Prenatal Development Lecture Notes PDF

LECTURE 2: PRENATAL DEVELOPMENT, BIOLOGY & BEHAVIOUR  Prenatal Development The Newborn Infant Genetic and Environment al Forces Behavioural Genetics OVERVIEW PRENATAL DEVELOPMENT Conception, De...

LECTURE 2: PRENATAL DEVELOPMENT, BIOLOGY & BEHAVIOUR  Prenatal Development The Newborn Infant Genetic and Environment al Forces Behavioural Genetics OVERVIEW PRENATAL DEVELOPMENT Conception, Developmental Processes, and Early Development Fetal Behavior, Experience, and Learning Hazards to Prenatal Development how do we go from this...? to this...? to this.... in 4 years?  350 BCE: Aristotle rejected the prevailing idea that the individual was preformed at the start of life in favour of epigenesis, the idea that there is an emergence of new structures and functions during development 17th Century - spermists believed that there was a “little man” within each sperm that would grow into a child A LITTLE HISTORY  the question of HOW we develop has been around for a very long time Recently developed research techniques and an increased understanding of genetics have led to a revolution in embryology, the study of prenatal development A LITTLE HISTORY  the question of HOW we develop has been around for a very long time Recently developed research techniques and an increased understanding of genetics have led to a revolution in embryology, the study of prenatal development A LITTLE HISTORY CONCEPTION Results from the union of two gametes, the egg and the sperm Gametes are produced through a specialised cell division, meiosis, which results in each gamete’s having only half the genetic material of all other normal cells in the body  Approximately 120 to 150 males are conceived for every 100 females because the sperm bearing the Y chromosome are lighter and swim faster to the egg than those bearing an X chromosome However, male embryos are miscarried at higher rates than female embryos, and boys are more vulnerable to developmental disorders SEX DIFFERENCES BEGIN Males are also more vulnerable to illness AT CONCEPTION throughout the life span Sex Differences Begin at Conception  THE ZYGOTE The fertilised egg, or zygote, has a full complement of human genetic material, half from each parent Marks the beginning of the three periods of prenatal development  Germinal: Begins with conception and lasts until the zygote becomes implanted in the uterine wall. Rapid cell division takes place.  Embryonic: Following implantation, major development occurs in all the organs and systems of the body. Development takes place through the processes of cell division, cell migration, cell differentiation, and cell death, as well as hormonal influences.  Fetal: Continued development of physical structures and rapid growth of the body. Increasing levels of behavior, sensory experience, and learning. PERIODS OF PRENATAL DEVELOPMENT  Four major developmental processes transform a zygote into an embryo and then into a fetus 1. Cell division results in the proliferation of cells 2. Cell migration is the movement of cells from their point of origin to somewhere else in the embryo 3. Cell differentiation transforms the embryo’s unspecialised stem cells into roughly 350 different types of cells 4. The selective death of certain cells, THE CELLS or apoptosis, also enables prenatal development  Hormones play a crucial role in sexual differentiation  All human fetuses can develop either male or female genitalia, depending on the presence or absence of testosterone One of the many ways in which the fetus acts as an instigator of its own development THE ROLE OF HORMONES THE BLASTOCYST By the 4th day after conception, the zygote arranges itself into a hollow sphere of cells with a bulge of cells, the inner cell mass, on one side  The inner cell mass eventually forms into the embryo Identical twins originate from the splitting in half of the inner cell mass, resulting in the development of genetically identical individuals (100%) Fraternal twins result when two eggs are released into the fallopian tube at the same time and are fertilised by different sperm - genetically the same as any siblings (50%)  After implantation, the inner cell mass becomes the embryo and the rest of the cells develop into its support system The neural tube is a U-shaped groove formed from the top layer of differentiated cells in the embryo  It eventually becomes the brain and the spinal THE EMBRYO cord  The support system includes:  Placenta: Permits the exchange of materials between the bloodstream of the fetus and that of the mother  Umbilical cord: The tube that contains the blood vessels that travel from the placenta to the developing organism and back THE EMBRYO again PROTECTING THE FETUS The placental membrane is a barrier against some, but not all toxins and infectious agents The amniotic sac, a membrane filled with fluid in which the fetus floats, provides a protective buffer for the fetus EMBRYO AT 4 WEEKS FACE DEVELOPMENT FROM 5½ TO 8 WEEKS FETUS AT 9 WEEKS FETUS AT 11 WEEKS FETUS AT 16 WEEKS FETUS AT 18 WEEKS FETUS AT 20 WEEKS FETUS AT 28 WEEKS http://www.ted.com/talks/view/lang///id/1270 CEPHALOCAUDAL DEVELOPMENT Prenatal development from the 4th week on is cephalocaudal Areas near the head develop earlier than those farther away  By 12 weeks after gestation, most of the movements that will be THE FETUS: present at birth have appeared AN ACTIVE  Swallowing amniotic fluid promotes the CONTRIBUTOR normal development of the palate and aids in the maturation of the digestive TO ITS OWN system  Movement of the chest wall and pulling DEVELOPMENT in and expelling small amounts of amniotic fluid help the respiratory system become functional FETAL REST-ACTIVITY CYCLES Become stable during the second half of pregnancy Circadian rhythms are also apparent Near the end of pregnancy, the fetus’s sleep and wake states are similar to those of the newborn SENSATION The sensory structures are present relatively early in prenatal development and play a vital role in fetal development and learning  The fetus experiences tactile stimulation as a result of its own activity, and tastes and smells the amniotic fluid  It responds to sounds from at least the 6th month of gestation  Prenatal visual experience, however, is negligible FETAL LEARNING At 32 weeks’ gestation, the fetus decreases responses to repeated or continued stimulation, a simple form of learning called habituation FETAL LEARNING Newborn infants have been shown to recognise rhymes and stories presented before birth Newborns also prefer smells, tastes, and sound patterns that are familiar because of prenatal exposure (De Caspar & Spence, 1986)  time to learn SENSITIVE PERIODS time to develop SENSITIVE PERIODS A key element in experience- expectant plasticity is timing There are a few sensitive periods when the human brain is particularly sensitive to particular kinds of external stimuli EXPERIENCE-EXPECTANT PLASTICITY The process through which the normal wiring of the brain occurs in part as a result of the kinds of general experiences that every human who inhabits any reasonably normal environment will have Is accompanied by vulnerability  If the expected experience is not available, as in the case of congenital cataracts, development will be impaired EXPERIENCE-DEPENDENT PLASTICITY The process through which neural connections are created and reorganised throughout life as a function of an individual’s experience TERATOGENS Environmental agents that have the potential to cause harm during prenatal development Timing is a crucial factor in the severity of the effects of potentially harmful agents  Many agents cause damage only if exposure occurs during a sensitive in development SENSITIVE PERIODS TERATOGENS Most teratogens show a dose-response relation  Increases in exposure to potential teratogens are associated with greater probabilities of fetal defects and with more severe problems Individual differences also influence the effects of teratogens TERATOGENS Identifying teratogens is made difficult by the existence of sleeper effects in which the impact of a given agent may not be apparent for many years Teratogens include legal as well as illegal substances... SOME ENVIRONMENTAL HAZARDS TO FETUS OR NEWBORN p. 62 TERATOGENS Maternal alcoholism can lead to fetal alcohol syndrome (FAS), which is associated with mental retardation, facial deformity, and other problems  TERATOGENS Cigarette smoking during pregnancy is linked to retarded growth and low birth weight  Cigarette smoking has also been linked to SIDS (sudden infant death syndrome), although the ultimate causes of SIDS are still unknown  Parents can reduce the risk of SIDS by not smoking, putting babies to sleep on their backs rather than on their stomachs, using firm mattresses and no pillows as bedding for infants, and avoiding wrapping infants in lots of blankets or clothing THE NEWBORN INFANT State of Arousal Negative Outcomes at Birth  INTERACTING WITH THE ENVIRONMENT State: The infant’s level of arousal and engagement in the environment  Ranges from deep sleep to intense activity  Is an important influence in the newborn’s exploration of the world  SIX STATES OF AROUSAL 1. Active sleep 2. Quiet sleep 3. Crying 4. Active awake 5. Alert awake 6. Dozing NEWBORN STATES  Newborns sleep twice as much as young adults The pattern of two different sleep states changes dramatically  REM (rapid eye movement) sleep: An active sleep state associated with dreaming in adults and is characterised by quick, jerky eye movements under closed lids  Non-REM sleep: A quiet or deep sleep state characterised by the absence of motor activity or eye movements and by regular, slow brain waves, SLEEP breathing, and heart rate SLEEP REM sleep constitutes fully 50% of a newborn’s total sleep time and declines rapidly to only 20% by 3 or 4 years of age... According to autostimulation theory, brain activity during REM sleep in the fetus and newborn makes up for natural deprivation of external stimuli and facilitates the early development of the visual system CRYING Early in infancy, crying reflects discomfort or frustration Crying gradually becomes more of a communicative act  With experience, parents become better at interpreting the characteristics of the cry itself CRYING Many effective soothing techniques, including swaddling (wrapping a baby tightly in cloths or a blanket), involve moderately intense and continuous or repetitive stimulation Parents of babies with colic, (excessive crying for no apparent reason) should seek social support and relief from frustration— and remember that colic typically ends within a few months RISK FACTORS Tend to occur together in the world A negative outcome is more likely when there are multiple risk factors Despite multiple risk factors, however, some individuals do well  Refers to successful development in the face of multiple and seemingly overwhelming developmental hazards DEVELOPMENTAL RESILIENCE Resilient children often experience responsive care from a particular caregiver and possess personal characteristics such as intelligence and responsiveness to others Genetic and Environmental Forces Behavioural Genetics THE INTERPLAY OF HEREDITY AND ENVIRONMENT Both heredity and environment influence individuals’ characteristics  When scientists first began to investigate the contributions of heredity and environment, they generally emphasised one factor or the other as the prime influence  Recent efforts to map the human genome established that individuals differ from one another by less than 1.5% of their genes  Three key elements  Genotype: The genetic material an individual inherits MODEL OF  Phenotype: The observable expression INTERACTION of the genotype, including body characteristics and behaviour  Environment: Includes every aspect of the individual, and his or her surroundings, other than genes  FUNDAMENTAL 1. RELATIONS Parents’ genetic contribution to the child’s genotype 2. Contributions of the child’s genotype to his or her own phenotype 3. Contribution of the child’s environment to his or her own phenotype 4. Influence of the child’s phenotype on his or her environment FUNDAMENTAL RELATIONS Parents’ Child’s Genotype Genotype Child’s Child’s Environment Phenotype  GENETICS Genetic material is passed on as chromosomes— long, threadlike molecules made up of DNA  Carry all the biochemical instructions involved in the formation and functioning of an organism  Genes are sections of chromosomes that are the basic units of heredity for all living things  Genes do not code directly ‘for’ behaviours or traits. Rather, genes operate at the level of the cells to create subtle biochemical structural and functional differences between people that — over the course of development AND and in concert with the environment — act in a Humans typically have 23 pairs of probabilistic way to guide brain development, chromosomes behaviours and exposure to environments. This is very important  Gene - molecular unit of heredity (in a living organism) - stretches of DNA and RNA, which then specifies all proteins and RNA chains Allele - one of a number of alternative forms of the same gene (what people tend to mistakenly call genes - “hair colour gene” for example) GENES Genome: total complement of genes in an organism (stored on one or more chromosome) Genes do NOT produce or control behaviour directly  Role in building and modifying the physical structures of the body  Those structure interact with the environment and produce behaviour  E.g., gene --> brain systems that react to external stimuli -- organize aggressive behaviours ALLELES About a third of human genes have two or more different forms, known as alleles  The dominant allele is the form of the gene that is expressed if present  The recessive allele is not expressed if a dominant allele is present  A person who inherits two of the same alleles for a trait is described as homozygous  A person who inherits two different alleles for a trait is described as heterozygous Humans typically have 23 pairs of chromosomes, with corresponding alleles on each chromosome in the pair GENES WORK TOGETHER Most traits studied by psychologists are influenced by multiple genes (polygeny) Most genes influence more than one phenotypic trait (pleiotropy) - classic example is Phenylketonuria (mutations on a single gene that codes for the enzyme that converts the amino acid phenylalanine to tyrosine). GENETIC ORIGINS OF HUMAN DISEASES AND DISORDERS Over 5,000 human diseases and disorders are presently known to have genetic origins Recessive gene: PKU, sickle-cell anemia, cystic fibrosis Single dominant gene: Huntington’s disease Sex-linked inheritance: Fragile-X syndrome (FMR1 gene on the X-chromosome), hemophilia (mutation on x-chromosome leading to faulty clotting factors) Errors in meiosis (resulting in a zygote with fewer or more than the normal complement of chromosomes): Down syndrome (trisomy-21), Kleinfelter syndrome (XXY) Dominant RECESSIVE Mandelian Inheritance GENETIC ORIGINS OF HUMAN DISEASES AND DISORDERS In some cases, as with sickle-cell anemia, a gene can have both  Deleterious effects: A debilitating blood disorder when both alleles are present  Benefits: Protection against malaria (prevents the disease from taking hold once the person is infected)  https://www.newscientist.com/article/dn20450-how-sickle- cell-carriers-fend-off-malaria/ Many syndromes are known to have a genetic basis, but the specific genetic mechanism has not been established  Dyslexia, Tourette’s Syndrome, ASD  SEX CHROMOSOMES Determine the individual’s biological sex at birth  Females have two X chromosomes in the 23rd pair, whereas males have an X and a Y chromosome  A gene on the Y chromosome encodes the protein that triggers the formation of the testes, which subsequently produce testosterone They don’t really “look” like an X and a Y! THE MALE DISADVANTAGE The Y chromosome has only about a third as many genes on it as the X chromosome  Because many alleles on the X chromosome do not have a corresponding allele on the Y chromosome that could suppress the action, males are more likely than females to suffer a variety of inherited disorders caused by recessive alleles on the X chromosome (e.g., colour blindness) BEHAVIOURAL GENETICS The science concerned with how variation in behaviour and development results from the combination of genetic and environmental factors Behavioural geneticists believe that most traits of interest are multifactorial  They are affected by many environmental factors as well as by many genes THE CASE OF MAO-A: MONOAMINE OXIDASE A “THE WARRIOR GENE” MAO-A is an enzyme that is encoded by the MAOA gene. In the promoter region of this gene there are repeats of a base sequence. The 2R (two repeats) variant is associated with an increase in likelihood of committing serious crime/violence Young men who had experienced severe maltreatment were in general more likely to engage in antisocial behaviour than those who had experienced none However, the effect was much stronger for those individuals who had a relatively inactive MAOA gene The Case of MAO-A: Monoamine oxidase A IMPORTANTLY, what this graph actually shows is NOT that having low MAO-A activity predisposes you to antisocial behaviour BUT that having high MAO-A activity mitigates/lessens the effect of being abused on future criminal behaviour. So, when MAO-A is high, you are protected against the effects of abuse. When it is low, abuse matters. CHILDREN’S OWN BEHAVIOUR Children are active creators of the environment in which they live  By virtue of their nature and behaviour, they evoke certain kinds of responses from others  They also actively select surroundings and experiences that support their interests, talents, and personality characteristics THE FAMILY STUDY The mainstay of modern behavioural genetics research A trait of interest is measured among groups of people who vary in genetic relatedness Correlations between the measure of the trait in individuals with different relationships are examined to see if they are higher for individuals who  Are genetically more similar  Share the same environment  TYPES OF FAMILY Twin-Study Designs: STUDIES Correlations for pairs of monozygotic twins on a trait of interest are compared to those of dizygotic twins Adoption Studies: Researchers examine whether adopted children are more like their biological or their adopted relatives MINNESOTA STUDY OF TWINS REARED APART HTTPS://MCTFR.PSYCH.UMN.EDU/RESEARCH/UM%20RESEARCH.HTML Located and studied twin siblings who have not met since they were infants  The team of investigators were struck by the similarities they found in traits like IQ, reaction to stress, and traditionalism  These similarities may be influenced by selective placement and similarities in fostering environments as well as by genetic factors  The “Jim twins”: A Cautionary Tale? Adopted at the age of four weeks. Both of Both named their pet dog "Toy." the adopting couples, unknown to each Both had some law-enforcement training other, named their son James. Upon and had been a part-time deputy sheriff in reunion of the twins when they were 39 Ohio. years old, Jim and Jim have learned that: Each did poorly in spelling and well in math. Both twins are married to women named Each did carpentry, mechanical drawing, Betty and divorced from women named and block lettering. Linda. Each vacation in Florida in the same three- One has named his first son James Alan block-long beach area. while the other named his first son James Allan. Both twins began suffering from tension headaches at eighteen, gained ten pounds Both twins have an adopted brother whose at the same time, and are six feet tall and name is Larry. 180 pounds. AVERAGE FAMILIAL IQ CORRELATIONS  How much variation in a phenotypic (observable) trait in a population is due to genetic variation among individuals in that population The concept of heritability applies only to traits that differ between individuals. If a trait exists in precisely the same form across all individuals, it may be inherited, but it cannot be heritable.” E.g. height vs number of eyes Heritability is a statistical concept. No matter what the numbers are, heritability estimates tell us nothing about the HERITABILITY specific genes that contribute to a trait. Heritability applies ONLY to populations and tells us nothing about individuals (e.g. A heritability of.40 informs us that, on average, about 40% of the individual differences that we observe in, say, shyness may in some way be attributable to genetic individual difference. It does NOT mean that 40% of any person's shyness is due to his/her genes and the other 60% is due to his/her environment.) If something has high heritability, it means that the difference in this trait across a population is due more to genetic differences than to environmental differences. That can change, however, if the environment changes and causes changes in the trait. (e.g., Amsterdam famine study) SHARED VS. NONSHARED FACTORS Most obvious source of shared environment is growing up together in the same family  Behavioral geneticists, however, have found surprisingly little effect of shared environment on some aspects of development Nonshared environment effects include experiences unique to the individual  Siblings may have quite different experiences within the same family and their experiences outside the family may diverge sharply  The primary effect of nonshared environmental factors is to increase the differences among family members NEXT WEEK Infancy and Toddlerhood – physical and cognitive development