Chapter 2: Heredity & Prenatal Development
LO 1. The influence of heredity on development
 Heredity  transmission of genetic material across generations
 Chromosomes contain genes; 46 in total; 23 pairs
o 22 pairs = autosomes
o 23rd pair = sex chromosomes (XX = girl; XY= boy)
 Ova  X; Sperm  X or Y
 Genes  segments of DNA that regulate development of traits
o Allele  one version of a gene pair
 Homozygous  alleles are same
 Heterozygous  alleles are different
 Recessive trait  expressed if both alleles are recessive
 Dominant trait  always expressed
*Review Table 2.1 and note which traits are dominant and which are recessive*
Chromosomal Abnormalities
 Down Syndrome  Extra chromosome on 21st pair
o Cognitive/ motor deficits; cardiovascular issues; characteristic facial features
 Sex Linked Chromosomal Abnormalities
o Klinefelter’s Syndrome/ Turner’s syndrome)
o Abnormalities in number/ structure of sex chromosomes  Infertility
Genetic Abnormalities
 Phenylketonuria (PKU) recessive; can’t metabolize phenylalanine (early screening & diet)
 Sickle Cell Anemia  RBC clump   oxygen; more common in black North Americans
 Huntington’s disease (not in lecture) dominant; degeneration of brain cells (onset30s)
 Tay-Sach’s Disease  recessive; degeneration of nervous system; fatal in childhood
 Cystic Fibrosis  recessive; mucus clogs lungs/ pancreas  affects digestion/ respiration
Prenatal Genetic Testing
 Amniocentesis 
 Chorionic Villus Sampling (CVS) 
 Ultrasound
 Blood tests
LO 2. Heredity and the Environment
 Genotypes  set of traits we inherit (genetic blueprint)
 Phenotypes  actual trait expression; influenced by heredity & environment
 Epigenetics heritable variations in gene expression
 Estimating genes vs/ environmental influences
o Kinship studies  are genetically closer relatives more similar?
o Twin studies  are identical (MZ) twins more similar than fraternal (DZ)?
o Adoption studies  are children more similar to biological vs. adopted parent?
Chapter 2: Heredity & Prenatal Development
LO 3. Conception
 Conception  union of an ovum and sperm cell
o Zygote fertilized ovum containing 46 chromosomes (23 pairs)
o Dizygotic Twins two ova are fertilized by different sperm (fraternal)
o Monozygotic Twins  one zygote splits into two identical parts (identical)
 Infertility in men  low sperm count/ motility
o Causes 
 Infertility in women  irregular/ lack of ovulation
o Causes 
 Assistive reproductive technology
o Fertility drugs 
o Artificial insemination 
o Invitro fertilization 
LO 3. Prenatal Development
 Germinal (zygotic) stage  first 2 weeks
o Zygote rapidly divides to form blastocyst
o Blastocyst travels down fallopian tube and implants into uterine wall
 Embryonic stage  3-8 weeks
o Organogenesis  organ systems differentiate
 Cephalocaudal  head to toe
 Proximodistal  center to extremities
o Amniotic sac 
o Placenta 
 Fetal stage  8 weeks- birth
o Organs and brain mature / refine
o Fetal perception (e.g., sound/ light) and movement
 Environmental influences effects depend on timing, intensity, duration & type of exposure
o Teratogens  toxic environmental agents
o Maternal lifestyle  malnutrition, stress, drugs, pathogens