Introduction to Genetics PDF

INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM are the physical structures which acted as messenge...

INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM are the physical structures which acted as messengers of heredity. CHROMOSOME STRUCTURE AND TYPES Each of the chromosomes is composed of sister chromatids. It has a “waist line” called The prokaryotic (bacteria) genetic material is centromere or primary constriction, the site usually concentrated in a specific clear region where the kinetochore proteins attach. The of the cytoplasm called nucleiod. The kinetochore is the site of the spindle fiber bacterial chromosome is a single, circular, attachment. double stranded DNA molecule mostly attached to the plasma membrane. It does CLASSIFICATION ACCDG TO POSITION not contain any histone protein. Besides the OF CENTROMERE chromosomal DNA many bacteria may also Metacentric carry extra chromosomal genetic elements in The centromere occupies a middle the form of small, circular and closed DNA position with reference to the length molecules, called plasmids. These generally of the chromosome. The two arms remain floated in the cytoplasm and bear thus resulted are almost equal in algae, fungi, plants and animals different genes. While the eukaryotic cell length. During anaphasic movement has genetic material in the form of genomic in cell division, metacentric organelle DNA enclosed within the nucleus. Genes or chromosomes ap­pear ‘V’ shaped. the hereditary units are located on the Submetacentric near the center chromosomes which exist as chromatin When the centromere is located network in the non-dividing cell/interphase. some distance away from the middle region of the chromosome, one German biologist Walter Flemming in the chromosome arm will be shorter early 1880s revealed that during cell division than the other. During anaphasic the nuclear material organize themselves into movement, sub metacentric visible thread like structures which were chromosomes appear ‘L’ shaped. named as chromosomes which stains deep Acrocentric with basic dyes. The term chromosome was In this case, the centromere is coined by W. Waldeyer-Hartz in 1888. situated almost near one end of the Chrome is coloured and soma is body, hence chromo­some. As a result, one arm they mean “colored bodies” and can be of the chromosome will be extremely defined as higher order organized short and the other very long. The arrangement of DNA and proteins. It contains centromere is said to occupy a many genes or the hereditary units, subterminal position. regulatory elements and other nucleotide Telocentric sequences. Chromosomes also contain When the centromere is situated DNA-bound proteins, which serve in exactly at one end, the chromosome packaging the DNA and control its functions. will be having only one long arm. Chromosomes vary both in number and Telocentric chromosomes are very structure among organisms and the number rare. of chromosomes is characteristic of every There are normally two copies of each species. Benden and Bovery in 1887 reported chromosome present in every somatic cell. that the number of chromosomes in each The number of unique chromosomes (n) in species is constant. W.S. Sutton and T. such a cell is known as its haploid number, Boveri in 1902 suggested that chromosomes and the total number of chromosomes (2n) is its diploid number. The suffix ‘ploid’ refers to 1 INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM chromosome ‘sets’. The haploid set of the cell increases in volume by imbibing chromosome is also known as the genome. water & nutrients and building of In a diploid cell, there are two of each kind of new protoplasm. chromosome (termed homologous Cytoplasmic organelles such as chromosomes) except the sex chromosomes. endoplasmic reticulum, golgi In humans one of the sex has two of the apparatus, mitochondria and same kind of sex chromosomes and the other chloroplast are formed. has one of each kind. In humans there are 23 Synthesis phase (S) pairs of homologous chromosomes (2n=46). The DNA content C becomes 2C The human female has 44 non-sex after this phase. Each chromatin chromosomes, termed autosomes and one fiber is replicated or doubled. pair of homomorphic sex chromosomes given Gap 2 (G2) the designation XX. The human male has 44 There is active synthesis of RNA autosomes and one pair of heteromorphic and proteins necessary for sex chromosomes, one X and one Y chromosome synthesis. Mitotic chromosome. spindles are also formed. The double chromatin fiber is packed to form a chromosome, the colored CHROMOSOME BEHAVIOR DURING bodies during cell division. CELL CYCLE M-Phase (Dividing) Mitosis CELL CYCLE Mitosis is undergone by all somatic cells and sex cells. In multicellular A cell cycle is a series of events that takes organisms, it is a means of place in a cell as it grows and divides. A cell increasing the number of cells by spends most of its time in what is called replacing worn out tissues. In interphase, and during this time it grows, unicellular organisms, it is simple a replicates its chromosomes, and prepares for mode of reproduction. Mitosis is cell division. The cell then leaves interphase, subdivided into four distinct stages: undergoes mitosis, and completes its Prophase division. The resulting cells, known as The chromosomes shorten, daughter cells, each enter their own thicken and become visible interphase and begin a new round of the cell as thick rods. The cycle. chromosomes are Interphase (Non-dividing) longitudinally double, each Nucleus at interphase is very distinct half is a chromatid. and enclosed by a define nuclear Nucleoli and nuclear membrane. Within the nucleus are membrane completely one or more small round dense disappear by late bodies called nucleoli and a granular prophase. In animal cell, network of darkly stained material the centriole divides and called chromatin. At interphase, spindle radiates from the there are three stages that are not aster. morphologically distinguishable but Metaphase biochemically distinct. The nuclear membrane Gap 1 (G1) disappears and spindle The nucleus and cytoplasm are fiber soon appears. The enlarging toward mature size. The chromosomes which are 2 INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM maximally condensed align with haploid chromosome number. at the equatorial plane. These two haploid cells proceed to The spindle fibers attach on the second division (Meiosis II) the opposite sites of the involving only the separation of centromeres. chromatids producing four haploid Anaphase cells. This is also known as The centromeres become equational division. functionally double. The chromatids of the Meiosis I (Reductional Division) chromosomes begin to Prophase I move towards the opposite 5 distinct substages: poles. The poleward Leptotene/Leptonema. movement of the The chromosomes appear chromosomes is due to the as long threads with many depolymerization of the bead-like structures spindle fibers attached to (chromomeres) along their the centromeres. length. In some plants, the Telophase chromosomes are clumped Upon reaching the opposite on one side of the nucleus poles, the chromosomes (synizesis) while in some regroup into two nuclear animals, it tends to be structures. The drawn towards the part of chromosomes begin to the nuclear membrane uncoil & lengthen and close to the centriole. finally lose their visible Zygotene/Zygonema. identity. Synapsis or pairing of Cytokinesis homologous chromosomes (cytoplasmic division) begins. The paired usually follows mitosis. In chromosomes form a plants, the cytoplasm is bivalent consisting of four divided by cell plate chromatids. Synapsis is formation where separation very precise so that starts from the inside of the homologues pair side by cell towards the periphery. side. A synaptonemal In animals, cell cytokinesis complex is formed in occurs by furrowing or between homologous pair cleavage formation that that is essential in crossing starts from the periphery. over. Pachytene/Pachynema. Meiosis The chromosomes are Meiosis is also preceded by G1, S thicker due to further and G2 of the cell cycle. It consists coiling. The two of two divisions which follow each chromosomes in a bivalent other in rapid sequence. The first are closely appressed. division (Meiosis I) also referred to Chromatid breaks and their as reductional division, involves the repair occur along the separation of homologous chromosome. Repairing of chromosomes resulting in two cells breaks may entail 3 INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM exchange of segments from one another so that between sister and each anaphase group is non-sister chromatids in a composed of haploid bivalent. This is known as number (n) chromosomes. crossing-over which is This process accounts for cytologically observed the reductional phase of through formation of Meiosis I. chiasma at the point of Telophase I exchange. Crossing-over The chromosomes regroup generates variation in the and their structures begin population. to relax. The nuclear Diplotene. With the membrane as well as synaptonemal complex no nucleolus reappear forming longer functional, the two haploid daughter cells. longitudinal separation of Cytokinesis homologues in a bivalent In some species, no starts from the centromere cytokinesis happens after and proceeds toward both Meiosis I. A brief ends except at the transitional stage called chiasma. interkinesis occurs before Diakinesis. Bivalents are the cell proceeds to the maximally condensed and next stage. distributed throughout the nucleus. By the end of this Meiosis II (Equational Division) stage, nucleolus and The division proceeds in a manner nuclear membrane have similar to mitosis except that there disappeared, the spindle are two haploid cells (from meiosis I) has formed and Prophase I that undergo each stage. is completed. Prophase II Metaphase I The chromosomes begin to The bivalents align at the condense. The nucleus equatorial plane. The and nuclear member bivalents are so oriented disintegrate. that each homologue is on Metaphase II each side of the metaphase Spindle fibers are formed plane with their and the chromosomes align centromeres attached at at the equatorial plane. the spindle fibers. Anaphase II Anaphase I Sister chromatids of a The univalent (or univalent separate and homologue) in each proceed to the opposite bivalent separate from poles as individual each other. Movements of chromosomes. the univalent to the Telophase II opposite poles is due to Chromosomes uncoil and depolymerization of the lengthen, nuclear spindle fibers. The membrane and nucleolus homologues segregate reappear. 4  INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM KARYOTYPE Cytokinesis genome = complete set of chromosome forming four cells with haploid chromosome number. GAMETOGENESIS Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis. During meiosis, two cell divisions separate the paired chromosomes in the nucleus and then separate the chromatids that were made during an earlier stage of the cell’s life cycle, resulting in gametes that each contain half the number of chromosomes as the parent. The production of sperm is called spermatogenesis and the production of eggs is called oogenesis. DNA Fiber 1. chromatin 2. nucleosome 3. H1 histone 4. chromatosome 5. solenoid groups of nuclesome 6. looping 7. folding H1 histone = linker 8. chromosome centromere - serve as point of attachment of euchromatin spindle fibers during cell division - lighter portion kinetochore - transcription is found - region where you can find centromere & protein synthesis satellite - found at the end of chromosome arm - tells you where nucleus is found telomere - tells you the lifespan of the cell. found at the end of chromosome - longer telomere = longer life cell 5 heterochromatin - darkly stained chromosome near centromere - portions of DNA where there is no/little transcription INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM G2: - same ____________________________________ How many types = 23 How man is the total = 46 P1: - Dyads mawawala kasi icconsider na G1: as tetrads because of paketin(?) - Chromosome same number ng - Tetrads = ch/2 chromatid - HC = ch/2 M1: - same S: - C = ch(2) - Dyads same as ch 6 INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM A1: A2: T2: T1: - Tignan lang yung isang side kasi naghati na - HC = 0 P2 & M2: - same 7 INTRODUCTION TO GENETICS S-BIOL327A | MS. JONNACAR SAN SEBASTIAN MODULE 2 | MIDTERM Gametogenesis = formation of gametes 45 items mc - 2pts each Spermatogonium - 2n (mitosis) Spermatids = immature sperms 8