Genetics: Understanding DNA, Genes, and Chromosomes

Genetics: Key Concepts

Vocabulary Terms:

• Chromosome: A structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
• Gene: A unit of heredity transferred from parent to offspring, determining some of the offspring's characteristics.
• Homologous Pairs: Chromosomes containing genes for the same traits but potentially different alleles. These are usually paired during mitosis.
• Allele: One of two or more alternative forms of a gene that arise by mutation and are found at the same location on a chromosome.
• Sister Chromatid: Identical copies of a chromosome formed by DNA replication, joined by a common centromere. It's essentially half of a duplicated chromosome.
• Nucleotide: A compound consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit of nucleic acids like DNA.
• Phenotype: The set of observable characteristics of an individual resulting from the interaction of their genotype with the environment.
• Homozygous: Refers to a particular gene having identical alleles on both homologous chromosomes. Represented by two capital letters (e.g., XX) for a dominant trait, or two lowercase letters (e.g., xx) for a recessive trait.
• Genotype: The genetic makeup of a cell that determines one of its characteristics.
• Heterozygous: Having two different alleles of a particular gene or genes.

DNA Structure and Function

DNA Structure:

• Nucleotide Components: Sugar, phosphate, nitrogen base.
• Nitrogenous Bases: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G).

DNA Coding and Non-coding Regions

• Coding DNA: Sequences of DNA that code for proteins. These are separated by non-coding regions called introns, which have no apparent function.
• Non-coding DNA: Components of an organism's DNA that do not encode protein sequences.

Mutations

Mutation: Changes in the DNA sequence. For example, a change from CGG-AGT-CTG to CAG-AGT-CTG.

• Spontaneous Mutations: Occur through natural biological processes.
• Induced Mutations: Caused by external factors like sunburn or chemicals.
• Chromosome Mutation: A change in the structure of a chromosome.
• Gene Mutation: A change in the nucleotide sequence of a gene.

Relationship Between DNA, Genes, and Chromosomes

Genes are segments of DNA that contain the code for specific proteins. Chromosomes are structures within cells that house these genes. Genes are located on chromosomes, which reside in the cell nucleus.

Chromosomes

Humans have 23 pairs of chromosomes, totaling 46.

• Sex Chromosomes: Females typically have two X chromosomes (XX), making them the homogametic sex. Males typically have one X and one Y chromosome (XY), making them the heterogametic sex.
• Gametes: Each gamete (sperm or egg cell) contains 23 chromosomes.

Gamete: A mature haploid male or female germ cell capable of uniting with another of the opposite sex in sexual reproduction to form a zygote.