Chapter 1: Introduction Module 1.2 The Start of Life
The Beginning of Life
Gametes (male and female reproductive cells) from male (sperm) and female (ovum) join, these fused gametes create a zygote
In humans, the male sex cell (sperm) and the female sex cell (the ovum) provide the developing baby with 23 chromosomes each.
Each Zygote carries 46 chromosomes, all of the genetic instructions to create a human being
Period of the Zygote
Monozygotic (one zygote) Identical Twins
Dizygotic (two zygotes) Fraternal Twins
What causes multiple births?
Fertility drugs, age of mother
Racial, ethnic, and national differences
The Code of Life
Genes-basic unit of genetic information
Rod-shaped DNA portions in 23 pairs
Contain genetic blueprint for individuals
Replicate through mitosis
Mixing and Matching of Genes
Basics of genetics:
DOMINANT TRAITS – expressed traits
RECESSIVE TRAITS – not expressed, but still there
Genotype and Phenotype
A genotype is the underlying combination of genetic materials present in an organism, but invisible; a phenotype is the visible trait, the expression of the genotype.
Genotype can be:
Homozygous - allele contains similar genes from each parent
Heterozygous - allele contains different forms of genes from parents
Cracking the Genetic Code
The Human Genome
National Human Genome Research Institute
( http://www.genome.gov/ )
The field of behavioral genetics , a combination of psychology and genetics, studies the effects of genetics on behavior.
When Development Deviates…
When Development Deviates…
Down Syndrome - extra chromosome on 21 st pair; 1 in 500/higher in older mothers
Fragile X Syndrome -Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females. The inheritance is different from common dominant or recessive inheritance patterns. A fragile area on the X chromosome (called FMR1) has repeats in the genetic code. The more repeats, the more likely there is to be a problem. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely.
Sickle-cell Anemia - Sickle cell anemia is an inherited disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots . These clots give rise to recurrent painful episodes called "sickle cell pain crises." Sickle cell anemia is inherited as an autosomal recessive trait , which means it occurs in someone who has inherited hemoglobin S from both parents. Sickle cell disease is much more common in certain ethnic groups, affecting approximately one out of every 500 African Americans.
When Development Deviates…
Tay-Sachs Disease - Tay-Sachs disease is a familial disorder (it affects more than 1 member of a family) that results in early death. It is found predominantly in Ashkenazi Jewish families. An enzyme deficiency that interferes with metabolism of crucial nerve tissue chemicals. Tay-Sachs disease is inherited as a recessive gene, and 1 in 25 members of the Ashkenazi Jewish population carries the gene.
Klinefelter’s Syndrome - Klinefelter syndrome is a chromosome disorder in males. People with this condition are born with at least one extra X chromosome. Klinefelter syndrome is one of the most common chromosomal abnormalities . About one in every 500 to 800 males is born with this disorder. Approximately 3% of the infertile male population have Klinefelter syndrome.
Potential tests for deviation in development:
Important to remember : Majority of babies born healthy!!
Nature and Nurture
Virtually all traits, characteristics, and behaviors are joint result of the combination and interaction of nature and nurture.
Genetic and environmental factors work in tandem, affecting and being affected by the other, creating the unique individual that each of us is and will become
Genetic influences have been identified in physical characteristics, intelligence, personality traits and behaviors, and psychological disorders.
There is some speculation that entire cultures may be predisposed genetically toward certain types of philosophical viewpoints and attitudes.
Nurture (environment) includes…
And everything else!
Nature and Nurture - Physical Similarities
More genetically similarity more likely to share physical characteristics
Monozygotic twins: best example of relationship between genetic similarity and shared physical characteristics
Nature and Nurture - Intelligence
Relative contributions of nature and nurture highly researched
Closer genetic link = greater correspondence of overall IQ scores
Intelligence (as measured) by IQ score) is central human characteristic that differentiates humans from other species
IQ scores of identical twins become increasingly similar over time
This does not discount importance of environmental influence on intelligence
Nature and Nurture - Personality
Research evidence indicates some of most basic personality traits have genetic roots
Two of “Big Five” personality traits linked to genetic factors:
Nature and Nurture - Personality Research Suggests…
Examination reveals specific gene very influential in determining risk-taking (novelty-seeking gene affects production of dopamine)
Twins reared apart studies: certain traits reflected contribution of genetics considerably more than others
Some less basic personality trait links: political attitudes, religious interests and values, attitudes toward human sexuality
Relative influence of nature and nurture:
Role of genetics is often to produce tendency toward future course of development
Role of environment affects when and whether a certain behavioral characteristic will actually be displayed
Theory about Nature/Nurture:
Sandra Scarr suggests three ways child’s genetic predisposition may influence his or her environment:
Let’s have a baby! Fertilization
Moment of conception:
Joining of sperm and ovum = zygote
Fertilization joins the sperm and ovum to start the journey of prenatal development.
Stages of Prenatal Development
The prenatal period consists of three stages: germinal, embryonic, and fetal.
Fertilization two weeks:
Fertilized egg now called blastocyst
Travels to and implants in uterus
Characterized by methodical cell division
With division comes cell specialization
2 weeks 8 weeks:
Organism firmly secures to uterus and called an embryo
Development of major organs and basic anatomy
Three distinct layers that ultimately form different set of structures:
Ectoderm - form skin, hair, teeth, sense organs, brain, spinal cord
Endoderm - inner layer forms digestive system, liver, pancreas, respiratory system
Mesoderm - sandwiched between other two and forms muscles, bones, blood, circulatory system
Embryonic Stage (cont.)
At end of embryonic stage:
One inch long, gills and tail-like structure; rudimentary eyes, lips, teeth, stubby bulges that become arms and legs; head grows rapidly and begins to represent significant portion of body (50% of total length); rapid growth of nerve cells (100,000 neurons produced EVERY MINUTE); nervous system begins to function at 3 weeks and at 5 weeks weak brain waves detected
8 weeks Birth:
Formally starts when differentiation of major organs has occurred
Organism now called fetus
Characterized by rapid development
Organs become more differentiated and begin working
Interconnections between body parents become more complex and integrated
Brain becomes more sophisticated
Fetal Stage (cont.)
Increases in length 20 times and proportions change dramatically
See Figure 2.13
At 4 months = 4 ounces; at 7 months = 3 pounds; at birth = 7 pounds
Brain waves indicate several different stages of sleep and wakefulness; hear and feel vibrations
Hormones released between 8 and 24 weeks that lead to gender differentiation
No two fetuses are alike; broad similarities in sequence of development
Differences due to genetics and the environment of womb
Infertility - 15% of couples; inability to conceive after 12 to 18 months
Maternal infertility influenced by age; hormone imbalance, damaged fallopian tubes or uterus, stress, abuse of alcohol or drugs
Paternal infertility influenced by illicit drugs, tobacco, STDs
Miscarriage - spontaneous abortion; 15-20% pregnancies ends in miscarriages; many times genetic abnormality
Abortion - voluntary termination pregnancy; aftereffects; may contribute to increase in future pregnancies
Threats to Development
The prenatal environment significantly influences the development of the baby. The diet, age, prenatal support, and illnesses of mothers can affect their babies’ health and growth
Teratogen - environmental agent or other factor that produces a birth defect
Timing and quantity of exposure crucial; sensitivity to specific teratogen related to racial and cultural background; different organ systems vulnerable at different times during development (e.g., brain development)
Teratogen Sensitivity Timeline
Parent’s Prenatal Influence
Mothers’ use of drugs, alcohol, tobacco, and caffeine can adversely affect the health and development of the unborn child. The behavior of fathers and others can also affect the child.
Mother’s Prenatal Influence
Diet - Mother’s diet supports development of fetus; global concern; postnatal enrichment of prenatal undernourishment can sometimes overcome some of effects
Age - More older women giving birth due to societal transformations; mothers over 30 at greater risk for variety pregnancy and birth complications; condition of ovum; Down syndrome; adolescent mothers more likely to deliver premature babies
Prenatal support - Young mothers often face adverse social and economic factors which can affect infant health; social support and poverty contribute to lack of resources for prenatal support
Mother’s Prenatal Influence (cont.)
Health - Rubella prior to 11 th week of pregnancy; mumps increase miscarriage risk; syphilis directly transmitted to fetus; STD (gonorrhea) transmitted; AIDS (AZT during pregnancy reduces transmission to around 5%)
Drug use - Poses serious risk to unborn child (legal, illegal, OTC drugs), Thalidomide, DES: diethylstilbestrol to prevent miscarriage later raised daughter risk of vaginal/cervical cancer, Birth control: fetal damage, Illicit drugs: marijuana, cocaine (crack babies)
Alcohol use: even small amounts can disrupt development of fetus; FAS; FAE
Tobacco use - Reduces oxygen content and increases carbon monoxide in mother’s blood fetus respiration slows and heart beat increases and increases miscarriage risk (100,000 miscarriages caused by smoking); low birth weight; shorter; 50% more likely to have mentally retarded or disruptive child
Father’s Prenatal Influence
Relatively little research
Tobacco use - secondhand smoke may influence mother’s health
Drug & Alcohol use - alcohol and drug use may impair sperm leading to chromosomal damage
Treatment of mother - physical and emotional abuse can cause maternal stress
Becoming an Informed Consumer Optimizing the Prenatal Environment
Avoid X-rays and birth control pills; get rubella vaccination