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Transcript
Genetics and Human Development Human Karotype . GENETIC FOUNDATIONS OF DEVELOPMENT • Each of us carries a “genetic code” that we inherited from our parents • A fertilized human egg carries this human code • fertilized human egg cannot grow into any other species Human Genetics • Each of us began life as a single cell weighing about one twenty-millionth of an ounce • This cell contained our entire genetic code Chromosomes • Nucleus of each human cell contains chromosomes • thread-like 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 DNA Molecule http://videos.howstuffworks.com/hsw/21318-human-genome-the-dna-molecule-and-chromosomes-video.htm Genes • Genes - units of hereditary information – short segments of DNA • Genes direct cells to reproduce themselves and to assemble proteins • Proteins – the building blocks of cells – the regulators that direct the body’s processes (Mader, 2008) Human Genome Project • Preliminary map of the human genome • the complete set of developmental instructions for creating proteins that initiate the making of a human organism • Each human has 20,000 – 30,000 genes Enduring Nature of Genes • Three processes by which cells split and are formed –Mitosis –Meiosis –Fertilization. Mitosis • All body cells, 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. Meiosis • Sex cell division is different type of cell division • Eggs and sperm (or gametes) are formed in 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 these has only half of the genetic material of the parent cell. • By the end of meiosis, each egg or sperm has 23 unpaired chromosomes. • http://videos.howstuffworks.com/hsw/6015-genetics-fertilization-and-meiosis-video.htm Fertilization • During fertilization, an egg and a sperm fuse to create a single cell, called a zygote • In the zygote, the 23 unpaired chromosomes from the egg and sperm combine to form one set of 23 paired chromosomes • One chromosome of each pair is from the mother’s egg and the other from the father’s sperm. • Each parent contributes half of the offspring’s genetic material. • http://videos.howstuffworks.com/hsw/11519-the-reproductive-system-process-of-conception-video.htm The 23rd Pair of Chromosomes • Ordinarily, in females the 23rd pair consists of two chromosomes called X chromosomes • In males the 23rd pair consists of an X and a Y chromosome • The presence of a Y chromosome is what makes an individual male Sources of Variability • Combining genes of two parents increases genetic variability in the population • chromosomes in the zygote are not exact copies of the parents • Another source of variability comes from DNA – a mutated gene, which is a permanently altered segment of DNA Genotype and Phenotype • Genotype -- all of a person’s genetic material • Phenotype -- observable characteristics • Phenotypes include – physical characteristics (such as height, weight, and hair color) – psychological characteristics (such as personality and intelligence) Genetic Principles • • • • Dominant-recessive genes Sex-linked genes Genetic imprinting Polygenically determined characteristics Dominant-Recessive Genes Principle • Dominant -- one gene of a pair always exerts its effects • Recessive gene – exerts its influence only if the two genes of a pair are both recessive – may be overridden by a dominant gene – May be carried from generation to generation but not expressed in phenotype Sex-Linked Genes • X-linked inheritance -- mutated gene is carried on the X chromosome – very different implications for males than females (Turner, 2006) – males have no “backup” copy to counter the harmful gene – females have a second X chromosome, which is likely to be unchanged • Females who have one changed copy of the X gene are known as “carriers” Polygenic Inheritance • Genetic transmission is usually quite complex – Few characteristics reflect the influence of only a single gene or pair of genes • polygenically determined characteristics - determined by the interaction of many different genes Chromosome Abnormalities • Down syndrome -- caused by the presence of an extra copy of chromosome 21 – once in every 700 live births – Women aged 16 - 34 are less likely to give birth to a child with Down syndrome • Sex-Linked Chromosome Abnormalities Sex-Linked Chromosome Abnormalities • Klinefelter syndrome – extra X chromosome • Fragile X syndrome -- results from an abnormality in the X chromosome – X chromosome becomes constricted and often breaks • Turner syndrome -- females have either an X chromosome missing or part of one X chromosome is deleted • XYY syndrome – male has extra Y Gene-Linked Abnormalities • Phenylketonuria (PKU) – individual cannot properly metabolize phenylalanine, an amino acid – once in every 10,000 to 20,000 live births – left untreated, phenylalanine builds up in the child, producing mental retardation and hyperactivity • Sickle-cell anemia -- genetic disorder that impairs the body’s red blood cells – most often in African Americans – red blood cell becomes a hook-shaped “sickle” that cannot carry oxygen properly – 1 in 400 African American babies is affected • 1 in 10 African Americans is a carrier • 1 in 20 Latin Americans is a carrier • Other diseases that result from genetic abnormalities – cystic fibrosis – diabetes – hemophilia – Huntington disease – spina bifida – Tay-Sachs disease Twins • Monozygotic Twins – identical • Dizygotic Twins - no more alike than any other siblings – they simply gestated together • http://videos.howstuffworks.com/health/frate rnal-twins-videos-playlist.htm#video-8197 • Conjoined twins The Hensel Twins • http://www.youtube.com/watch?v=7ZUzi0RhBpM