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Chapter Two PRENATAL DEVELOPMENT Conception and Genetics Conception – Ovum – Sperm – Zygote Chromosomes – – – – 23 pairs DNA Genes 23rd Pair: X and Y chromosomes Gametes (Ovum & Sperm) – Meiosis – Only 23 chromosomes Human Chromosome #20 Conception and Genetics Homozygous Pair Heterozygous Pair • When the two sets of instructions are the same at any given locus • When the two sets of instructions are different at any given locus Conception and Genetics Genotype: genetic blueprint Phenotype: observable characteristics Dominant-recessive pattern – Dominant genes always express their characteristics – Both recessive genes must be present to express their characteristics Conception and Genetics Polygenic Inheritance – Many genes blend together to increase – the genetic outcomes seen in the phenotype Multifactorial Patterns – Expression of traits that are influenced by both genes and environment Genomic Imprinting – Some genes are biochemically marked at the time ova and sperm develop Mitochondrial Inheritance – Genes passed only from mother to child The Genetics of Hair Type Conception and Genetics Twins • Identical (Monozygotic) • Fraternal (Dizygotic) Twins in genetic research Assisted Reproductive Technology The use of assisted reproductive technology to help postmenopausal women get pregnant is controversial. What are the arguments for and against this practice? Development from Conception to Birth Stages of Prenatal Development Development from Conception to Birth The Germinal Stage: Zygote From conception to implantation • Implantation is complete 10 days to 2 weeks after conception Blastocyst divides into two sections • Specialization of cells needed to support development • Placenta • Umbilical cord • Chorion • Amnion Migration of the Zygote Development from Conception to Birth The Embryonic Stage: Embryo Forms the foundations of all body organs Neural tube develops All major organs and systems begin to develop Development from Conception to Birth The Fetal Stage: Fetus – – – – Growth statistics Refinement of all organ systems Surfactant Age of viability The Fetal Stage Nervous System: Neurons Dendrites Axons Synapses The Fetal Stage Nervous System Neural tube Glial Cells The Fetal Stage Nervous System Neuronal proliferation: The rapid development of neurons between the 10th and 18th week of gestation. Neuronal migration: The movement of neurons to specialized regions of the brain. Structure of the Neuron Sex Differences in Prenatal Development Between weeks 4 and 8, males begin to secrete testosterone from primitive testes Prenatal hormonal influences Sex Differences in Prenatal Development Girls • Slightly faster skeletal development Boys • • • • • • Slightly heavier and longer at birth More vulnerable to prenatal problems More likely to be aborted spontaneously Have more birth injuries and birth defects X-related problems may be a factor Slightly more active before birth Prenatal Behavior Fetuses • Respond to sound with body movements as early as 25 weeks • Can distinguish between familiar and novel stimuli by 32 weeks • Can learning prenatally • Influenced by prenatally music Questions to Ponder How would you deal with a risk of passing on a severe genetic illness to any child that you and your partner might have? If you are having a baby, would you add music and reading to your child prenatally to your pregnancy routine? Why or why not?
