luteum after the secondary oocyte is released. Estrogen: The main female hormone; released from developing follicles and triggers the release of luteinizing hormone (LH). Luteinizing Hormone (LH): Triggers ovulation, releasing the secondary oocyte from Ovulation the follicle. Ovulation https://www.youtube.com/watch?v=lCYqLtmo670 Birth Control- Woman Making Twins Birth control pills are synthetic hormones Identical twins (progesterone and estrogen). 1 egg and sperm Prevent ovulation by maintaining consistent hormone levels. Egg divides after fertilization Without a peak in estrogen, the ovary Babies develop in same doesn't release an egg placenta ○ (no egg = no fertilization). Pill thickens cervical mucus to block sperm. Uterine lining unreceptive to implantation Fraternal twins of a fertilized egg. 2 eggs and 2 sperm ○ Hormonal Imbalance: May affect mood and libido. Babies develop in separate placentas  Check Your Understanding Check Your Understanding True or False: Sperm is produced in the prostate gland Which of the following are not involved in the production of semen? a. Cardiac cells True or False: Identical twins are the result of a single egg fertilized by two sperm cells b. Prostate gland c. Seminal vesicle d. Epidermal True or False: All of a biological female's eggs are produced before she is born e. More than one of the above Check Your Understanding Which of the following best describes the function of luteinizing hormone (LH) during the female reproductive cycle? a. Causes the thickening of the endometrium b. Stimulates the primary oocyte to complete meiosis I c. Stimulates the release of the secondary oocyte from the follicle. d. Causes the endometrium to break down during menstruation Homologous chromosomes e. None of the above are correct concerning luteinizing hormone  PROPHASE OF MEIOSIS I END OF INTERPHASE Nuclear membrane breaks apart Centrosomes move poleward, making spindle fibers DNA condenses into chromosomes. Homologous chromosomes perform crossing over. TELOPHASE AND CYTOKINESIS METAPHASE OF MEIOSIS I ANAPHASE OF MEIOSIS I OF MEIOSIS I PROPHASE OF MEIOSIS II Homologous chromosomes (tetrads) randomly align on metaphase plate Homologous chromosomes pulled apart by Homologous chromosomes separate and the spindle fibers Centrosomes duplicate and the nuclear nuclear membrane reforms. The cytoplasm membrane breaks down. separates forming two haploid daughter cells  TELOPHASE AND CYTOKINESIS METAPHASE OF MEIOSIS II ANAPHASE OF MEIOSIS II OF MEIOSIS II Sister chromatids separate and the nuclear membrane reforms. The cytoplasm separates forming four genetically unique haploid daughter cells Chromosomes line up on the metaphase plate Sister chromatids are pulled apart by the spindle fibers