Chapter 2: Heredity, Prenatal Development, and Birth — Vocabulary Flashcards

Key terms and definitions from the lecture notes on heredity, prenatal development, and birth.

Genes

Basic units of heredity: sequences of nucleotides on chromosomes that code for proteins.

Chromosomes

Structure in the nucleus that carries genes; humans have 46 chromosomes (23 pairs).

Autosomes

The 22 pairs of non-sex chromosomes that are similar in length and appearance.

Sex chromosomes

The 23rd chromosome pair (XX or XY) that determines biological sex.

Mitosis

Cell division creating two genetically identical diploid daughter cells.

Meiosis

Cell division producing four haploid gametes with half the chromosome number.

Gametes

Sex cells (sperm or ova) that combine at conception.

Zygote

Fertilized egg formed when sperm and egg unite.

Embryo

Early stage after implantation; develops into the fetus.

Fetus

Developing organism from about 9 weeks until birth.

Genotype

Sum total of all the genes a person inherits; genetic makeup.

Phenotype

Observed traits and characteristics that are expressed.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Alleles

Different versions of a gene.

Dominant

Allele that expresses itself in the phenotype even when paired with a different allele.

Recessive

Allele that expresses itself only when paired with an identical allele.

Polygenic

Traits influenced by multiple genes, often producing continuous variation.

Incomplete dominance

When the dominant allele does not fully mask the recessive allele; heterozygotes show an intermediate phenotype (example: sickle cell context in notes).

Carrier

Individual with one recessive allele who is usually unaffected but can pass the allele to offspring.

Sickle cell disease

Autosomal recessive disorder with abnormal hemoglobin; risk increases with low oxygen.

Cystic fibrosis

Autosomal recessive disorder causing thick mucus in lungs and digestive system.

Phenylketonuria (PKU)

Autosomal recessive metabolic disorder; inability to metabolize phenylalanine.

Tay‑Sachs disease

Autosomal recessive disorder causing lipid buildup in brain; early death.

Albinism

Recessive condition with little or no pigment in skin, hair, eyes; vision problems.

Huntington’s disease

Autosomal dominant neurodegenerative disorder; midlife onset affecting movement, behavior, cognition.

Tourette syndrome

Neurodevelopmental tic disorder with motor and vocal tics.

Achondroplasia

Autosomal dominant form of disproportionate short stature.

Fragile X syndrome

X‑linked disorder causing cognitive/behavioral challenges; more severe in males.

Hemophilia

X‑linked bleeding disorder; problems with blood clotting.

Down syndrome (Trisomy 21)

Autosomal disorder due to an extra chromosome 21; intellectual disability and distinctive features.

Trisomy 13

Patau syndrome; extra chromosome 13; multiple defects; often early death.

Trisomy 18

Edwards syndrome; extra chromosome 18; multiple defects; often early death.

Turner syndrome

Sex‑chromosome disorder (XO) in females; short stature, infertility.

Klinefelter syndrome

Sex‑chromosome disorder (XXY) in males; small testes, infertility, low testosterone.

Autosomal dominant disorders

Disorders caused by a single mutated gene on autosomes; one copy suffices to manifest.

Sex‑linked (X‑linked) disorders

Disorders linked to genes on the X chromosome; often more severe in males.

Placenta

Organ connecting mother and fetus; nourishes via the umbilical cord.

Umbilical cord

Connects fetus to the placenta; carries blood, nutrients, and oxygen.

Neural tube

Early structure that differentiates into the brain and spinal cord.

Neurogenesis

Formation of neurons; largely completed by about five months of gestation.

Myelin

Fatty sheath around axons that speeds neural transmission; forms white matter.

Teratogen

Environmental factor that can cause birth defects or developmental abnormalities.

Critical period

Specific times during development when exposure to teratogens is particularly harmful.

Alcohol (FASD/FAS)

Teratogenic effects of alcohol during pregnancy; can cause fetal alcohol spectrum disorders or fetal alcohol syndrome.

Fetal Alcohol Syndrome (FAS)

Most severe FASD; facial features and cognitive/behavioral deficits.

Tobacco (smoking during pregnancy)

Maternal smoking exposes fetus to nicotine, CO, and tar; linked to low birth weight and SIDS.

Lead exposure

Environmental lead exposure linked to fertility problems and adverse birth outcomes.

Toxoplasmosis

parasitic infection; risk to fetus from undercooked meat/cat litter; can cause birth defects.

Rh disease

Rh incompatibility between mother and fetus; can cause anemia and jaundice; risk in later pregnancies.