Genetic_Bases_of_Child_Development-Chapter_2

Genetic Bases of Child Development

Mechanisms of Heredity

Conception

• One egg is released by the female.

• Approximately 200 to 500 million sperm are released by the male, but only a few hundred make the 6 to 7 inch journey to the fallopian tube.

• Both eggs and sperm contain 23 chromosomes.

• Upon fertilization, the egg contains 22 pairs of autosomes and 2 sex chromosomes.

Chromosomes and DNA

• Each chromosome is a single molecule of DNA.

In Vitro Fertilization (IVF)

The IVF Process

• IVF is a treatment for infertility where eggs and sperm are combined outside the uterus, and the resulting fertilized egg is implanted in the uterus.

• The process includes:

  1. Hormone treatments to stimulate egg production.

  2. Extraction of multiple eggs from the ovaries.

  3. Laboratory mixing of eggs with sperm to achieve fertilization.

  4. Incubation of fertilized eggs for about 48 hours.

  5. Embryo implantation in the uterus or freezing for future use.

• The first baby born from IVF was in 1978.

Structure of DNA

• DNA consists of nucleotides arranged in a spiral staircase structure.

• A gene is defined as a section of DNA that provides specific biochemical instructions.

Genes and Heredity

Definitions

• Genotype: The complete set of genes of an individual.

• Phenotype: Physical, behavioral, and psychological characteristics that develop when the genotype interacts with the environment.

Single Gene Inheritance

Dominant and Recessive Traits

• Dominant and recessive describe inheritance patterns of traits.

• A recessive phenotype requires two copies of the recessive allele (one from each parent).

• An individual with one dominant allele and one recessive allele expresses the dominant phenotype.

Gene Dominance

• Dominance occurs when one allele's effect on phenotype masks that of another allele.

• Recessive traits can be carried without appearing in the individual (e.g., a dark-haired individual can carry a recessive light hair gene).

Expression of Recessive Genes

• A recessive gene can be masked by a dominant gene; blue eyes, for example, require contributions from both parents.

• Observable dominant and recessive traits include:

  • Widow's Peak

  • Bent Pinkie

  • Earlobe Attachment

  • Rolling of Tongue

  • Cleft Chin

  • Dimples

  • Handedness

  • Natural Curly Hair

Allelic Relationships

Homozygous vs Heterozygous

• Homozygous: Both copies of a gene match (AA or aa).

• Heterozygous: Copies do not match (Aa).

  • Homozygous dominant (AA) has two dominant alleles.

  • Homozygous recessive (aa) has two recessive alleles.

  • Heterozygous (Aa) has one dominant and one recessive allele.

Genetic Disorders

Inherited Disorders

• Genetic disorders can be inherited; examples include:

  • Huntington's Disease

  • Sickle Cell Anemia

Huntington's Disease (HD)

• HD is an inherited neurological disorder characterized by involuntary movements, emotional disturbances, and cognitive decline.

• Approximately 30,000 Americans have HD, with many more carrying the gene.

• HD is caused by an abnormal gene on chromosome 4 that produces a defective protein with excessive "CAG" repeats.

• Symptoms typically appear in mid-life, and the gene is dominant, giving children of affected parents a 50% chance to inherit it.

Symptoms of Huntington's Disease

• Symptoms include:

  • Chorea (involuntary movements)

  • Impulsivity and balance problems

  • Emotional issues, including depression and irritability.

  • Cognitive challenges such as trouble concentrating or organizing.

Sickle Cell Anemia (SCA)

Inheritance and Causes

• Sickle cell disease is caused by inherited abnormal hemoglobin, leading to sickled red blood cells.

• Individuals inherit two faulty copies of the hemoglobin gene to develop the disease.

• The sickle cell trait (SCT), which is not a disease, occurs when one faulty gene is inherited and does not typically produce symptoms.

Epidemiology

• Sickle cell disease is more common in specific ethnic groups, particularly those with ancestry from malaria-prone regions (e.g., African, Middle Eastern, Indian descent).

Chromosome Abnormalities

Down Syndrome

• The most common form of Down syndrome involves trisomy 21, resulting from an extra copy of chromosome 21.

• Most cases are not inherited and occur randomly during cell division.

• Maternal age is a significant risk factor; older women have a higher chance of having a child with Down syndrome.

Research on Heredity and Environment

Gender and Trait Development

• Traits result from the interaction of genetics and the environment.

• Researchers study twins and adoption cases to analyze hereditary vs. environmental influences.

• Examples include studies on intelligent children seeking stimulating environments (niche picking), which enhances their abilities.