chapter 3
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This document provides an overview of genetics and heredity. It discusses DNA and chromosomes, how genes determine traits (phenotype) from our genetic code (genotype), how a single cell develops into a full organism through cell differentiation and gene interactions, and different patterns of inheritance such as dominant/recessive genes. It also covers genetic abnormalities like Down syndrome and how nature and nurture both influence traits and conditions over one's lifetime. Genetic counseling and testing are discussed as ways to learn about genetic risks but also have uncertainties.
chapter 3
- 1. Prepared by Madeleine Lacefield Tattoon, M.A.1Part IHeredity and EnvironmentChapter ThreeThe Genetic CodeFrom One Cell to ManyFrom Genotype to PhenotypeChromosomal and Genetic Abnormalities
- 2. 2The Genetic Code“Genes play a leading role in the drama of human development, yet they rarely take center stage. Genes are pervasive and powerful, but they are also hidden and elusive.”
- 3. 3What Genes AreDNA (deoxyribonucleic acid)Molecule that contains the chemical instructions for cells to manufacture various proteins.Chromosomea molecule of DNA that contains the instructions to make proteinsHumans have 46 chromosomes (23 pairs), and about 25,000 genes.Genomethe code for making a human beingEvery person has a slightly different code, but the human genome is 99.5% the same for any 2 people.
- 4. 4What Genes AreGenes are as section of chromosomes and the basic unit for the transmission of heredity, consisting of a string of chemicals that code for the manufacture of certain proteins.
- 5. 5The Beginnings of Life“…development begins at conception…each human reproductive cell or gamete, contains 23 chromosomes, half of that person’s 46…”gamete A reproductive cell; that is, a sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote
- 6. 6The Beginnings of LifeMatching Genesconception occurs in the usual wayzygotethe single cell formed from the fusing of two gametes, a sperm and an ovum genotypeAn organism’s entire genetic inheritance, or genetic potential
- 7. 7The Beginnings of LifeMale or Female?
- 8. 8From One Cell to Manyphenotypethe observable characteristic of a person, including appearance, personality, intelligence, and all other traits
- 9. 9From One Cell to ManyNew Cells, New FunctionsGene-Gene Interactionsoccurs through cell differentiation, gene-gene (polygenic), and gene-environment interactionMultifactorial refers to a trait that is affected by many factors, both genetic and environmentalThe Human Genome Project is an international effort to map the entire human genomeresearchers have found that humans have only about 25,000 genes, 99% of which are present in the genomes of other creatures as well
- 10. 10From One Cell to ManyAdditive Heredityan allele is a slight, normal variation of a particular genesome alleles are…additive genes combine to make a phenotype
- 11. 11From One Cell to ManyDominant-Recessive Hereditythe interaction of a pair of alleles in such a way that the phenotype reveals the influence of one allele (the dominant gene) more than that of the other (the recessive gene)a special case of the dominant-recessive pattern occurs with genes that are x-linked, located on the x chromosome
- 12. 12From One Cell to ManyMore ComplicationsA small alteration in the sequence of base pairs or several extra repetitions in one triplet ma be inconsequential or may cascade to create a major problem
- 13. 13From One Cell to ManyTwins, Clones, Assisted Reproduction (ART)dizygotic (fraternal) twins result from two sperm penetrating two ova, and share 50% of their genesmonozygotic (identical) twinsoriginate from one zygote, and share 100% genesa cloneoriginates from a live organismARTgeneral term for the technique designed to help infertile couples conceive and then sustain a pregnancy
- 14. 14From One Cell to ManyAssisted Reproduction (ART)general term for the technique designed to help infertile couples conceive and then sustain a pregnancy
- 15. 15From Genotype to PhenotypeScientist in many nations have studied thousands of twins, both monozygotic and dizygotic, raised together in the same home and raised separately in different homes
- 16. 16From Genotype to PhenotypeGenes affect every aspect of human behavior, including social and cognitive behaviorMost environmental influences on children raised in the same home are not shared
- 17. 17From Genotype to PhenotypeEach child’s genes elicit other people’s responses, and these responses shape development. In other words, a child’s environment is partly the result of his or her genes.Children, adolescents, and especially adults choose environments that are compatible with their genes (called niche-picking), and thus genetic influences in adulthood
- 18. 18From Genotype to PhenotypeCarriera person whose genotype includes a gene that is not expressed in the phenotype…such an unexpressed gene occurs in half of the carrier’s gametes and thus is passed on to half of the carrier’s children, who will most likely be carriers, too…Generally, only when the gene is inherited from both parents does the characteristic appear in the phenotype.
- 19. 19From Genotype to PhenotypeAddiction…inherited biochemistry making people vulnerable to various addition……any one can abuse drugs or alcohol…but genes create an addictive pull that can be overpowering, extremely weak, or somewhere in between…
- 20. 20From Genotype to PhenotypeVisual AcuityNew borns cannot focus more than 2 feet awayChildren see better each year until about age 8Many adolescents become nearsighted when eyeball shape changesVision is more likely to improve than to worsen until age 40
- 21. 21From Genotype to PhenotypeVisual AcuityIn middle age, the elasticity of the lens decrease and the eyeball shape change again, so that many people become farsighted and need reading glassesAmong the old, eye diseases, including cataracts, are commonAbout 10 percent of people over age 90 are blind
- 22. 22From Genotype to PhenotypeNearsightedness and GenesIf children have a vision problem it is most often myopia (nearsightedness)Nearsightedness is a symptom in more than 150 genetic syndromesCaused by physical trauma or illness, such as the rubella virus, or poor nutrition (such as vitamin A deficiencyThese factors cause “high” nearsightedness, so severe that it can lead to blindness
- 23. 23From Genotype to PhenotypeCulture and Cohortgenes are not the major cause of poor visionhistorical and multicultural research finds that environment also influences nearsightednessif diet is deficient of vitamin A
- 24. 24From Genotype to PhenotypePractical Applicationdevelopmental application of nature-nurture interactionfamily history of genetic problemssomeone inherited a problemalcoholism in the geneslack of outdoor play
- 25. 25From Genotype to PhenotypePractical Applicationtype 2 diabetes (adult-onset diabetes)a chronic disease which the body does not produce enough insulin to adequately metabolize carbohydrate (glucose)… it typically developed in people aged 50 - 60…today it often appears in younger peoplebegins when a person is vulnerable and has more body fat than is ideal
- 26. 26From Genotype to Phenotype
- 27. 27Chromosomal and Genetic Abnormalitiesabnormalities caused by identifiable problems…those with an extra chromosome or a single genestudy of these problems is relevant to the study of development…providing insight into the complexities of nature and nurtureknowing their origins helps limit these effectsinformation combats the prejudice that surrounds such problems
- 28. 28Chromosomal and Genetic AbnormalitiesNot Exactly 46 Chromosomesa variable that most often correlates with chromosomal abnormalities is the age of the motheroccur not only in the formation of gametes but also in their early duplicationmosaic is having a condition (mosaicism) that involves having a mixture of cells, some normal and some with an odd number of chromosomes or a sense of missing genes
- 29. 29Chromosomal and Genetic AbnormalitiesDown Syndromea condition in which a person has 47 chromosomes instead of the usual 46, with three rather than two chromosomes at the 21st positionpeople with Down Syndrome typically have distinctive characteristics, including unusual facial features, heart abnormities, and language difficulties
- 30. 30Chromosomal and Genetic AbnormalitiesAbnormalities of the 23rd Pairhumans have at least 44 autosomes and one X chromosomean embryo cannot develop without an X chromosomean odd number of X chromosomes impairs cognition and psychosocial development and sexual maturationif a child has three sex chromosomes instead of two he/she may seem normal until puberty
- 31. 31Chromosomal and Genetic AbnormalitiesDominant-Gene Disorderseveryone carries genes or alleles that could produce serous diseases or handicaps in the next generation7,000 single-gene disorderstheir dominant effects are apparent in the phenotype
- 32. 32Chromosomal and Genetic AbnormalitiesFragile X Syndromea genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of moleculesthe actual cause is too many repetitions of a particular part of a gene’s code
- 33. 33Chromosomal and Genetic AbnormalitiesRecessive-Gene Disordermost recessive disorders are not X-linkeddouble recessive patterns are lethal…one recessive gene is protectivesometimes a person who carried a lethal gene has many descendants who marry each other… the genetic disease then becomes common in that group
- 34. 34Chromosomal and Genetic AbnormalitiesGenetic Counseling and Testingconsultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive
- 35. 35Chromosomal and Genetic AbnormalitiesWho Should Get Counseling, and When? genetic counselingconsultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive
- 36. 36Chromosomal and Genetic AbnormalitiesIs knowledge Always Power?Genetic counselors, scientist, and the general public usually favor testinghaving some information is better than having nonehigh risk individuals (who might hear bad news) do not always want to knowthe truth might jeopardize their marriage, their insurance coverage, or their chance of parenthood
- 37. 37Chromosomal and Genetic AbnormalitiesCoping with Uncertaintymuch is uncertain in genetic testing and counseling those who learn that they have a harmful dominant gene have new information, as well as new uncertaintiesinteraction of genes and the environment makes development overt the life span unpredictable, even if the genes are known