Prenatal Development PDF

Heredity : Limitation & Potential Genetic and Environmental Influences Transmission of Traits Conception & Genetics  Process of Conception A woman produces one ovum (egg cell) per month from one of her two ovaries, roughly midway between menstrual periods. If the ovum is not fe...

Heredity : Limitation & Potential Genetic and Environmental Influences Transmission of Traits Conception & Genetics  Process of Conception A woman produces one ovum (egg cell) per month from one of her two ovaries, roughly midway between menstrual periods. If the ovum is not fertilized, it travels from the ovary down the fallopian tube toward the uterus where it gradually disintegrates and is expelled as part of the menstrual fluid. If the couple had intercourse during the crucial days when the ovum is the fallopian tube, the sperm ejaculated may travel the distance through woman’s vagina, cervix, uterus and fallopian tube and can penetrate the wall of the ovum.  Chromosomes, DNA, and Genes Every cell in the human body contains 23 pairs of chromosomes, or strings of genetic material. Sperm and ovum, collectively called 03 gametes, contain 23 single (unpaired) chromosomes. At conception, chromosomes in the ovum and the sperm combine to form 23 pairs in an entirely new cell called a zygote. Chromosomes, DNA, and Genes The nucleus of each human cell contains chromosomes, which are threadlike structures made up of deoxyribonucleic acid, or DNA. DNA is a complex molecule that has a double helix shape, like a spiral staircase, and contains genetic information. Genes, the units of hereditary information, are short segments of DNA. Mitosis All cells in your body, except the sperm and egg, have 46 chromosomes arranged in 23 pairs. These cells reproduce by a process called mitosis. During mitosis, the cell’s nucleus—including the chromosomes—duplicates itself and the cell divides. Two new cells are formed, each containing the same DNA as the original cell, arranged in the same 23 pairs of chromosomes. Meiosis A different type of cell division— meiosis — forms eggs and sperm (or gametes ). During meiosis, a cell of the testes (in men) or ovaries (in women) duplicates its chromosomes but then divides twice , thus forming four cells, each of which has only half of the genetic material of the parent cell. By the end of meiosis, each egg or sperm has 23 unpaired chromosomes.  During fertilization , an egg and a sperm Fertilization fuse to create a single cell, called a zygote. In the zygote, the 23 unpaired chromosomes from the egg and the 23 unpaired chromosomes from the sperm combine to form one set of 23 paired chromosomes. One chromosome of each pair from the mother’s egg and the other from the father’s sperm.  Determination of Sex Twenty-two pairs of chromosomes, called autosomes, contain most of the genetic information for the new individual. 02 The twenty-third pair, the sex chromosomes, determines the sex. The X chromosome, is one of the largest chromosomes in the body and carries a large number of genes. The Y chromosome, is quite small and contains only a few genes.  Determination of Sex Zygotes containing two X chromosomes develop into females (XX), and those containing one X and one Y chromosome develop into males (XY). Half of the man’s sperm contains X chromosomes and the other half contains Y chromosomes. The sex of the individual is determined by the chromosomes in the sperm. Multiple Births VENUS MARS JUPITER SATURN NEPTUNE Two-thirds of twins are fraternal twins, or twins that come from two sets of ova and sperm. Such twins, also called dizygotic twins (meaning that they originate from two zygotes). One-third of twins are identical twins (monozygotic, or arising from one zygote). Identical twins result when a single zygote, for unknown reasons, separates into two parts, each of which develops into a separate individual. Because identical twins develop from the same zygote, they have identical genes.  Genotype and Phenotype GENOTYPE PHENOTYPE It is the unique 04 It is the genetic buleprint 03 individual’s whole of each individual. 02 set of actual characteristics. Dominant and Recessive Genes The simplest genetic rule is the dominant–recessive pattern, in which a single dominant gene strongly influences phenotype. Dominant and Recessive Genes People whose chromosomes carry either two dominant or two recessive genes are referred to as homozygous. Those with one dominant and one recessive gene are said to be heterozygous. Polygenic Inheritance It is a pattern of inheritance in which many genes influence a trait. For example, geneticists believe that children get several genes for skin color from each parent (Barsh, 2003). Multifactorial Inheritance Inheritance affected by both genes and the environment. Genetic and Chromosomal Disorders Autosomal disorders are caused by genes located on the autosomes (chromosomes other than sex chromosomes). Most disorders caused by recessive genes are diagnosed in infancy or early childhood. The genes that cause sex-linked disorders are found on the X chromosome.  Chromosomal Errors Chromosomal Error or Chromosomal Anomaly/ Abberation This refers to a variety of problems that occur when a child has too many or too few chromosomes. These errors involves autosomes or sex chromosomes. Some of these abnormalities come from whole chromosomes that do not separate properly during meiosis. Chromosomal Errors Pregnancy and Prenatal Development  Preganancy and Prenatal Development Pregnancy is a physical condition in which a woman’s body is nurturing a developing embryo or fetus. Prenatal development, or gestation, is the process that transforms a zygote into a newborn. Pregnancy is customarily divided into trimesters—three periods of 3 months each. First Trimester Pregnancy begins when the zygote implants itself in the lining of the woman’s uterus (also called the womb). The zygote then sends out chemical messages that cause the woman’s menstrual periods to stop. The cervix thickens and secretes mucus that serves as a barrier to protect the developing embryo from harmful organisms that might enter the womb through the vagina. First Trimester Prenatal care during the first trimester is critical to prevent birth defects, because all of the baby’s organs form during the first 8 weeks. Second Trimester During the second trimester of pregnancy, from the end of week 12 through week 24, morning sickness usually disappears, resulting in increases in appetite. The pregnant woman gains weight, and the uterus expands to accommodate a fetus that is growing rapidly. Consequently, the woman begins to “show” sometime during the second trimester. Third Trimester At 25 weeks, the pregnant woman enters her third trimester. Weight gain and abdominal enlargement are the main experiences of this period. The woman’s breasts may begin to secrete a substance called colostrum in preparation for nursing. 2 Developmental Patterns Proximodistal Pattern Development happens in an orderly way from the center of the body outward to the extremities. Cephalocaudal Pattern Development proceeds from the head down. 3 Stages of Prenatal Development Germinal Period 90% The germinal period is the period of prenatal development that takes place in the first 70% two weeks after conception. It includes the creation of the fertilized egg (the zygote ), cell division, and the attachment of the multicellular organism to the uterine wall. Cell division happens rapidly, and by the 4th day, the zygote contains dozens of cells. On day 5, the cells become a hollow, fluid-filled ball called a blastocyst. On day 6 or 7, the blastocyst comes into contact with the uterine wall, and by the 12th day, it is completely buried in the uterine tissue, a process called implantation. 3 Stages of Prenatal Development Embryonic Period 90% The embryonic period is the period of prenatal development that occurs from two to 70% eight weeks after conception. During the embryonic period, the rate of cell differentiation intensifies, support systems for cells form, and organs appear. Organogenesis is the technical term for organ development. 3 Stages of Prenatal Development Embryonic Period 90% The cells of the nervous system, the neurons, form a structure called the neural tube, from which the brain and spinal cord will develop. During the week 3, a primitive heart and forerunners of kidney also develop along 70% with three sacs that will become the digestive system. In week 4, Spots that will become the eyes appear on the embryo’s head, and its heart begins to beat. The backbone and ribs become visible as bone and muscle cells move into place. The face starts to take shape, and the endocrine system begins to develop. By week 5, Its arms and legs are developing rapidly. Five fingers are visible on its hands. Its eyes have corneas and lenses, and its lungs are beginning to develop.  3 Stages of Prenatal Development Embryonic Period In week 6, the embryo’s brain begins to produce 90% patterns of electrical activity and it moves in response to stimuli. During the week 7, They have visible skeletons and fully developed limbs. The bones are beginning to harden and the muscles are maturing. The ears are completely developed. 70% During the last week of the embryonic stage, week 8, the liver and spleen begin to function. These organs allow the embryo to make and filter its own blood cells. Its heart is well developed and efficiently pumps blood to every part of the body. 3 Stages of Prenatal Development Fetal Period 90% The final phase is the fetal stage, which begins at the end of week 8 and continues until birth. The fetus grows from a weight of about 1/4 ounce and a length of 1 inch to a baby weighing about 7 pounds and having a length of about 20 inches moving its head. 70% It has become active, moving its arms and legs, opening and closing its mouth, and The face, forehead, eyelids, nose, and chin are distinguishable, as are the upper arms, lower arms, hands, and lower limbs. In most cases, the genitals can be identified as male or female. By the end of week 22, babies have developed viability or the ability to live outside the womb.  Problems in Prenatal Development Teratogen A teratogen is any agent that can potentially cause a birth defect or negatively alter cognitive and behavioral outcomes. Teratogens include drugs, incompatible blood types, environmental pollutants, infectious diseases, nutritional deficiencies maternal stress, advanced maternal and paternal age, and environmental pollutants. The dose, genetic susceptibility, and time of exposure to a particular teratogen influence both the severity of the damage to an embryo or fetus and the type of defect: 1) Dose —the dose effect is rather obvious—the greater the dose of an agent, such as a drug, the greater the effect. 2) Genetic susceptibility —the type or severity of abnormalities caused by a teratogen is linked to the genotype of the pregnant woman and the genotype of the embryo or fetus. 3) Time of exposure — For example, teratogens do more damage when they occur at some points in development than at others.  Problems in Prenatal Development Prescription and Nonprescription Drugs Prescription drugs that can function as teratogens include antibiotics, such as streptomycin and tetracycline; some antidepressants; certain hormones, such as progestin and synthetic estrogen. Nonprescription drugs that can be harmful include diet pills and aspirin. Psychoactive Drugs Psychoactive drugs are drugs that act on the nervous system to alter states of consciousness, modify perceptions, and change moods. Examples include caffeine, alcohol, and nicotine, as well as illegal drugs such as cocaine, methamphetamine, marijuana, and heroin.  Problems in Prenatal Development Incompatible Blood Types Incompatibility between the mother’s and the father’s blood types poses another risk to prenatal development. Incompatible blood types may result in any number of problems, including miscarriage or stillbirth, anemia, jaundice, heart defects, brain damage, or death soon after birth. Maternal Diseases Maternal diseases and infections can produce defects in offspring by crossing the placental barrier, or they can cause damage during birth. For example, rubella, or German measles, causes a short-lived mild reaction in adults but may be deadly to a fetus. Most infants exposed to rubella in the first trimester show some degree of hearing impairment, visual impairment, and/or heart deformity.  Problems in Prenatal Development Environmental Hazards A number of substances found in the environment may have detrimental effects on prenatal development. X-ray radiation can affect the developing embryo or fetus, especially in the first several weeks after conception. Maternal Emotions Some psychologists have suggested that maternal emotions can affect prenatal development. They argue that stressful psychological states such as anxiety and depression lead to changes in body chemistry. Fetal Assessment and Treatment Ultrasonography has become a routine part of prenatal care across the globe. Ultrasound images are produced by the echoes that result from bouncing sound waves off of internal tissues. Chorionic Villus Sampling (CVS) and amniocentesis, can be used to identify chromosomal errors and many genetic disorders prior to birth. Fetoscopy involves insertion of a tiny camera into the womb to directly observe fetal development. Fetoscopy makes it possible for doctors to correct some kinds of defects surgically  THANKS References: Boyd, Denise R, Helen L. Bee, and Paul A. Johnson. Lifespan Development. Toronto: Pearson Canada, 2011. Santrock, J. W. (2016). CREDITS: This presentation template was Essentials of life-span created by Slidesgo, including icons by Flaticon, and infographics & images by Freepik development. Fourth edition. New York, NY: Please keep this slide for attribution McGraw-Hill Education.