Embryonic Development and Genetics Notes

Embryonic Development

Cleavage

  • First cleavage: longitudinal furrow from animal to vegetal pole; zygote divides into two blastomeres.

  • Second cleavage: longitudinal, vertical to first; four blastomeres result.

  • Third cleavage: latitudinal, above equator; eight blastomeres form – four micromeres (smaller, upper) and four macromeres (larger, lower, due to yolk).

  • Fourth & Fifth cleavages: Longitudinal and latitudinal divisions resulting in 16 and 32 blastomeres respectively.

  • Morula: Mass of blastomeres, resembling a berry.

Blastulation

  • Morula transforms into a spherical blastula with a single cell layer surrounding a blastocoel (coelom).

  • Blastocoel forms from the eight-cell stage, expanding with division.

  • Cells in the animal pole remain smaller than those in the vegetal pole.

Gastrulation

  • Mono-layer blastula converts to a double-layer embryo (triple in vertebrates) called a gastrula.

  • First Differentiation Phase: Three germ layers:

    • Ectoderm (external)

    • Endoderm (internal)

    • Mesoderm (intermediate)

  • Germ layers are the origin of all vertebrate organs.

  • Gastrulation begins with vegetal pole cells flattening and invaginating, reducing and eventually replacing the blastocoel with a gastrocoel (archenteron).

  • Blastopore: Opening of the gastrocoel to the outside.

Organs Development in Amphioxus

  • Ectoderm: nervous tube, epidermis

  • Mesentoderm: Mesoderm (Somites and lateral mesoderm), Endoderm (digestive tube and its derivatives), Notochord

  • Main components: nervous system, notochord, mesoderm, digestive tract

Development of Nervous System

  • Ectoderm near blastopore migrates to form a neural plate that then invaginates and forms neural tube.

  • Neurulation: Formation of the neural tube. Embryo is now a neurula.

  • Neural tube differentiates into brain vesicle and spinal cord (central nervous system).

Development of Notochord

  • Notochord forms from the middle part of mesentoderm.

  • Notochordal Groove: Groove which forms notochordal rod.

Development of Mesoderm

  • Mesoderm forms from the back side of the mesentoderm layer and Archenteric Pouches separate from Archenteron coelom and becomes Mesodermic Sacs.

  • Upper part (back) of the sac represents somite.

  • Lower part is lateral mesoderm, which differentiates into Parietal and Splanchic Mesoderm layers. Coelom appears between the two layers.

Enteron Development

  • Remaining mesentoderm forms endoderm, leading to the formation of the intestine (enteron) and its derivatives.

Congenital Malformation in Humans

  • Structural faults from abnormal embryo organ formation (Teratology).

  • Causes:

    • Genetic factors (e.g., chromosomal abnormalities like Down syndrome).

    • Environmental factors (e.g., radiation, drugs).

  • Critical period: First weeks of pregnancy.

  • Maternal health factors: smoking, caffeine, herbal medicine, alcohol, toxoplasmosis, folic acid, management of diseases.

  • Diagnosis: Ultrasound, blood tests, embryonic cell tests.

Multiple Birth and Twin Formation

  • Fraternal twins: Two separate eggs, fertilized by different sperm; non-identical.

  • Identical twins: One fertilized egg divides; very similar; can be Siamese (attached).

  • Multiple twins: rare in humans, 3 or 4 babies resulting from fertility treatments.

Stem Cells

  • Unspecialized cells with division and regeneration capabilities to repair ruined cells.

  • Sources: early embryonic stages, umbilical cord blood, placenta, bone marrow.

  • Types:

    • Embryonic Stem Cells: Unlimited division, high specialization ability.

    • Adult Stem Cells: Limited existence, decreasing number with age, may be abnormal.

    • Umbilical Cord Stem Cells: similar to adult, resist freezing.

  • Applications: Disease cause determination, immunity rejection overcome for transplants, genetic engineering, drug experiments, cell therapy.

Cloning in Animals

  • Asexual reproduction method; economically important.

  • Dolly the sheep (1997): Cloned from adult sheep mammary gland cells by Ian Wilmot.

Techniques to treat the Infertility

  • Artificial Fertilization: Transferring cleaned and concentrated sperms into eggs.

    • Reasons : Ovulation or Fallopian tubes in the female.

    • Reduce sperms numbers or hormone failure for the male.

  • Types:

    • In vivo Fertilization: Injecting sperm into uterus at ovulation, with ovary-stimulating medicine.

    • In Vitro Fertilization: Fertilizing egg with sperm in test tube; transferring embryos to uterus.

  • Embryo Freezing: Freezing extra embryos for future use (-170°C in liquid nitrogen).

  • Oocyte Freezing: Freezing immature eggs; less successful due to chromosome damage possibilities (-170°C in liquid nitrogen).

  • Sperm Freezing: Freezing sperm for later use (-170°C in liquid nitrogen); doesn't usually affect fertility. Used for men undergoing chemotherapy or testicle removal.

Genetics

Introduction and History

  • Genetics: Study of inherited variations and responsible genetic expression.

  • Bateson (1906): Coined term "Genetics".

  • Brief History:

    • Selected genetic variations for useful types.

    • Mendel's heredity system (1866).

    • Discovery of Mendel's experiments (1900).

    • Watson and Crick DNA molecular structure (1953).

  • DNA’s abilities:

    • Transport DNA from one organism to another by viruses and plasmids.

    • Modulate recipient cells’ function.

    • Replicate inside the cell and outside with PCR.

Pre-Mendel Genetics

  • Mesopotamia: Studies on wheat, rice, cotton, beans, cattle, and horses (4000-800 BC).

  • Nile Valley: Selected wheat qualities (5000 BC).

  • Greek Philosophers (Hippocrates): Human quality repetition, diseases like eye and blindness certain families, discovered Down's syndrome symptoms.

  • Europeans (Maupertuis): Pedigrees and probability future generations. (Albinism).

Mendelian Genetics

  • Gregor Johan Mendel: Discovered basic genetics principles, experimenting on Pisum sativum (Pea Plant).

  • Life cycle.

  • High number offspring.

  • Variations and genetic mutations when organisms are exposed to unsuitable conditions.

  • Control breeding and mating.

  • Breed and maintenance easily. (bacteria, fungi, animals, drosophila, mice, chicken).

Genetic Terminologies and Symbols

  • Allele: Alternative forms of a gene.

  • Genes: DNA sequence with specific function.

  • Phenotype: The properties signs of the organism, controlled by genetic.

  • Genotype: Genetic information code of individual.

  • Homozygous: Genotypes with the same alleles (TT, tt).

  • Heterozygous: Genotypes with two different alleles for a trait (Tt).

Monohybrid Cross

  • Hybridization between two individuals and includes a pair of opposing traits.

  • Reciprocal occurs between two individuals, One has dominant pure trait, other has recessive pure

Mendel's Postulates:

  • Paired genetic factors are distributed independently from each other during gametogenesis

  • Punnet Square can help determine of recombinant during fertilization easily.
    *Test Cross determine the purity trait that dominates the individual with a recessive individuals for the same trait.
    *Back Cross is a cross between hybrid members of one generation into one of them or same similar

Post-Mendel Genetics

  • Incomplete Dominance: Hybrid phenotype differs from parents, traits blended.

  • Codominance: Expression from all of two alleles in hybrid individual without being dominant or recessive.

  • Lethal Alleles causes some negative defects as they are transfered from pure side dominant or other recessive cases

  • Penetrance Gene refers to when individual inherits the allele, he possesses this individual's phenotypic. Gene is the name of when Heterogeneous is made with alleles that Heterogeneous range from phenotypically

  • Environmental is when living organim has its traits, and determine inherited traits, which analyse and determine gene because some phenotypic's depend on envronment.

  • Genetic and Interactions, produces New phenotypes because of this action, the alleles that exist interact with genes that has some genetic change of ratio eg Epistatis that is when genes prevent over expression, or when there are any different that is unexpected and doesn't get change or that gives member traits that don't make it the grandparent.

  • Multiple alleles variety cause there are are variations or alternatives for one allele. Examples including people's red or any other cells. Transfusion of types blood from any place with donor has to be tested

  • Inheritance multi genes: transfer genes result influence or add more information