Life 102 Exam 3

Cell Division and Reproduction

1. Differences Between Binary Fission, Mitosis, and Meiosis

  • Binary Fission: A simple cell division process in prokaryotes resulting in two identical cells. No mitotic spindle involved; DNA replicates, the cell elongates, and pinches in half.

  • Mitosis: A process of cell division in eukaryotes that results in two daughter cells, each with the same number of chromosomes as the parent cell.

  • Meiosis: A specialized type of cell division that reduces the chromosome number by half, producing four genetically diverse haploid gametes.

2. Asexual vs. Sexual Reproduction

  • Asexual Reproduction:

    • Pros: Fast reproduction, requires only one parent, no need for fertilization.

    • Cons: Lack of genetic diversity, vulnerabilities to environmental changes.

  • Sexual Reproduction:

    • Pros: Genetic diversity, adaptation to changing environments.

    • Cons: Requires two parents, more complex and time-consuming.

3. Cell Cycle Stages: G1, S, G2, M and Checkpoints

  • G1 Phase: Cell growth; organelles duplicate, and the cell prepares for DNA synthesis.

  • S Phase: DNA replication occurs; each chromosome duplicates to form sister chromatids.

  • G2 Phase: Further growth and preparation for mitosis ensuring all DNA is replicated and undamaged.

  • M Phase: Mitosis occurs, resulting in cell division.

  • Checkpoints:

    • G1 Checkpoint: Checks for DNA damage and cell size.

    • G2 Checkpoint: Ensures DNA has been copied correctly before mitosis.

    • M Checkpoint: Checks spindle attachment to chromosomes.

4. Purpose of Checkpoints in Cell Cycle

  • Prevents errors in cell division; ensures cell doesn't divide with damaged DNA or incomplete replication.

  • Checkpoints occur at G1, G2, and during M phase.

5. Stages of Mitosis

  • Prophase: Chromatin condenses into visible chromosomes; nuclear envelope breaks down.

  • Metaphase: Chromosomes align at the cell's equator; spindle fibers attach to centromeres.

  • Anaphase: Sister chromatids separate and move to opposite poles of the cell.

  • Telophase: Chromatids reach poles; nuclear envelope reforms around each set, chromosomes de-condense.

6. Cytokinesis

  • In Animal Cells: Cell membrane pinches inwards to form two daughter cells.

  • In Plant Cells: Cell plate forms along the center of the cell, developing into a new cell wall.

7. Haploid vs. Diploid

  • Haploid (n): Cells contain one set of chromosomes (e.g., gametes).

  • Diploid (2n): Cells contain two sets of chromosomes (e.g., somatic cells).

8. Zygote vs. Gamete

  • Gamete: A haploid reproductive cell (sperm or egg).

  • Zygote: A diploid cell formed by the fusion of two gametes.

9. Steps of Meiosis

  • Meiosis I: Homologous chromosomes separate.

    • Prophase I: Homologous chromosomes pair and undergo crossing over.

    • Metaphase I: Paired chromosomes align.

    • Anaphase I: Homologous chromosomes separate to opposite poles.

    • Telophase I: Nuclear membranes form; cytokinesis occurs, resulting in two haploid cells.

  • Meiosis II: Similar to mitosis:

    • Prophase II: Chromosomes condense.

    • Metaphase II: Chromosomes align at equator.

    • Anaphase II: Sister chromatids separate.

    • Telophase II: Formation of four genetically diverse haploid cells.

10. Crossing Over

  • Occurs during Prophase I of meiosis; homologous chromosomes exchange genetic material, increasing genetic variation.

11. Gene Loci and Recombination

  • Genes that are close together on a chromosome are less likely to recombine than those further apart; distance impacts recombination frequency.

12. Germ-line Cells

  • Cells that give rise to gametes; critical for heredity and genetic diversity.

13. Sister Chromatids vs. Homologous Chromosomes

  • Sister Chromatids: Identical copies of a chromosome, joined at the centromere.

  • Homologous Chromosomes: Chromosome pairs (one from each parent) with similar genes at corresponding loci.

  • Found during all phases of meiosis and in mitosis as well.

14. Mitosis vs. Meiosis DNA and Ploidy

  • Mitosis: Produces two diploid daughter cells, DNA content is identical to parent cell.

  • Meiosis: Produces four haploid daughter cells, DNA content is halved.

15. Chromosome Duplication and Separation

  • DNA is duplicated during S phase in both mitosis and meiosis, then separated during the respective anaphases of each process.

16. Gregor Mendel

  • Known as the father of genetics for his work on inheritance patterns in pea plants, discovering foundational principles of heredity.

17. Laws of Inheritance

  • Law of Segregation: Alleles segregate during gamete formation.

  • Law of Independent Assortment: Genes for different traits are inherited independently.

  • Law of Dominance: Dominant alleles mask the expression of recessive alleles.

18. Mendel's Experiments and Results

  • F1 Monohybrid Cross: Resulted in a 3:1 phenotypic ratio.

  • F1 Dihybrid Cross: Resulted in a 9:3:3:1 phenotypic ratio.

19. Genes, Traits, Genotype, and Phenotype

  • Genes: Units of heredity.

  • Traits: Physical characteristics determined by genes.

  • Genotype: Genetic makeup of an organism.

  • Phenotype: Observable traits resulting from genotype.

20. Allele Combinations and Inheritance

  • Homozygous: Two identical alleles.

  • Heterozygous: Two different alleles.

  • Dominant: Allele that expresses its trait.

  • Recessive: Allele only expressed in the absence of a dominant allele.

Genetics

21. Punnett Square

  • A tool used to predict genotypes and phenotypes of offspring in genetic crosses (monohybrid and dihybrid).

22. Potential Offspring from Crosses

  • Monohybrid Cross: 3:1 phenotypic ratio; genotypes include homozygous dominant, heterozygous, homozygous recessive.

  • Dihybrid Cross: 9:3:3:1 ratio for phenotypes; includes combinations of alleles from both parents.

23. Test Cross

  • A breeding experiment used to determine the genotype of an individual with a dominant phenotype by crossing it with a homozygous recessive individual.

24. Mendelian vs. Non-Mendelian Inheritance

  • Mendelian: Traits controlled by single genes (dominant/recessive).

  • Non-Mendelian: Involves multiple genes or alleles affecting traits.

25. Co-Dominance vs. Incomplete Dominance

  • Co-Dominance: Both alleles are expressed equally (e.g. AB blood type).

  • Incomplete Dominance: Blending of traits (e.g. red and white flowers producing pink).

26. Pleiotropy vs. Epistasis

  • Pleiotropy: One gene affects multiple traits (e.g. sickle cell anemia affecting blood cells and health).

  • Epistasis: One gene affects the expression of another gene (e.g. coat color in mice).

27. Polygenic vs. Multiple Alleles

  • Polygenic: Trait controlled by multiple genes (e.g. skin color).

  • Multiple Alleles: More than two alleles for a gene in a population (e.g. ABO blood type).

28. Blood Types and Medicine

  • Blood types (A, B, AB, O) result from multiple alleles and are critical in transfusions. Compatibility is essential for safe blood donation.

29. Universal Donor and Recipient

  • Universal Donor: Type O (no antigens present).

  • Universal Recipient: Type AB (both antigens present, able to accept any blood type).

30. Heterozygous Advantage

  • Example: Sickle cell trait provides resistance to malaria while homozygous individuals suffer from sickle cell disease.

31. Probability in Genetics

  • Use product rule for independent events and sum rule for mutually exclusive events when calculating probabilities of genetic traits.

32. Female vs. Male Sex Genotype

  • Female: XX

  • Male: XY

33. X-Inactivation

  • Occurs in female mammals; one X chromosome in each cell is randomly inactivated to balance gene dosage between sexes.

34. Calico Cats

  • Mainly female due to X-inactivation in cats; different color patches result from inactivated orange or black alleles on X chromosomes.

35. Somatic vs. Sex-Linked Mutations

  • Somatic Mutations: Occur in non-gamete cells, not heritable.

  • Sex-Linked Mutations: Mutations in genes located on sex chromosomes; often affect males more due to single X chromosome.

36. Nondisjunction

  • Failure of chromosomes to separate properly during cell division; can lead to aneuploidy (e.g. Down syndrome).

37. Sex-Chromosome Distribution

  • Abnormal distributions can lead to conditions such as Turner syndrome (X0) or Klinefelter syndrome (XXY).

38. Germ-Line Cell Stages

  • Include oogonia/spermatogonia, primary oocytes/spermatocytes, secondary oocytes/spermatids; acquire specialization and undergo meiosis.

39. Trisomy

  • A condition where an individual has three instances of a particular chromosome instead of the usual two (e.g. Trisomy 21 - Down syndrome).

40. Structure, Shape, and Function of DNA

  • DNA is a double helix, composed of nucleotide subunits; carries genetic information.

41. Semiconservative DNA Replication

  • Each new DNA molecule contains one original and one new strand, preserving half of the original molecule during replication.

42. Complementary Base Pairing

  • Adenine pairs with Thymine; Guanine pairs with Cytosine, maintaining DNA structure and facilitating replication.

43. Anti-Parallel Structure of DNA

  • Two strands run in opposite directions, ensuring proper base pairing during replication and transcription.

44. Steps of DNA Replication

  • Initiation (primase adds RNA primer), elongation (DNA polymerase adds nucleotides), and termination (completion of replication).

45. Function of a Primer

  • RNA primer initiates DNA synthesis; composed of RNA nucleotides, it is essential for DNA polymerase to begin synthesis.

46. Functions of Key Enzymes in DNA Replication

  • Primase: Synthesizes RNA primers.

  • DNA Helicase: Unwinds the DNA double helix.

  • DNA Polymerase: Adds complementary nucleotides; proofreads.

  • DNA Ligase: Joins Okazaki fragments on the lagging strand.