Modern+Genetics - Modern Genetics: A Brief Overview Brief...

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Unformatted text preview: Modern Genetics: A Brief Overview Brief Dr. Leilani Brown Genes, Chromosomes, & DNA Genes, Genes are composed of Deoxyribonucleic Genes Acid (DNA). DNA determines the nature of every cell in DNA the body and how it functions. the Chromosomes are the rod-shaped portions Chromosomes of DNA that are arranged in 23 pairs and are located in the nucleus of human cells. Only our red blood cells lack a nucleus. Only Genes and Chromosomes Genes Genes are DNA sequences Genes arranged in specific locations and order on the chromosomes. chromosomes. Humans have a total of 46 Humans chromosomes. Offspring receive 23 Offspring chromosomes from each parent at conception. parent Chromosomes are Chromosomes different sizes. different Did You Know? Did For each chromosome, there are millions of For different combinations of genes possible. different Each person, unless they are an identical Each twin, is genetically unique. twin, Less than 3 percent of all pregnancies Less produce identical twins. Most people are genetically unique. Most Nature and Nurture Nature Nature refers to the Nature biological (genetic) inheritance of an organism. Nurture refers to the Nurture environmental experiences of the organism. organism. The nature vs. nurture The debate is over which has the most influence on development. on What do you think? What Most researchers agree Most that development is influenced by both nature and nurture. nature Fertilization Fertilization When one sperm joins with one ovum, they When combine their genetic material in unique ways to form a zygote. ways The zygote will become a new and unique The person. In the photo, we can see that the ovum is huge compared to the tiny sperm. Mitosis and Meiosis Mitosis Body cells duplicate by mitosis; dividing into two identical copies each with 46 chromosomes. chromosomes. Sperm and egg cells go through a different Sperm process, called meiosis. Sperm and egg cells each contain only 23 Sperm chromosomes, so that the offspring receives 23 from each parent. 23 Genetic Variation is Built Into the System Built When the sperm and egg contribute their 23 When chromosomes, it is largely a random chance that determines which of each pair of chromosomes is contributed. chromosomes Other processes, such as random Other transformations of particular genes, add variability. variability. The result is tens of trillions of possible The genetic combinations. The Collaborative Gene The Did You Know? Humans have only 20,000 to 25,000 genes. The activity of genes is to make proteins. That activity, gene expression, is influenced That by the environment and by groups of other genes. genes. Events both inside and outside of the cell Events influence gene expression. Gene Regulation Gene Chemical signals from Chemical other genes tell each gene when to “turn on” and “turn off”. on” Most of our genes are Most not turned on most of the time. the Scientists are working Scientists to discover how genes are regulated. Environment also Environment plays a role in gene expression. expression. Molecules Everywhere Molecules Modern genetic research is concerned with Modern molecules and the chemistry of turning genes on and off. genes This is the world of molecular genetics. It determines who we are and what we do. Genes also interact with the environment to Genes influence our personal characteristics. influence Genetic Principles Genetic While much is still unknown about gene While expression, there are several principles that tell us some important things about genes. tell Dominance-Recessive Principle: a Dominance-Recessive dominant gene is expressed even if only one of a pair is present. of Recessive genes need both pairs for Recessive expression. Did You Know? Did Some examples of dominant genes are: Brown hair, dimples, and far-sightedness. Some examples of recessive genes are: Blond hair, near-sightedness, and freckles. Eye color is due to a blending of many Eye different genes. It is neither dominant or recessive, but is due to polygenic inheritance. inheritance. Sex-linked Genes Sex-linked Most are carried on Most the X chromosome. the Also called X-linked Also genes. genes. Males only have one Males X chromosome. chromosome. Females have two X Females chromosomes and one is usually normal. is Usually refers to Usually mutated (altered) genes carried on the X chromosome such as hemophilia. hemophilia. Males can both carry Males and express X-linked diseases. diseases. Females usually are Females carriers. carriers. Genetic Imprinting Genetic Occurs when genes have differing effects Occurs depending on whether they were inherited from the mother or the father. from Turner syndrome is an example of genetic Turner imprinting. Chromosome Abnormalities Chromosome Down Syndrome results from an extra copy Down of Chromosome 21 and causes mental retardation. retardation. Occurs approximately once in every 700 Occurs live births. live African American children rarely have this African disorder. disorder. Women over 38 are at increased risk of Women conceiving a child with this disorder. conceiving Sex-linked Chromosome Abnormalities Abnormalities Females have two X chromosomes, while Females males have an X and Y chromosome. males To be viable, a human infant has to have at To least one X chromosome. least Sometimes an extra copy is made of an X or Sometimes Y or one X chromosome is missing in females. females. Figure 3-6 in your text lists some diseases Figure linked to these abnormalities. linked Gene-linked Abnormalities Gene-linked Harmful genes Harmful account for about 7000 genetic diseases. 7000 Most of these Most disorders are rare. disorders One common disorder One is PKU disease. All infants in the US are tested for this disease. tested Other disorders: Cystic Fibrosis Sickle-cell Anemia Tay-Sachs Disease Diabetes Spina bifida Ethical Issues Genetic testing is loaded with ethical issues. Genetic counselors are trained physicians or Genetic biologists who are able to provide parents at risk with information about the chances of genetic disease in their offspring. genetic ...
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