Ch 3: Forming a New Life

Explain how conception occurs and what causes multiple births; Describe the mechanisms of heredity in normal and abnormal human development; Explain how heredity and environment interact in human development; Describe prenatal development, including environmental influences; Discuss the importance of high-quality prenatal care.

Conception

Development starts as sperm and egg meet and an entirely new individual is created.

Fertilization

Is the process in which a sperm cell unites with an egg cell, resulting in the formation of a single celled zygote.

Dizygotic twins (fraternal twins)

Twins conceived by two different ova with two different sperm; no more genetically alike than any other siblings.

Monozygotic twins (identical twins)

Twins resulting from the division of a single zygote after fertilization; they are genetically similar.

Why is there a rise in multiple birth rates?

The rise in multiple birth rates can be attributed to factors such as increased use of fertility treatments, advanced maternal age, and higher rates of women having children later in life. This rise is linked to pregnancy complicated, premature delivery, LBW, and infant disability or death.

Chromosomes

Coils of DNA that consist of segments called genes.

Genes

Segments of DNA that make up chromosomes, carrying hereditary information.

Human genome

The complete sequence of genes in the human body.

Mutation

A permanent alteration in genes resulting from a mistake in copying as cells divide.

Autosomes

The twenty-two pairs of chromosomes that are not related to sexual expression.

Sex chromosomes

The twenty-third pair of chromosomes, one from the father and one from the mother, that determines sex.

Alleles

Genes that can produce alternative expressions of a characteristic like hair color.

Homozygous

The state when both alleles for a trait are the same.

Heterozygous

The state when alleles for a trait are different.

Dominant inheritance

A pattern of inheritance where the dominant allele is always 'expressed,' showing up as a trait.

Recessive inheritance

A pattern of inheritance where the person must have two recessive alleles, one from each parent, for the trait to be expressed.

Polygenetic inheritance

The interaction of many genes, which determines most traits.

Phenotype

The observable characteristics of a person.

Genotype

The genetic makeup of the person containing both expressed and unexpressed characteristics.

Multifactorial transmission

A combination of genetic and environmental factors that determines certain complex traits such as intelligence.

Epigenesis

The turning on and off of genes by the developing body or when triggered by the environment.

Genetic imprinting

The differential expression of certain genetic traits depending on whether the trait is inherited by the mother or the father.

Birth disorders

Fairly rare, affecting about 3% of live births, but are the leading cause of infant death in the United States. Most common is Down syndrome, then cleft lip.

Dominant defects

Abnormal traits controlled by a dominant gene (e.g., Huntington’s disease); less likely to be lethal.

Recessive defects

Abnormal traits expressed only if the child is homozygous for that gene; tend to be lethal.

Incomplete dominance

A pattern of inheritance in which a child receives two different alleles, resulting in a phenotype that is a partial expression of a trait.

Chromosomal abnormalities

Typically due to errors in cell division leading to an extra or missing chromosome.

Down syndrome

The most common chromosomal abnormality, accounting for about 40% of all cases of moderate-to-severe mental retardation, usually due to an extra 21st chromosome.

Genetic counseling

Helps prospective parents assess their risk of bearing children with genetic or chromosomal defects.

Karyotype

A photographic chart showing chromosomal abnormalities that indicate risk of transmission to a child.

Behavioral genetics

The field determining the relative influence of heredity and environment on traits.

Heritability

A statistical estimate of the contribution of heredity to individual differences in a specific trait.

Concordance

The tendency of twins to share the same trait or disorder.

Twin studies

Research involving twins reared together, used to help determine heritability.

Adoption studies

Research involving twins reared apart, used to help determine heritability.

How do heredity and the enviornment work together?

The interaction between genetic predispositions and environmental influences that shape individual traits and behaviors, resulting in reaction ranges of traits, and canalization of traits.

Reaction range

The potential variability of a trait, such as body size, depending on environmental conditions.

Canalization

A concept that places a limit on the variability of certain traits (e.g., motor development is highly canalized, reading skills are more subject to variations).

Passive correlations

Genotype-environment correlation where biological parents provide a gene for a trait and an encouraging environment for that trait.

Reactive correlations

Genotype-environment correlation referring to children with different genetic makeups evoking different reactions from others.

Active correlations (niche-picking)

Genotype-environment correlation where older children freely select environments consistent with their genetic tendencies.

Nonshared environmental effects

Unique environments that influence each child differently, including parent/sibling interactions, illnesses, accidents, and varying experiences outside the home.

What are the stages of prenatal development?

The stages of prenatal development include the germinal stage (Until 2 weeks), embryonic stage (2-8 weeks), and fetal stage (8 weeks until birth), each marking significant growth and differentiation processes leading to a fully formed fetus.

Gestation

Refers to the period between conception and birth, normally between 37 and 41 weeks.

Gestational age

Usually dated from the first day of an expectant mother’s last menstrual cycle.

Germinal stage (prenatal)

The first prenatal stage, from fertilization to 2 weeks, characterized by rapid cell division and duplication.

Embryonic stage (prenatal)

The second prenatal stage, from 2 to 8 weeks, characterized by rapid growth and development of major body systems and organs.

Fetal stage (prenatal)

The final prenatal stage, from 8 weeks to birth, characterized by increased differentiation of body parts and greatly enlarged body size.

Blastocyst

The form a zygote takes when it travels down the fallopian tube and enters the uterus, before implantation.

Implantation

The process where the blastocyst completes its attachment on the uterine wall.

Spontaneous abortion

Also known as miscarriage; the risk of this is highest in the embryonic stage.

Ultrasound

High-frequency sound waves used to detect the outline of a fetus and its movements.

Teratogens

Environmental agents that can interfere with normal development (e.g., drugs, alcohol, nicotine, maternal illnesses).

Prenatal Development Monitoring Tools

An array of tools to assess an unborn baby’s progress and well-being, including amniocentesis, chorionic villus sampling, embryoscopy, fetoscopy, maternal blood tests, ultrasound, preimplantation genetic diagnosis, and umbilical cord sampling.

Risks of poor prenatal care

Include low birth weight, birth defects, infections, and premature birth.

Preconception care

Care that begins before pregnancy to identify preventable risks, consisting of physical examinations, vaccinations, risk screening for genetic disorders and infectious diseases, and counseling to avoid smoking and alcohol, proper weight maintenance, and ingestion of folic acid supplements.

Disparities in prenatal care

Differences in access to and quality of prenatal care experienced by various population groups, often influenced by socioeconomic status, ethnicity, and geographic location. Black and hispanic mothers are more at risk for perinatal death.