Human genetics and development

Human Genetics and Development

Overview of Human Genetics

  • Human genetics involves the study of genes and heredity, particularly how characteristics are passed from parents to offspring.

  • Key components include DNA, chromosomes, genes, gametes, and types of reproduction.

DNA

  • Definition: DNA is the genetic material that contains instructions for life.

  • Location: Found in the nucleus of a cell.

  • Function: Passes genetic information during reproduction.

Chromosomes

  • Definition: Structures formed when DNA condenses prior to cell division.

  • Human Chromosome Count: Human body cells typically contain 46 chromosomes.

Genes

  • Definition: Segments of DNA located on chromosomes that contain the information necessary for building and maintaining an organism.

  • Function: Carry heritable traits.

Gametes

  • Definition: Special reproductive cells (sperm and eggs) involved in sexual reproduction.

  • Chromosome Count: Each gamete contains half the number of chromosomes compared to parent cells (23 chromosomes).

Types of Reproduction

Asexual Reproduction

  • Involves a single parent organism.

  • Offspring are genetically identical to the parent (clones).

  • Example: Bacteria reproduce by splitting into two.

Sexual Reproduction

  • Requires two parent organisms.

  • Offspring have genetic variation, receiving DNA from both parents.

  • Gamete Fusion: Gametes join to form a new organism.

Fertilization

Overview

  • The process where the male sperm and female egg combine to form a zygote.

Egg Cells

  • Description: Female gametes are larger than male gametes and contain nutrients for the embryo.

  • Production: Eggs are formed and stored in ovaries, with a set number present at birth. One matures and is released monthly during a female's reproductive years.

Sperm Cells

  • Description: Male gametes are smaller and specialized for mobility.

  • Function: Swim to find and fertilize an egg.

  • Production: Formed in the testes and produced in large quantities after puberty.

Fusion of Gametes

  1. Millions of sperm are released into the female body.

  2. Sperm swim towards the egg.

  3. Upon entering the egg, it forms a protective layer to prevent other sperm from entering.

  4. Fusion of the sperm and egg nuclei occurs, resulting in fertilization.

  5. A single fertilized egg (zygote) formed contains 46 chromosomes (23 from each parent).

  6. The zygote divides to form an embryo, which implants in the uterus and continues to develop.

Sex Inheritance in Humans

Determination of Sex

  • The sex of the embryo is determined at fertilization based on the combination of sex chromosomes from each parent.

  • Female (XX): Inherits two X chromosomes.

  • Male (XY): Inherits one X and one Y chromosome.

Chromosome Pairs

  • Humans have 23 pairs of chromosomes.

  • The first 22 pairs are autosomes (matching pairs) and the 23rd pair determines sex (XX or XY).

  • Matching pairs carry genes that control similar traits, while sex chromosomes control sexual characteristics.