Cellular Basis of Reproduction and Inheritance

Parent and Daughter Cells

• Parent cells are the original cells that divide to produce new cells.

• Daughter cells are the cells resulting from the division of a parent cell.

• In mitosis, daughter cells are genetically identical to the parent cell; in meiosis, they are genetically unique.

Sexual vs. Asexual Reproduction

• Asexual reproduction involves a single parent and produces genetically identical offspring (clones).

• Sexual reproduction involves two parents and produces genetically diverse offspring.

• Example: Bacteria reproduce asexually by binary fission; humans reproduce sexually.

Prokaryotic vs. Eukaryotic Cell Division

• Prokaryotic cells divide by binary fission, a simple process where the cell duplicates its DNA and splits in two.

• Eukaryotic cells divide by mitosis (for somatic cells) or meiosis (for gametes).

Mitosis vs. Meiosis

• Mitosis produces two genetically identical diploid cells for growth and repair.

• Meiosis produces four genetically unique haploid cells (gametes) for sexual reproduction.

Chromatin vs. Chromosomes

• Chromatin is the loose, uncondensed form of DNA and proteins in the nucleus.

• Chromosomes are condensed, organized structures of DNA visible during cell division.

Autosomes vs. Sex Chromosomes

• Autosomes are non-sex chromosomes (in humans, pairs 1–22).

• Sex chromosomes determine biological sex (X and Y in humans).

Diploid vs. Haploid Cells

• Diploid (2n) cells have two sets of chromosomes (somatic cells).

• Haploid (n) cells have one set of chromosomes (gametes).

Somatic Cells vs. Gametes

• Somatic cells are body cells (diploid).

• Gametes are reproductive cells (sperm and egg; haploid).

Organization of DNA into Chromosomes

• Genes are segments of DNA that code for proteins.

• Centromere is the region where sister chromatids are joined.

• Histones are proteins around which DNA winds to form nucleosomes.

• Sister chromatids are identical copies of a chromosome, joined at the centromere.

• Homologous pairs are pairs of chromosomes (one from each parent) with the same genes.

• Karyotype is an organized profile of an individual's chromosomes.

Eukaryotic Cell Cycle

• Interphase: Cell grows and DNA replicates; consists of G1 (growth), S (DNA synthesis), and G2 (preparation for division).

• Mitotic phase: Includes mitosis (nuclear division) and cytokinesis (cytoplasm division).

• Checkpoints: G1, G2, and M checkpoints ensure proper division.

Cancer

• Most cancers are caused by uncontrolled cell division due to mutations in genes regulating the cell cycle.

Mitosis: Stages and Structures

• Prophase: Chromosomes condense, spindle forms.

• Prometaphase: Nuclear envelope breaks down, spindle fibers attach to kinetochores.

• Metaphase: Chromosomes align at the metaphase plate.

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

• Telophase: Nuclear envelopes reform, chromosomes decondense.

Key Structures in Cell Division

• Homologous chromosomes: Chromosome pairs with the same genes.

• Spindle microtubules: Pull chromosomes apart.

• Centrosomes: Organize spindle fibers.

• Cell plate: Forms in plant cells during cytokinesis.

• Cleavage furrow: Forms in animal cells during cytokinesis.

Cytokinesis

• Division of the cytoplasm.

• In animal cells, a cleavage furrow forms.

• In plant cells, a cell plate forms.

Meiosis: Stages and Genetic Variation

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Genetic variability arises from crossing over (exchange of genetic material between homologues) and independent assortment (random distribution of homologues).

Nondisjunction

• Occurs when chromosomes fail to separate properly during meiosis, leading to gametes with abnormal chromosome numbers (e.g., Down syndrome).

Animal Reproduction and Development

Sexual vs. Asexual Reproduction in Animals

• Asexual reproduction: Offspring arise from a single parent; no fusion of gametes.

• Sexual reproduction: Involves fusion of male and female gametes.

Forms of Asexual Reproduction

• Binary fission: Parent splits into two equal parts (e.g., protozoa).

• Budding: New individual grows from the body of the parent (e.g., hydra).

• Fragmentation/regeneration: Parent breaks into pieces, each can regenerate into a new organism (e.g., starfish).

Advantages and Disadvantages

• Asexual reproduction: Rapid, no mate needed, but less genetic diversity.

• Sexual reproduction: Increases genetic diversity, but slower and requires more energy.

Hermaphroditism

• Organisms possess both male and female reproductive organs (e.g., earthworms).

Internal vs. External Fertilization

• Internal fertilization: Sperm fertilizes egg inside the body (e.g., mammals).

• External fertilization: Eggs and sperm released into the environment (e.g., fish, amphibians).

Structures of Sexual Reproduction in Vertebrates (Humans)

• Oogenesis (egg production):

  • Ovaries: Produce eggs and hormones.

  • Oviducts (fallopian tubes): Site of fertilization; transport eggs.

  • Uterus: Site of embryo development.

  • Endometrium: Uterine lining; supports embryo.

  • Vagina: Birth canal; receives sperm.

  • Cervix: Opening to uterus.

• Spermatogenesis (sperm production):

  • Testes: Produce sperm and hormones.

  • Scrotum: Holds testes outside body for temperature regulation.

  • Testicle: Another term for testis.

  • Epididymis: Stores and matures sperm.

  • Vas deferens: Transports sperm.

  • Seminal vesicle, prostate gland, bulbourethral gland: Add fluids to semen.

Egg vs. Sperm

• Motility: Sperm are motile; eggs are non-motile.

• Size: Eggs are much larger than sperm.

• Number produced: Many sperm, few eggs.

Path of Sperm in Mammals

• Sperm path: Seminiferous tubules → Epididymis → Vas deferens → Urethra → Vagina → Uterus → Oviduct (site of fertilization).

Pregnancy and Placenta

• Pregnancy occurs in the uterus.

• The placenta is the vascular structure that supports embryo/fetus by exchanging nutrients and wastes with the mother.

Early Development of Animals

• Zygote: Fertilized egg.

• Embryo: Early developmental stage.

• Cleavage: Rapid cell divisions without growth.

• Morula: Solid ball of cells.

• Blastula/blastocyst: Hollow ball of cells.

• Gastrula: Stage with three germ layers:

  • Ectoderm: Forms skin, nervous system.

  • Mesoderm: Forms muscles, bones, circulatory system.

  • Endoderm: Forms digestive tract, lungs.

Plant Reproduction and Development

Asexual and Sexual Reproduction in Plants

• Asexual reproduction:

  • Fragmentation: Part of plant grows into new plant.

  • Stolon: Horizontal stem (e.g., strawberry runners).

  • Tubers: Swollen underground stems (e.g., potatoes).

  • Rhizomes: Underground stems (e.g., ginger).

  • Spores: Haploid cells that grow into new plants (e.g., ferns, mosses).

Flower Structure and Function

• Stamen: Male reproductive organ.

• Anther: Produces pollen.

• Filament: Supports anther.

• Carpel/Pistil: Female reproductive organ.

• Stigma: Receives pollen.

• Style: Connects stigma to ovary.

• Ovary: Contains ovules; develops into fruit.

• Ovule: Contains female gametophyte; develops into seed.

• Sepal: Protects flower bud.

• Petal: Attracts pollinators.

Sexual Reproduction in Flowering Plants

• Male gametophyte (pollen grain) is produced in the anther.

• Pollination: Transfer of pollen to stigma.

• Female gametophyte (embryo sac) is produced in the ovule.

• Fertilization: Sperm from pollen fertilizes egg in ovule.

Double Fertilization

• One sperm fertilizes the egg (forms zygote), another sperm fuses with two nuclei to form endosperm (nutritive tissue).

Seed Plant Development: Key Structures

• Endosperm: Provides nutrition to developing embryo.

• Embryo: Young plant.

• Fruit: Develops from ovary; aids in seed dispersal.

• Cotyledon: Seed leaf; stores food.

• Radicle: Embryonic root.

• Seed coat: Protective outer layer.

• Plumule: Embryonic shoot (foliage leaves).