2.6: Key Terms

active genotype-environment correlation

event in which individuals select particular environments or experiences based on their genotype

age of viability

age at which a fetus born prematurely (before the thirty-seventh week of pregnancy) may have a chance of survival outside the womb, usually with intensive medical intervention

allele

variant of a gene

amniocentesis

test in which a needle is inserted through the mother’s abdomen to take a sample of the amniotic fluid and look for chromosomal disorders and some types of genetic defects

Apgar test

test administered to a newborn one minute after delivery and again at five minutes after delivery to assess their condition after birth; detects major abnormalities

attachment

the emotional connection a child feels toward their caregiver based on consistency and quality of care

autosome

chromosome in the nucleus that is not a sex chromosome

behavioral genetics

interdisciplinary field that focuses on the study of heredity-behavior relationships

blastocyst

small cluster of a few hundred cells formed shortly after conception

bonding

one-way relationship consisting of a caregiver’s emotional connection to the infant

cephalocaudal growth

growth that occurs from head to feet, allowing a fetus to grow longer

cesarean birth

medical procedure in which a doctor makes an incision in a birth mother’s abdomen and uterus to deliver the fetus and placenta

chorionic villus sampling

prenatal test that uses a placental tissue sample to determine whether chromosomal or genetic disorders are present in the fetus

chromosomal disorder

condition that occurs with an incorrect number of chromosomes or results from structural abnormalities of the chromosome

chromosome

strand of the DNA sequence in the nucleus of an individual’s cells that carries genes transmitting hereditary information

codominant trait

characteristic observed when two different alleles are expressed at the same time

conception

union of sperm and ovum (egg)

congenital disorder

any abnormality present at birth

contraception

method used to reduce chances of conception

dizygotic twins

(or fraternal) twins that occur when two ova are fertilized at the same time

DNA (also, deoxyribonucleic acid)

molecule that contains an individual’s genetic information

DNA methylation

process whereby methyl groups are added to or removed from DNA, potentially causing changes in gene expression

dominant trait

characteristic observed when only one copy of the allele is needed to express a phenotype

embryonic period

second developmental period of pregnancy, during which the blastocyst becomes an embryo and organogenesis begins

evocative (or reactive) genotype-environment correlation

event in which an individual’s genetically influenced traits elicit an environmental response

failure to thrive

situation in which a premature infant’s height and weight are below the third percentile

fallopian tube

part of the female reproductive system where egg is released and through which it travels to reach the uterus

fetal period

last developmental period of pregnancy, during which the fetus grows quickly

gamete

sex cell, the ovum or sperm, that carries twenty-three chromosomes

gene

hereditary unit composed of a specific DNA sequence that occupies a specific location along a chromosome in an individual

genome

complete sequence of an organism’s DNA

genotype

individual’s particular genetic composition of alleles at specific locations

genotype × environment interaction

event that occurs when the expression of a genotype depends on the environment

germinal period

first developmental period of pregnancy, when conception occurs and the blastocyst travels through the fallopian tubes to the uterus

heterozygous

trait in which an individual receives different alleles from each biological parent for a given trait

homozygous

trait in which an individual receives identical alleles from each biological parent for a given trait

hormone

chemical released by glands that controls and regulates bodily functions

implantation

process in which a blastocyst embeds within the uterus

in vitro fertilization (IVF)

form of assisted reproductive technology (ART) in which a fertilized egg is transferred into a uterus for implantation

incomplete dominance

form of genetic expression in which both inherited alleles are partially expressed

infertility

inability to successfully conceive after one year of trying

low birth weight

birth weight less than 5 lb 8 oz

mass-to-specific growth

growth in which large movements and structures develop before smaller or more specified movements and structures

meiosis

type of cell division that occurs during gamete production and results in their containing only one member of each chromosome pair

mitosis

type of cell division in which a cell duplicates itself and its DNA

monozygotic twins

(or identical) twins that occur when a zygote splits into two clusters of cells, creating two genetically identical zygotes

multifactorial inheritance

phenotype resulting from multiple genetic and environmental factors

natural childbirth

a childbirth method using nonpharmaceutical techniques to help minimize pain and the need for medical intervention for the birth mother

neonatal behavioral assessment scale (NBAS)

test assessing a newborn’s neurological and physical health, typically given three to four days after birth

organogenesis

the formation of organs during the embryonic period

ovary

part of the female reproductive system that releases eggs (ova)

oxytocin

hormone that helps initiate labor and plays a role in forming bonds with others

parental leave

policies that allow parents to take time off work, often paid, to care for a newborn for a period of time

passive genotype-environment correlation

event that occurs when parents provide offspring with both genes and environment

phenotype

observable expression of someone’s genome

placenta

a temporary organ connecting the uterus to the umbilical cord that provides respiration and nourishment for the embryo in addition to eliminating metabolic wastes

pleiotropy

most common form of genetic expression in which one gene influences multiple traits

polygenic trait

trait influenced by several genes

preterm (premature/preemie) infant

any infant born before thirty-seven weeks’ gestation and weighing less than 5.5 lb

proximodistal growth

growth that occurs from the center of the body outward

recessive trait

trait that requires two identical alleles to be expressed

single-gene disorder

condition caused by variation in a single gene

spontaneous abortion

(also, miscarriage) loss of a pregnancy during the first twenty weeks

teratogen

disease, drug, or environmental agent that can harm an embryo or fetus physically or influence health or behavior after birth

testes

parts of the male reproductive system that help create and sustain sperm

umbilical cord

a flexible tube connecting the embryo and the placenta

urethra

part of the human reproductive system that, in males, transports and releases sperm

uterus

part of the female reproductive system where a fertilized egg implants to develop

vagina

muscular canal that connects the uterus to the outside of the female body

vas deferens

tube that transports sperm from the testes to the urethra

vulva

external aspects of the female reproductive system including the labia, clitoris, and vaginal opening

zygote

single cell formed at conception and consisting of forty-six chromosomes, twenty-three from each parent