Development and Inheritance

Development and Inheritance Notes

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

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.

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.

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.

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.

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.

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

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.

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

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.

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

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

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

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

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.