Genetics and Cell Division

• Genetics and cell division involve understanding how cells divide and how genetic information is passed on

Key Definitions

• An allele is an alternative form of a gene arising from mutation, affecting traits and residing at the same chromosomal location
• Chromosomes, found in the cell nucleus, consist of DNA coiled around proteins, transmitting genetic information from parents
• A gene is a specific DNA sequence that serves as the basis of heredity, containing protein-producing information influencing traits

Stages of Cell Division

• Interphase includes G1, S, and G2 phases, preparing the cell for division through growth and DNA replication
• Mitosis results in two identical daughter cells, involving prophase, metaphase, anaphase, and telophase
• Meiosis is a specialized division reducing chromosome number by half, creating four diverse gametes
• Cells reproduce through cell division, creating new cells called daughter cells

Genetic Variation Mechanisms

• Crossing over is the exchange of genetic material during meiosis, creating new allele combinations
• Independent assortment is the segregation of different genes' alleles independently, contributing to offspring variation

Types of Cells and Chromosome Sets

• Diploid cells contain two chromosome sets, one from each parent, found in somatic cells
• Haploid cells contain a single chromosome set, typical of gametes
• Homologous chromosomes are chromosome pairs within a diploid organism that carry the same genes in the same order, one from each parent

Mitosis Stages

• Prophase involves chromatin condensing into chromosomes, nuclear membrane breakdown, and spindle apparatus formation
• Metaphase involves chromosome alignment along the metaphase plate and attachment to the mitotic spindle
• Anaphase involves sister chromatid separation and movement to opposite poles by spindle fibers

Meiosis Overview

• Meiosis I separates homologous chromosomes, forming two haploid cells with duplicated chromosomes
• Meiosis II separates sister chromatids, creating four haploid gametes, similar to mitosis
• Zygote formation is the union of sperm and ovum, forming a diploid zygote which starts a new organism

Key Cell Types

• Gametes are reproductive cells (sperm and ovum) which are haploid and combine to form a zygote during fertilization
• Daughter cells are new cells formed from cell division, from either mitosis or meiosis, ensuring genetic continuity

Cell Division in Unicellular Organisms

• Unicellular organisms like bacteria often clone themselves during cell division.
• The daughter cells become separate, genetically identical organisms, as seen in bacteria.
• This process in unicellular organisms is known as asexual reproduction, specifically binary fission.

Cell Division in Multicellular Organisms

• In multicellular organisms, cell division produces new cells that contribute to growth or repair.
• Daughter cells become parts of the organism as opposed to creating a new organism.
• Skin cells dividing to heal a paper cut is an example of cell division in multicellular organisms.
• Gametes (sex cells) are created through a modified version of cell division.

Chromosomes and DNA

• Chromosomes play a vital role in cell division.
• DNA (deoxyribonucleic acid) is the genetic material found in a cell's nucleus.
• DNA contains the genetic code or instructions for everything within an organism.
• DNA, when spread out, appears grainy and is called chromatin.
• Before cell division, DNA replicates (copies) itself to pass information to daughter cells
• During cell division, DNA condenses into an X-shaped structure called a chromosome.
• Each side of the X-shaped chromosome is a genetically identical sister chromatid.
• Sister chromatids form a sideways V-shape and are joined by a structure called a centromere.

Chromosome Number

• Different organisms have different numbers of chromosomes.
• Human somatic cells (all cells except gametes) have 23 pairs of chromosomes, a total of 46.
• Human gametes (eggs and sperm) have only one chromosome from each pair, totaling 23.
• Gametes are genetically different from their parent cells.
• During fertilization, a sperm cell and an egg cell contribute 23 chromosomes each.
• The fused cell, called a zygote, then has 23 pairs of chromosomes, totaling 46.

Preview of the Cell Cycle

• The information provided serves as an overview to prepare for studying the cell cycle.
• The cell cycle refers to the life cycle of a cell.

Explore genetics and cell division, covering alleles, chromosomes, and genes. Understand interphase, mitosis, and meiosis stages. Learn genetic variation mechanisms like crossing over.