| What are the criteria of classification of chromosomes? | According to banding patterns (uniqueness of each chromosome structurally and functionally) lengths, shape, position of centromere, which gives arm ratios=p/p+q (p=length of petit arm and q=length of long arm (letter after p)
(Metacentric- p/p+q=1/2 both arms of both strands are equal)
(submetacentric- p/p+q<1/2 short p arm and longer q arm)
(acrocentric p/p+q<<<1/2 very short p and long q)
(telocentric p/p+q=0 No p arm) |
| What is a nucleosome? | DNA rolled around histone octamer (H2A H2B H3 H4 dimers) 1.75 turns making the chromatin by fusing with each other with H1 |
| What are the two types of chromosomes? | Interphase chromosomes (not condensed) / Mitotic chromosomes (condensed especially at metaphase) |
| What is the karyotype? | 46 human chromosomes at mitosis, species specific. |
| Describe human karyotype? | 2n number of 46 chromosomes, diverse in sizes and centromere placements, each is a double structure consisting of 2 chromatids, connected to a common centromere, it is matching up of mitotic chromosomes into pairs. |
| How are chromosomes present in eukaryotes in different mitotic phases? | Chromatin (interphase) condensed chromatin/ chromosome (mitosis) associated with proteins (histones and non-histones) |
| How and why are DNA molecules packed in nucleus? | DNA consists of 1m length nucleic acid chain, but nucleus is 10 microm, they are packed using proteins, when we talk about DNA and protein packing we are talking about chromosomes and chromatins. |
| What are chromatin? | organized complex of nuclear DNA combined with histones, they enable DNA packing and regulate DNA expression, its basic unit is mucleosome (octamer of histone H2A,H2B,H3..) consisting of dimer of each of those histone proteins., there are two types of proteins that bind to DNA histones and non-histones. |
| How is chromatin classified? | -Euchromatin (relaxed thin fiber- fiber A (d=35-60 A) /Less unstained filaments in interphase/filaments appear dark and dense at metaphase (condensation), genetically active, clear during interphase (decondensed) )
-Heterochromatin (Condensed fiber B (d=200-300 A), Densly stained filaments, Content of proteins is higher than euchromatin, correspond to 80% of DNA) Can be (constitutive of facultative) |
| Talk about constitutive heterochromatin. | Stable, conserved heterochromatic properties during all phases, fiber called fiber A e.g centromeres |
| Talk about facultative heterochromatin. | Regions that appear heterochromatic at specific times, reversible, euchromatin that are condensed and inactive, but can be reversed into euchromatin, condenses and decondenses. throughout cell cycle, cell type, development stage (Barr Body). |
| What is a Barr Body? | Small dense structure corresponding to inactivated X chromosome. |
| Talk about X-inactivation. | Gives a Barr body that is inactive were no transcription occurs, , discovered by Lyon and called sometimes lyonization 15% of the inactive X chromosome remains active. |
| When does Barr body occur? | Level of gene activity by one X is the normal dosage for a human body, so one X for normal females is kept inactive to maintain normal usage. It is random happening separately in every somatic cell, pattern of X is put randomly by the ancestor somatic cell were one paternal or maternal X will become inactive for all daughter cells. |
| What kind of chromatin are Barr body and why? | facultative heterochromatin
Because the inactive kind of X is heterochromatin while the other is euchromatin, and it can be reversed at certain stages of development, so it varies from euchromatin to heterochromatin. |
| Compare between mitosis and meiosis. | Mitosis (one division of somatic cell or precursor of germ cell/ diploid cell to give 2 diploid cells)
Meiosis (two divisions one reductional and one equational of germ layer/ diploid cell gives 4 haploid cells called ootids by oogenesis or sperms by spermatogenesis |
| What are the main differences between oogenesis and spermatogenesis? | Spermatogenesis (in testes, enlargement of diploid cell (spermatogonium) to primary spermatocyte undergoing first meiotic division into secondary spermatocyte that undergoes meiosis 2 to sproduce spermatid which differentaites into spermatozoa with equal amounts of cytoplasm/ continuous)
Oogenesis (form ova in ovaries ftwo meiotic divisions almost all of cytoplasm of primary Oocyte derived from Oogonium is found in one of the daughter cells the other is called polar body. secondary oocytes give ootids which then become eggs./ not equal cytoplasm/not continuous) |
| How are genetic information in haploid cells present? | Each have a maternal or paternal chromosome however crossing over might occur during P1 which results in reshuffling alleles between paternal and maternal chromosome which creates gene complex. |
| What are the quantities of chromosomes and genetic information in each phase of mitosis and meiosis? | Mitosis (always 2n,2C in telophase-G1 4n in S-G2-P-M-A)
Meiosis (2n in in gametocyte n in secondary gametocyte/ 2C in primary gametocyte before Mitosis 4C after mitosis 2c after M1 c after M2) |
