chapter 2 biological beginnings © 2013 the mcgraw-hill companies, inc. all rights reserved

Chapter 2

BIOLOGICAL BEGINNINGS

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The Role of Heredity on

Development

• Heredity• One’s nature based on biological transmission of traits and characteristics

• Genetics• Field within the science of biology that studies heredity

• Genetics Influence our• Physical traits• Behavioral traits• Psychological problems

HEREDITY AND GENETICS

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• The nucleus of each human cell contains chromosomes• Chromosomes: Threadlike structures made up of

deoxyribonucleic acid, or DNA• DNA: A complex molecule with a double helix shape;

contains genetic information

THE COLLABORATIVE GENE

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• Genes: Units of hereditary information composed of DNA• Genes direct cells to reproduce themselves and

manufacture the proteins that maintain life

• Segments of DNA within chromosomes

• Regulate development of traits

• Transmitted by single gene or may be polygenic

• Approx. 20,500 genes in every cell (2008)

• Genome - The complete set of developmental instructions for creating proteins that initiate the making of a human organism

THE COLLABORATIVE GENE

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FIGURE 2.2 - CELLS, CHROMOSOMES, DNA, AND GENES

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• Mitosis: Cellular reproduction in which the cell’s nucleus duplicates itself with two new cells being formed

• Strands of DNA break apart, duplicate and are rebuilt• Each containing the same DNA as the parent cell, arranged

in the same 23 pairs of chromosomes• Cell division by which growth occurs• Mutations can develop throughout our lives

GENES AND CHROMOSOMES

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• Meiosis: A specialized form of cell division that occurs to form eggs and sperm (or gametes)

• 23 chromosome pairs divide

• Result is a new cell with only 23 chromosomes• 22 pairs are autosomes• 23rd pair are sex chromosomes

GENES AND CHROMOSOMES

SOURCES OF VARIABILITY

• Meiosis• Crossing Over

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• Fertilization: A stage in reproduction whereby an egg and a sperm fuse to create a single cell, called a zygote• Zygote: A single cell formed through fertilization

FERTILIZATION

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• Monozygotic Twins (MZ)• Derived from a single zygote that has split in two• Identical twins

• Dizygotic Twins (DZ)• Derived from two zygotes

• Probability of twins increases• Maternal age• Use of fertility drugs

SOURCES OF VARIABILITY

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FIGURE 2.4 - THE GENETIC DIFFERENCE BETWEEN MALES AND FEMALES

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• Mutation• DNA - A mistake by cellular machinery, or damage

from an environmental agent may produce a mutated gene, which is a permanently altered segment of DNA

SOURCES OF VARIABILITY

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• Genotype: A person’s genetic heritage; the actual genetic material

• Phenotype: The way an individual’s genotype is expressed in observed and measurable characteristics

SOURCES OF VARIABILITY

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• Dominant-Recessive genes principle• Recessive gene is influential only if both genes are

recessive

• Sex-Linked genes• When a mutated gene is carried on the X chromosome,

the result is called X-linked inheritance

GENETIC PRINCIPLES

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• Genetic imprinting• Occurs when genes have differing effects depending on

whether they are inherited from the mother or the father

• Polygenetic inheritance• Occurs when most characteristics are determined by the

interaction of many different genes

GENETIC PRINCIPLES

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• Traits are determined by pairs of genes• Each member of pair is an allele

• Homozygous• Both alleles for a trait are the same

• Heterozygous• Alleles for a trait are different

GENETIC PRINCIPLES

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FIGURE 2.5 - HOW BROWN-HAIRED PARENTS CAN HAVE A BLOND-HAIRED CHILD

TRANSMISSION OF DOMINANT AND RECESSIVE TRAITS

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FIGURE 2.5 – CHROMOSOMAL ABNORMALITIES

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FIGURE 2.7 - SOME GENE-LINKED ABNORMALITIES

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• Ultrasound sonography – • A prenatal medical procedure in which high frequency

sound waves are directed into the pregnant woman’s abdomen

PRENATAL DIAGNOSTIC TESTS

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• Amniocentesis • Prenatal medical

procedure in which a sample of amniotic fluid is withdrawn by syringe and tested for chromosomal or metabolic disorders

PRENATAL DIAGNOSTIC TESTS

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• Chorionic villi sampling • Prenatal medical

procedure in which a small sample of the placenta is removed

PRENATAL DIAGNOSTIC TESTS

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• Maternal blood or triple screening • Identifies pregnancies that have an elevated risk for

birth defects such as spina bifida and Down syndrome

• Noninvasive prenatal diagnosis (NIPD) • Focuses on the isolation and examination of fetal cells

circulating in the mother’s blood and analysis of cell-free fetal DNA in maternal plasma

• Fetal sex determination • Noninvasive techniques have been able to determine the

sex of the fetus at an earlier point by assessing cell-free DNA in maternal plasma

PRENATAL DIAGNOSTIC TESTS

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• Infertility• Inability to conceive after 12 months of regular

intercourse without contraception

• In vitro fertilization (IVF)• Eggs and a sperm are combined in a laboratory dish

• Adoption• Social and legal process by which a parent-child

relationship is established between persons unrelated at birth

INFERTILITY AND REPRODUCTIVETECHNOLOGY

CONCEPTION Against All Odds

FERTILIZATION

1 5 2814

• Egg is viable for

24 hours

• Sperm is viable for

3 to 5 days

• “Unsafe period” is from

day 9 to 15 if ovulation occurs on day 14

day 7 to 17 could be unsafe

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FEMALE REPRODUCTIVE ORGANS

Figure 2.8

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CONCEPTION

• Ova• Begin to mature at puberty• Monthly release of mature egg into Fallopian tube• Egg is propelled by cilia• If not fertilized, egg is discharged in the menstrual

flow

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Figure 2.9

CONCEPTION

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CONCEPTION

• Sperm• Self propelled and smaller than ova• Sperm with “Y” chromosome swim faster than sperm

with “X” chromosome• From 200 to 400 million in ejaculate; only 1 in 1,000

arrive in vicinity of ovum• Sperm are attracted by chemical odor secreted by ova

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• The field that seeks to discover the influence of heredity and environment on individual differences in human traits and development

• Twin study: A study in which the behavioral similarity of identical twins is compared with the behavioral similarity of fraternal twins

BEHAVIOR GENETICS

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• Adoption study: A study in which investigators seek to discover whether, in behavior and psychological characteristics, adopted children are more like their adoptive parents or more like their biological parents

BEHAVIOR GENETICS

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FIGURE 2.11 - EXPLORING HEREDITY-ENVIRONMENT CORRELATIONS

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• Shared environmental experiences : Siblings’ common experiences, such as their parents’ personalities and intellectual orientation, the family’s socioeconomic status, and the neighborhood in which they live

• Nonshared environmental experiences: The child’s own unique experiences, both within the family and outside the family, that are not shared by another sibling

SHARED AND NONSHARED ENVIRONMENTAL EXPERIENCES

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• Epigenetic view: Emphasizes that development is the result of an ongoing, bidirectional interchange between heredity and environment

• Gene x Environment (G x E) interaction : The interaction of a specific measured variation in the DNA and a specific measured aspect of the environment

THE EPIGENETIC VIEW AND GENE X ENVIRONMENT (G X E) INTERACTION

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• The relative contributions of heredity and environment are not additive

• Complex behaviors have some genetic loading that gives people a propensity for a particular developmental trajectory

CONCLUSIONS ABOUT HEREDITY-ENVIRONMENT INTERACTION