Biology Meiosis and Cell Cycle Quiz

Chapter Overview

• This course covers cell division (mitosis and meiosis), the cell cycle, and the organization of genetic material.

Learning Objectives

• Understand the functions of cellular division and the organization of genetic material in chromatin and chromosomes.
• Define key chromosomal and genetic material terminology.
• Understand the major phases and processes occurring in the cell cycle during mitosis.
• Explain how the mitotic spindle contributes to chromosomal movement in all phases of mitosis.
• Understand the difference between animal and plant cell cytokinesis.
• Understand why cellular checkpoints are important and what happens when they malfunction.
• Explain how genetic material is passed through generations.
• Understand chromosomal numbers in humans, haploid vs diploid cells, and the human life cycle.
• Describe differences between asexual and sexual reproduction.
• Explain the major outcomes of meiosis, major phases of meiosis I and meiosis II.
• Explain how genetic diversity occurs.
• Compare and contrast mitosis and meiosis.

Cellular Division

• The ability of organisms to produce more of their own kind.
• The continuity of life is based on the reproduction of cells, or cell division.
• Mitosis and meiosis

Functions of Cellular Division

• In unicellular organisms, cell division reproduces the entire organism.
• Multicellular eukaryotes depend on cell division for development from a fertilized egg, growth, and repair.

Introducing the Cell Cycle

• Cell division is an integral part of the cell cycle.
• The cell cycle is the life of a cell from formation to its own division.
• Most cell division results in two daughter cells with identical genetic information.
• The exception is meiosis, a special type of division that can produce sperm and egg cells (gametes).
• Meiosis produces non-identical daughter cells.

Cellular Organization of the Genetic Material

• Genome: all the DNA in a cell.
• A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
• DNA molecules in a cell are packaged into chromosomes.
• Eukaryotic chromosomes consist of chromatin which is a complex of DNA and protein (histones) that condenses during cell division.
• Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.

Distribution of Chromosomes During Eukaryotic Cell Division

• In preparation for cell division, DNA is replicated, and the chromosomes condense.
• Each duplicated chromosome has two sister chromatids.
• Sister chromatids: joined copies of the original chromosome, attached along their lengths by cohesins.
• Cohesins : protein complexes that attach sister chromatids.
• The centromere is the narrow "waist" of the duplicated chromosome, where the two chromatids are most closely attached.

The Two Major Phases of the Cell Cycle

• Interphase (G1, S, and G2): Cell growth and copying of chromosomes in preparation for cell division.
• Mitotic phase (Mitosis and Cytokinesis): Mitosis is the division of the genetic material in the nucleus, and Cytokinesis is the division of the cytoplasm.

Interphase: G1, S, and G2

• Cell growth and copying of chromosomes in preparation for cell division.
• About 90% of the cell cycle.
• G1 phase: Cells increase in size and get ready for S phase.
• S phase: DNA replication occurs.
• G2 phase: Cells continue to grow, and get ready for Mitosis

Mitosis consists of Stages

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase and Cytokinesis

G2 of Interphase

• A nuclear envelope encloses the Nucleus
• Two centrosomes have formed and are Regions that organize microtubules.
• Chromosomes duplicated in S phase cannot be seen because they have not condensed.

Prophase

• Chromatin fibers tightly coil into discrete chromosomes becoming visible.
• Duplicated chromosomes appear as two sister chromatids.
• Mitotic spindle begins to form.
• Centrosomes and the microtubules extending from centrosomes.
• Centrosomes move away from each other.

Prometaphase

• Nuclear envelope fragments, chromosomes are even more condensed.
• Microtubules from each centrosome invade nuclear area.
• Kinetochore: protein structure at the centromere on each sister chromatid.
• Some microtubule become kinetochore microtubules jerking chromosomes back and forth.
• Any non-kinetochore microtubules elongate the cell.

Metaphase

• Centrosomes are now at opposite poles of the cell.
• Chromosomes have arrived at the metaphase plate, an imaginary plane in the middle of the cell.
• Centromeres lie at the metaphase plate.
• Kinetochore of each sister chromatid attaches to kinetochore microtubules.

Anaphase

• Shortest phase of mitosis.
• Cohesins between chromatids are cleaved, allowing each pair to separate (becoming an independent chromosome).
• Two new daughter chromosomes move towards opposite poles.
• Centromeres lead, because microtubules attached to kinetochore.

Telophase and Cytokinesis

• Two daughter nuclei form.
• Nuclear envelope reappears.
• Chromosomes start to decondense.
• Mitosis is now complete, creating two genetically identical nuclei.
• Cytokinesis: Division of the cytoplasm.
• Involves formation of a cleavage furrow, pinching the cell in two (animal cells).

Animal and Plant Cell Cytokinesis

• Plant Cells: Vesicles contain cell wall material derived from Golgi apparatus. A cell plate forms during cytokinesis.
• Animal Cells: Contractile ring of microfilaments. A cleavage furrow forms during cytokinesis.

###How do Cells Know When to Divide?

• Cell Cycle is tightly regulated.
• Some cells divide frequently (intestinal cells) and others rarely divide (neuronal cells).
• Cancerous cells can escape the usual controls and proliferate.
• Molecular clocks drive the cell cycle
• Cell cycle control system has checkpoints where the cell cycle stops until go ahead signal has been issued.
• Regulatory proteins drive the cell cycle

Cellular Checkpoints

• Regulatory proteins drive the cell cycle.
• Three important checkpoints are those in the G1, G2, and M phases
• If the cell does not receive the go-ahead signal, it will exit the cycle and enter the G0 phase, a non-dividing state.

Cancer Cells

• Have lost their cell cycle checkpoints (due to internal and external factors)
• Can become immortal, continuously divide, provided they have enough nutrients.
• HeLa cells: Harvested from a women named Henrietta Lacks (in 1951).

Meiosis

• A special type of cell division that can produce sperm and egg cells (gametes).
• Produces non-identical daughter cells.
• Heredity: Transmission of traits from one generation to the next.
• Variation: Differences in appearance offspring show from parents and siblings
• Genetics is the scientific study of heredity and variation

Inheritance of Genetic Material

• Offspring inherit genetic material from parents.
• Genes are the units of heredity and are made up of segments of DNA.
• Locus: A gene's specific position along a chromosome.
• Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs).
• Offspring acquire genes from parents by inheriting chromosomes.
• Human somatic cells have 23 pairs of chromosomes (total of 46)
• Karyotype: an ordered display of the pairs of chromosomes from a cell.
• Diploid cells have 2 sets of chromosomes and haploid cells have one.

Comparison of Asexual and Sexual Reproduction

• Asexual: A single individual passes all of its genes to its offspring without the fusion of gametes. A clone is genetically identical to individuals from the same parent.
• Sexual: Two parents give rise to offspring that have unique combinations of genes from the two parents.

Cellular Organization of the Genetic Material (Somatic and Gametes)

• Somatic cells (Non-reproductive cells) have two sets of chromosomes (diploid).
• Gametes (Reproductive cells: sperm and eggs) have half the number of chromosomes as somatic cells (haploid).
• In an unfertilized egg, the sex chromosome is X.
• In a sperm cell, the sex chromosome may be either X or Y.
• Sex chromosomes are X and Y.
• Females have XX chromosomes and males have XY chromosomes.
• Autosomes are the 22 pairs of chromosomes that are not involved in determining sex.
• Aneuploidy: abnormal number of chromosomes.

Sets of Chromosomes in Human Cells, Cell

• Humans have 23 pairs of chromosomes.
• The sex chromosomes are called X and Y.
• Human females have a homologous pair of X chromosome (XX).
• Human males have one X and one Y chromosome.
• The remaining 22 pairs of chromosomes are called autosomes.

Sets of Chromosomes in a Cell (Homologous)

• The two chromosomes in each pair are called homologous chromosomes or homologs.
• Chromosomes in a homologous pair have the same length and shape and carry similar genes
• Each pair of homologous chromosomes includes one chromosome from each parent.
• Non sister chromatids are chromatids in a homologous pair, one from each parent.

Behavior of Chromosome Sets in the Human Life Cycle

• A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism
• Fertilization: The union of gametes
• Zygote: The fertilized egg. Has one set of chromosomes from each parent.
• The zygote produces somatic cells by mitosis and develops into an adult.

Animal Life Cycles

• Gametes are the only haploid cells in animals.
• Produced by meiosis and undergo no further cell division before fertilization.
• Gametes fuse to form a diploid zygote that divides by mitosis.
• Only diploid cells can undergo meiosis.

Meiosis

• Meiosis reduces chromosome sets from diploid to haploid cells.
• Meiosis is preceded by chromosome replication.
• Meiosis takes place in two consecutive cell divisions called meiosis I and meiosis II.
• Each daughter cell has half as many chromosomes as the parent cell.
• Meiosis produces four haploid daughter cells.
• Crossover allows for genetic recombination.
• The two cell divisions result in four daughter cells rather than the two daughter cells in mitosis.

Comparing Mitosis and Meiosis

• Mitosis: Conserves the number of chromosome sets, and produces cells that are genetically identical to the parent cell.
• Meiosis: Reduces the number of chromosome sets from two to one (haploid), and produces cells that differ genetically from each other and from the parent cell.