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Genetics God’s Provision for the Community of Life Heredity – The transmission of characteristics from parents to offspring by means of genes in the chromosomes of the cells Differentiation of Cells When certain cells in a growing organism are called out to do a specific task it is called differentiation. This happens in asexual reproduction when organisms grow into new organisms and in sexual reproduction when the embryo first begins to grow Sexual Reproduction – A type of reproduction that requires the joining together of sex cells. There needs to be two different (male and female) sex cells for reproduction These cells are called haploid cells because they contain half the normal amount of chromosomes Haploid cells are made through the process of meiosis (NOT MITOSIS!) Fertilization occurs in sexual reproduction when an egg and a sperm unite This makes a zygote and the cell is called a diploid cell because it contains a normal amount of chromosomes Meiosis – A special type of cell division that makes sex cells (haploid). Also called reduction division because the number of chromosomes is reduced. (Not the same as Mitosis) Spermatogenesis is meiosis that forms sperm cells Oogenesis is meiosis that forms an egg cell First Meiotic Division Interphase – Cell replicates DNA (Chromosomes) Prophase I –Chromosomes coil tightly –Nucleolus and nuclear envelope is dismantled –Additional sets of Centrioles are produced Metaphase I –Spindle apparatus is formed –Homologous chromosomes (pair of Chromatids) line up on the “equator” of the cell Anaphase I –Homologous chromosomes become separated. Complete replicated chromosomes are dragged to opposite ends of the cell Telophase I –Nucleolus and Nuclear envelope forms in each new daughter cell. –Each daughter cell has half the original amount of chromosomes and their copies Second Meiotic Division Prophase II –Nucleolus and nuclear envelope are dismantled –Additional sets of Centrioles are produced Metaphase II –Spindle apparatus is formed –Chromatids (Copies of chromosomes) line up on the “equator” of the cell Anaphase II –Chromatids are dragged to opposite ends of the cell Telophase II –Nucleolus and Nuclear envelope forms in each new daughter cell. –Each daughter cell has half the original amount of chromosomes Differentiation –Daughter cells become Gametes Classical Genetics Gregor Mendel (18221884) – Austrian monk who conducted experiments dealing with the heredity of pea plants. Known as the father of genetics. Genetics – The scientific study of heredity. He used pea plants which normally selfpollinate, which made the patterns easier to recognize. Pea Flower Genotype – The genes that are present in the chromosomes (examples: Aa, AA, aa) Phenotype – The physical characteristic the gene gives Homozygous – A genotype where both genes have the same trait Heterozygous – A genotype where one gene is different from the other Dominant Traits – The trait that shows up in when the offspring is heterozygous (Capital letters) Recessive Trait – The trait that does not show up when the dominant trait is present. For this trait to show up, both genes have to be recessive. (Lower case letters) AA–Homozygous Dominant Aa-Heterozygous/Hybrid aa-Homozygous Recessive Alleles – Different forms of a gene for a particular trait. (Examples: R = round, r = wrinkle) It takes 2 alleles to make a gene. Hybrid – An organism that has two different alleles for a particular trait (Heterozygous) Liger Dihybrid – An organism that is a hybrid for two different traits. These traits are inherited independently because they are on different chromosomes. Linkage groups – Traits that are inherited together because they are on the same chromosome. The Law of Dominance – Dominant traits show up in the offspring even if a gene of a different trait is present. Incomplete Dominance – When the dominant and recessive traits are mixed or blended in the offspring Law of Segregation – When hybrids are crossed with each other, the recessive trait segregates, or separates, again for some of the offspring. Law of Independent Assortment – Different traits in an organism are inherited independently from each other. Classical Genetics (Cont.) Seeds Law of Dominance –Pure yellow (YY) crossed with pure green (yy) Y y y Y y y Y Y Yy Yellow Hybrid Yy Yellow Hybrid Yy Yellow Hybrid Yy Yellow Hybrid Law of Segregation –Yellow Hybrids (Yy) crossed Y Y y y Y y Y y YY Pure Yellow Yy Yellow Hybrid Yy Yellow Hybrid yy Pure Green Flowers Incomplete Dominance –Red flowers (RR) crossed with White flowers (WW) R W W R W W R R RW Pink Hybrid RW Pink Hybrid RW Pink Hybrid RW Pink Hybrid Incomplete Dominance and Law of Segregation –Pink Hybrids (RW) Crossed R R W W R W R W RR Pure Red RW Pink Hybrid RW Pink Hybrid WW Pure White Genetic Research in the 20th Century Sutton’s Hypothesis – 1902 Sutton wrote a paper which hypothesized the following things –An organism’s heredity is determined by its parents sex cells –“Heredity factors” were tiny particles on chromosomes (later called genes) –Different “factors” were found on different chromosomes Morgan’s Research – Researched the genetic traits of the fruit fly, which gave us proof that Mendel and Sutton were correct in their thinking Sex Chromosomes – All Chromosomes in male and female flies were the same except one pair. The pair of chromosomes that are different are the sex chromosomes because they determine the sex of the organism. –Morgan named the two chromosomes in the female X (female = XX) –He named the similar one in the male X, but the different one Y (male = XY) –Most organisms function this way with the male determining the sex of the offspring. –However there are some organisms where the sex chromosome in the female is different. Sex-linked Traits – Traits that are carried on the X chromosomes and appear in relation to the sex of the organism –Examples: Eye color in fruit flies, Hemophilia, Color blindness, faulty enamel etc. Sex-linked traits Male (XY) crossed with Female (XX) X X X Y X X XX Female X XX Female Y XY Male XY Male Eyes r Male w/white eyes (X Y) crossed with Female w/ R R pure red eyes (X X ) Xr R X XR Y R X XR Xr Y XRXr Female Red R r X X Female Red XRY Male Red R X Y Male Red R (X Y) Male w/red eyes crossed with Female w/ R r hybrid red eyes (X X ) XR R X Xr Y R X Xw XR Y XRXR Female Red R r X X Female Red XRY Male Red r XY Male White r (X Y) Male w/white eyes crossed with Female w/ R r hybrid red eyes (X X ) Xr R X Xr Y R X Xr Xr Y XRXr Female Red r r XX Female White XRY Male Red r XY Male White Variety Crossing over – There is an exchange of genetic material when the homologous pairs are together during synapsis. … (Homologous pair = 1 from mom, 1 from dad: All four chromatids = Tetrad) Assortment of chromosomes – During meiosis the homologous pairs line up we have number of homologous pairs 2 different combinations 23 2 =8,388,608 You can make 8,388,608 different gametes. These factors are used to breed certain characteristics from plants and animals –Examples Wheat, corn, cows, hogs, chickens, dogs, etc. Human Genetics Dominant Gene Inheritance: Dominant/Recessive Free/Attached Ear Lobes Full/Thin Lips Curly/Straight Hair Polydactyly/Normal Freckles/No Freckles Roll Tongue/ Not Dimples/No Dimples Normal Arches/Flat Feet Gene Frequency – The extent, which a certain gene exists in a population This does not mean it is dominant or recessive. Polydactyly – (Having more than 5 fingers or toes on a limb) A dominant trait that is very rare Cystic Fibrosis– (Having a thickened mucus in the lungs which may cause life threatening infections) A recessive trait that occurs in 1 out of every 25 Americans (Fairly common) Incomplete Dominance Sickle-Cell Anemia Recessive trait that causes a formation of abnormal hemoglobin. When oxygen is low, long chains of hemoglobin molecules form and cause the red blood cells to become sickle shaped. 1 H If represents the 2 normal trait and H represents the sickle trait, then because of incomplete dominance we have the following: 1 1 –H H Normal hemoglobin is produced. Round Cells 1 2 –H H (Heterozygous) Some normal and some abnormal hemoglobin is produced. Some Sickle, some Round. 2 2 –H H Abnormal hemoglobin is produced. Sickle Cells Multiple Gene Inheritance – When there are more than two alleles for a particular trait –Blood Type – The alleles for blood type are A, B, and O, and are denoted A B O I , I , and I –A – Sugar added to the ID tag on a Red Blood Cell –B – Different sugar added to the ID tag on a Red Blood Cell –O– Add neither sugar to the ID tag on a Red Blood Cell This gives us 4 different blood types –Type A –Type B –Type AB –Type O A A I I A O I I or B B B O I I or I I A B I I O O I I Pleiotropy and Polygenic Inheritance Pleiotropy Inheritance – Where a gene may influence several traits Polygenic Inheritance – Where many genes influence one trait (skin color and height) The more genes you have influencing the trait the more variety you have. Sex-linked Traits Hemophilia – (A condition where a persons blood does not clot) A recessive trait found on the X chromosome. The following are phenotypes and genotypes that exist. –Normal XHXH –Carrier XHXh –Hemophilia XhXh XHY XhY Carrier – A person who has the trait present in their genotype, but the trait does not show in the phenotype Colorblindness – (A condition where a person is not able to see all the colors) A recessive trait found on the X chromosome. The following are phenotypes and genotypes that exist. –Normal XBXB –Carrier XBXb –Colorblind XbXb XBY XbY Genetic Advances – Through these advances we have been able to detect different genetic diseases present in fetuses. Spina Bifida Corrective Surgical Procedure Positive – We can treat these diseases sooner and better than before. Negative – Many babies are aborted as a result of these tests even though there could be false positives. Eugenics – The attempt to improve the human race by controlling breeding and sterilizing those that are “genetically inferior.”