Genetics: Heredity, DNA, and Chromosomes

Introduction to Genetics

• Genetics involves the study of heredity.
• Heredity is how traits pass from one generation to the next.
• Advantageous traits are passed down through generations.
• Variability refers to the different traits within a population.
• Adaptation is a structure or behavior that allows an organism to survive in its environment.
• Genes, the units of heredity, determine individual traits.
• Variation is a result of heredity and influences how individuals and species survive.

DNA

• DNA stands for Deoxyribonucleic acid.
• DNA is located in the nucleus of cells.
• The base unit of DNA is a nucleotide, consisting of a phosphate group, a sugar, and a nitrogenous base

Nitrogenous Bases

• Adenine (A) pairs with Thymine (T), connected by 2 hydrogen bonds.
• Guanine (G) pairs with Cytosine (C), connected by 3 hydrogen bonds

DNA Structure

• DNA has a double helix structure, resembling a twisted ladder.

Genes, Chromosomes, and DNA

• Chromosomes are long strands of genetic information located in the nuclei of cells.
• Human cells contain 46 chromosomes, which include 22 pairs of autosomes and 1 pair of sex chromosomes (XX/XY)
• Each chromosome includes thousands of genes.
• A gene is a sequence of nucleotide bases that codes for a specific protein, determining different characteristics like blood type, and hair or eye color.
• Humans have approximately 3.223 million base pairs.
• There are about 24,000 genes
• The average human gene length is 27,000 base pairs.

Karyotypes

• Karyotypes are diagrams showing all the chromosomes an individual possesses.
• Every species has a specific number of chromosomes

Chromosome Division

• Somatic cells (body cells) have 22 pairs of chromosomes.
• Gametes (sex cells) have 1 pair of chromosomes (X+Y)
• There are a total of 23 chromosome pairs.
• Chromosomes include genes.
• A karyotype is a chromosomal map.

Chromosome Disorders

• Monosomy involves only one chromosome present in one of the pairs (e.g., Turner syndrome, 23rd chromosome).
• Trisomy involves three chromosomes present at a pair (e.g., Down syndrome, 21st chromosome).

Mitosis

• Involved in cell division for growth and repair.
• Mitosis results in asexual reproduction.
• Mitosis produces 2 identical daughter cells.
• Interphase: the majority of a cell's life.
• Prophase: occurs before the stage where DNA is copied.
• Metaphase: chromosomes line up in the middle.
• Anaphase: chromosomes are pulled apart and away.
• Telophase: a new nucleolus forms at both ends.
• Cytokinesis: the cytoplasm splits, resulting in 2 cells.

Meiosis

• Meiosis is involved in the formation of gametes (sperm and egg).
• It is for sexual reproduction.
• Meiosis produces 4 unique cells via crossing over.
• 23 chromosomes total results in no pairs, referred to as HAPLOID.
• Occurs in the testes for men and the ovaries for women.