Human Genetics: Meiosis, Development, and Aging (PDF)

Because learning changes everything.® Chapter 03 Meiosis, Development, and Aging Cells HUMAN GENETICS Concepts and Applications Fourteenth Edition Ricki Lewis © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC...

Because learning changes everything.® Chapter 03 Meiosis, Development, and Aging Cells HUMAN GENETICS Concepts and Applications Fourteenth Edition Ricki Lewis © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  Learning Outcomes 1. Describe the structures of the male and female reproductive systems. 2. Explain why meiosis is necessary to reproduce. 3. Summarize the events of meiosis. 4. List the steps in sperm and oocyte formation. 5. Describe early prenatal development. 6. Explain how the embryo differs from the fetus. 7. Define critical period. 8. List some teratogens. 9. Describe common diseases that begin in adulthood. 10. © McGraw Hill Explain how rapid aging syndromes occur. 2  Human Development Genes orchestrate our physiology after conception through adulthood. First cell forms when a sperm from a male and an oocyte from a female join. Loading… Sperm and oocytes are gametes. Each reproductive system has: Paired structures, called gonads Tubular structures that transport these cells Hormones and secretions that control reproduction © McGraw Hill 3  The Male Reproductive System 1 Sperm cells are made in the seminiferous tubules of the testes. Sperms mature, stored in the epididymis. The prostate gland, seminal vesicles, and bulbourethral glands add secretions to form the seminal fluid. Sperm from each ductus deferens exit through the urethra and out the penis. © McGraw Hill 4  The Male Reproductive System 2 Loading… Access the text alternative for slide images. © McGraw Hill 5  The Female Reproductive System 1 Oocytes mature in the ovaries. Each month, an ovary releases an oocyte into one of two uterine tubes. The oocyte is fertilized, it continues to the uterus where it divides and develops. If it is not fertilized, the body expels it, along with the uterine lining via the menstrual flow. Hormones control the cycle of oocyte maturation and the preparation of the uterus to nurture a fertilized ovum. © McGraw Hill 6  The Female Reproductive System 2 Access the text alternative for slide images. © McGraw Hill 7  Meiosis (1) Gametes form from special cells called germ line cells Meiosis is a cell division that halves the chromosome number Homologous pairs have the same genes in the same order but carry different alleles, or variants, of the same gene Gametes are haploid and somatic cells are diploid for each chromosome Absence of meiosis could lead to genetically overloaded cells Mixes up trait combinations Provides genetic diversity which can enable a population to survive an environmental challenge © McGraw Hill 8  Meiosis (2) Consists of two divisions: Meiosis 1 = The reduction division Reduces the number of chromosomes from 46 to 23 Meiosis 2 = The equational division Produces four cells from the two produced in Meiosis 1 Note: As in mitosis, meiosis occurs after an interphase period when DNA is replicated (doubled) Each division contains a prophase, a metaphase, an anaphase, and a telophase © McGraw Hill 9  Mitosis vs Meiosis Table 3.1 Comparison of Mitosis and Meiosis Mitosis Meiosis One division Two divisions Two daughter cells per cycle Four daughter cells per cycle Daughter cells genetically identical Daughter cells genetically different Chromosome number of daughter cells Chromosome number of daughter cells same as that of parent cell (2n) half that of parent cell (1n) Occurs in somatic cells Occurs in germline cells Occurs throughout life cycle In humans, completes after sexual maturity Used for growth, repair, and asexual Used for sexual reproduction, reproduction producing new gene combinations © McGraw Hill 10  Overview of Meiosis Loading… Access the text alternative for slide images. © McGraw Hill 11  Meiosis 1 Access the text alternative for slide images. © McGraw Hill 12  Prophase 1 (1) A spindle forms. Homologs pair-up and undergo crossing over. Chromosomes condense. Synapsed chromosomes separate but remain attached at a few points. © McGraw Hill 13  Prophase 1 (2) Prophase 1 (early) Synapsis and crossing over occurs. Prophase 1 (late) Chromosomes condense, become visible. Spindle forms. Nuclear envelope fragments. Spindle fibers attach to each chromosome. Access the text alternative for slide images. © McGraw Hill 14  Crossing Over Access the text alternative for slide images. © McGraw Hill 15  Metaphase 1 Homologous pairs align along the equator of the cell. Random alignment of chromosomes causes independent assortment of the genes that they carry. Metaphase 1 Paired homologous chromosomes align along equator of cell. Access the text alternative for slide images. © McGraw Hill 16  Independent Assortment Access the text alternative for slide images. © McGraw Hill 17  Anaphase 1 and Telophase 1 (1) Homologs separate in anaphase 1 Unlike in mitosis, the centromeres of each replicated chromosome in meiosis 1 remain together. Homologs move to opposite poles by telophase 1 Note: During a second interphase, chromosomes unfold into thin threads. Proteins are manufactured, but D N A is not replicated a second time. © McGraw Hill 18  Anaphase 1 and Telophase 1 (2) Anaphase 1 Homologous chromosomes separate to opposite poles of cell. Telophase 1 Nuclear envelopes partially assemble around chromosomes. Spindle disappears. Cytokinesis divides cell into two. Access the text alternative for slide images. © McGraw Hill 19  Meiosis 2 Access the text alternative for slide images. © McGraw Hill 20  Prophase 2 and Metaphase 2 Chromosomes are again condensed and visible. Chromosomes align along the equator of the cell. Access the text alternative for slide images. © McGraw Hill 21  Anaphase 2 and Telophase 2 Centromeres divide Newly formed, unreplicated chromosomes, move to opposite poles Nuclear envelope reforms Separate into individual cells Access the text alternative for slide images. © McGraw Hill 22  Results of Meiosis 1 Four nonidentical haploid daughter cells Each carries a new assortment of genes and chromosomes that hold one copy of the genome Access the text alternative for slide images. © McGraw Hill 23  Results of Meiosis 2 Meiosis generates astounding genetic variety. A person can produce 223 (8,388,6082) possible combinations of chromosomes Thus, fertilization of gametes can generate more than 70 trillion (8,388,608 × 8,388,608) genetically unique individuals! Crossing over contributes almost limitless genetic diversity. © McGraw Hill 24  Gametes Mature Meiosis happens in both sexes, but different distributions of cell components create the distinctions between sperm and oocytes. The gametes of the maturing male and female proceed through similar stages as they form, but with vastly different timetables. A male begins manufacturing sperm at puberty and continues throughout life, whereas a female begins meiosis when she is a fetus. Meiosis in the female completes only if a sperm fertilizes an oocyte. © McGraw Hill 25  Spermatogenesis 1 A diploid spermatogonium divides by mitosis to produce a stem cell and another cell that specializes into a mature sperm. In meiosis 1, the primary spermatocyte produces two haploid secondary spermatocytes. In meiosis 2, each secondary spermatocyte produces two equal-sized spermatids. Spermatids then mature into tadpole-shaped spermatozoa. © McGraw Hill 26  Spermatogenesis 2 Access the text alternative for slide images. © McGraw Hill 27  Spermatogenesis 3 Access the text alternative for slide images. © McGraw Hill 28  Sperm Structure Loading… Access the text alternative for slide images. © McGraw Hill 29  Oogenesis 1 Begins with a diploid oogonium In meiosis 1, primary oocyte divides unequally forming a small polar body and a large secondary oocyte In meiosis 2, the secondary oocyte divides to form another polar body and a mature ovum Prof. P.M. Motta/Univ. “La Sapienza”, Rome/Science Source © McGraw Hill 30  Oogenesis 2 Unlike spermatogenesis, oogenesis is a discontinuous process. Oocytes arrest at prophase 1 until puberty. After puberty, meiosis 1 continues in one or several oocytes each month but halts again at metaphase 2. Meiosis is only completed if the ovum is fertilized. A female ovulates about 400 oocytes between puberty and menopause. Most oocytes degrade, because fertilization is so rare. © McGraw Hill 31  Oogenesis 3 Access the text alternative for slide images. © McGraw Hill 32  The Making of Oocytes Access the text alternative for slide images. © McGraw Hill 33  Oogenesis vs Spermatogenesis Access the text alternative for slide images. © McGraw Hill 34  Meiosis and Mutations Gametes of older people more likely to have new mutations Genetic errors in oocytes from older females are typically extra or absent chromosomes. Older males more likely to produce sperm with “paternal age effect” Dominate single-gene diseases These mutations may arise because spermatogonia stem cells divide every 16 days, from puberty on © McGraw Hill 35  Paternal Age Effect Table 3.2 Paternal Age Effect Conditions Disease Phenotype Achondroplasia Short-limbed dwarfism Crouzan Premature fusion of skull bones in infancy, causing wide- syndrome spaced and bulging eyes, beaked nose, short upper lip, small upper jaw, and jutting lower jaw Hutchinson- Thin hair, weak bones, tough and wrinkled skin, stiff joints Gilford progeria and blood vessel linings syndrome Multiple Cancers of thyroid, parathyroid, and adrenal glands endocrine neoplasia 2 Pfeiffer syndrome Premature fusion of skull bones in infancy, short and fused fingers and toes Thanatophoric Severe short-limbed dwarfism dysplasia © McGraw Hill 36  Prenatal Development A prenatal human is considered an embryo for the first 8 weeks, when rudiments of all body parts form. The embryonic period begins when the fertilized ovum divides by mitosis. During the first week, the embryo is in a “preimplantation” stage because it has not yet settled into the uterine lining. Prenatal development after the eighth week is the period when structures grow and specialize. From the start of the 9th week until birth, the prenatal human organism is a fetus. © McGraw Hill 37  Fertilization 1 Union of sperm and oocyte In the female, sperm are capacitated and drawn to the oocyte Acrosomal enzymes aid sperm penetration Chemical and electrical changes in the oocyte surface block entry of more sperm Two genetic packages meet and merge, forming a zygote © McGraw Hill 38  Fertilization 2 Access the text alternative for slide images. © McGraw Hill 39  Cleavage A day after fertilization, the zygote divides by mitosis, beginning a period of frequent cell division called cleavage Resulting early cells are called blastomeres Developing embryo becomes a solid ball of 16+ cells called a morula The ball of cells hollows out, and its center fills wit fluid, creating a blastocyst © McGraw Hill 40  Blastocyst Some of the blastocyst cells form a clump on the inside lining called the inner cell mass. Develops into the embryo. Outermost blastocyst cells form the trophoblast Secrete the hormone human chorionic gonadotropin (h C G) that prevents menstruation. A sign of pregnancy Implantation in the uterus occurs around day 7. Takes about a week © McGraw Hill 41  From Ovulation to Implantation (left): Petit Format/Science Source; (middle): Professors P.M. Motta and J. Van Blerkom/Science Source (right): Petit Format/Science Source/Science Source Access the text alternative for slide images. © McGraw Hill 42  Embryo Formation The primary germ layers form in the second week after fertilization: Ectoderm (outermost layer) Mesoderm (middle layer) Endoderm (innermost layer) This three-layered structure is the gastrula Cells in each layer begin to form specific organs controlled by genes called homeotic Epigenetic effects oversee differentiation as cells in each germ layer develop into organs. © McGraw Hill 43  Supportive Structures Structures that support and protect the embryo include: Chorionic villi Yolk sac Allantois Umbilical cord Amniotic sac By 10 weeks the placenta is fully formed from the chorionic villi It continues to secrete hormones that maintain pregnancy and sends nutrients to the fetus © McGraw Hill 44  The Primordial Embryo Access the text alternative for slide images. © McGraw Hill 45  Stages of Early Prenatal Development Table 3.3 Stages and Events of Early Human Prenatal Development Stage Time Period Principal Events Fertilized 12 to 24 hours Oocyte fertilized; zygote has 23 pairs of ovum following ovulation chromosomes and is genetically distinct Cleavage 30 hours to third day Mitosis increases cell number Morula Third to fourth day Solid ball of cells Blastocyst Fifth day through Hollowed fluid-filled ball forms trophoblast second week (outside) and inner cell mass, which implants and flattens to form embryonic disc Gastrula End of second week Primary germ layers form © McGraw Hill 46  Multiple Births Twins & other multiples arise early in development Dizygotic twins (DZ; Fraternal) Two sperm fertilize two oocytes Same genetic relationship as any two siblings Monozygotic twins (MZ; Identical) Arise from a single fertilized ovum Three types of MZ twins can form, depending upon when the fertilized ovum or very early embryo splits Exposed to slightly different uterine environments © McGraw Hill 47  Types of Identical Twins Access the text alternative for slide images. © McGraw Hill 48  Conjoined Twins Patty Hensel © McGraw Hill 49  The Embryo Develops 1 Organogenesis is the transformation of the simple three germ layers into distinct organs During week 3, a band called the primitive streak appears along the back of the embryo Followed by the connective tissue progenitor cells, notochord, neural tube, heart, central nervous system, arms, legs and other organ rudiments By week 8, all the organs that will be present in the newborn have begun to develop © McGraw Hill 50  The Embryo Develops 2 (a): Petit Format/Science Source; (b): Science History Images/Alamy Stock Photo Access the text alternative for slide images. © McGraw Hill 51  The Fetus Grows 1 During the fetal period, body proportions approach those of a newborn Bone replaces softer cartilage Nerve and muscle functions become coordinated Anatomical differences between the sexes appear at week 6 After the SRY gene is expressed in males. By week 12, sucks thumb, kicks, makes fists and faces, and has the beginnings of teeth By the fourth month, the fetus has hair, eyebrows, lashes, nipples, and nails © McGraw Hill 52  The Fetus Grows 2 Vocal cords will be formed by 18 weeks. But the fetus makes no sound because it doesn’t breathe air. By the end of the second trimester, the woman feels distinct kicks and jabs and may detect fetal hiccup. In the final trimester, fetal brain cells link into networks as organs elaborate and grow, and fat fills out the skin. The digestive and respiratory systems mature last. © McGraw Hill 53  16-Week Fetus Nestle/Petit Format/Science Source © McGraw Hill 54  Birth Defects The time when genetic abnormalities, toxic substances, or viruses can alter a specific structure is called the critical period About two-thirds of birth defects develop during the embryonic period More severe than those that arise during the fetal period Some birth defects are caused by a mutation that acts at a specific point in prenatal development. Phocomelia is a suppression of limb development © McGraw Hill 55  Critical Periods of Development Access the text alternative for slide images. © McGraw Hill 56  Teratogens Are chemical or other agents that cause birth defects Examples: Thalidomide Opioid drugs Alcohol Fetal alcohol syndrome Nutrients Vitamins Viral infections Zika virus; HIV; German measles (rubella) © McGraw Hill 57  Fetal Alcohol Syndrome Access the text alternative for slide images. © McGraw Hill 58  Studying Human Embryos and Fetuses How teratogens cause congenital disorders limited by inability to study prenatal humans Animal studies might not be applicable to humans Prenatal human structures can be studied using: Donated or generated stem cells Experiments on very early human embryos allowed in some nations “Extra” fertilized ova from people using assisted reproductive technology Blastoids generated from iP S C’s Gastruloids © McGraw Hill 59  A Human Gastruloid Mimics a Gastrula Naomi Moris/University of Cambridge Access the text alternative for slide images. © McGraw Hill 60  Maturation and Aging “Aging” means moving through the life cycle Age 30 seems to be a turning point for decline. Some researchers estimate that, after this age, the human body becomes functionally less efficient by about 0.8 percent each year. Many diseases that begin in adulthood, or are associated with aging, have genetic components. These diseases tend to be complex © McGraw Hill 61  Adult-Onset Inherited Disorders Genes may impact health throughout life. Environmental factors can affect how certain genes can create risks that appear later. A powerful environmental influence is malnutrition. Single-gene disorders that strike in childhood tend to be recessive. Dominantly inherited conditions affect health in early to middle adulthood. © McGraw Hill 62  Syndromes That Resemble Accelerated Aging Genes control aging both passively (as structures break down) and actively (by initiating new activities). Progeroid syndromes are single-gene disorders that speed aging-associated changes. The most severe progeroid syndromes are the progerias, which shorten life expectancy. Most accelerated aging conditions are caused by the inability of cells to adequately repair D N A © McGraw Hill 63  Premature Aging Syndromes Table 3.4 Premature Aging Syndromes Average Life Disease Incidence Expectancy Ataxia telangiectasia 1 ⁄ 60,000 19–25 Cockayne Syndrome 1 ⁄ 100,000 20 Hutchinson-Gilford