Cytogenetics Meiosis, Development, and Aging Flashcards
Two divisions of the genetic material
Reduction Division (Meiosis 1)
Equational Division (Meiosis 2)
Reduces the no. of replicated chromosomes from 46 to 23
Reduction Division (Meiosis I)
Produces 4 cells from the 2 cells formed in the 1st division by splitting the replicated chromosomes
Equational Division (Meiosis II)
Gametes are formed from special cells
Germline Cells
Halved the chromosomes no during meiosis
Contribute 23 diff chromosomes, constituting 1 copy of the genome
Chromosomes pairs are Homologous pair: same genes in the same order but carries diff alleles
Haploid Cells
Gametes
W/o meiosis, sperm and oocyte would each contain 46 chromosomes and the fertilized ovum have twice the normal no of chromosomes
Polyploid
Occurs after an interphase period where DNA is being replicated
Reduction Meiosis (Meiosis I)
The homologs exvhange parts or cross over
All 4 chromatids that comprise each homologous chromosome pairs aligh as exhage occur
After crossing over, each homolog bears some genes from each parent
New gene combinations arise from corssing over when the parents carry different alleles
Toward the end of prophase I, the synapsed chromosomes separate but remain attached at a few points along their lengths
Synapsis and Cross Over
Different Phases of Reduction Meiosis (Meiosis I)
Prophase I
Metaphase I
Anaphase I
Telophase I
Homologs align down the center of the cell
Each member of homologous pair attaches to a spindle fiber at an opposite pole
generates genetic diversity
Metaphase I
Caused by random alignment of chromosomes
Means that the fate of a gene on 1 chromosome is not influenced by a gene on a different chromosome.
Accounts for the basic law of inheritance
Independent Assortement of Genes
Homologs separte and move to opposite poles
Anaphase I
Nuclear envelope partially assemble around chromosomes
Telophase I
Divides cell into 2 haploid cells
Cytokinesis
___ 4 Haploid Cell (each carrying a new assortment of genes and chromosomes that hold a single copy of the genome
Net Result
The centromeres of each replicated chromosome in meiosis I remain together and unfold during
The single DNA replication, followed by the double division of meiosis, halves the chromosomes number: Haploid Cell
Equational Meiosis (Meiosis II)
Where DNA replication happens
S-Phase
Chromosomes become condensed and visibe again
Prophase II
Align down the center of the cell
Metaphase II
Centromeres part
Newly chromosomes formed (each has unreplicated form)
Anaphase II
Nuclear enveloped form around the four nuclei, which then separate into individual cells
Telophase II
Formation of sperm cells
Spermatogenesis
Diploid stem cell of sperm
Divides mitotically to form 2 daughter cells
Spermatogonium
2 Daughter cells
- Type A: magiging stem cells
- Type B: become primary Spermatocyte
Forms 2 haploid cells called secondary Spermatocytes
Primary Spermatocytes
Primary to Secondary Spermatocyte
Meiosis I
Spermatid to Sperm
Meiosis II
Divides to yield 2 equal-sized spermatids in the replicated form
Secondary Spermatocyte
Spermatid elongates and sheds its excess cytoplasm
Spermatids develop sperm flagellum
Spermiogenesis (Maturation)
Produces Sperm/Spermatozoa
Spermiogenesis (Maturation)
Anatomy of Sperm
Head
Midpiece
Tail
Contains Genetic Material (DNA)
Head
Mitochondria of the sperm
Midpiece
Locomotor of the sperm
Tail
Begins when a oogonium that self renews and also yields a lineage whose cells differentiate
Oogenesis
Stem cells of ooctyes
Oogonium/Oogonia
As it grows:
Cytoplasm accumulates
DNA replicates
Becomes Primary Oocytes
Oogonium/Oogonia
Primary-Secondary Oocyte
Meiosis I
Production only occurs in fetus
Divides into 2 cells called First Polar Body
Each cell is haploid w/ 1 chromosome set and in replicated form
Meiosis is arrested in late PROPHASE I and resumes during puberty
Primary Oocyte
Secondary Oocyte-Ovum
Meiosis II
Divides unequally in meiosis II to produce another small polar body w/ unreplicated chromosomes
If it’s NOT fertilized by a sperm:
It will yield an ovum and tiny second polar body
Meiosis is arrested during METAPHSE II and resumes only after fertilzation
Secondary Oocyte
For the first 8 weeks
Rudiments of all body parts form
Begin when the fertilized ovum divides by mitosis
Prenatal Human: Embryo