Prenatal Development Lesson 2 PDF
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Nurul Husna
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This document is a lesson on prenatal development, covering topics such as mechanisms of heredity, chromosomes, egg and sperm union, genetic disorders, behavioral genetics, and environmental influences. It includes detailed information on periods of prenatal development.
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Introduction to Human Development LESSON 2 “PRENATAL DEVELOPMENT ” By Nurul Husna Mechanisms of Heredity: Chromosomes 1. Mechanisms of heredity: Human eggs contain 23 chromosomes selected from the mother’s 46 Human sperm contain 23 chromosomes sele...
Introduction to Human Development LESSON 2 “PRENATAL DEVELOPMENT ” By Nurul Husna Mechanisms of Heredity: Chromosomes 1. Mechanisms of heredity: Human eggs contain 23 chromosomes selected from the mother’s 46 Human sperm contain 23 chromosomes selected from the father’s 46 Think of it as mixing two hands of cards (1 from mother and 1 from father), shuffling this mix, and then dealing a hand of cards The dealt hand is your 23 pairs of chromosomes Mechanisms of Heredity: Egg and Sperm United 1. The human egg and sperm unite, resulting in a zygote that contains a complete set of 23 paired chromosomes (46 in total) 2. The 46 chromosomes contain around 25,000 genes 3. Sex chromosomes: 23rd pair determines the child’s sex Mechanisms of Heredity: Sex Chromosomes 1. Sex chromosomes (23rd pair) Males: XY chromosomes X from mother and Y from father Females: XX chromosomes X from mother and X from father Two Types of Genetic Disorders 1. Inherited disorders: genetic problem Example: Huntington’s disease (brain disorder that caused uncontrolled movement, emotional problem and loss of thinking ability) 2. Abnormal chromosomes: extra, missing, or damaged chromosomes that result in abnormal development Examples: Down syndrome Behavioral Genetics: Mechanisms and Methods 1. Dizygotic or fraternal twins: result from two different eggs fertilized by two different sperm No more genetically similar than other siblings 2. Monozygotic or identical twins: result from the union of one egg and one sperm that splits in two soon after conception Are genetically identical PRENATAL DEVELOPMENT Periods of Prenatal Development 1. Prenatal development takes an average of 38 weeks Time measured from date of conception Usually occurs about two weeks after woman’s last menstrual period 2. Divided into three periods: Period of the zygote (weeks 1-2) Period of the embryo (weeks 3-8) Period of the fetus (weeks 9-38) Periods of Prenatal Development: The Zygote 1. Period of the zygote (weeks 1-2): After fertilization, the zygote travels down the fallopian tube and is implanted in the uterine wall Implantation triggers hormonal changes to prevent menstruation Other cells form the placenta, which supports the baby’s development Events of the Period of the Zygote Periods of Prenatal Development: The Embryo 2. Period of the embryo (weeks 3-8): Body structures, internal organs, and the three layers of the embryo develop: Ectoderm (outer layer: becomes hair, skin, nervous system) Mesoderm (middle layer: becomes muscles, bones, circulatory system) Endoderm (inner layer: becomes digestive system and lungs) The amniotic sac fills with fluid; the umbilical cord connects the embryo to the placenta The umbilical cord’s blood vessels join the placenta to the embryo Allow exchange of nutrients, oxygen, vitamins, and waste products between mother and embryo Periods of Prenatal Development: The Fetus 3. Period of the fetus (weeks 9-38): Begins at week 9 and ends at birth Fetus becomes much larger and bodily systems begin to function Final development of many systems essential to human life occurs All regions of the brain grow, particularly the cerebral cortex Week 9: differentiation of the ovaries and testes Week 12: circulatory system begins to function Week 16: movements felt by mother Week 20: eyebrow, eyelashes, scalp hair Skin thickens and is covered by protective greasy substance (vernix) Weeks 22-28: age of viability (can survive) Weeks 22 and beyond: senses active; fetus can remember voices, music, tastes ENVIRONMENTAL INFLUENCES ON PRENATAL DEVELOPMENT The developing fetus is subject to many environmental hazards: Nutrition|Stress|Age of parents Teratogens Environmental hazards General Risk Factors 1. Nutrition A pregnant woman should increase both her caloric and nutrient intake 2. Stress Causes greater harm when experienced early in pregnancy 3. Mother’s age Prenatal development is most likely to proceed normally when women are between 20 and 35 years of age Teratogens: Drugs and Diseases Teratogens: drugs, diseases, or environmental hazards causing abnormal prenatal development Drugs (Examples: alcohol, aspirin, caffeine, and nicotine) Nicotine use increases likelihood of miscarriage, low birth weight, birth defects Diseases (Examples: AIDS, genital herpes, rubella (German measles), syphilis) Some (rubella, syphilis) attack the fetus directly through the placenta; others (AIDS, genital herpes) attack the fetus during birth Medications that may help treat a woman after she becomes ill do not prevent damage to the fetus Teratogens: Environmental Hazards Environmental Hazards (Examples: air pollution, X rays) Exposing the fetus to environmental hazards such as polluted air can affect both physical and mental development of the fetus before birth and of the child after birth Can also lead to the child’s developing health issues such as leukemia after birth