LIFE D CH-2

Chapter 2: Heredity, Prenatal Development, and Birth

Introduction

• Overview of heredity and its influence on development.

• Genetic processes during conception, including genetic and chromosomal disorders.

• Discussion of prenatal development and teratogens.

• The roles of both parents on fetal development.

• Explanation of birth processes and complications.

Heredity

Nature and Genes

• Heredity: The genetic contribution to an individual’s development.

• Genes: Sequences of nucleotides that serve as recipes for proteins influencing cell structure and function.

• Chromosomes: Normal human cells contain 46 chromosomes (23 pairs). Each parent contributes one chromosome to each pair.

• Approximately 20,500 genes in humans (Human Genome Project).

Cell Division

• Mitosis: The process where a cell's nucleus copies chromosomes and divides into two identical cells.

• Meiosis: The process for gamete production (sperm and ova), resulting in cells with half the genetic information (23 chromosomes).

• Significance of genetic variation during meiosis, making identical offspring extremely rare (1 in trillions).

Genetic Definitions

Genotype vs Phenotype

• Genotype: The complete set of genes inherited.

• Phenotype: The observable traits expressed.

• Homozygous: Same version of a gene from both parents.

• Heterozygous: Different versions of a gene from each parent.

  • Dominant (expressed) vs Recessive (expressed only if similar gene).

  • Alleles: Different gene versions.

Polygenic Traits

• Many traits are influenced by multiple genes (polygenic), leading to complex inheritance patterns.

• Incomplete Dominance: Scenario where the dominant allele does not completely mask the effects of a recessive allele (e.g., sickle cell disease).

Genetic Disorders

Overview

• Most genetic disorders linked to dominant genes, although usually less serious.

• Sickle Cell Disease: Recessive disorder, carriers may exhibit symptoms under stress.

• Cystic Fibrosis, Huntington’s Disease: Examples of recessive and dominant disorders, respectively.

• Sex-linked Disorders: Disorders occurring on the X chromosome, more common in males due to single X availability.

Types of Genetic Disorders

• Recessive Disorders: Require two copies for expression (e.g., Sickle Cell Disease, Cystic Fibrosis).

• Dominant Disorders: Only require one copy for expression (e.g., Huntington’s Disease).

• Sex-linked Disorders: Recessive disorders found on X chromosome; females need two copies, males need only one.

Chromosomal Abnormalities

• Causes: Often related to maternal age; arises from uneven division during gamete formation.

• Down Syndrome (Trisomy 21): Characterized by an extra chromosome 21, affecting cognitive and physical features.

• Conversion of sex linked disorders including Turner syndrome (missing part of X chromosome) and Klinefelter syndrome (extra X chromosome in males).

Genetic Counseling

• Assists individuals in understanding genetic conditions that can affect health or offspring.

• Reasons for counseling include family history, ethnicity, and results of genetic testing.

Behavioral Genetics

• The scientific study examining the relationship between genetics and environmental influences on behavior.

• Genotype-Environment Correlations: Three types:

  1. Passive: Children inherit both genes and environments.

  2. Evocative: Environment reacts to individual traits.

  3. Active: Individuals seek environments that nurture their genetic predispositions.

• Genotype-Environment Interactions: Evidence from adoption studies shows how genetic predispositions impact behavior under environmental influences.

• Epigenetics: Studies on modifications that affect gene expression influenced by environmental factors.

Human Genome Project

• Initiated in 1990, completed in 2003, aimed to sequence human DNA and understand genetic influence on diseases.

• Development of databases to catalog genetic variation.

• Research on ethical implications of genetic information and targeted drug therapies.

Prenatal Development

Overview

• Divided into the germinal, embryonic, and fetal periods.

Germinal Period

• Lasts around 14 days from fertilization to implantation.

• Formation of a zygote and subsequent blastocyst.

• Major cell division occurs through mitosis.

Embryonic Period

• Starting at the third week, the implanted blastocyst is now termed an embryo.

• Formation of essential structures including blood vessels and placenta support.

• Developmental growth occurs in cephalocaudal and proximodistal directions.

Fetal Period

• Begins at the ninth week until birth.

• All body parts formed by the third month, continuing development includes sensory capabilities and functioning systems.

• The age of viability occurs around 24 weeks.

Prenatal Brain Development

• Initiates at the third week with the formation of the neural plate.

• Neurogenesis: Production of neurons largely completes by five months gestation.

• Continued growth of synapses and pathways into early childhood.

Teratogens

• Environmental factors that can affect fetal development such as diseases, drugs, and alcohol.

• Critical consideration: timing and level of exposure, as well as genetic susceptibility.

• Common Teratogens: Alcohol leads to Fetal Alcohol Spectrum Disorders; tobacco impacts infant health.

• Education and awareness are critical in prenatal care.