DEP 3103 EXAM 2 STUDY GUIDE Chapter 3 3 1 Genetic foundations of development each of us is made of up trillions of units called cells nucleus Chromosomes which store and transmit genetic info human chromosomes come in 23 matching pairs except for the XY pair in males one is inherited from mom and the other from dad Genotype the complex blend of genetic info that determines our species and influences all our unique characteristics 23 pairs of chromosomes Phenotype directly observable characteristics PHysical PHenotype Can also be affected by environmental influences Alleles forms of the same gene on a pair of chromosomes Two forms of each gene occur at the same place on the chromosomes one inherited from the mother and one from the father Each form of a gene is called an allele If the alleles from both parents are alike the child is homozygous and will display the inherited trait If the alleles differ then the child is heterozygous and relationships between the alleles determine the phenotype Genes a segment of DNA along the length of the chromosome Mitosis a unique feature of DNA is that it can duplicate itself a single cell complex human being composed of many cells EACH CELL CONTAINS THE IDENTICAL GENETIC INFO Meiosis gametes sex cells sperm and egg ova are formed through cell division halves the number of chromosomes normalls present in body cells When sperm and ovum unite at fertilization zygote 46 chromosomes ALLOWS FOR GENETIC VARIABILITY Crossing over chromosomes next to each other break at one or more points along their length and exchange segments so that genes from one are replaced by genes from another new heredity combinations 3 2 The sex of a new organism is determined by whether an X bearing or a Y bearing sperm fertilizes the ovum Chromosomes 1 22 autosomes and the 23rd pair consists of sex chromosomes 3 3 Sometimes a zygote that has started to duplicate separates into two clusters of cells that develop into two individuals These are identical or monozygotic twins because they have the same genetic makeup 1 in 330 births Some environmental causes temp change varying oxygen levels late fertilization and some genetic runs in families Fraternal or dizygotic twins the most common type of multiple birth result from the release and fertilization of two ova Genetically no more alike than any other brother or sister 1 in 60 births Older maternal age fertility drugs in vitro fertilization more fraternal twinning Genetic link 3 4 Genetic Inheritance Dominant recessive inheritance Only one allele affects the child s characteristics dominant the second allele with no affect recessive Still heterozygous individuals with just one recessive allele Db can pass that trait to their children they are called carriers Incomplete dominance a pattern of inheritance in which both alleles are expressed in the phenotype resulting in a combined trait or one that is intermediate between the two Sickle cell trait X Linked Inheritance harmful allele is carried on the X chromosome males are more likely to be affected because their sex chromosomes do not match color blindness Genomic Imprinting chemically marked so that one pair member either the mother s or the father s is activated regardless of its makeup Mutation a sudden but permanent change in a segment of DNA may affect one or two genes or many some mutations may occur spontaneously and other by hazardous environmental agents Polygenic Inheritance many genes determine the characteristic in question height weight intelligence personality Chromosomal Abnormalities mistakes occurring during meiosis when the sperm and ovum are formed a chromosome pair does not separate properly or a part of a chromosome breaks off physical and mental symptoms Down syndrome 1 in 770 live births results from a failure of the 21st pair of chromosomes to separate during meiosis so the new individual inherits 3 of these chromosomes instead of the normal 2 a k a trisomy 21 mental retardation memory and speech problems slow motor development increased chances with maternal age 35 3 5 Genetic counseling a communication process designed to help couples assess their chances of giving birth to a baby with a hereditary disorder and choose the best course of action in view of risks and family goals those who have difficulty bearing children women who delay childbearing past 35 years those with a family history of inherited disorders the genetic counselor helps people consider appropriate options taking a chance and conceiving choosing from a variety of reproductive technologies or adoption Prenatal Diagnostic Methods medical procedures that permit detection of developmental problems before birth women of advanced maternal age amniocentesis needle abdomen test for problems ultrasound sound waves to uterus picture physical stuff maternal blood analysis test mom s blood for things 3 6 Conception once every 28 days an ovum bursts from one of her ovaries spot where it was released corpus luteum secretes hormones that prep the uterus to receive a fertilized ovum Not preggo The corpus luteum shrinks and the lining is discarded with menstruation sperm swim upstream in the female reproductive tract through the cervix opening of uterus fallopian tube where fertilization takes place Most conceptions result from intercourse during ovulation 3 day period Periods of prenatal development begins with fertilization and ends with birth 1 Zygote lasts about 2 weeks from fertilization until the tiny mass of cells drifts down the fallopian tube and attaches itself to the wall of the uterus Implantation 7th to 9th days the blastocyst burrows deep into the uterine lining The placenta and umbilical cord end of 2nd week placenta permits food and oxygen to reach developing organism and permits waste products to be carried away umbilical cord delivers blood to the developing organism and removes waste BY THE END OF THE PERIOD OF THE ZYGOTE THE DEVELOPING ORGANISM HAS FOUND FOOD AND SHELTER IN THE UTERUS THESE BEGINNINGS HAPPEN BEFORE MOST MOTHERS KNOW THAT THEY ARE PREGGO 2 Embryo 6 weeks lasts from implantation through the eighth week of pregnancy during these brief 6 weeks the most rapid prenatal changes take place groundwork for body structures and internal organs Last half of the first month embryonic disk ectoderm nervous system and skin mesoderm muscles skeleton circulatory system and other internal organs endoderm digestive system lungs urinary tract and glands Second month rapid growth in
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