Biological Beginnings CHAPTER 2 GENOTYPE AND PHENOTYPE Genotype

Biological Beginnings CHAPTER 2

GENOTYPE AND PHENOTYPE Genotype – genetic makeup of an individual Phenotype -- observable characteristics of an individual Phenotypes include physical characteristics (such as height, weight, and hair color) psychological characteristics (such as personality and intelligence)

GENETIC FOUNDATIONS OF DEVELOPMENT Each of us carries a “genetic code” that we inherited from our parents A fertilized human egg carries this human code Fertilized human egg cannot grow into any other species Each of us began life as a single cell which contained our entire genetic code

CHROMOSOMES Nucleus of each human cell contains 46 chromosomes Chromosomes -- thread-like structures made up of deoxyribonucleic acid, or DNA is a complex molecule that has a double helix shape, like a spiral staircase, and contains genetic information

(c) 2008 The Mc. Graw-Hill Companies, Inc.

GENES Genes - units of hereditary information short segments of DNA A human has approximately 20, 000 - 25, 000 Genes direct cells to reproduce themselves and to assemble proteins Proteins the building blocks of cells the regulators that direct the body’s processes over 300, 000 different proteins (Mader, 2008)

HUMAN GENOME PROJECT Preliminary map of the human genome -- the complete set of developmental instructions for creating proteins that initiate the making of a human organism Each human has 20, 000 – 30, 000 genes Human genome consists of many genes that collaborate both with each other and with non -genetic factors inside and outside the body Genetic expression is affected by their environment � Hormones and other aspects of cell environment can turn genes on or off

MITOSIS All body cells, except the sperm and egg, have 46 chromosomes arranged in 23 pairs Body cells reproduce by a process called mitosis During mitosis, the cell’s nucleus—including the chromosomes—duplicates itself and the cell divides Two new cells are formed, each containing the same DNA as the original cell

MEIOSIS Sex cell division is different type of cell division Eggs and sperm (or gametes) are formed in meiosis A cell of the testes (in men) or ovaries (in women) duplicates its chromosomes but then divides twice, thus forming four cells Each of these has only half of the genetic material of the parent cell By the end of meiosis, each egg or sperm has 23 unpaired chromosomes

FERTILIZATION Zygote -- an egg and a sperm fuse to create a single cell In the zygote, the 23 unpaired chromosomes from the egg and sperm combine to form one set of 23 paired chromosomes One chromosome of each pair is from the mother’s egg and the other from the father’s sperm Each parent contributes half of the offspring’s genetic material

THE 23 RD PAIR OF CHROMOSOMES Slight difference in the 23 rd pair In females, the 23 rd pair consists of two chromosomes called X chromosomes In males, the 23 rd pair consists of an X and a Y chromosome The presence of a Y chromosome is what makes an individual male

SOURCES OF VARIABILITY Combining genes of two parents increases genetic variability in the population Chromosomes in the zygote are not exact copies of the parents Another source of variability comes from DNA mutated gene -- a permanently altered segment of DNA

ALLELES Two forms of the same gene Appear at the same place on both chromosomes in a pair One inherited from each parent Homozygous – the two alleles are alike Heterozygous – the alleles differ

DOMINANT-RECESSIVE GENES PRINCIPLE Dominant -- one gene of a pair always exerts its effects Recessive gene -- exerts influence only if the two genes of a pair are both recessive may be overridden by a dominant gene may be carried from generation to generation but not expressed in phenotype Mutated genes are nearly always recessive as are the majority of disease carrying genes

SEX-LINKED GENES X-linked inheritance -- mutated gene is carried on the X chromosome �males have no “backup” copy to counter the harmful gene Males are therefore more likely to display the trait as part of their phenotype �females have a second X chromosome, which is likely to be unchanged Females who have one changed copy of the X gene are known as “carriers” (Turner, 2006)

MORE INHERITANCE PATTERNS Incomplete Dominance � Both alleles of a single gene are expressed � Results in combined trait or intermediate between the two Genetic transmission is usually quite complex � few characteristics reflect the influence of only a single gene or pair of genes Polygenically determined characteristics -- determined by the interaction of many different genes

CHROMOSOME ABNORMALITIES Down syndrome -- caused by the presence of an extra copy of chromosome 21 once in every 700 live births women aged 16 - 34 are less likely to give birth to a child with Down syndrome Sex-Linked Chromosome Abnormalities

GENE-LINKED ABNORMALITIES Phenylketonuria (PKU) -- individual cannot properly metabolize phenylalanine, an amino acid left untreated, phenylalanine builds up in the child, producing mental retardation and hyperactivity Sickle-cell anemia -- genetic disorder that impairs the body’s red blood cells most often in African Americans red blood cell becomes a hook-shaped cannot carry oxygen properly “sickle” that

GENETIC COUNSELING Helps couples: Assess chances of hereditary disorders Choose best course of action � � Risks Family goals Recommended when: � � � Couple has had difficulties Aware of genetic problems Woman is over 35

ENVIRONMENT HEREDITY INTERACTION Reaction range- a limit on the possible phenotype expressions of a particular genotype for example, how much can a stimulating environment increase intelligence Canalization- the degree to which genetically determined traits are resistant to environmental influences. Higher canalization implies greater resistance.

HEREDITY-ENVIRONMENT CORRELATIONS Genes influence the environments to which an individual is exposed � Passive genotype-environment correlation Biological parents select environments for their offspring � Evocative genotype-environment correlation Characteristics of the child elicit certain types of environments and treatment � Active (niche picking) genotype-environment correlation Children seek out environments that they find compatible and stimulating

THE EPIGENETIC VIEW Development is the result of an ongoing, bidirectional interchange between heredity and the environment Heredity and environment operate together— or collaborate—to produce a person’s intelligence, temperament, height, weight, ability to pitch a baseball, ability to read, etc. (Gottlieb, Wahlsten, & Lickliter, 2006)

WADDINGTON’S EPIGENETIC LANDSCAPE

GOTTLIEB DIAGRAM Environment Behavior Physiology Genetics

PRENATAL DIAGNOSTIC METHODS Amniocentesis Chorionic Villus Sampling Fetoscopy Ultrasound Maternal Blood Analysis Preimplantation Genetic

AMNIOCENTESIS AND CHORIONIC VILLUS SAMPLING

THREATS TO PRENATAL DEVELOPMENT Teratogens –any agent than can potentially harm a developing fetus Dose- risk increases at higher doses Genetic susceptibility- mother’s and developing baby’s genotype can affect type and severity of effects Timing – some substance only cause damage at certain critical periods. Also they type of damage that is likely varies by prenatal developmental period. Generally the embryonic period has the greatest risk of structural defects

APGAR SCALE Used to assess the health of newborns at one and five minutes after birth A score, or reading, of 0, 1, or 2 on each of these five health signs heart rate, respiratory effort, muscle tone, body color, and reflex irritability Anoxia -- an insufficient supply of oxygen

APGAR SCALE Appearance Pulse Grimace Activity Respiration 0 Blue, pale Absent No Limp response Absent 1 Body pink; Extremities blue Slow (below 100) Grimace Some flexion of extremities Slow, irregular 2 Completely pink Rapid (over 100) Cry Active motion Good, strong cry (c) 2008 The Mc. Graw-Hill Companies, Inc. Score

THREATS TO NEWBORNS Low birth weight -- less than 5 ½ pounds at birth Very low birth weight - under 3 pounds Extremely low birth weight - under 2 pounds. Preterm -- born three weeks or more before full term Small-for-date -- birth weight is below normal when the length of the pregnancy is considered

INCIDENCE AND CONSEQUENCES OF LOW BIRTH WEIGHT Incidence of low birth weight varies considerably from country to country Related to poverty, maternal health status, maternal nutrition More health and developmental problems than normal-weight infants At school age, more likely to have a learning disability, attention deficit hyperactivity disorder, or breathing problems such as asthma (Moss, 2006) (Wocadlo & Rieger, 2006)

INTERVENTIONS FOR LOW BIRTH WEIGHT/PRETERM INFANTS Kangaroo care -- a way of holding an infant so that there is skin-to-skin contact for two to three hours per day over an extended time in early infancy Massage therapy -- firm stroking with the palms of the hands three times per day for 15 -minute periods Bonding -- formation of a connection, especially a physical bond, between parents and the newborn in the period shortly after birth (Feldman & others, 2003) (Field & others, 1986)

CULTURAL DIFFERENCES IN CHILDBIRTH Pregnancy as a medical condition vs. natural process Variations in who is present at the delivery � All women Mother’s relatives, father’s relatives or both Father � Community members � Medical staff, midwife, doula, tribal leaders, religious leaders Religious and community significance Different handling and significance in the pain of childbirth How is the child announced and presented to the family and community

THE POSTPARTUM PERIOD Postpartum period -- lasts for about six weeks after childbirth or delivery or until the mother’s body has completed its adjustment and has returned to a nearly pre-pregnant state Physical and psychological adjustments Involution -- process by which the uterus returns to its pre-pregnant size

POSTPARTUM ADJUSTMENTS Baby blues -- two to three days after birth, many women begin to feel depressed, anxious, and upset Postpartum depression -- a major depressive episode about four weeks after delivery Fathers also undergo considerable adjustment in the postpartum period, even when they work away from home all day