Cell Reproduction Quiz

Cell Reproduction

• Human body cells (somatic) have 46 chromosomes
• Human gametes (sperm or eggs) have 23 chromosomes
• A typical body cell contains two matched (homologous) sets of chromosomes, this configuration is known as diploid (2n)
• Human cells containing one set of chromosomes are called gametes (sex cells), these are eggs and sperm, and are designated haploid (1n)
• Homologous chromosomes are the same length and have specific nucleotide segments called genes in exactly the same location (locus)
• Genes are the functional units of chromosomes, determining specific characteristics (traits) by coding for specific proteins
• Traits are the variations of characteristics, such as hair color
• Each copy of a homologous pair originates from a different parent, therefore the genes (alleles) are not identical, although they code for the same traits (e.g. hair color)
• Variation within a species is due to specific combinations of genes inherited from both parents
• A slightly altered sequence of nucleotides within a gene can result in an alternative trait
• For example, there are three possible gene sequences (A, B, and O) on a human chromosome that code for blood type

Eukaryotic Chromosomal Structure and Compaction

• DNA must be tightly packaged to fit inside the cell's nucleus
• Long strands of DNA are condensed into compact chromosomes
• Level 1 of chromosome compaction: Short stretches of DNA double helix wrap around a core of eight histone proteins
• The DNA-histone complex is called chromatin
• The beadlike histone-DNA complex is called a nucleosome
• DNA connecting nucleosomes is called linker DNA
• Nucleosomes and linker DNA coil into a chromatin fiber
• This coiling further condenses the chromosome about 50 times shorter than the extended form
• A variety of fibrous proteins pack the chromatin
• After replication, chromosomes are composed of two linked sister chromatids
• When fully compact, identically packed chromosomes are bound together by cohesion proteins
• The connection between sister chromatids is called the centromere

The Cell Cycle

• The cell cycle is an ordered series of events (cell growth and division) that produces two new daughter cells
• Cells proceed through precisely timed and regulated stages of growth, DNA replication, and nuclear/cytoplasmic division, producing two identical cells
• The cell cycle has two major phases
  • Interphase: Cell growth and DNA replication
  • Mitotic phase: Replicated DNA and cytoplasmic contents are separated, and the cell cytoplasm is typically partitioned by cytokinesis
• Interphase stages:
  • G1 phase (First Gap): Cell is active biochemically, building blocks of chromosomal DNA, associated proteins, and sufficient energy reserves are made to replicate each chromosome
  • S phase (Synthesis of DNA): DNA replication occurs, producing identical pairs of DNA molecules (sister chromatids); the centrosome is also duplicated in this phase
  • G2 phase (Second Gap): Cell replenishes energy stores, synthesizes proteins for chromosome manipulation and movement, duplicates organelles, and may continue growing; final preparations for the mitotic phase
• Mitotic phase (karyokinesis): The nuclear division of the cell into a series of phases, including prophase, prometaphase, metaphase, anaphase, and telophase
• Cytokinesis: The physical separation of cytoplasmic components into the two daughter cells. Animal cells use a cleavage furrow, while plant cells use a cell plate

Go Phase

• Cells in Go phase are not actively preparing to divide
• Go is a quiescent (inactive) stage that occurs when cells exit the cell cycle
• Some cells enter Go temporarily due to environmental conditions like nutrient availability or growth factors
• Cells remain in Go until conditions improve or an external signal triggers the onset of G1
• Other cells, like mature cardiac muscle and nerve cells, remain in Go permanently

Test your knowledge on cell reproduction concepts, focusing on the differences between somatic and gamete cells. This quiz covers topics such as diploid and haploid cell structures, homologous chromosomes, and the role of genes in determining traits. Challenge yourself to understand the basics of genetic variation and inheritance.