5 The Influence of Heredity on Development Heredity defines our nature.It is based on the biological transmission of physical and psychological traits from generation to generation.The field of biology that studies heredity is called GENETICS.Traits are transmitted by:ChromosomesGenesIntroduction to the first topic: Heredity. Next slides will cover Chromosomes and Genes individually.
6 Chromosomes and Genes CHROMOSOMES Rod-shaped structures found in cells Typical human cells have 46 (23 pairs)Each contains thousands of segments called genes.GENESBiochemical materials that regulate how traits developSome traits are transmitted by a single pair of genes.Other traits are POLYGENIC (using several pairs).We (humans) have approximately 20-25,000 genes.Genes are segments of strands of deoxyribonucleic acid (DNA).DNA forms a double spiral (HELIX) that looks like a twisting ladder.Each “rung” on the ladder consist of 4 basic chemicals that are placed in pairs of either:Adenine and ThymineCytosine and GuanineThe sequence of the rungs are the individual genetic code that cause the developing organism to grow arms, wings, skin, or scales.The number of genes in humans was originally thought to be much higher due to the complex nature of the human life form. Certain types of round worms also have about 20,000 genes.Next slide shows diagram drawing of DNA
8 Beginnings of Life – Mitosis & Meiosis Life begins as a single cell or zygote that divides repeatedly.There are TWO types of cell division.Mitosis and Meiosis
9 Mitosis Mitosis: genetic code carried into new cells in our bodies DNA breaks apart (unzips); and the double helix duplicates.DNA forms two camps on either side of cell; cell divides. Each incomplete rung combines with its partner to form a new ladder; resulting identical copies of the DNA strand separate when cell divides; each is newly formed cell; genetic code is identical in new cells unless mutations occur through environmental influences such as radiation; mutations occur by chanceNext slide is graphic Figure 2.2 p. 25 showing Mitosis
11 MeiosisSperm and ova are produced through meiosis or reduction division.46 chromosomes within the cell nucleus first line up into 23 pairs.DNA ladders unzip, leaving unpaired halves of chromosome; when cell divides each member of each pair goes to each newly formed cell.Each new cell nucleus contains only 23 chromosomes, not 46.23 chromosomes come from the mother and 23 chromosomes come from the father; 22 pairs are autosomes and 23rd pair are sex chromosomes.Next slide shows Figure 2.3 on p Depicts the X and Y Chromosomes that determine the sex of the individual.This answers Truth or Fiction # 1. Your father determined whether you are female or male. TRUE. He did so by supplying a Y or an X sex chromosome. If we receive another X sex chromosome from our fathers, we develop into females. If we receive a Y sex chromosome (named after its Y shape) from our fathers, we develop into males.
12 Identical and Fraternal Twins Sometimes a zygote divides into two cells that separate and becomes two individuals or twins. There are two types of twins:Monozygotic (MZ): zygote divides into two cells that separate so each develops into individual with same genetic makeup - IDENTICALDizygotic (DZ): two ova are produced in the same month and they are each fertilized by a different sperm cell - FRATERNALDZ runs in families through the maternal side; if mother or grandmother was a twin, or mother has had twins already the chances increase of her bearing twins againOvulation: as a woman nears end of child-bearing years, ovulation becomes less regular causing multiple ovum to be released some months, thus increasing likelihood of twinsFertility Drugs also increase the chances of multiple births by causing more than one ovum to be released.Sometimes a zygote divides into two cells that separate so that each develops into a separate individual, or twins. There are two types of twins.
13 Dominant and Recessive Traits Traits are determined by pairs of genes; each member of a pair of genes is termed an allele.Homozygous: both of the alleles for a trait are the sameHeterozygous: alleles for a trait differIncomplete dominance/codominance: effects of both alleles are shown - a sort of “averaging”Dominant trait: trait whose influence will be shown each time the gene is presentRecessive trait: trait whose influence will be shown only when it is paired with a second recessive geneCarriers: people who bear one dominant gene and one recessive traitTraits can be hair, color, eye color, etc. Next slide shows Figure 2.4 on p. 26Answer to “T - F”? # 2. You can carry the genes for a deadly illness and not become sick yourself. TRUE. This occurs when genes are recessive and dominant genes cancel their effects.
14 Figure 2.4 – Transmission of Dominant and Recessive Traits ScienceDaily (Jan. 31, 2008) New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye color of all blue-eyed humans alive on the planet today. What is the genetic mutationﾒOriginally, we all had brown eyes, said Professor Eiberg from the Department of Cellular and Molecular Medicine. But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a switch, which literally turned off the ability to produce brown eyes. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin. The switch, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris effectively diluting brown eyes to blue. The switchﾕs effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin color is a condition known as albinism.
15 Figure 2.1 – Examples of Dominant and Recessive Traits
17 Chromosomal Abnormalities Chromosomal or genetic abnormalities can cause health problems.Some disorders are caused by abnormalities in the 22 pairs of autosomes.Others are found in the 23rd pair (sex chromosomes).Some genetic abnormalities are caused by combinations of genes called:Multifactorial problemsThese reflect both a predisposition AND environmental contributors.Overview of Chromosomal Abnormalities; next slides will cover specific problems - Down’s Syndrome, sex-linked chromosomal abnormalities,
18 Characteristic features: Down SyndromeCaused by an extra chromosome of the 21st pair, resulting in 47 chromosomes.Probability of having a Down Syndrome child increases with advancing age of parents.Characteristic features:rounded face, protruding tongue, broad, flat nose, sloping fold of skin over the inner corners of the eyesShow deficits in cognitive and motor developmentTypically die from cardiovascular problems by middle age, although modern medicine has extended life expectancy.Down’s Syndrome, Down Syndrome, or Trisomy 21. See Figure 2.5 on p. 27
20 Sex-Linked Chromosomal Abnormalities Sex-linked chromosomal abnormalities: disorders stemming from abnormal number of sex chromosomesMost individuals with disorder are infertile.Approx. 1 male in 700/1000 has extra Y chromosome resulting in heightened male secondary sex characteristics
21 Sex-Linked Chromosomal Abnormalities XYY’s somewhat taller and develop heavier beards.Once termed “supermales” due to the characteristics.But often have more problems than XY’sSuch as mild delays in language development
22 Klinefelter Syndrome (XXY) 1 male in 500 has syndromeCaused by extra X sex chromosomeProduces less testosterone than normal malesTherefore, the testes, deepening of voice, musculature, and male pattern of body hair does not develop properly.Usually have enlarged breasts (gynecomastia)Typically mildly retarded, particularly languageTreated with testosterone replacement therapy, they see improvement in sex characteristics and mood elevation but remain infertile.
23 Turner Syndrome (X) Approx. 1 girl in 2,500 has syndrome Female has single X chromosome.External genitals are normal, ovaries poorly developed, producing little estrogenShorter than average and infertileCognitive deficits with low estrogen: problems with visual-spatial skills, mathematics, and nonverbal memory
24 Triple X Syndrome (XXX) Approx. 1 girl in 1,000 has syndromeNormal in appearanceTend to show lower-than-average language skillsPoorer memory for recent eventsDevelopment of external sex organs appear normalIncreased incidence of infertility
26 Genetic Abnormalities A number of disorders attributed to genes:Phenylketonuria (PKU)Huntington’s DiseaseSickle-Cell AnemiaTay-Sachs DiseaseCystic FibrosisSex-Linked Genetic AbnormalitiesThis slide is an overview of the types of Genetic Abnormalities that will be discuss individually on separate slides
27 Phenylketonuria (PKU) Enzyme disorder transmitted by a recessive gene affecting 1 child in 8,000.Cannot metabolize an amino acid called phenylalanine; builds up in body and impairs functioning of the central nervous system (CNS)Results are mental retardation, psychological disorders, physical problemsNo cure, but PKU can be detected in new born children through blood or urine analysis; if identified placed on diets low in phenylalanine within three weeks of birth and develop normally
28 Huntington’s DiseaseAffects approx. 1 in 18,000 AmericansFatal, progressive degenerative disorderDominant traitPhysical symptoms include uncontrollable muscle movementsPsychological symptoms include loss of intellectual functioning and personality changeOnset during middle adulthoodHalf of their offspring will have disorderAffects 1 in 18,000 AmericansNo cure, but helpful medicines
29 Caused by a recessive gene Most common among African Americans Sickle-Cell AnemiaCaused by a recessive geneMost common among African Americans1 in 10 African Americans1 in 20 Latino/a AmericansRed blood cells take on the shape of a sickle and clump together, obstructing blood and oxygen supply.Decreased oxygen can impair cognitive and academic functions.Physical problems include: painful swollen joints, jaundice, and potentially fatal conditions such as pneumonia, stroke, and heart and kidney failure
30 Caused by recessive gene Causes CNS to degenerate resulting in death Tay-Sachs DiseaseCaused by recessive geneCauses CNS to degenerate resulting in deathCommonly found among children in Jewish families of Eastern European background1 in 30 Jewish Americans carry recessive geneChildren with disorder progressively lose control of muscles experiencing visual and auditory sensory losses, develop mental retardation, become paralyzed, and die by end of early childhood (age 5).CNS (Central Nervous System)
31 Cystic FibrosisCaused by recessive geneMost common fatal hereditary disease among European AmericansApprox. 30,000 Americans have disorder, 10 million more are carriers (1 in 31 people)Children suffer from excessive production of thick mucus that clogs the pancreas and lungs.Most victims die of respiratory infections in their 20s.
33 Sex-Linked Genetic Abnormalities Duchenne Muscular Dystrophy: weakening of muscles, inability to walk, general wasting away, and sometimes deathInvolve recessive genesFemales with two X sex chromosomes are less likely to show sex-linked disorder.Sons of female carriers are more likely to be afflicted.
35 Genetic Counseling and Prenatal Testing Genetic counselors compile information about a couple’s genetic heritage to explore if their children will have a genetic abnormality.Couples with likelihood of passing on genetic abnormality can make informed decision as to alternative family plans, such as adoption.Prenatal testing can also indicate if the embryo or fetus is carrying genetic abnormalities.Amniocentesis, Chorionic Villus Sampling, Ultrasound, and Blood Tests are examples of prenatal testing.The website: - offers a tremendous wealth of information on Genetic Counseling. Individuals can purchase a kit and have their genetic code read.
36 AmniocentesisPerformed on mother usually around 14 – 16 weeks after conception, although sometimes earlierAmniotic Fluid containing cells sloughed off by fetus is withdrawn from the amniotic sac with a syringe.Cells are separated, grown in a culture, and examined for chromosomal abnormalities.Routine test for women over 35 to detect for Down’s Syndrome as chances for syndrome dramatically increase as women approach age 40.Test also can determine the sex of child.Amniocentesis does carry some risk of miscarriage.Approx. 1 in 100Next slide shows graphic of procedure
38 Chorionic Villus Sampling (CVS) Similar to AmniocentesisPerformed between weeksSyringe inserted through vagina into uterus and sucks out threadlike projections (villi) from the outer membrane that covers the amniotic sac and fetus.Results available in daysCVS slightly higher risk than amniocentesis of spontaneous abortion; both increase the risk of miscarriage
39 UltrasoundSound waves that are too high in frequency to be heard by human ear are used to obtain information about the fetus.Ultrasound waves are reflected by the fetus, and the computer uses the information to generate a picture of the fetus.Picture is termed a sonogram.Used to guide the syringe in amniocentesis and CVS and to locate fetal structures when intrauterine transfusions are needed for survival of fetus as with Rh diseaseUsed to track growth of fetus, detect multiple pregnancies, detect structural abnormalitiesProcedure is able to detect sex of fetusSee Figure 2.7 on p. 31 of text
40 Blood TestsUsed to identify sickle-cell anemia, Tay-Sachs disease, and cystic fibrosisAlpha-fetoprotein (AFP) assay used to detect neural tube defects such as spina bifida and chromosomal abnormalities.Neural tube defects cause elevation in the AFP level in the mother’s blood.High AFP levels related to increased risk of fetal death.
42 Heredity and the Environment Inheritance, nutrition, learning, exercise, accident, and illness all influence development of traits.GenotypesSet of traits we inherit from our parents (our blueprint)PhenotypesActual set of traits; develop because of both genetic and environmental influences (what actually transpires)CanalizationEnvironmental conditions may prevent an individual from reaching their full potential, but if environmental influences improve, there is a tendency to “snap back” to the genetically determined “canal.”Personality and intelligence are apparently less canalized (environment playing stronger role than with physical development).The key to understanding this topic is “POTENTIAL”. We have the genotypes we are born with…providing “potential” for certain attributes, and the environment we are born and raised in help to determine the development or lack of development of those potentials.Canalization = is a measure of the ability of a population to produce the same phenotype regardless of variability of its environment or genotype.
43 Genetic - Environmental Correlation One problem in sorting out the influences of heredity (nature) and environment (nurture) is that genes partly determine the environments to which people are exposed.Psychologist Sandra Scarr describes 3 types of correlations between genetic and environmental influences as they relate to age of individuals:Passive CorrelationParents intentionally and unintentionally place children in certain environments; it is called passive because child has no choiceEvocative CorrelationA child’s genotype is connected with behaviors that elicit or evoke certain types of social responses from others, and these responses in turn become part of the environment of the childActive CorrelationAs we mature, we become more proactive in creating our environment.Choosing environments that allow us to develop inherited preferences is termed niche-picking.Good place to ask students if they can relate these concepts to their own development. What did their parents expose them to at an early age and how did that influence their preferences? What type of socialization skills did they get, and how have they taken more control over their environment as they have matured? Do they think they are more what nature dictated or what nurture has provided…or a little of both?
45 Strategies for Understanding Research strategies used to aid in sorting out effects of heredity and environmentKinship StudiesStudy distribution of traits among relatives with differing degrees of relatednessIf genes are dominant in manifesting a trait, people who are most closely related should be more likely to share it.Twin StudiesStudy both MZ twins sharing 100% genes and DZ twins sharing 50% genesStudy of MZ twins raised apart from infancy show similarities much the same as those raised together, leading us to believe there is a strong genetic component to traits.Adoption StudiesStudy children separated from biological parents at an early ageWhen children raised by adoptive parents demonstrate more similarities of traits with natural parents, again a strong argument for genetic predominance seems to prevail.
47 CONCEPTION: The Players (Ova & Sperm) Conception: union of an ovum and a sperm cell that occurs when the chromosomes of each combine to form 23 new pairsOvaWomen are born with approx. 400,000 ova - all they will ever have but in an immature formDuring woman’s reproductive years, approx. 400 (1 in 1,000) will ripen and be released.Ova are much larger than sperm cells but barely visible to the human eye.SpermDevelop in stages, starting with 46 chromosomes, and after meiosis ends with 23 - half X’s and half Y’sEach is about 1/500th of an inch - one of the smallest types of cells in the body.
50 CONCEPTION: The Journey & Meeting Against All Odds Journey of the SPERMY chromosomes have greater motility (faster swimmers).120 to 150 boys are conceived for every 100 girls.Male fetuses experience higher rate of spontaneous abortion during first month of pregnancy.At birth, boys outnumber girls by ratio of 106:100.Boys also have higher incidence of infant mortality, further equalizing sex ratio.Answer to T/F? # 3: Approximately boys are conceived for every 100 girls. = TRUE, but male fetuses suffer a higher rate of spontaneous abortion than females.Answer to T/F? # 4: Sperm travel about at random inside the woman’s reproductive tract. = FICTION - Actually, sperm are apparently attracted to the ovum by chemical changes that occur when it is released.
51 CONCEPTION: The Journey & Meeting Against All Odds Journey of the SPERMApprox. 150 million sperm ejaculated but only 1 in 1,000 will approach an ovumSperm surviving initial obstacles may reach fallopian tubes 60 to 90 minutes after ejaculation.About 2,000 may finally enter correct tube.Still fewer manage to maneuver the final 2 inches against currentJourney is “blind” but not random.Sperm are “egged on” by a change in calcium ions that occurs when an ovum is released by a follicle.
52 CONCEPTION: The Journey & Meeting Against All Odds Destination: ConceptionOnly ONE sperm that reach an egg enters.Ova are surrounded by a gelatinous layer that must be penetrated for fertilization to occur.Many sperm secrete an enzyme that can briefly thin the layer.But it only allows one sperm to penetrate.Once a sperm has entered, CONCEPTION has taken place and the layer thickens, locking other sperm out.Chromosomes from the sperm cell line up across from corresponding chromosomes within the egg cell.Form 23 new pairs with unique set of genetic instructionsSee figure 2.9 on p. 34
54 INFERTILITYApproximately 1 in 6 American couples experiences problems with conception.The term infertility is not usually applied until conceiving on their own has been unsuccessful for 1 year.Once viewed as primarily a female problemIt is a male problem 40% of the time.Next slides will detail male and female infertility problems
55 INFERTILITY PROBLEMS IN MEN Low sperm countMost common problem in menDeformed spermGenetic factorsEnvironmental poisonsLow motility (poor swimmers)Infectious diseases (such as STI’s)Chronic diseases (such as diabetes)Injury of the testesOverheating, as seen in long distance runners or from using narrow bicycle seatsAn “autoimmune” responseMan’s body attacks his own sperm as a foreign agents
56 INFERTILITY PROBLEMS IN WOMEN Irregular ovulation or failure to ovulateMost common problem in womenDeclining hormone levelsSo-called “fertility” drugs (e.g., clomiphene & pergonal) may cause multiple births by stimulating more than one ovum to ripen during a monthEndometriosisInflammation of the tissue that is sloughed off during menstruationCan be treated with hormones or surgeryMore common among women who delay childbearingObstructions/malfunctions of reproductive tractInfections may scar the fallopian tubes and other organs impeding passage of sperm or ovaPelvic inflammatory disease (PID)From bacterial or vial infections, including STIs gonorrhea & chlamydiaAntibiotics may help infections but infertility may be irreversible.
57 Methods Used to Help Infertile Couples Bear Children Artificial InseminationSperm collected and quick-frozenInjected into woman’s uterus at ovulationIn Vitro Fertilization (IVF) “test-tube” babiesOva and sperm are placed in a laboratory dish for fertilization.Injected for implantation into mother’s uterus for gestationMay take several attempts because only a minority of tries meet with success; several embryos may be injected at oncePerformed rather routinely; expensive; no guaranteesAnswer to T-F? # 5: :Test-tube babies are grown in a laboratory dish throughout their 9-month gestation period. FICTION = This is not true: they are conceived in laboratory dishes but then implanted in the uterus for gestation.Good topic for class discussion on IVVF would be the recent news story of the “Octo-Mom” … producing 8 live babies form IVF. Much controversy surrounds the ethical standards of multiple implantations, students will usually have strong opinions on this topic.
58 Methods Used to Help Infertile Couples Bear Children Surrogate MothersWomen who carry babies to term for other womenUsually paid and sign a contract to surrender parental rights to childCan sometimes be a woman and man’s ova and sperm fertilized IVF and implanted in surrogateOr can be surrogates ova and artificial insemination by man if woman’s ovum are not viable
60 Selecting the Sex of Your Child Preimplantation Genetic Diagnosis (PGD)Developed to detect genetic disordersAlso revels sex of embryoOva are fertilized in vitroAfter a few days of cell division, chromosomal structure examined microscopically to reveal sexEmbryos of the desired sex are implanted where one or more may grow to termAgain...implantation cannot be guaranteed.Answer to T-F? Q # 6: You can select the sex of your child. Answer: TRUE, the method for doing so is called preimplantation genetic diagnosis (PGD).This is also a good topic for class discussion on the implications and ramifications of sex selection. Will more people choose boys than girls? If so, how will that impact the ratio of M/F births?