Development and Inheritance

Development and Inheritance Notes

Unit Overview

• Unit 11 covers Development and Inheritance, focusing on human developmental stages, genetic mechanisms, and related concepts.

Module 27.1: Stages of Development

• Gestation: Duration an embryo/fetus develops in the uterus.
  • Pregnancy: State of the female during gestation.
• Development: Gradual anatomical and physiological changes.
  • Embryonic Development: First 2 months post-fertilization; studied in embryology.
  • Fetal Development: Begins at week 9 until birth.
• Trimesters: Development divided into three trimesters, each lasting approximately three months.

Module 27.2: Fertilization Process

• Fertilization: Fusion of sperm (23 chromosomes) and ovum (23 chromosomes) resulting in a zygote (46 chromosomes).
  • Occurs typically in the uterine tube after ovulation.
• Steps in Fertilization:
  1. Oocyte at Ovulation: Release of secondary oocyte surrounded by corona radiata.
  2. Fertilization: Sperm activates oocyte, causes meiosis completion.
  3. Pronuclei Formation: Sperm and egg nuclei reorganize into pronuclei.
  4. Spindle Formation and Cleavage: Chromatin condenses; start of mitotic divisions (cleavage).
  5. Amphimixis: Fusion of pronuclei forms a zygote.
  6. Blastomere Formation: First cleavage yields two blastomeres (30 hours post-fertilization).
• Sperm must penetrate layers around the oocyte using acrosomal enzymes.

Module 27.3: Cleavage and Implantation

• Cleavage:

  • Zygote undergoes rapid cell divisions to form a pre-embryo (morula) by day 4 and a blastocyst by day 6.
  • Blastocyst: Hollow ball of cells; functions in implantation into the uterine wall by day 7.

• Trophoblast: Outer layer of cells that will contribute to the placenta; absorbs nutrients.

• Inner Cell Mass: Forms the embryo; insulated from uterine environment.

Module 27.4: Gastrulation and Germ Layers

• Gastrulation: Process forming three germ layers - ectoderm, mesoderm, endoderm.
  • Ectoderm: Forms skin and nervous system.
  • Mesoderm: Forms muscles, bones, and circulatory system.
  • Endoderm: Forms digestive and respiratory systems.

Module 27.5: Extra-embryonic Membranes and Placenta Formation

• Four extra-embryonic membranes are formed:
  1. Yolk Sac: Nutrient source for the embryo in early development.
  2. Amnion: Surrounds embryo, contains amniotic fluid for protection.
  3. Allantois: Forms part of the umbilical cord; involved in waste management.
  4. Chorion: Contributes to the placenta; interfaces fetal and maternal blood.

Module 27.6: Early Embryonic Development

• Embryo undergoes significant changes during weeks 2-3.
  • Formation of main structures and organ systems begins around week 6.

Module 27.8: Organogenesis

• Organogenesis: Development of organs occurs during the first trimester.
  • By the end of the first trimester, basic structures and functions are developing, leading to the fetus stage.

Module 27.9: Maternal Changes During Pregnancy

• Physiological stresses on maternal systems:
  • Increased blood volume, nutrient requirements, changes in organ positions due to expanding uterus.

Module 27.10: Labor and Delivery

• Stages of labor:
  1. Dilation Stage: Cervix enlarges; amnion may rupture.
  2. Expulsion Stage: Fetus is delivered.
  3. Placental Stage: Post-delivery expulsion of the placenta.
• Premature labor risks and outcomes discussed.

Module 27.11: Neonatal and Postnatal Development

• Neonatal Period: First 28 days of life; dependent on maternal systems.
  • Development continues with crucial nourishment through breastfeeding.

Module 27.12: Life Stages of Postnatal Development

• Follows a sequence from neonatal, infancy, childhood, adolescence, to maturity,
  • Each stage involves developmental changes influenced mainly by hormonal regulation.

Module 27.14: Genetics Overview

• Genotype: Genetic makeup; influences phenotype, which is the expressed physical traits.
• Understanding of heredity and the role of alleles in trait expression.

Module 27.15: Patterns of Inheritance

• Patterns such as autosomal inheritance and sex-linked inheritance explored.
  • Simple vs. polygenic inheritance distinguished.

Module 27.17: Clinical Implications of Genetic Disorders

• Discussion of chromosomal abnormalities and their implications such as Down syndrome, Turner syndrome, and Klinefelter syndrome.
  • The overview of the human genome and its significance in the study of genetics and hereditary diseases.