Introduction to genetics Flashcards
G1 phase
Growth phase where a cell grows in size and prepares later for DNA replication
S-phase
DNA replication occurs
G2 phase
Cell preparing proteins like microtubules, needed for cell division during mitosis
M-phase
Mitosis
G0-phase
Some cells may remain in quiescent, non-dividing stage
Structure of DNA
double stranded helix
Nitrogenous Bases: 4 types
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Bases have specific pairing
A=T, C=G
Two strands run in opposite directions, one from ______ and the other from ________
5’ to 3’ , 3’ to 5’
DNA replication
- Parent DNA molecule; two complementary strands of base-paired nucleotides
- Parental strands unwind and separate at several points along the DNA molecule, forming replication forks
- Each parental strand provides a template that attracts and binds complementary bases, A with T and G with C
- Sugar-phosphate back-bone of daughter strands closed. Each new DNA molecule consists of one parental and one daughter strand, as a result of semiconservative replication.
Cell division
A process by which a cell (parent cell) , divide into two or more cells (daughter cells)
Mitosis (produces body cells)
generates 2 identical diploid daughter cells and are capable of dividing
Meiosis (produces sex cells)
Generates 4 haploid cells called gametes and cannot divide again until fertilization
Diploid
2N , actual number of chromosomes in a cell
Haploid
N, half the number of chromosomes in a sperm or egg cell
In humans one set of chromosomes
23 pairs / 46 chromosomes
how many chromosomes in sperm/egg cell
23 chromosomes
Mitosis + cytokinesis
mitotic phase/ M phase
WHAT IS cytokinesis
division of nuclei, cytoplasm, organelles & cell membrane
Cytokinesis completion signals the end of the cell division
The period of one mitosis to the next is referred to as
interphase
4 stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Prophase
DNA condenses into visible threads
Nuclear envelope disintegrates
Metaphase
Chromosomes line up in the middle of the cell
Anaphase
Chromosomes (sister chromatids) separate in opposite directions
Telophase
Chromosomes restored to less compact, non-mitotic state
Nuclear envelope form around daughter nuclei
Error in Mitosis
- Error in cell mitosis will activate programmed cell death ( apotosis ) , which will kill the cell
- Can lead to cancer or tumour formation
meiosis essential
for sexual reproduction
Meiosis occurs in 2 stages
Meiosis 1, meiosis 11
Meiosis 1
Homologous pairs in a diploid cell separate producing two haploid cells (23 chromosomes)
Meiosis 11
By the end of Meiosis 1, sister chromatids are finally split, creating 2 haploid cells per daughter cell (23 chromosomes)
End product of meiosis is
4 haploid cells from two haploid cells
