Bio Lab Quiz #4 Flashcards
Mitosis vs Meiosis:
Mitosis the process of making new body cells. Meiosis is the type of cell division that creates egg and sperm cells. Mitosis is a fundamental process for life.
Gametogenesis:
the development of primordial germ cells (PGCs) into mature gametes (eggs and sperm)
Histology:
tissue sections stained with dyes
Primordial germ cells
Primordial germ cells divide by mitosis and at this stage are called oogonia and spermatogonia. Eventually, they begin meiosis. During the first meiotic division homologous chromosomes separate and during this period germ cells are called primary (1o) oocytes and primary (1o) spermatocytes. During the second meiotic division individual chromosomes separate and the germ cells are called secondary (2o) oocytes and spermatocytes. At the end of meiosis they become ootids and spermatids. Primordial germ cells migrate through the embryo to the gonads during development.
Primordial germ cells form outside the embryo proper in an extraembryonic tissue called the allantois. Then they migrate through the hindgut of embryo to the genital ridge/gonad (this will become the ovary or the testes depending on the sex of the embryo).
PCG Mitosis - oogonia and spermatogonia
PCG Meiosis - oocytes and sp’ cytes
Meiosis (1. Homologous chromosomes separate, 2. Ind chromosomes separate)
Male
mitosis, PGCs arrive at gonad, Arrest as Prospermatogonia and enclosed by Sertoli Cells to form cords, after birth Prospermatogonia move to edge of tubule, become spermatogonial stem cells.
In between the tubules are blood vessels and Leydig cells that make testosterone.
In the adult testes, the sperm are produced in the seminiferous tubules
In Seminiferous Tubules: Spermatogonial stem cell and sertoli cells (support sperm cell, nursing function)
Spermatogenesis: Sp’ gonia - mitosis and meiosis
Spermiogenesis: elongation of nucleus and cytoplasm, nucleus condenses, flagellum forms
Female
mitosis, after arrival gonad Entry into meiosis(oocytes), divided several times to form interconnected cells called cysts (remain as cyst until right before birth), Arrest in Prophase I of meiosis and stay there until ovulation, in cysts break apart into individual cells surrounded by granulosa cells to form Primordial Follicles around time of birth.
Differences between spermatogenesis and oogenesis
Oogenesis is finite form all eggs you will ever have before birth and one haploid gamete bc other turn into polar bodies but in spermatogenesis you can keep making more and at the end get four haploid gamete
Hematoxylin
Has little affinity for tissue when used alone but in combination with metals it is a powerful nuclear stain
Mayer’s= Aluminum
Hematoxylin-metal complex acts as a basic dye
Eosin - Counter or Secondary Stains
cytoplasmic stain
Eosin is an acidic dye which stains the more basic proteins within cells (cytoplasm) and in extracellular spaces (collagen)
Sea urchins as a model system
Sea urchins are used as a model of fertilization:
Fertilization and development are external
Eggs are large
Sperm structure:
-haploid nucleus of compact DNA
-acrosome vesicle (protease and sugars) has enzymes so releases can get through jelly coat during fertilization
-midpiece (mitochondria)
-tail flagellum
Egg Structure (starting from outside):
-jelly coat contains chemicals to attract or activate sperm
-vitelline envelope, species specific binding of sperm (gets released during fertilization and raises to form the fertilization envelope which is the first sign of fertilization.
-cell membrane, flow of ions during fertilization, fuses with sperm membrane
-cytoplasm contains cortical granules (hold proteases) lifting of fertilization envelope, actin microfilaments
Recognition of Egg and Sperm Steps of Fertilization
Sperm Egg Interaction Steps: sperm contact jelly layer, acrosome reaction, digestion of jelly layer, binding to vitelline envelope, fusion of acrosomal process membrane and egg membrane
In step 1, chemicals in the jelly coat attract activate sperm (species specific sperm activating peptides.
In step 4, the sperm expresses bindin and the egg vitelline envelope expresses a species specific binding receptor
Fast Block
Fast Block to Polyspermy: Change in membrane potential that allows one sperm to go in and is dependent on sodium.
Fusion of sperm and egg membranes causes a brief influx of sodium ions.
This leads to a change in membrane potential (-70mV to +20mV)
This block is short and not permanent
During the first embryonic division, one cell divides into two equal size cells. Polyspermic embryos divide abnormally into 3 or 4 unequal size cells.
Slow Block
Slow Block to Polyspermy (weird fragmented embryos that die and are lethal): Cortical granule reaction and takes over after fast block to block polyspermy.
The cortical granule reaction changes the structure of the vitelline envelope and makes it into fertilization envelope
Has one enzyme that digest proteins holding VE onto cell membrane and when releases becomes fertilization envelope and has one enzyme that helps water to come in and makes fertilization envelope
