Unit Two Chapter 3 3 1 What are the genetic foundations of development What is the difference between genotype and phenotype What are alleles What are chromosomes What are genes and how are they transmitted from one generation to the next through mitosis and meiosis The genetic foundations of development include phenotype and genotype Phenotypes are physical characteristics which are directly observable and depend on environmental influences i e hair color Genotype is the genetic information i e DNA and genes Alleles are the forms of the same gene on a pair of chromosomes i e gene for dark hair gene for light hair Dark hair gene is dominant light is recessive Chromosomes are rod like structures that store and transmit genetic information There are 46 chromosomes total and 23 pairs The 23rd chromosome determines sex XY male XX female Chromosomes are ordered shortest to longest Genes represent segments of DNA 43 chromosomes 23 pairs In mitosis DNA breaks apart and duplicates itself This allows a fertilized egg zygote to go from one cell to trillions In meiosis sex cells produce which leads to gamete formation This then allows our species to survive over history and adapt to our environment Meiosis is the only time when chromosomes aren t paired together 3 2 How is sex determined Sex is determined by the 23rd pair of chromosomes XY Male XX Female 3 3 Name the two types of twins and describe how each one is created Fraternal dizygotic Twins These types of twins are created when there is a release of two zygotes or fertilized ova no more alike than ordinary siblings that are 5 years apart Identical Monozygotic Twins These types of twins are created when one zygote divides into two clusters of cells that eventually develop into two individuals Called identical because they have the same genetic makeup 3 4 Describe patterns of genetic inheritance What are examples of each type What are some implications of various types of genetic inheritance What are chromosomal abnormalities What are examples of chromosomal abnormalities You only need to know the ones covered in class Patterns of inheritance include Alleles which are the forms of the same gene on a pair of chromosomes Ex Dark hair gene is dominate light hair is recessive Dominant recessive inheritance which can be homozygous NN pp which have two of the same allele or heterozygous Np which have one of each allele X linked inheritance which is similar to dominant recessive but becomes a problem when there s a problem on X chromosome Since men only have one X chromosome their gene is XY they are much more likely to inherent recessive disorders carried on X chromosome PKU and sickle cell anemia Polygenic Inheritance is the characteristics inherited on a continuum such as height weight intelligence and personality Determined by many genes Chromosomal abnormalities are a major cause of serious developmental problems such as down syndrome results from problems with 21st chromosome Most chromosomal defects result from mistakes occurring during meiosis when the ovum and sperm are formed A chromosome pair does not separate properly or part of a chromosome breaks off Creates problems such as mental retardation memory and speech problems slow motor development risk greatly increases with maternal age rises sharply after 35 3 5 What are genetic counseling and prenatal diagnostic methods Who might be the best candidates for genetic counseling and prenatal diagnostic methods How do they help prospective parents determine the best course of action Genetic counseling is a communication process designed to help couples asses their chances of giving birth to a baby with a hereditary disorder and chose the best course of action in view of risks and family goals Individuals likely to choose genetic counseling include those who have had difficulty bearing children women who delay childbearing past age 35 those with a family history of inherited disorders or diseases Prenatal Diagnostic methods are methods of detecting problems on baby before birth These may come in using amniocentrisis extracts fluid from uterus to see if there s any Ultrasounds and maternal blood analysis which is the sampling of the mother s blood problems does have a risk of miscarriage also the lowest risk of the other methods Genetic counselors help people consider all appropriate options which can include taking a chance and conceiving choosing from among a variety of reproductive technologies or adopting a child 3 6 Describe conception and the three periods of prenatal development What are the milestones reached in each period During which prenatal period does the most rapid change take place During conception which lasts approximately 38 weeks it is divided into three periods 1 the period of the zygote 2 the period of the embryo 3 the period of the fetus In the period of the zygote it is 2 weeks long fertilization mitosis implantation inning of the uterus lining and the start of placenta begin Ovary releases egg drops into fallopian tube where fertilization happens Food shelter in the uterus placenta permits food and oxygen to each developing organism permits waste products to be carried away Umbilical cord removes waste but delivers blood with oxygen nutrients to the developing baby In the period of the embryo 6 weeks long most sensitive period of development Arms legs face organs muscles all develop heart starts beating First month nervous system develops arms legs face organs muscles all develop digestive system and lungs Second month rapid growth in eyes ears nose jaws neck buds become arms legs fingers and toes Responds to touch In the period of the fetus it is 30 weeks long Growth finishing Everything becomes connected can kick bend its arms open and close its hands and mouth and suck its thumb Fetus is at 11 weeks By 12th week external genitals are formed and heartbeat can be heard Mother can feel movements during second trimester Can be stimulated by light and sound and can respond to sounds lights Third trimester occurs When a baby can still survive age of viability between 22 and 26 weeks The cerebral cortex enlarges fetus spends more time awake Period of the embryo is the period with the most rapid change groundwork is laid for all body structures and internal organs 3 7 What are teratogens What factors impact how teratogens impact prenatal development What are examples of known teratogens Why is it difficult to determine how environmental agents impact prenatal
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