Lecture 6: Meiosis, germ cells and fertilization Flashcards
Diploid
two sets of chromosomes, one from each parent
Haploid
One set of chromosomes
Gamete
Specialized reproductive cells; sperm or eggs generated through meiosis
Fertilization
Haploid gametes fuse to form diploid cell (zygote)
Zygote
Divides by mitosis to become multicellular organism
Germline cells
Gametes and their precursors
Somatic cells
form the rest of the body and leave no progeny
4 chromatid structure name
Bivalent
Stable pairing requires ____
Crossing over-form chiasma
Synaptonemal complex
Structure of two paired homologs, important for crossing over
Pseudoautosomal region
Small region of homology between x and y allowing them to pair
5 phases of prophase
Leptotene Zygotene Pachytene Diplotene Diakineses
Leptotene
Homologs begin to condense/pair
Zygotene
Homologs pair and synaptonemal complexes form
Pachytene
Synapsis complete, crossing over occurs
Diplotene
Synaptonemal complex begins to break down; homologs begin to separate but remain attached at chiasma
Diakinesis
Reach maximum condensation; separation of homologs and transition into metaphase
Non-disjunction
Homologs fail to separate properly. Common during egg development, more common with higher age
Aneuploid
Cells with abnormal chromosome number
Female eggs first arrest at
Prophase 1 of Meiosis 1, completed at ovulation
Femalge eggs second arrest
Metaphase 2 of meiosis 2, complete meiosis after fertilization
Male meiosis begins
At puberty and proceeds without arrest
What dictates which cells become primary germ cells
Signaling from neighboring cells
What determines if gonad is ovary or testes
Sex cells at genital ridge, not sex chromosome in PGC
Y chromosome in sperm directs genital ridge to develop into testis.
Default pathway is female
Sry gene
Sex determining region on Y chromosome. Necessary and sufficient for testis development
Expression of Sry causes
Cells to differentiate into sertoli cells and leydig cells (testis support cells)
Sertoli cells secrete
Anti-mullerian hormone which suppresses female development
Leydig cells secrete
Testosterone
In absence of Sry
Genital ridge become ovary, PGC becomes egg
Somatic cells become follicle cells and theca cells
Which hormones trigger ovulation and allow primary oocyte to complete M I
FSH + LH
Syncitium
Progeny of spermatogonium don’t complete cytokineses, they remain connected through cytoplasmic bridges
This gives them access to diploid genome for their development
Capacitation
Process required for a sperm to acquire capacity to fertilize an egg
Fertilization
Sperm binds to zona pellucida, undergo acrosome reaction (allows penetration of zona pellucida)
Cortical reaction
Egg fuses with sperm, cortical granules are released, other sperm can no longer bind
Sperm contribute ____ & _____ for meiosis
Centrioles and centrosomes
In polyspermy, extra ____ are present, causing what
Extra mitotic spindles are present, causing faulty segregation and aneuploidy
