Genetics, Cell Structure, and Reproduction: Foundations for Anatomy & Physiology

Genetics and Genomics

Introduction to Genetics and Genomics

Genetics is the study of heredity and the variation of inherited characteristics, while genomics focuses on the structure, function, evolution, and mapping of genomes. These fields are foundational for understanding how traits are passed from one generation to the next and how genetic variation arises in populations.

• Gene: A segment of DNA that codes for a specific protein or function.

• Genome: The complete set of genetic material in an organism.

• Genomics: The study of the entirety of an organism's genes, including interactions and functions.

• Application: Understanding genetic diseases, inheritance patterns, and evolutionary relationships.

Cell Structure: Prokaryotes vs. Eukaryotes

Prokaryotic Cells

Prokaryotes are single-celled organisms lacking a nucleus and membrane-bound organelles. Their genetic material is found in a region called the nucleoid.

• Key Structures: Capsule, cell wall, plasma membrane, pilus, flagellum, ribosomes.

• Examples: Bacteria and Archaea.

• Function: Prokaryotes perform essential life processes such as metabolism and reproduction.

Eukaryotic Cells

Eukaryotes have a true nucleus and various membrane-bound organelles. They can be single-celled or multicellular, including all plants, animals, fungi, and protists.

• Key Structures: Nucleus, mitochondria, cytoplasm, plasma membrane, ribosomes, capsule (in some).

• Examples: Human cells, plant cells, fungal cells.

• Function: Specialized organelles allow for compartmentalization of cellular processes.

Somatic Cells and Gametes

Somatic Cells

Somatic cells are all body cells except for reproductive cells. They contain the full set of chromosomes (diploid) and are produced by mitosis.

• Diploid: Contains two sets of chromosomes (humans: 46 chromosomes).

• Function: Growth, repair, and maintenance of tissues.

• Produced by: Mitosis.

Gametes

Gametes are reproductive cells (sperm and egg) that contain half the number of chromosomes (haploid). They are produced by meiosis.

• Haploid: Contains one set of chromosomes (humans: 23 chromosomes).

• Function: Sexual reproduction; combine during fertilization to form a diploid zygote.

• Produced by: Meiosis.

Chromosomes and Karyotypes

Chromosome Structure and Types

Chromosomes are long DNA molecules containing genetic information. Humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes.

• Autosomes: Non-sex chromosomes (22 pairs).

• Sex Chromosomes: Determine biological sex (XX for female, XY for male).

• Karyotype: The number and appearance of chromosomes in the nucleus of a cell.

Sex Determination and Variation

Sex is typically determined by the combination of sex chromosomes, but genetic and hormonal factors can result in a spectrum of physical traits.

• Primary Sex Characteristics: Genitalia and reproductive organs.

• Secondary Sex Characteristics: Traits such as body hair and breast development, influenced by genetics and hormones.

• Variation: Differences in chromosomal and hormonal factors can lead to diverse presentations of sex characteristics.

• Prevalence: Variations occur in approximately 1 in 1,500 to 1 in 2,000 births.

DNA: The Blueprint of Life

Structure of DNA

DNA (deoxyribonucleic acid) is the molecule that carries genetic instructions. It consists of two strands forming a double helix, composed of nucleotides.

• Nucleotide: The basic unit of DNA, consisting of a sugar, phosphate, and nitrogenous base.

• Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).

• Base Pairing: A pairs with T, G pairs with C.

Example DNA Sequence: GTTTA

DNA Replication

DNA replication is the process by which DNA makes a copy of itself during cell division, ensuring genetic information is passed to daughter cells.

• Process: DNA unwinds, and each strand serves as a template for a new complementary strand.

• Result: Two identical DNA molecules, each with one old and one new strand.

Cell Division: Mitosis and Meiosis

Mitosis

Mitosis is the process by which somatic cells divide to produce two genetically identical diploid daughter cells.

• Purpose: Growth, tissue repair, and asexual reproduction.

• Chromosome Number: Maintained (diploid).

$\text{Mitosis:} \quad \text{1 cell} \rightarrow \text{2 identical diploid cells}$

Meiosis

Meiosis is the process by which gametes are produced, resulting in four genetically unique haploid cells.

• Purpose: Sexual reproduction and genetic diversity.

• Chromosome Number: Halved (haploid).

• Key Features: Crossing over and independent assortment increase genetic variation.

$\text{Meiosis:} \quad \text{1 cell} \rightarrow \text{4 unique haploid cells}$

Comparison Table: Prokaryotes vs. Eukaryotes

Feature	Prokaryotes	Eukaryotes
Nucleus	No	Yes
Organelles	No membrane-bound organelles	Membrane-bound organelles present
Cell Type	Single-celled	Single-celled or multicellular
Examples	Bacteria, Archaea	Humans, plants, fungi

Comparison Table: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Cell Type Produced	Somatic cells	Gametes
Number of Daughter Cells	2	4
Chromosome Number	Diploid (2n)	Haploid (n)
Genetic Variation	Identical to parent	Unique due to crossing over

Key Terms and Definitions

• Homologous Chromosomes: Chromosome pairs, one from each parent, that are similar in shape, size, and genetic content.

• Haplotypes: Clusters of genes inherited together on a chromosome.

• Haplogroups: Groups of related haplotypes that share a common ancestor.

• Crossing Over: Exchange of genetic material between homologous chromosomes during meiosis, increasing genetic diversity.

Additional info: Some content inferred and expanded for clarity and completeness, including definitions, examples, and tables.