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Download Biology Chapter 6 Advanced Genetics The Continuity of Life: Part II
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Biology Chapter 6 Advanced Genetics The Continuity of Life: Part II 6A - Chromosome and Gene Changes mutation: any sudden inherited change two types of mutations: (1) CHROMOSOME mutations: (2) GENE mutation: the chromosome number is changed or the sequence or number of genes on a chromosome is changed the gene itself is changed Mutations Affecting Chromosome Numbers genome: a single haploid diploid Read page 151 parthenogenesis: I. complete set of an organism's chromosomes gamete - contains a complete genome cell - contains two complete genomes the development of an unfertilized egg (example - drone bees) Euploidy: the addition or loss of an entire genome polyploids (extremely rare in animals): any cell that has multiple genomes A. Triploids: three genomes they are sterile Living triploids do not occur in animals and humans. plants - grapes, oranges, other fruits (they lack seeds must reproduce asexually) B. Tetraploid: four genomes common in plants; rare in animals human liver cells (92 chromosomes) plants - white or Irish potatoes n=12; 2n=24; 4n=48 american upland cotton (52 chromosomes) Although there are a few well-known natural tetraploids, most of today's triploids and tetraploids results from human intervention and are kept alive only by cultivation. The Mule: II. Read pages 152-153 female horse X male donkey = mule 64 chromosomes 62 chromosomes 63 chromosomes Aneuploids: lack or have extra chromosomes (not a complete genome) common in plant kingdom (esp. cultivated crops like wheat) nondisjunction: trisomy: the failure of a pair of homologous chromosomes to separate during the first division of meiosis an abnormal condition in which there are 3 chromosomes 10th Biology Chapter 6 / Advanced Genetics 2 in a set instead of 2. example in humans - Down's Syndrome (mongolism) is caused by a trisomy of the 22nd (or 21st) chromosome. Characterized by - low mentality, shortness, stubby hands and feet, and an extra fold of skin on the eyelids and other defects. Trisomic conditions of #13 & 17 human chromosomes are occasionally born (individual is deformed; life expectancy is only a few months) monosomy: a condition in which there is only 1 of a chromosome set Various aneuploids of the sex chromosomes: Turner's syndrome (XO) - this female lacks the second sex chromosome; characteristics: underdevelopment of the female sex glands; shortness; and other deformities 1 in approximately 6,000 female births Klinefelter's syndrome (XXY) - male with an extra X sex chromosome; characteristics: usually mentally retarded; underdeveloped sex organs 1 in approximately 6,000 male births Trisomy X (XXX) - female with 3 X sex chromosomes characteristics: some resemble women with Turner's syndrome; some are so called "super females" having a tendency toward male characteristics; usually mentally retarded; usually sterile Mutations Within the Chromosome crossing over: the exchange of segments between homologous chromosomes during meiosis Crossing over results in gametes with the normal amount of genes, but often in unexpected combinations. translocation: the transfer of a chromosome segment to a nonhomologous chromosome Some of the gametes formed after translocation have extra genes and some formed are missing genes. Approximately 4% of the people with Down's syndrome have a translocation of genes from the 22 chromosome (to one of the others 14, 15, 21) Gene Action & Gene Mutations Genes may be turned off (inactive); turned on (active); or altered (mutated). Not all of the approximately 100,000 genes you have in each nucleus are functioning. Factors that control gene action: (1) concentration of the proteins they produce (2) chemicals (3) environment (temperature) (4) sex hormones 10th Biology Chapter 6 / Advanced Genetics sex-limited characteristic: a trait expressed in only one sex even though the genes are present in the autosomes of both sexes example - brightly colored feathers of roosters humans: body hair, beard, breast development, and milk production Gene Mutations gene mutation: (or point mutation) the alteration of an individual gene codons of mRNA can be affected in 3 basic ways: 1. addition (of a nucleotide) 2. deletion 3. substitution Effects of mutations spontaneous mutations: a mutation that occurs naturally mutagen: a substance that induces mutation somatic mutation: a mutation affecting the somatic cells (nongamete cell) A mutation in a somatic cell will usually do 1 of 3 things: (1) produce an odd protein (2) have no effect (3) kill the cell germ mutation: a mutation in a cell that forms gametes many germ mutations are eliminated by a genetic screen genetic screen: a mechanism designed by God that prevents badly deformed or genetically defective individuals from living and reproducing (natural abortions [miscarriage] & still births) example of human gene mutations: sickle-cell anemia albinism achondroplastic dwarfism 6B – Modern Genetics gene pool - all the genes in a population of a given organism (all the genes that a type of organism can conceivably possess) a difference between individual organisms of the variations same kind Techniques to manipulate the gene pool 3 10th Biology Chapter 6 / Advanced Genetics Mass Selection: Hybridization: Inbreeding: Eugenics: 4 the method for selecting breeding stock in which only the desirable organisms are selected Example: loblolly pine (killed by southern pine beetles) It attempts to cultivate an already existing trait, not to develop a new trait Breeders are seeking a pure line of some characteristic already in the gene pool, not expanding the gene pool. the crossbreeding of two genetically unrelated individuals Examples: crossing two strains of corn two kinds of apples Egyptian married to an Englishman cross between an orange and a tangerine cross between a peach and a plum Heterosis (Hybrid vigor) - and increased capacity for growth in a hybrid Examples: resistance to disease larger bodies more milk production more crop yield per acre the mating of an organism with itself or with close relatives Produces pure strains (organisms which are homozygous for various traits) In animals, inbreeding often results in inferior offspring. the science that deals with the improvement of the human race by applying principles of genetics means well-born "good genes" Read pages 167-168 Eugenic Practices 1. artificial insemination - the mechanical injection of sperm into a female's body Long time practice among the cattle breeders in U.S. responsible for approx. 95% or the cattle born in the U.S. At the present there are approx. 1 million people alive in america (some over 20 years old) who are the result of artificial insemination. several places in the U.S. have sperm banks where frozen human sperm are kept (by liquid nitrogen). 10th Biology Chapter 6 / Advanced Genetics 5 First done with humans in 1785 in London by a doctor named John Hunter. Two types of artificial insemination: 1. AIH - using semen of the husband 2. AID - using semen of a donor AIH: AID: Few Christians object to human in artificial insemination between a husband and wife. Some Christians consider artificial insemination with a donor's sperm unacceptable, contending that it is immoral for a woman to bear a child of a man who is not her husband. Those who condone AID argue that true purity is not violated by this clinical technique. Scientific Considerations: 1. possibility of accidental incest sperm donors remain anonymous avg. sperm-bank donor is used for up to 6 pregnancies and some for as many as 50 pregnancies potential for inbreeding (half brothers and half sisters) 2. accidental transmission of unknown genetic traits Most doctors only take oral histories from donors - only 29% performed a blood test Theological Considerations: 1. Is AID an act of adultery? One of the major factors in adultery is the attitude. Jesus said that "anyone who looks at a women lustfully has already committed adultery with her in his heart" (Matt. 5:28). There is no such attitude discernable in AID. Another factor is action. Paul talks about becoming "one body" with a prostitute (I Cor. 6:12-16); such a union is not found in AID. Therefore it is not appropriate to call AID a form of adultery. 2. The biblical view of parenthood While AID may be allowable in particular cases of last resort to a married couple, this does not sanction its use outside the bounds of marriage. Producing children for single parents and lesbians or making surrogate arrangements goes far beyond the bounds of a biblical view of parenthood. Somewhere in the process a child has ceased to be a gift of God. Ps. 127:3 "Lo, children are an heritage of the Lord: and the fruit of the womb is His reward." 2. in-vetro fertilization (ectogenesis) (test tube baby) removing an ovum from a female's body and then 10th Biology Chapter 6 / Advanced Genetics fertilize it with sperm in the lab (allows an ovum to be fertilized and grown outside the womb for a short period of time) In order for the zygote to develop properly it must be implanted again in a female's body. world's first: Louise Brown born July 25, 1978 Scientific Considerations: (1) hyperfertilization more than 1 egg is harvested and fertilized; may be associated with higher rates of chromosomal abnormality (trisomy) (2) May by-pass the natural screening of sperm It appears that the female reproductive tract selectively eliminates abnormal sperm so that very few reach the site of fertilization. (3) high rate of miscarriages or natural abortions any technique that increases that risk also increases the risk of problems for the mother Ethical Considerations: (1) The slippery slope argument Moral choices often lead to unintended consequences in the future. A pratice that may be moral can often very naturally lead to immoral consequences. (A) The possibility of establishing surrogate mothers as an alternative form of reproduction. Might lead to an entirely new profession prenatal baby care. Could easily develop into a system in which women hire other women to carry their babies while they themselves pursue their careers. (B) Artificial embryonation (AE) A couple pays a fee for a woman to be artificially inseminated by the husband. After a few days the woman returns to the clinic so that the doctor can flush out the embryo and implant it in the wife. (C) Oocyte fusion product (OFP) two ova are fused together; would create only female offspring and requires only ova from females; possible means of reproduction for lesbian couples (D) surrogate father embryos could be fertilized in the lab, implanted in men's abdomens, and delivered by Cesarean section. Such a procedure has already been performed by Dr. Cecil Jacobsen at George Washington Univ. Med. School with male chimps who delivered healthy chimps via Cesarean section. (E) Embryo adoption (EA) Donor sperm is used, and a couple "adopts" the embryo the same way they might adopt a child. (2) The conflict between ends and means Theological Considerations: (1) The basis for the sanctity of human life 6 10th Biology (2) 3. Chapter 6 / Advanced Genetics We are seen as special in God's creation because we are made in His image (Gen. 1:27). Human beings are distinct from animals, because we are created in the image of God. (Gen. 1:27; 5:1-2) (a) loss of fetal life Even with the more improved technigues, there is still a 90% loss of fertilized ova. (b) the practice of destroying fertilized ova if they appear abnormal In most clinics parents must agree to abort a fetus that is found to be defective. (c) the practice of hyperfertilization Many ova are fertilized simultaneously, one (sometimes 4) is selected for implantation, and the others are thrown away. The effect IVF will have on a biblical view of marriage motherhood will be affected lead to the breakdown of the family unit Gentic Engineering - the manipulation of chromosomes or genes by methods other than normal reproduction examples: recombinate DNA research cloning The Problems of Eugenics 1. 2. 3. Gov't domination Genetic failures Dehumanization Genetic disorder (inherited disorder) - any undesirable function or shape of an individual's body that is caused by a gene or a group of genes. Some are not apparent at birth. Presently there is not cure for genetic disorders. Some are apparently the wearing out or turning off of a particular gene (diabetes). When an individual has a genetic disorder, every cell in his body has the genetic information for that disorder. Genetic Screening - the determining of an individual's genetic makeup Three basic screening methods widely used: 1. 2. 3. 7 analysis of prospective parents analysis of the unborn analysis of the newborn