Genetic
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DEP2004-4GeneticsSP20.pptxAn Orientation to Lifespan Development
Lesson #4
Earliest Development
Module 2.1 Prenatal Development
Genes and Chromosomes: The Code of Life
Gametes
Male reproductive cell: sperm
Female reproductive cell: ovum
Humans begin life as a zygote—a single cell, formed by fusion of two gametes
Process of fusion called meiosis
Genes composed of DNA sequences (deoxyribonucleic acid = DNA)
Humans have more than 25,000 genes
Genes arranged along 46 chromosomes (in 23 pairs)
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The Contents of a Single Human Cell
At the moment of conception, humans receive about 25,000 genes,
contained on 46 chromosomes in 23 pairs.
Genes and Chromosomes: The Code of Life
All cells duplicate through mitosis
Nearly all cells contain same 46 chromosomes of zygote
Tens of trillions possible genetic combinations
Multiple Births: Two—or More—for the Genetic Price of One
Less than 3 percent of pregnancies produce twins; three or more children even rarer
Chromosomes
At the moment of conception, humans receive 23 pairs of chromosomes, half from the mother and half from the father. These chromosomes contain thousands of genes.
Genes and Chromosomes: The Code of Life
Multiple Births: Two—or More—for the Genetic Price of One
Monozygotic twins
Genetically identical
Form when cluster of cells in ovum split off in first few weeks
Dizygotic twins
No more genetically similar than two siblings
Formed when two separate ova are fertilized by two separate sperm
Genes and Chromosomes: The Code of Life
Multiple Births: Two—or More—for the Genetic Price of One
Multiple births (triplets, quadruplets, etc.)
Can form from either of the previously mentioned mechanisms
Fertility drugs increases likelihood of multiple births
Older women more likely to have multiple births
Race impacts likelihood of multiple births
Caucasian: 1 in 86
African American: 1 in 70
Rising Multiples
The number and rate of twin births have risen considerably over the past three decades.
Source: Centers for Disease Control and Prevention (CDC)/National Center for Health Statistics (NCHS, 2012.
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Genes and Chromosomes: The Code of Life
Boy or Girl? Establishing the Sex of the Child
23rd chromosome determines the sex of the child
Females are XX
Males are XY
Father’s sperm determines sex
New techniques are available to specify in advance the sex of the child
Determining Sex
When an ovum and sperm meet at the moment of fertilization, the ovum is certain to provide an X chromosome, whereas the sperm will provide either an X or a Y chromosome. If the sperm contributes its X chromosome, the child will have an XX pairing on the 23rd chromosome and will be a girl. If the sperm contributes a Y chromosome, the result will be an XY pairing—a boy. Does this mean that girls are more likely to be conceived than boys?
The Basics of Genetics: Mixing and Matching of Traits
Gregor Mendel (mid-1800s) uncovers basic genetics
Dominant trait
Recessive trait
Genotype
Phenotype
Homozygous
Heterozygous
An Austrian monk, Gregor Mendel (mid-1800s), working with peas, discovered that when two competing traits were present only one could be expressed.
The trait that is expressed when two competing traits are present is called the DOMINANT TRAIT.
The trait that is present in the organism but not expressed is called the RECESSIVE TRAIT.
GENOTYPE is the underlying combination of genetic material present (but not outwardly visible) in an organism.
PHENOTYPE is an observable trait, the trait that is actually seen.
Alleles are genes for traits that may take alternate forms.
HOMOZYGOUS is inheriting from parents similar genes for a given trait.
HETEROZYGOUS is inheriting from parents different forms of a gene for a given trait.
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The Basics of Genetics: Mixing and Matching of Traits
Transmission of Genetic Information
When parents are homozygous are dominant for a recessive gene, none of the children will be affected or carriers.
When one parent is heterozygous and one parent homozygous dominant for a recessive gene, none of the children will be affected, but 50 percent become carriers.
When parents are heterozygous for a recessive gene, 25 percent of children will be affected and 50 percent will be carriers.
The Basics of Genetics: Mixing and Matching of Traits
Inherited and Genetic Disorders: When Development Deviates from the Norm
Some disorders are inherited (ex: PKU)
Some result from damaged genes
Some genes spontaneously change their form (spontaneous mutation)
Exposure to some things (ex: X-rays) can produce malformed genetic material
The Basics of Genetics: Mixing and Matching of Traits
Inherited and Genetic Disorders: When Development Deviates from the Norm
Disorders
Down syndrome
Fragile X
Sickle-Cell anemia
Tay-Sachs disease
Klinefelter’s syndrome
DOWN SYNDROME is a disorder produced by the presence of an extra chromosome on the 21st chromosome pair, once referred to as mongolism.
FRAGILE X SYNDROME is a disorder produced by injury to a gene on the X chromosome, producing mild to moderate mental retardation.
SICKLE-CELL ANEMIA is a blood disorder that gets its name from the shape of the red blood cells in those who have it.
TAY-SACHS DISEASE is an untreatable disorder that produces blindness and muscle degeneration prior to death.
One male out of every 400 is born with KLINEFELTER’S SYNDROME, a disorder resulting from the presence of an extra X chromosome that produces underdeveloped genitals, extreme height, and enlarged breasts.
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Genetic Counseling: Predicting the Future from the Genes of the Present
Genetic Counseling: Discipline focuses on helping people deal with issues related to inherited disorders
Genetic counselors use a variety of data:
Family history
Parents’ ages
Blood, skin, urine samples
Karyotype is a chart containing enlarged photos of each chromosome
Genetic Counseling: Predicting the Future from the Genes of the Present
Prenatal Testing: Tests done once woman is pregnant
Ultrasound sonography
Chorionic villus sampling (CVS)
Amniocentesis
ULTRASOUND SONOGRAPHY is a process in which high-frequency sound waves scan the mother’s womb to produce an image of the unborn baby whose size and shape can then be assessed.
CHORIONIC VILLUS SAMPLING (CVS) is a test used to find genetic defects that involves taking samples of hairlike material that surrounds the embryo.
AMNIOCENTESIS is the process of identifying genetic defects by examining a small sample of fetal cells drawn by a needle inserted into the amniotic fluid surrounding the unborn fetus.
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Amniocentesis
In amniocentesis, a sample of fetal cells is withdrawn from the amniotic sac
and used to identify a number of genetic defects.
Genetic Counseling: Predicting the Future from the Genes of the Present
Screening for Future Problems
Currently genetic counselor tests parents for susceptibility to disorders due to genetic abnormalities
More than 1,000 disorders, such as Huntington’s disease, can be predicted based on genetic testing
Germ line therapy: Process by which genetic modifications can correct defective genes in unborn children
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Review: Earliest Development
A child receives 23 chromosomes from each parent.
These 46 chromosomes provide a genetic blueprint.
A genotype is the combination of genetic material.
A phenotype is the visible trait.
Recessive linked disorders can only be transmitted if both the mother and father pass on the recessive gene.
Genetic counselors use a variety of data.
Techniques used to assess the health of an unborn child include ultrasound, CVS, and amniocentesis.
The Interaction of Heredity and Environment
Module 2.1 Prenatal Development
The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes
Temperament is patterns of arousal and emotionality that represent consistent and enduring characteristics in an individual
Interaction of Factors
Multifactorial transmission: Determination of traits by a combination of genetic and environmental factors
Some genotypes are not as sensitive to the environment as others
The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes
Studying Development: How Much Is Nature? How Much Is Nurture?
The question is not whether a behavior is caused by nature or nurture, but by how much
Nonhuman Animal Studies: Controlling Both Genetics and Environment
Scientists study effects of environmental stimulation by:
Placing genetically similar animals in different environments
Placing genetically different animals in similar environments
The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes
Studying Development: How Much Is Nature? How Much Is Nurture?
Contrasting Relatedness and Behavior: Adoption, Twin, and Family Studies
Differences between monozygotic twins separated at birth can give information on the role of environment
If monozygotic twins are more similar than dizygotic on a trait, genetics plays a role
People genetically unrelated raised in the same environment provide information about the role of the environment
Biological and adoptive parents and their children help us see effects of heredity and environment
Both play a role in traits, characteristics, and behaviors
Genetics and the Environment: Working Together
Physical Traits: Family Resemblances
Genetic similarities result in similar physical features
Intelligence: More Research, More Controversy
Genetics is important but environment also important
The closer the genetic link between two individuals, the greater the correspondence between their IQ scores.
Genetics and the Environment: Working Together
Genetic and Environmental Influences on personality: Do We Inherit Our Personality?
Some personality traits have genetic components
Two of the “Big Five” have been linked to genetic stability:
Neuroticism
Extroversion
Certain traits reflect the contribution of genetics more than others:
Direct examination of genes
Studies of twins
The environment also plays a role in personality
Genetics and the Environment: Working Together
Psychological Disorders: The Role of Genetics and Environment
Several disorders brought about by genetic factors:
Schizophrenia spectrum disorder
Major depression
Alcoholism
Autism spectrum disorder
Attention-deficit hyperactivity disorder
The psychological disorder of schizophrenia has clear genetic components. The closer the genetic links between someone with schizophrenia and another family member, the more likely it is that the other person will also develop schizophrenia.
Genetics and the Environment: Working Together
Psychological Disorders: The Role of Genetics and Environment
Genetics alone does not influence development of disorders
If genetics is the sole cause, the concordance rate for identical twins would be 100 percent
Genetics can produce a tendency toward future development of disorder
Environment determines if the genetic tendency will be displayed
Review: The Interaction of Heredity and Environment
Behavioral characteristics are often determined by both genetics and environment.
The genotype is the genetic contribution while phenotype is the expression of the genes in observable traits.
Traits, characteristics, and behaviors are all due to nature and nurture.
Some personality traits have been linked to genetic factors.
Children may influence their environment through genetic traits.
They can create an environment that matches their disposition.
Applying Lifespan Development
How might an environment different from the one you experienced have affected the development of personality characteristics that you believe you inherited from one or both of your parents?
