PSYCH 11 - Chapter 2: Heredity, Prenatal Development, and Birth

The Germinal Period (1)

(about 14 days in length) lasts from conception to implantation of the fertilized egg in the lining of the uterus. At ejaculation millions of sperm are released into the vagina, but only a few reach the egg and typically only one fertilizes the egg. Once a single sperm has entered the wall of the egg, the wall becomes hard and prevents other sperm from entering. After the sperm has entered the egg, the tail of the sperm breaks off and the head of the sperm, containing the genetic information from the father, unites with the nucleus of the egg. It is typically fertilized in the top section of the fallopian tube and continues its journey to the uterus. As a result, a new cell is formed. This cell, containing the combined genetic information from both parents, is referred to as a zygote.

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.

genetic counseling

A service that assists individuals identify, test for, and explain potential genetic conditions that could adversely affect themselves or their offspring is referred to as genetic counseling.

Maternal Factors: Teenage Pregnancy

A teenage mother is at a greater risk for having pregnancy complications including anemia, and high blood pressure. These risks are even greater for those under age 15. Infants born to teenage mothers have a higher risk for being premature and having low birthweight or other serious health problems. Premature and low birthweight babies may have organs that are not fully developed which can result in breathing problems, bleeding in the brain, vision loss, and serious intestinal problems. Again, the risk is highest for babies of mothers under age 15. Reasons for these health issues include that teenagers are the least likely of all age groups to get early and regular prenatal care. Additionally, they may engage in negative behaviors including eating unhealthy food, smoking, drinking alcohol, and taking drugs. Additional concerns for teenagers are repeat births.

Second-hand and third-hand smoke:

A woman being exposed to secondhand smoke during pregnancy has also been linked to low- birth weight infants. In addition, exposure to thirdhand smoke, or toxins from tobacco smoke that linger on clothing, furniture, and in locations where smoking has occurred, results in a negative impact on infants' lung development. Rehan, Sakurai, and Torday found that prenatal exposure to thirdhand smoke played a greater role in altered lung functioning in children than exposure postnatally.

Prescription and Over-the-Counter Drugs:

A woman should not be taking any prescription drug during pregnancy unless it was prescribed by a health care provider who knows she is pregnant. Some prescription drugs can cause birth defects, problems in overall health, and development of the fetus.

Alcohol is the most common teratogen:

Alcohol use during pregnancy is the leading preventable cause of intellectual disabilities in children in the United States. Alcohol consumption, particularly during the second month of prenatal development but at any point during pregnancy, may lead to neurocognitive and behavioral difficulties that can last a lifetime. In extreme cases, alcohol consumption during pregnancy can lead to fetal death, but also can result in Fetal Alcohol Spectrum Disorders (FASD), which is an umbrella term for the range of effects that can occur due to alcohol consumption during pregnancy.

German measles (or rubella):

An infection that causes mild flu-like symptoms and a rash on the skin. Rubella has been associated with a number of birth defects. If the mother contracts the disease during the first three months of pregnancy, damage can occur in the eyes, ears, heart or brain of the unborn child. Deafness is almost certain if the other has German measles before the 11th week of prenatal development and can also cause brain damage. Women in the United States are much less likely to be afflicted with rubella, because most women received childhood vaccinations that protect her from the disease.

Teratogens

Are environmental factors that can contribute to birth defects, and include some maternal diseases, pollutants, drugs, and alcohol.

Factors influencing prenatal risks that might result from exposure to a particular teratogen: #5

Being male or female: Males are more likely to experience damage due to teratogens than are females. It is believed that the Y chromosome, which contains fewer genes than the X, may have an impact.

Example of a passive-environment correlation:

Certain behavioral characteristics, such as being athletically inclined, may run in families. The children have inherited both the genes that would enable success at these activities, and given the environmental encouragement to engage in these actions.

Example of active genotype-environment correlation

Children who are musically inclined seek out music instruction and opportunities that facilitate their natural musical ability.

The most severe form of FASD is Fetal Alcohol Syndrome (FAS):

Children with FAS share certain physical features such as flattened noses, small eye holes, and small heads. Cognitively, these children have poor judgment, poor impulse control, higher rates of ADHD, learning issues, and lower IQ scores. These developmental problems and delays persist into adulthood and can include criminal behavior, psychiatric problems, and unemployment.

Illicit Drugs:

Common illicit drugs include cocaine, ecstasy and other club drugs, heroin, marijuana, and prescription drugs that are abused. It is difficult to completely determine the effects of a particular illicit drug on a developing child because most mothers who use, use more than one substance and have other unhealthy behaviors. These include smoking, drinking alcohol, not eating healthy meals, and being more likely to get a sexually transmitted disease.

Maternal Factors: Depression

Depression is a significant medical condition in which feelings of sadness, worthlessness, guilt, and fatigue interfere with one's daily functioning. Women who have experienced depression previously are more likely to have depression during pregnancy. Consequences of depression include the baby being born premature, having a low birthweight, being more irritable, less active, less attentive, and having fewer facial expressions.

Maternal Factors: Weight Gain during Pregnancy

During pregnancy most women need only an additional 300 calories per day to aid in the growth of the fetus. Gaining too little or too much weight during pregnancy can be harmful. Women who gain too little may have a baby who is low-birth weight, while those who gain too much are likely to have a premature or large baby. There is also a greater risk for the mother developing preeclampsia and diabetes, which can cause further problems during the pregnancy.

Maternal Factors: Stress

Feeling stressed is common during pregnancy, but high levels of stress can cause complications including having a premature baby or a low-birthweight baby. Babies born early or too small are at an increased risk for health problems. Stress-related hormones may cause these complications by affecting a woman's immune systems resulting in an infection and premature birth. Additionally, some women deal with stress by smoking, drinking alcohol, or taking drugs, which can lead to problems in the pregnancy. High levels of stress in pregnancy have also been correlated with problems in the baby's brain development and immune system functioning, as well as childhood problems such as trouble paying attention and being afraid.

Gottlieb suggests an analytic framework for this debate that recognizes the interplay between the environment, behavior, and genetic expression. This bidirectional interplay suggests that the environment can affect the expression of genes just as genetic predispositions can impact a person's potentials. Additionally, environmental circumstances can trigger symptoms of a genetic disorder.

For example, a person who has sickle cell anemia, a recessive gene linked disorder, can experience a sickle cell crisis under conditions of oxygen deprivation. Someone predisposed genetically for type-two diabetes can trigger the disease through poor diet and little exercise.

Example of Epigenetics

Fraga et al. (2005) found that when examining differences in DNA, a group of monozygotic twins were indistinguishable during the early years. However, when the twins were older there were significant discrepancies in their gene expression, most likely due to different experiences. These differences included susceptibilities to disease and a range of personal characteristics.

Dizygotic

Fraternal twins, two eggs or ova are released and fertilized by two separate sperm. 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.

XX chromosome pair

Genetically female

XY chromosome pair

Genetically male

Factors influencing prenatal risks that might result from exposure to a particular teratogen: #4

Genetics: Genetic make-up also plays a role on the impact a particular teratogen might have on the child. The genetic make- up of the mother can also have an effect; some mothers may be more resistant to teratogenic effects than others.

Sexually Transmitted Diseases:

Gonorrhea, syphilis, and chlamydia are sexually transmitted infections that can be passed to the fetus by an infected mother. Mothers should be tested as early as possible to minimize the risk of spreading these infections to their unborn child. Sexually transmitted diseases (STDs) can cause premature birth, premature rupture of the amniotic sac, an ectopic pregnancy, birth defects, miscarriage, and still births. Most babies become infected with STDS while passing through the birth canal during delivery, but some STDs can cross the placenta and infect the developing fetus.

Examples of dominant traits

Having facial dimples, curly hair, normal vision, and dark hair.

Maternal Factors: High Blood Pressure (Hyertension)

Hypertension is a condition in which the pressure against the wall of the arteries becomes too high. There are two types of high blood pressure during pregnancy, gestational and chronic. Gestational hypertension only occurs during pregnancy and goes away after birth. Chronic high blood pressure refers to women who already had hypertension before the pregnancy or to those who developed it during pregnancy and it continued after birth. About 8 in every 100 pregnant women have high blood pressure. High blood pressure during pregnancy can cause premature birth and low birth weight (under five and a half pounds), placental abruption, and mothers can develop preeclampsia.

Monozygotic

Identical twins occur when a fertilized egg splits apart in the first two week 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.

Heterozygous

If we receive a different version of the gene from each parent.

Homozygous

If we receive either the same version of a gene from our mother and father.

Genotype-Environment Interactions

Involve genetic susceptibility to the environment.

Pollutants:

Lead: An environmental pollutant of significant concern is lead poisoning, which has been linked to fertility problems, high blood pressure, low birth weight, prematurity, miscarriage, and slowed neurological development. Pesticides: The chemicals in certain pesticides are also potentially damaging and may lead to birth defects, learning problems, low birth weight, miscarriage, and premature birth. Bisphenol A: Prenatal exposure to bisphenol A (BPA), a chemical commonly used in plastics and food and beverage containers, may disrupt the action of certain genes contributing to certain birth defects. Radiation: If a mother is exposed to radiation, it can get into the bloodstream and pass through the umbilical cord to the baby. Radiation can also build up in body areas close to the uterus, such as the bladder. Exposure to radiation can slow the baby's growth, cause birth defects, affect brain development, cause cancer, and result in a miscarriage. Mercury: Mecury, a heavy metal, can cause brain damage and affect the baby's hearing and vision. This is why women are cautioned about the amount and type of fish they consume during pregnancy.

passive genotype-environment correlation

Occurs when children passively inherit the genes and the environments their family provides.

active genotype-environment correlation

Occurs when individuals seek out environments that support their genetic tendencies. Also referred to as niche picking.

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 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. Also results in short stature and other physical characteristics.

Prenatal Assessment: Ultrasound

One of the main screening tests done in combination with blood tests. The ultrasound is a test in which sound waves are used to examine the fetus. There are two general types. Transvaginal ultrasounds are used in early pregnancy, while transabdominal ultrasounds are more common and used after 10 weeks of pregnancy (typically, 16 to 20 weeks). Ultrasounds are used to check the fetus for defects or problems. It can also find out the age of the fetus, location of the placenta, fetal position, movement, breathing and heart rate, amount of amniotic fluid, and number of fetuses. Most women have at least one ultra sound during pregnancy, but if problems are noted, additional ultrasounds may be recommended.

Human Immunodeficiency Virus (HIV):

One of the most potentially devastating teratogens is HIV. HIV and Acquired Immune Deficiency Syndrome (AIDS) are leading causes of illness and death in the United States. One of the main ways children under age 13 become infected with HIV is via mother-to-child transmission of the virus prenatally, during labor, or by breastfeeding. There are some measures that can be taken to lower the chance the child will contract the disease. HIV positive mothers who take antiviral medications during their pregnancy greatly reduce the chance of passing the virus to the fetus. The risk of transmission is less than 2 percent; in contrast, it is 25 percent if the mother does not take antiretroviral drugs. However, the long-term risks of prenatal exposure to the medication are not known. It is recommended that women with HIV deliver the child by c-section, and that after birth they avoid breast feeding.

examples of recessive traits

Red hair, being nearsighted, and straight hair

evocative genotype-environment correlation

Refers to how the social environment reacts to individuals based on their inherited characteristics.

Phenotype

Refers to the features that are actually expressed.

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 the development. An individual typically has small testes, some great development, infertility, and low levels of testosterone.

Maternal Factors: Rh Disease

Rh is a protein found in the blood. Most people are Rh positive, meaning they have this protein. Some people are Rh negative, meaning this protein is absent. Mothers who are Rh negative are at risk of having a baby with a form of anemia called Rh disease. A father who is Rh-positive and mother who is Rh-negative can conceive a baby who is Rh-positive. Some of the fetus's blood cells may get into the mother's bloodstream and her immune system is unable to recognize the Rh factor. The immune system starts to produce antibodies to fight off what it thinks is a foreign invader. Once her body produces immunity, the antibodies can cross the placenta and start to destroy the red blood cells of the developing fetus. As this process takes time, often the first Rh positive baby is not harmed, but as the mother's body will continue to produce antibodies to the Rh factor across her lifetime, subsequent pregnancies can pose greater risk for an Rh positive baby. In the newborn, Rh disease can lead to jaundice, anemia, heart failure, brain damage and death.

Maternal Factors: Gestational Diabetes

Seven percent of pregnant women develop gestational diabetes. Diabetes is a condition where the body has too much glucose in the bloodstream. Most pregnant women have their glucose level tested at 24 to 28 weeks of pregnancy. Gestational diabetes usually goes away after the mother gives birth, but it might indicate a risk for developing diabetes later in life. If untreated, gestational diabetes can cause premature birth, stillbirth, the baby having breathing problems at birth, jaundice, or low blood sugar.

The Human Genome Project (HGP)

Started in 1990, 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. Data on genetic variation can improve our understanding of differential risk for disease and reactions to medical treatments, such as drugs.

Epigenetics

Studies modifications in DNA that affect gene expression and are passed when the cells divide. Environmental factors, such as nutrition, stress, and teratogens are thought to change gene expression by switching genes on and off. These gene changes can then be inherited by daughter cells. This would explain why monozygotic or identical twins may increasingly differ in gene expression with age.

Adoption studies provide evidence for genotype-environment interactions. Results have shown...

That children whose biological parents exhibited psychopathology, exhibited significantly fewer behavior problems when their adoptive parents used more structured parenting than unstructured. Additionally, elevated psychopathology in adoptive parents increased the risk for the children's development of behavior problems, but only when the biological parents' psychopathology was high. Consequently, the results show how environmental effects on behavior differ based on the genotype, especially stressful environments on genetically at-risk children.

Maternal Factors: Paternal Impact

The age of fathers at the time of conception is also an important factor in health risks for children. Offspring of men over 40 face an increased risk of miscarriages, autism, birth defects, achondroplasia (bone growth disorder) and schizophrenia. These increased health risks are thought to be due to accumulated chromosomal aberrations and mutations during the maturation of sperm cells in older men. However, like older women, the overall risks are small.

Factors influencing prenatal risks that might result from exposure to a particular teratogen: #2

The amount of exposure: Some substances are not harmful unless the amounts reach a certain level. The critical level depends in part on the size and metabolism of the mother.

Genes

The basic building block of the nature perspective. Are specific sequence of nucleotides and are recipes for making proteins

Prenatal Brain Development

The brain undergoes dramatic changes from conception to birth. Begins in the third gestational week with the differentiation of stem cells, which are capable of producing all the different cells that make up the brain

After conception, most cells of the body are created by a process called mitosis. Define mitosis.

The cell's nucleus making an exact copy of all the chromosomes and splitting into two new cells.

incomplete dominance

The dominant gene does not completely suppress the recessive gene. Example: 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.

age of viability

The first chance of survival outside the womb. The point at which a fetus can survive if born prematurely. 24 weeks.

The gametes are formed in a process called meiosis. Define 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.

Prenatal Development is divided into three periods:

The germinal period, the embryonic period, and the fetal period.

By 24 weeks (5 months), the fetus...

The majority of the neurons in the brain have developed, although they are still rudimentary, and the glial or nurse cells that support neurons continue to grow. Also, the fetus can feel pain.

Factors influencing prenatal risks that might result from exposure to a particular teratogen: #3

The number of teratogens: Fetuses exposed to multiple teratogens typically have more problems than those exposed to only one.

During the germinal period...

The organism begins cell division through mitosis. After five days of mitosis ther are 100 cells, which is now called a blastocyst. The blastocyst consists of both an inner and outer group of cells. The inner group of cells, or embryonic disk will become the embryo, while the outer group of cells, or trophoblast, becomes the support system which nourishes the developing organism. This stage ends when the blastocyst fully implants into the uterine wall.

The Embryonic Period (2)

The stage of prenatal development from approximately the third through the eighth week after conception, during which the basic forms of all body structures, including internal organs, develop. Starting the third week the blastocyst has implanted in the uterine wall. Upon implantation this multi-cellular organism is called an embryo. Now blood vessels grow forming the placenta.

Genotype

The sum total of all the genes a person inherits.

The Fetal Period (3)

The third and longest period of prenatal development, extending from the ninth week until birth.

Factors influencing prenatal risks that might result from exposure to a particular teratogen: #1

The timing of the exposure: Structures in the body are vulnerable to the most severe damage when they are forming. If a substance is introduced during a particular structure's critical period (time of development), the damage to that structure may be greater.

Most characteristics are not the result of a single gene; they are polygenic. Define polygenic.

They are the result of several genes.

Dominantgene

They express themselves in the phenotype even when paired with a different version of the gene.

Recessive gene

They express themselves only when paired with a similar version gene.

carriers

Those who have inherited only one recessive-gene and should be unaffected by this recessive trait.

Toxoplasmosis:

Tiny parasite that causes an infection. A healthy immune system can keep the parasite at bay producing no symptoms, so most people do not know they are infected. As a routine prenatal screening frequently does not test for the presence of this parasite, pregnant women may want to talk to their health-care provider about being tested. Toxoplasmosis can cause premature birth, stillbirth, and can result in birth defects to the eyes and brain. To avoid being infected, women should avoid eating undercooked or raw meat and unwashed fruits and vegetables, touching cooking utensils that touched raw meat or unwashed fruits and vegetables, and touching cat feces, soil or sand.

Prenatal Assessment: Amniocentesis

Ultrasounds help guide the more invasive diagnostic tests of Amniocentesis, a procedure in which a needle is used to withdraw a small amount of amniotic fluid and cells from the sac surrounding the fetus and later tested. There is a risk of miscarriage, and consequently they are not done routinely.

Tobacco is a widely used teratogen:

When a pregnant woman smokes the fetus is exposed to dangerous chemicals including nicotine, carbon monoxide and tar, which lessen the amount of oxygen available to the fetus. Oxygen is important for overall growth and development. Tobacco use during pregnancy has been associated with low birth weight, ectopic pregnancy (fertilized egg implants itself outside of the uterus), placenta previa (placenta lies low in the uterus and covers all or part of the cervix), placenta abruption (placenta separates prematurely from the uterine wall), preterm delivery, stillbirth, fetal growth restriction, sudden infant death syndrome (SIDS), birth defects, learning disabilities, and early puberty in girls.

Maternal Factors: Mothers over 35

Women over the age 35 are more likely to have an increased risk of: • Fertility problems • High blood pressure • Diabetes • Miscarriages • Placenta Previa • Cesarean section • Premature birth • Stillbirth • A baby with a genetic disorder or other birth defects

Neonatal Abstinence Syndrome (NAS)

a condition in which a child, at birth, goes through withdrawal as a consequence of maternal drug use.

Placenta

a structure connected to the uterus that provides nourishment and oxygen from the mother to the developing embryo via the umbilical cord. During this period, cells continue to differentiate.

sex-linked chromosomal abnormality

abnormalities that are transmitted from generation to generation, carried by a sex chromosome, usually an X sex chromosome. When the abnormality is on 23rd pair.

Of the 23 pairs of chromosomes created at conception, 22 pairs are similar in length. These are called...

autosomes

white matter

axons that form the neural pathways. They are covered in myelin, a fatty substance that is white in appearance.

gray matter

cell bodies, looks gray in appearance.

Genes are located...

chromosomes

Alleles

different versions of a gene

During the 4th - 6th months, the fetus...

eyes become more sensitive to light and hearing develops. The respiratory system continues to develop, and reflexes such as sucking, swallowing and hiccupping, develop during the 5th month. Cycles of sleep and wakefulness are present at this time as well.

Zygote

fertilized egg. This cell contains the combined genetic information from both parents.

neural plate

flat group of cells present in prenatal development that becomes the brain and spinal cord. The location of these stem cells in the embryo.

Growth during prenatal development occurs in two major directions:

from head to tail called cephalocaudal development and from the midline outward referred to as proximodistal development. This means that those structures nearest the head develop before those nearest the feet and those structures nearest the torso develop before those away from the center of the body (such as hands and fingers). The head develops in the fourth week and the precursor to the heart begins to pulse. In the early stages of the embryonic period, gills and a tail are apparent. However, by the end of this stage they disappear and the organism takes on a more human appearance. It is during this stage that the major structures of the body are taking form making the embryonic period the time when the organism is most vulnerable to the greatest amount of damage if exposed to harmful substances.

The cells used in sexual reproduction

gametes (sperm or ova/egg)

By the 3rd month, the fetus...

has all its body parts including external genitalia. In the following weeks, the fetus will develop hair, nails, teeth and the excretory and digestive systems will continue to develop.

At around 36 weeks (8 months), the fetus...

is almost ready for birth. It weighs about 6 pounds and is about 18.5 inches long. By week 37 all of the fetus's organ systems are developed enough that it could survive outside the mother's uterus without many of the risks associated with premature birth. The fetus continues to gain weight and grow in length until approximately 40 weeks. By then the fetus has very little room to move around and birth becomes imminent.

Between the 7th - 9th months, the fetus...

is primarily preparing for birth. It is exercising its muscles and its lungs begin to expand and contract. The fetus gains about 5 pounds and 7 inches during this last trimester of pregnancy, and during the 8th month a layer of fat develops under the skin. This layer of fat serves as insulation and helps the baby regulate body temperature after birth.

chromosomal abnormalities

occurs when a child inherits too many or two few chromosomes.

Three types of genotype-environment correlations:

passive, evocative (reactive), active

Genotype- Environment Correlations

refer to the processes by which genetic factors contribute to variations in the environment.

teratology

study of birth defects

Some genetic disorders are sex-linked; Define sex-linked.

the defective gene is found on the X-chromosome.

fetus

the developing human organism from 9 weeks after conception to birth.

neurogenesis

the formation of new neurons

Behavioral Genetics

the scientific study of the interplay between the genetic and environmental contributions to behavior.

Example of evocative genotype-environment correlation

whether one has a more outgoing or shy temperament will affect how he or she is treated by others.

The common reasons for genetic counseling include:

• Family history of a genetic condition • Membership in a certain ethnic group with a higher risk of a genetic condition • Information regarding the results of genetic testing, including blood tests, amniocentesis, or ultra sounds • Learning about the chances of having a baby with a genetic condition if the parents are older, have had several miscarriages, have offspring with birth defects, experience infertility, or have a medical condition