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Chapter 4: Pregnancy - Genetics and Heredity What person in your family do you most closely resemble, both physically, and in terms of your personality? What do the two of you have in common? Conception • Zygote: the cell that forms when a sperm fertilizes an egg • Monozygote: Identical Twins (1 egg + 1 sperm) Fertilized ovum splits into two identical cells – Always the same gender • Dizygote: Fraternal Twins (2 different eggs + different sperm) -- The twins will look different, may be the same gender, may not be. • Multiple Birth: More than two babies – May be identical, fraternal, or both • Conjoined Twins: Ovum splits apart, but the separation is not complete. Babies are joined at some part(s) of their bodies Genetics and Heredity • Genetic factors: The traits passed through the genes – Traits Include: Eye color, hair color, height, body build, blood types • Heredity: Characteristics that a child receives from both parents Chromosomes and Genes Chromosomes-threadlike structures that carry genes in living cells. • Half (23) come from the mother and half (23)come from the father • Each chromosome contains about 20,000 genes A child’s traits are passed through the parents germ cells (ovum and sperm) only half will be present in the child’s traits. GENES • Dominate Gene: More powerful, Trait actually seen in a person • Recessive Gene: Weaker Gene. It hides in the background. A recessive gene can only determine a characteristic when two recessive genes are present. • Carrier: Has a recessive gene that is not present. • Sex-Linked: For instance, a mother passes the recessive X gene to her son. – A color-blind male receives this trait from his mother, but she is usually not color-blind herself. Eye Color Possibilities for their Children: Mother: Brown Eyes (Bb) Father: Blue Eyes (bb) Bb: Brown Eyes (B is the Dominate Trait) bb: Blue Eyes (b is the Recessive Trait) Baby Boy or Baby Girl ??? • Conception is the union of the Egg and Sperm • Female Sex Cells (XX) Egg/Ovum • Male Sex Cells (XY) Sperm Mom XX Dad XY Baby Girl XX Mom XX Dad XY Baby Boy XY • Gender is determined by the FATHER Factors that Contribute to Multiple Births • • • • Family History Naturally Increased Hormones (More than 1 egg released) Fertility Drugs Maternal age: Mother’s between the ages of 35 and 40 rates double Likelihood of Multiple Pregnancies in the U.S. • • • • • Twins: Caucasians 1 in 83 Triplets: 1 in every 7,000births Quadruplets: 1 in every 572,000 births Quintuplets: 1 in every 47.5 million Sextuplets: 1 in every 4 billion Stages in Prenatal Development • Prenatal Development-development that takes places between conception and birth – Three stages: • Germinal stage-conception through the first two weeks of the pregnancy – Cell division occurs – Egg becomes embedded in the uterine wall – Amnion (fluid-filled sac)-surrounds the baby to protect it – Placenta(organ filled with blood)-nourishes the baby and removes wastes – Umbilical cord-connects the child to the placenta Embryonic Stage • • • • • • Most critical stage Lasts six weeks (2 weeks through 8 weeks) Baby is called an embryo. Arms, legs, fingers, toes, and face develop Heart, brain, and lungs also develop No bones yet, but cartilage provides the body structure. Fetal Stage • • • • • • 9 weeks through 40 weeks Baby is called a fetus Able to hear the baby’s heartbeat at a doctor’s visit Between months 4-5 the mother will feel the baby move(quickening) The baby can turn, swallow, and suck its thumb. Age of viability- 7 months or 28 weeks, age at which most babies could survive if they were born. Fetal Development Month by Month First Month • By the end of the first month, the embryo is about 1/10 of an inch long. The heart, which is no larger than a poppy seed, has begun beating. • Mother-Missed period First Month (four weeks) Two Months • The embryo is about 1 inch long and has distinct, slightly webbed fingers. Veins are clearly visible. The heart has divided into right and left chambers. • Mother-breasts swell, fatigue, morning sickness Two Months Three Months • By now the fetus is 2 1/2 to 3 inches long and is fully formed. He/She has begun swallowing and kicking. All organs and muscles have formed and are beginning to function. • Mother-breasts ache, abdomen grows, 2-4lbs weight gain. Three Months (12 weeks) Four Months • Your baby is covered with a layer of thick, downy hair called lanugo. His heartbeat can be heard clearly. This is when you may feel your baby's first kick. • Mother-Size change, increased appetite. 4 months Five Months • A protective coating called vernix caseosa begins to form on baby's skin. By the end of this month, your baby will be nearly 8 inches long and weigh almost a pound. • Mother-obvious large abdomen, 10-12 lbs. weight gain. 5 months (20 weeks) Six Months • Eyebrows and eyelids are visible. Your baby's lungs are filled with amniotic fluid, and he has started breathing motions. If you talk or sing, he can hear you. • Mother-Fetal movement is strong. Fetus kicks and thumps are felt.10-12 pounds weight gain. 6 Months Seven Months • By the end of the seventh month, your baby weighs about 3 1/2 pounds and is about 12 inches long. His body is well-formed. Fingernails cover his fingertips • Mother-Posture is affected by increased weight and size. 7 months (28 Weeks) Eight Months • Your baby is gaining about half a pound per week, and layers of fat are piling on. He has probably turned headdown in preparation for birth. He weighs between 4 and 6 pounds. • Mother-Backaches, leg cramps, shortness or breath, fatigue. Fetal kicks are felt. Weight gain of 18-20 pounds. Nine Months • Your baby is a hefty 6 to 9 pounds and measures between 19 and 22 inches. As he becomes more crowded, you may feel him move around less. Mother-“Lightening” – the fetus drops into the pelvis.Easier to breathe.Usual discomforts of late pregnancy.Weight gain of 24-30 pounds.Uterus is the size of a small watermelon.May have false labor. Birth!