DNA and Chromosomes

• Genes determine traits in an individual.
• Variation influences how individuals and a species can survive.

DNA

• DNA stands for Deoxyribonucleic acid.
• DNA is in the nucleus of cells.
• A nucleotide is the base unit of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base.
• Nitrogenous bases include Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).
• Adenine (A) pairs with Thymine (T) using 2 hydrogen bonds.
• Guanine (G) pairs with Cytosine (C) using 3 hydrogen bonds.
• DNA has a double helix structure, resembling a twisted ladder.

Chromosomes

• Chromosomes are long strands of generic information located in the nuclei of cells.
• A human cell has 46 chromosomes, including 22 pairs of autosomes and 1 pair of sex chromosomes (XX/XY).
• Each chromosome contains thousands of genes.
• A gene is a sequence of nucleotide bases that codes for a specific person and characteristic (e.g., blood type, hair color, etc.).
• Humans possess approximately 3,223 million base pairs, estimated to contain around 24,000 genes.
• The average human gene length is 27,000 base pairs.
• A karyotype is a diagram that shows all the chromosomes an individual possesses.
• Somatic cells (body) have 22 pairs of chromosomes, while gametes (sex) have 1 pair.
• The total chromosome pairs are 23.
• Monosomy is a condition where only 1 chromosome is present in a pair.
• Trisomy is the presence of three chromosomes in a pair.

Mitosis

• Mitosis is cell division for asexual reproduction, resulting in 2 identical daughter cells.
• Interphase is the majority of a cell's life.
• Prophase is the stage before being copied.
• Metaphase is when chromosomes line up in the middle.
• Anaphase is when chromosomes are pulled apart and away.
• Telophase is when a new nucleolus forms at both ends.
• Cytokinesis is when the cytoplasm splits, resulting in 2 cells.
• Mitosis is cellular replication for growth and repair, producing 2 identical cells with 46 chromosomes found in somatic cells (body).

Meiosis

• Meiosis is the formation of gametes (sperm and egg) for sexual reproduction
• In meiosis, 4 unique cells (genetically different) are produced through crossing over.
• There are 23 total chromosomes, with no pairs (HAPLOID).
• Meiosis occurs in the testes of men and the ovaries of women.

Definitions

• Genetics is the study of heredity
• Heredity is how traits are passed down from one generation to the next.
• Variability refers to traits within a population
• Adaptation is the structure or behavior that allows an organism to survive in its environment.