Developmental Psychology - Module 2 PDF

Prepared and compiled: CHRISTINE P. GULIMAN Instructor **COURSE CODE : Psych 202** **COURSE TITLE : Developmental Psychology** **MODULE 2 : The Biological Basis of Development**  **Learning Objectives:** 1. How does fertilization both natural and eternal occur? 2. Wha...

Prepared and compiled: CHRISTINE P. GULIMAN Instructor **COURSE CODE : Psych 202** **COURSE TITLE : Developmental Psychology** **MODULE 2 : The Biological Basis of Development**  **Learning Objectives:** 1. How does fertilization both natural and eternal occur? 2. What are the mechanisms of heredity and what could go wrong? 3. What are the major features and anticipated uses of the Human Genome Project? **Introduction:** This module introduces the process of fertilization, how heredity works and examine the Human Genome Project. **Let's begin!** Heredity is the genetic heritage passed down by our biological parents. It's why we look like them! More specifically, it is the transmission of traits from one generation to the next. These traits can be physical, such as eye color, blood type or a disease, or behavioral. **The Fertilization Process** The fusion of two specialized cells- the sperm and the egg/ovum, mark the beginning of development and the zygote- the fertilized ovum immediately begins to divide. This fertilized ovum contains all the genetic material that the organism will ever possess. **The Beginning** In our analysis of genetic material and its impact on our lives, we'll attempt to follow the way we receive genes from our parents, so let's begin with the male's sperm and the female's egg. **The Sperm** It is a tightly packed tip (the acrosome), containing 23 chromosomes, a short neck region, and a tail to propel it in its search for the egg. Sperm remain capable of fertilizing an egg for about 24 to 48 hours after ejaculation. The major purpose of the male's reproductive organs is to manufacture, store, and deliver sperm. The sperm has its sole objective the delivery of its DNA to the egg. **The Ovum (Egg)** The egg is round, and its surface is about the consistency of stiff jelly. When females are born, they already have primal eggs. From 1 to 2 million eggs have been formed in the ovaries. There is only one matured egg required each month. Eggs are usually fertilized about 12 hours after they are discharged from the surface of the ovary, or they die within 12 to 24 hours. **The Menstrual Cycle** The pituitary gland secretes a hormone that stimulates the ripening of eggs, and after two weeks one egg, which has ripened more than the others, is discharged from the ovary's surface. This process, called ***ovulation***, triggers a chemical reaction that inhibits the ripening of further eggs. It also prepares the uterine lining for a potential fertilized ovum. If fertilization does not occur, the prepared uterine lining is shed in menstruation and the entire process begins again. As a woman approaches the end of her egg-producing years, these last ova have been present for as many 40 years. This may explain why the children of older women are more susceptible to genetic defects. The eggs have been exposed to environmental hazards such as radiation too long to escape damage (Jones, 1993; Moore & Persaud, 1998). **The Implantation** When the egg is discharged from the ovary's surface it is enveloped by one of the ***fallopian tubes***. The diameter of each fallopian tube is about that of a human hair, but it almost unfailingly ensnares the egg and provides a passageway to the uterus. If fertilization occurs, it takes place soon after the egg enters the fallopian tube. Fusion of the two cells is quickly followed by the first cell division. As the fertilized egg, now called ***zygote***, travels toward ***implantation*** within the uterus, cell division continues. The cells multiply rapidly and after about seven days reach the uterine wall. The fertilized egg is now called ***blastocyst***. Although individuals may change in the course of their lives, their hereditary properties do not change. The zygote, containing all 4 chromosomes, represents the "blueprint" for our physical and mental makeup. **Heredity at Work** As your recall from module one, nature refers to the contribution of genetics to one's development. The basic building block of the nature perspective is the gene. Genes are specific sequence of nucleotides and are recipes for making proteins. Proteins are responsible for influencing the structure and functions of cells. Genes are located on the chromosomes and there are an estimated 20,500 genes for humans, according to the Human Genome Project (NIH, 2015). Normal human cells contain 46 chromosomes (or 23 pairs; one from each parent) in the nucleus of the cells. After conception, most cells of the body are created by a process called ***mitosis***. ***Mitosis*** is defined as the cell's nucleus making an exact copy of all the chromosomes and splitting into two new cells. However, the cells used in sexual reproduction, called the gametes (sperm or ova), are formed in a process called ***meiosis***. In meiosis the gamete's chromosomes duplicate, and then divide twice resulting in four cells containing only half the genetic material of the original gamete. Thus, each sperm and egg possesses only 23 chromosomes and combine to produce the normal 46. Given the amount of genes present and the unpredictability of the meiosis process, the likelihood of having offspring that are genetically identical (and not twins) is one in trillions (Gould & Keeton, 1997). Of the 23 pairs of chromosomes created at conception, 22 pairs are similar in length. These are called autosomes. The remaining pair, or sex chromosomes, may differ in length. If a child receives the combination of XY the child will be genetically male. If the child receives the combination XX the child will be genetically female. **Chromosomes and Genes** After the sperm andd egg unite, the new cell possess 23 pairs of chrommosomes, or 46 chromosomes, which represents our total biological heritage. Until 1956, the number of human chromosomes was though to be 48 (Korf, 1996). The sperm acctually determines sex, since it alone can carry a Y chromosome. Thus there are two kinds of sperms: the X chromosome carrier and the Y chromosome carrier. The Y carrier is smaller than the X, which contains more genetic material. The Y carrier is lighter and speedier andd can reach the egg more quickly. But it is also more vulnerable. One member of each pair of chromosomes has been contributed by the father and one by the mother. Each pair exccept the 23^rd^, is remarkably alike. The 23^rd^ pair defines the inddividual's sex: an XX combination indicates a female; XY indicates a male. The signficance of the chromosomes lies in the material they contain- the genes. Each gene is located at a particular spot on the chromosome, called the ***gene locus***. The genes, whose chemical structure is **DNA**, account for all inheritedd characteristics, from hair and eye color to skin shade, even the tendency toward baldness. **Genotypes and Phenotypes** The word genotype refers to the sum total of all the genes a person inherits. The word phenotype refers to the features that are actually expressed. Look in the mirror. What do you see, your genotype or your phenotype? What determines whether or not genes are expressed? Because genes are inherited in pairs on the chromosomes, we may receive either the same version of a gene from our mother and father, that is, be homozygous for that characteristic the gene influences. If we receive a different version of the gene from each parent, that is referred to as heterozygous. In the homozygous situation we will display that characteristic. It is in the heterozygous condition that it becomes clear that not all genes are created equal. Some genes are dominant, meaning they express themselves in the phenotype even when paired with a different version of the gene, while their silent partner is called recessive. Recessive genes express themselves only when paired with a similar version gene. Geneticists refer to different versions of a gene as alleles. Some dominant traits include having facial dimples, curly hair, normal vision, and dark hair. Some recessive traits include red hair, being nearsighted, and straight hair. Most characteristics are not the result of a single gene; they are polygenic, meaning they are the result of several genes. In addition, the dominant and recessive patterns described above are usually not that simple either. Sometimes the dominant gene does not completely suppress the recessive gene; this is called incomplete dominance. An example of this can be found in the recessive gene disorder sickle cell disease. The gene that produces healthy round-shaped red blood cells is dominant. The recessive gene causes an abnormality in the shape of red blood cells; they take on a sickle form, which can clog the veins and deprive vital organs of oxygen and increase the risk of stroke. To inherit the disorder a person must receive the recessive gene from both parents. Those who have inherited only one recessive-gene are called carriers and should be unaffected by this recessive trait. Yet, carriers of sickle cell have some red blood cells that take on the c-shaped sickle pattern. Under circumstances of oxygen deprivation, such as high altitudes or physical exertion, carriers for the sickle cell gene may experience some of the symptoms of sickle cell (Berk, 2004). **Monozygotic and Dizygotic Twins** Many students are interested in twins. Monozygotic or identical twins occur when a fertilized egg splits apart in the first two weeks of development. The result is the creation of two separate but genetically identical offspring. That is, they possess the same genotype and often the same phenotype. About one third of twins are monozygotic twins. Sometimes, however, two eggs or ova are released and fertilized by two separate sperm. The result is dizygotic or fraternal twins. These two individuals share the same amount of genetic material as would any two children from the same mother and father. In other words, they possess a different genotype and phenotype. Older mothers are more likely to have dizygotic twins than are younger mothers and couples who use fertility drugs are also more likely to give birth to dizygotic twins Consequently, there has been a n increase in the number of fraternal twins recently (Bortolus et al., 1999). Monozygotic Twins Dizygotic Twins **Genetic Disorders** Most of the known genetic disorders are dominant gene-linked; however, most dominant gene linked disorders are not serious or debilitating. For example, the majority of those with Tourette\'s Syndrome suffer only minor tics from time to time and can easily control their symptoms. Huntington\'s Disease is a dominant gene linked disorder that affects the nervous system and is fatal but does not appear until midlife. Recessive gene disorders, such as cystic fibrosis and sickle-cell anemia, are less common, but may claim more lives because they are less likely to be detected as people are unaware that they are carriers of the disease. Some genetic disorders are sex-linked; the defective gene is found on the X-chromosome. Males have only one X chromosome so are at greater risk for sex-linked disorders due to a recessive gene, such as hemophilia, color-blindness, and baldness. For females to be affected by the genetic defects, they need to inherit the recessive gene on both X-chromosomes, but if the defective gene is dominant, females can be equally at risk. such as hemophilia, color-blindness, and baldness. For females to be affected by the genetic defects, they need to inherit the recessive gene on both X-chromosomes, but if the defective gene is dominant, females can be equally at risk. +-----------------------------------+-----------------------------------+ | **Recessive Disorders | **Cases per Birth** | | (Homozygous):** The individual | | | inherits a gene change from both | | | parents. If the gene is inherited | | | from just one parent, the person | | | is a carrier and does not have | | | the condition. | | +-----------------------------------+-----------------------------------+ | **Sickle Cell Disease** (SCD) is | 1 in 500 Black births | | a condition in which the red | | | blood cells in the body are | 1 in 36,000 Hispanic births | | shaped like a sickle (like the | | | letter C) and affect the ability | | | of the blood to transport oxygen. | | | Carriers may experience some | | | effects, but do not have the full | | | condition. | | +-----------------------------------+-----------------------------------+ | **Cystic Fibrosis** (CF) is a | 1 in 3500 | | condition that affects breathing | | | and digestion due to thick mucus | | | building up in the body, | | | especially the lungs and | | | digestive system. In CF, the | | | mucus is thicker than normal and | | | sticky. | | +-----------------------------------+-----------------------------------+ | **Phenylketonuria (PKU)** is a | 1 in 10,000 | | metabolic disorder in which the | | | individual cannot metabolize | | | phenylalanine, an amino acid. | | | Left untreated intellectual | | | deficits occur. PKU is easily | | | detected and is treated with a | | | special diet. | | +-----------------------------------+-----------------------------------+ | **Tay Sachs Disease** is caused | 1 in 4000 | | by enzyme deficiency resulting in | | | the accumulation of lipids in the | 1in 30 American Jews is a carrier | | nerve cells of the brain. This | | | accumulation results in | 1 in 20 French Canadians is a | | progressive damage to the cells | carrier | | and a decrease in cognitive and | | | physical development. Death | | | typically occurs by age five. | | +-----------------------------------+-----------------------------------+ | **Albinism** is when the | Fewer than 20,000 US cases per | | individual lacks melanin and | year | | possesses little to no pigment in | | | the skin, hair, and eyes. Vision | | | problems can also occur. | | +-----------------------------------+-----------------------------------+ | **Autosomal Dominant Disorders | **Cases per Birth** | | (Heterozygous):** In order to | | | have the disorder, the individual | | | only needs to inherit the gene | | | change from one parent. | | +-----------------------------------+-----------------------------------+ | **Huntington's Disease** is a | 1 in 10,000 | | condition that affects the | | | individual's nervous system. | | | Nerve cells become damaged, | | | causing various parts of the | | | brain to deteriorate. The disease | | | affects movement, behavior and | | | cognition. It is fatal, and | | | occurs at midlife. | | +-----------------------------------+-----------------------------------+ | **Tourette Syndrome** is a tic | 1 in 250 | | disorder which results in | | | uncontrollable motor and vocal | | | tics as well as body jerking. | | +-----------------------------------+-----------------------------------+ | **Achondroplasia** is the most | 1 in 15,000-40,000 | | common form of disproportionate | | | short stature. The individual has | | | abnormal bone growth resulting in | | | short stature, disproportionately | | | short arms and legs, short | | | fingers, a large head, and | | | specific facial features. | | +-----------------------------------+-----------------------------------+ | **Sex-Linked Disorders:** When | **Cases per Birth** | | the X chromosome carries the | | | mutated gene, the disorder is | | | referred to as an X-linked | | | disorder. Males are more affected | | | than females because they possess | | | only one X chromosome without an | | | additional X chromosome to | | | counter the harmful gene. | | +-----------------------------------+-----------------------------------+ | **Fragile X Syndrome** occurs | 1 in 4000 males | | when the body cannot make enough | | | of a protein it needs for the | 1 in 8000 females | | brain to grow and problems with | | | learning and behavior can occur. | | | Fragile X syndrome is caused from | | | an abnormality in the X | | | chromosome, which then breaks. If | | | a female has fragile X, her | | | second X chromosome usually is | | | healthy, but males with fragile X | | | don't have a second healthy X | | | chromosome. This is why symptoms | | | of fragile X syndrome usually are | | | more serious in males. | | +-----------------------------------+-----------------------------------+ | **Hemophilia** occurs when there | 1 in 10,000 males | | are problems in blood clotting | | | causing both internal and | | | external bleeding. | | +-----------------------------------+-----------------------------------+ | **Duchenne Muscular Dystrophy** | 1 in 3500 males | | is a weakening of the muscles | | | resulting in an inability to | | | move, wasting away, and possible | | | death. | | +-----------------------------------+-----------------------------------+ **Chromosomal Abnormalities** A ***chromosomal abnormality*** occurs when a child inherits too many or two few chromosomes. The most common cause of chromosomal abnormalities is the age of the mother. As the mother ages, the ovum is more likely to suffer abnormalities due to longer term exposure to environmental factors. Consequently, some gametes do not divide evenly when they are forming. Therefore, some cells have more than 46 chromosomes. In fact, it is believed that close to half of all zygotes have an odd number of chromosomes. Most of these zygotes fail to develop and are spontaneously aborted by the mother's body. One of the most common chromosomal abnormalities is on pair 21. ***Trisomy 21 or Down syndrome*** occurs when there are three rather than two 21st chromosomes. A person with Down syndrome typically exhibits an intellectual disability and possesses certain physical features, such as short fingers and toes, folds of skin over the eyes, and a protruding tongue. There is as much variation in people with Down syndrome as in most populations, and those differences need to be recognized and appreciated. Other less common chromosomal abnormalities of live-born infants occur on chromosome 13 and chromosome 18. When the abnormality is on 23rd pair the result is a ***sex-linked chromosomal abnormality***. A person might have XXY, XYY, XXX, XO. Two of the more common sex-linked chromosomal disorders are Turner syndrome and Klinefelter syndrome. ***Turner syndrome*** occurs when part or all of one of the X chromosomes is lost and the resulting zygote has an XO composition. This occurs in 1 of every 2,500 live female births (Carroll, 2007) and affects the individual's cognitive functioning and sexual maturation. The external genitalia appear normal, but breasts and ovaries do not develop fully and the woman does not menstruate. Turner syndrome also results in short stature and other physical characteristics. Klinefelter syndrome (XXY) results when an extra X chromosome is present in the cells of a male and occurs in 1 out of 650 live male births. The Y chromosome stimulates the growth of male genitalia, but the additional X chromosome inhibits this development. An individual with ***Klinefelter syndrome*** typically has small testes, some breast development, infertility, and low levels of testosterone (National Institutes of Health, 2019). **Chromosomal Disorders** +-----------------------------------+-----------------------------------+ | **Autosomal Chromosome | **Cases per Birth** | | Disorders:** The individual | | | inherits too many or two few | | | chromosomes. | | +-----------------------------------+-----------------------------------+ | **Down Syndrome/Trisomy 21** is | 1 in 691 | | caused by an extra chromosome 21 | | | and includes a combination of | 1 in 300 births at age 35 | | birth defects. Affected | | | individuals have some degree of | | | intellectual disability, | | | characteristic facial features, | | | often heart defects, and other | | | health problems. The severity | | | varies greatly among affected | | | individuals. | | +-----------------------------------+-----------------------------------+ | **Trisomy 13** is caused by an | 1 in 7,906 | | extra chromosome 13. Affected | | | individuals have multiple birth | | | defects and generally die in the | | | first weeks or months of life. | | +-----------------------------------+-----------------------------------+ | **Trisomy 18** is caused by an | 1 in 3,762 | | extra chromosome 18 and the | | | affected individual also has | | | multiple birth defects and early | | | death. | | +-----------------------------------+-----------------------------------+ | **Sex-Linked Chromosomal | **Cases per Birth** | | Disorders:** The disorder occurs | | | on chromosome pair \#23 or the | | | sex chromosomes. | | +-----------------------------------+-----------------------------------+ | **Turner Syndrome** is caused | 1 in 2500 females | | when all or part of one of the X | | | chromosomes is lost before or | | | soon after conception due to a | | | random event. The resulting | | | zygote has an XO composition. | | | Turner Syndrome affects cognitive | | | functioning and sexual maturation | | | in girls. Infertility and a short | | | stature may be noted. | | +-----------------------------------+-----------------------------------+ | **Klinefelter Syndrome** is | 1 in 650 males | | caused when an extra X chromosome | | | is present in the cells of a male | | | due to a random event. The Y | | | chromosome stimulates the growth | | | of male genitalia, but the | | | additional X chromosome inhibits | | | this development. The male can | | | have some breast development, | | | infertility, and low levels of | | | testosterone. | | +-----------------------------------+-----------------------------------+ **The Human Genome Project** In 1990 the Human Genome Project (HGP), an international scientific endeavor, began the task of sequencing the 3 billion base pairs that make up the human genome. In April of 2003, more than two years ahead of schedule, scientists gave us the genetic blueprint for building a human. Since then, using the information from the HGP, researchers have discovered the genes involved in over 1800 diseases. In 2005 the HGP amassed a large data base called HapMap that catalogs the genetic variations in 11 global populations. Data on genetic variation can improve our understanding of differential risk for disease and reactions to medical treatments, such as drugs. Pharmacogenomic researchers have already developed tests to determine whether a patient will respond favorably to certain drugs used in the treatment of breast cancer, lung cancer or HIV by using information from HapMap (NIH, 2015). Future directions for the HGP include identifying the genetic markers for all 50 major forms of cancer (The Cancer Genome Atlas), continued use of the HapMap for creating more effective drugs for the treatment of disease, and examining the legal, social and ethical implications of genetic knowledge (NIH, 2015). From the outset, the HGP made ethical issues one of their main concerns. Part of the HGP's budget supports research and holds workshops that address these concerns. Who owns this information, and how the availability of genetic information may influence healthcare and its impact on individuals, their families, and the greater community are just some of the many questions being addressed (NIH, 2015). **Learning Materials** **Fertilization Video**- https://www.youtube.com/watch?v=\_5OvgQW6FG4 **Genome Video**- https://unlockinglifescode.org/media/animations/659\#660 **References** **Lally, M. & Valentine-French, S. (2019). *Lifespan Development: A Psychological Perspective Second Edition*. Retrieved from http://dept.clcillinois.edu/psy/LifespanDevelopment.pdf** **Dacey, J., & Travers, J. (2002, 1999, 1996). *Human Development Across the Lifespan, Fifth Edition.* Mc---Graw Hill Companies, Inc. 1221 Avenue of the Americas, New York, NY 10020**