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Lecture

ZOO 2090 Lecture Notes - Spermatocyte, Immature Ovum, Spermatid


Department
Zoology
Course Code
ZOO 2090
Professor
Roy Danzmann

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Developmental Biology: Midterm Review
Lecture 1:
Differentiation: generation of cellular diversity
Morphogenesis: growth and organization of biological form, cells from different
layers interact to form tissues and organs.
Growth: regulation of cell division
Reproduction: fusion of gametes (fertilization)
Knockout mice: mice in which expression of one gene is repressed, providing
models of human disorders
Fertilization: fusion of two haploid gametes (sperm and egg), triggers DNA and
protein synthesis and metabolic rate
Zygote: fertilized egg
Cleavage: series of rapid cell divisions
Blastula: Hollow sphere of cells (called blastomeres) produced during development
of embryo by repeated cleavage of egg.
- No change in size: cells become smaller as cytoplasm is divided into cells
- Unequal cleavage (micromeres, mesomeres, macromeres)
- Blastocoel is a fluid filled cavity within the blastula
Gastrulation: beginning of differentiation, migration of cells
Endoderm: inner layer
Mesoderm: middle layer (ex: Dermis)
Ectoderm: outer layer (ex: epidermis)
Blastopore: located at the vegetal pole, future anus (mouth is at animal pole).
Archenteron: future gut
Larve: free living, immature form of an animal which transforms into the adult via
metamorphosis
Metamorphosis: occurs in amphibians insects and marine invertebrate groups:
transition between larval and adult.
Lecture 2:
Germ cells: give rise to gametes (through the process of gametogenesis)
Somatic cells: give rise to other structures of the body.
Neotomy (paedomorphosis): sexual maturity in juvenile or larval stage, but at the
same age as an ancestral form
Progenesis: secual maturity in juvenile or larval stage, but at a different age then the
ancestral form
Indirect development: development from egg to adult from occurs through
intermediate paheses in which the animals are different morphologically ecologically

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etc. from the adult. (any development which involves a larval stage, ex: frogs and sea
urchins)
- Metamorphosis in sea urchins results in transfer from plankton to benthos
- Metamorphosis in frogs results in transfer from aquatic to terrestrial
existence
Replication DNA Transcription RNA RNA processing mRNA
Translation Protein
DNA : encodes all information necessary for cellular functions :
RNA: made from a DNA template and functions in protein synthesis (proteins are
translated by messenger RNA and carry out cellular functions
Nucleosome: DNA wrapped around 8 histones (which are negatively charged
proteins in which DNA is attracted to)
Ploidy: number of homologous sets of chromosomes in a cell (haploid=1 set,
diploid=2 sets)
Human Karyotype: 22 pairs of autosomes and 2 sex chromosomes
Allele: different molecular forms of a gene
Homozygous: same allele on both chromosomes
Heterozygous: different alleles on chromosome pairs
DNA replication: DNA strands separate, and each strand serves as a template. As
complementary strands are synthesized, 2 identical DNA molecules are produced.
Mitosis: chromosomal duplication (separation of sister chromatids). Mitosis occurs in
somatic cells and results in 2 identical daughter cells (diploiddiploid)
Contractile ring: microfilaments made of actin
Microtubules: filaments made of tubulin
Centriole: cell organelle made of microtubules
Meiosis: occurs during gamete production. Two consecutive rounds of cell division.
Separation of homologous chromosome pairs, and chromosome rearrangement
(Meiosis I) followed by separation of chromatids (Meiosis II) (diploidhaploid, no
DNA replication occurs in Meiosis II)
Recombination: „crossing over‟ recombination between homologous chromosomes
Oogenesis: formation of female gamete (egg) via meiosis
Spermatogenesis: formation of male gamete (sperm) via meiosis
Germ Cell Formation: arise from primordial germ cells. Vegetal region of frog
zygote contains the determinants for germ cell formation.
Germ Plasm: gives rise to germ cells. Migrates from vegetal pole into genital ridge.
Chromosome diminution: only fraction of the chromosome in the animal derived
blastomere survives, in other words, genes are lost. Chromosomes are kept intact only
in cells destined to become germ cells ( vegetal cells)
Characteristics of Early developing PGC:
- Gene expression is suppressed
- PGC does not express a large number of genes.

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Germ Cell Determination in Insects:
- Syncitial blastoderm: all the cleavage nuclei are contained within a common
cytoplasm
- Nuclei migrate to posterior pole and are enclosed in poleplasm (become pole
cells)
- Poleplasm: complex collection of mitochondria, fibrils and polar granules,
essential for PGC, if removed no PGCs or germ cells are formed. If moved to an
alternative region of egg, PGCs form in a new region.
PGCs in amniotes (Reptiles, Birds and Mammals):
o Extraembryonic membranes: embryos have membranes that are not part of
them (ex: amnion, chorion, allantois, yolk sac).
o Amniotes do not have poleplasm
o PGCs arise from stem cells in the extraembryonic tissues, then migrate to the
genital ridge, which becomes the gonads. Migration occurs through the
allantois.
o PGCs undergo mitotic division during migration and eventually arrest
o Stem cell factor: produced by cells along migration route and is critical for
successful germ cell production.
Summary of Migration Routes
Fish, amphibians
PGCs arise vegetal pole
move to genital ridge by extending filapodia over underlying cells
follow extra cellular matrix
Birds, reptiles
PGCs arise in extraembryonic membranes
Move to genital ridge via the blood circulation
Mammals
PGCs arise in extraembryonic membranes
Move to genital ridge by extending filapodia
Lecture 3:
Stem Cells: undifferentiated cells capable of differentiating into a number of other
cell types. Possess self renewing properties, in which daughter cell remains a stem
cell.
Totipotent: capable of differentiating into any cell type (ex: embryonic stem cells)
Pluripotent: capable of becoming many, but a limited number of cell types (ex: adult
stem cells)
Unipotent: capable of differentiating along only one lineage (a determined cell, ex:
spermatogenic stem cells)
Hematopoeitic cells of bone marrow: are pluripotent and require hormones and
growth factors for differentiation.
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