Genetics Basics Overview

Overview

This lecture introduces the basics of genetics, focusing on chromosomes, genes, alleles, and how traits are inherited and expressed.

Every cell has a nucleus containing a chromatin network (DNA in loose form).
During cell division (mitosis or meiosis), chromatin condenses into chromosomes.
Humans have 46 chromosomes, which are condensed pieces of DNA.

Genes are sections of DNA that code for specific characteristics like height, hair color, or blood group.
Genes are physically located in the same place on homologous chromosomes.
Alleles are different versions or variations of a gene (e.g., blue eyes or brown eyes).
Each individual inherits two alleles for each gene—one from each parent.

Homologous chromosomes come in pairs (one maternal, one paternal).
Each parent passes on only one allele for each gene through gametes due to meiosis.
During gamete formation, homologous chromosomes separate, ensuring children receive only one allele from each parent.

Dominant alleles are expressed even if only one is present, denoted by a capital letter (e.g., B).
Recessive alleles are only expressed if two copies are present, denoted by a lowercase letter (e.g., b).
Three possible allele combinations: homozygous dominant (BB), heterozygous (Bb), and homozygous recessive (bb).

Genotype refers to the combination of alleles (BB, Bb, or bb).
Phenotype is the physical appearance determined by the genotype (e.g., purple or white flowers).
Homozygous dominant and heterozygous genotypes both show the dominant trait; homozygous recessive shows the recessive trait.

Chromatin Network — Loose DNA found in the nucleus; condenses into chromosomes during division.
Chromosome — Condensed DNA structures carrying genetic information.
Gene — DNA segment coding for a specific trait.
Allele — Variation of a gene (e.g., blue or brown eye color).
Homologous Chromosomes — Chromosome pairs with the same genes at the same locations.
Paternal/Maternal Chromosome — Chromosomes inherited from father/mother, respectively.
Dominant Allele — Trait expressed with only one copy present (uppercase letter).
Recessive Allele — Trait expressed only with two copies present (lowercase letter).
Homozygous — Two identical alleles (BB or bb).
Heterozygous — Two different alleles (Bb).
Genotype — Genetic makeup (allele combinations).
Phenotype — Observable physical trait.

Review meiosis and chromosome separation for better understanding of inheritance.
Create flashcards for key terms and definitions as study aids.
Watch related videos for more in-depth topics, including monohybrid and dihybrid crosses.