Prelim Bio 2020 Module 5 - Hereditary PDF

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Prelim Bio 2020 Module 5 - Hereditary...

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Module 5: Hereditary Reproduction Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to: ● animals: advantages of external and internal fertilisation ● fungi: budding, spores ● bacteria: binary fission (ACSBL075) ● protists: binary fission, budding Reproduction in plants: Asexual reproduction: ○ does not involve the union of male and female gametes yet results in the formation of new plants- maintains continuity of plant species. The different processes of asexual reproduction: ■ vegetative propagation: New plant parts grow from vegetative organs such as roots, leaves, stems ■ Examples include Sweet potato (propagation by roots), Ginger (propagation by the stem) Vegetative propagation methods include: Cutting: ○ Stem from the plant is cut and is planted in the soil that will gradually grow and turn into another plant, Used for plants like rose, hibiscus, sugarcane Layering: ○ branch from plant is selected, bent and the bent portion is covered with soil while still being attached to the mother plant. ○ bent portion touching the soil develops roots and the part above the ground develops into individual plants. ○ Jasmine and bougainvillaea (paper flower) can be propagated this way. Grafting: ○ two different plants are joined, they grow as one plant. ○ One of the plants serves the purpose of being grounded by root formation which is termed as the stock. ○ Apart from the other plant is cut and joined with stock. This is known as scion and is the desired plant that we want to grow on the stock.

○ The type of fruits and flowers produced from the joined plant depends on the scion and not the stock. Sexual Reproduction: ● occurs when a male gamete and a female gamete unite to form a single-celled zygote which turns into a complete plant. ● Sexual reproduction occurs in flowering plants and involves multiple steps: ○ Male gametophytes are produced inside anthers and when matured become pollen grains ○ Inside the pollen grains, two nuclei are present; the tube nucleus and the generative nucleus. The tube nucleus forms the pollen tube and the generative nucleus prior to reproduction produces two haploid male gametes. ○ The ovule is created in the female plants from the placenta which is surrounded by a layer of tissue known as Nucellus. Both the external and internal layers of the ovule have a pore called micropile through which pollen tube will enter during fertilization. ○ The region inside the ovule surrounded by the nucellus where the female gametes reside is embryo sac. Inside the embryo sac, the following cells will be found: ■ A large nucleus near the micropyle which is the female gamete. ■ Two smaller nuclei situated on either side of the female gamete known as synergies. ■ A set of three nuclei situated at the other end of the embryo sac known as antipodal cells. ■ A diploid secondary nucleus situated at the centre of the embryo sac.

○ Pollen grains are carried to the stigma of the female flower where they stick to the stigma by interaction between different surface chemicals. ○ The intine elongates forming the pollen tube carrying the tube nucleus and the two male gametes. ○ The pollen tube enters the embryo sac through the micropyle. ○ The tube nucleus fuses with the synergies and they disintegrate.

○ One of the male gametes fuses with the ovum to produce zygote(2n). ○ The second male gamete (n) fuses with the secondary nucleus (2n) resulting in the formation of a triploid nucleus. This is known as Double Fertilization.

Reproduction in fungi: Budding: ● asexual reproduction in which a new organism is developed from a small outgrowth in the parents’ vegetative body, eg. Yeast. Process: ○ a small irregular growth is seen on the parent’s body. ○ in favourable condition, the growth becomes larger (by consecutive cell division) and when it can live without depending on the parent, the outgrowth detaches from the parent and leads its own life.

Sporulation: ● used asexual reproduction in fungi where reproduction occurs by formation of spores in sacs called a sporangium. Spores may be of the following types: Asexual spores: ■ They are innumerable, non-motile, uninucleate and are produced on the diplont mycelium. ■ The spores are of diverse type and are borne upon special structures called the sporophores. Endogenous spores: ■ The endogenous spores are produced within the special spore-producing cell the sporangium. ■ They may be branched or unbranched, motile or non-motile. Exogenous spores: ■ The spores producing externally or exogenously are either called the exogenous spores or conidia.

■ They are produced externally on the branched or unbranched conidiophores and may be septate or aseptate. ■ They may be unicellular or multicellular, uninucleate or multinucleate. Different genera may be recognized only by the presence of various-shaped and various coloured conidia.

Reproduction in Bacteria: Binary Fission: ● bacterial cells multiply in number. ● similar to mitosis but serves a different purpose because binary fission is bacterial reproduction and is used for increasing number of bacteria in a population Steps include: ○ begins in the origin of replication-the first part of the DNA to be copied. ○ As it continues, two origins move towards opposite ends of the cell, pulling the rest of the chromosome along with them making the bacterial cell longer. ○ Once complete and the new chromosomes move to opposite cell ends and cleared the centre of the cell, division of the cytoplasm can take place. ○ In this process, the membrane pinches inward and a new dividing wall forms down the middle of the cell. (Bacteria have a cell wall) ○ Finally, the septum itself splits down the middle, and the two cells are released Reproduction in Protists: Protists are eukaryotic organisms but are not animals, plants or fungus can reproduce asexually by a number of process including: Binary Fission: ■ Similar to bacteria, protists also have the capability to multiply in number by binary fission a process by which one protist is split into two protists and keeps continuing this process for continuation of generation. Budding: ■ budding occurs when a new organism grows from the body of the parent organism and is detached from the parent once it attains maturity to form its own colony. Advantages of Internal and External Fertilization in animals: internal Fertilization:

External Fertilization:

● Increased possibilities of unions of gamete ● Results in the production of a large numb Because of all conditions required for fusion of zygotes and thus more offsprings can be produced of gametes is maintained inside the body ● Easier to find mates as the gametes ● More protection against outside environments can drift (wind, water etc). and predators, and therefore a higher chancereleased of ● More genetic variation surviving until birth. ● More selective of their mates ● Less chance of desiccation of gametes

➔ Analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals Features of fertilisation in mammals: ● Occurs when sperm and ovum fuse and the result is a single-celled zygote. ● For successful fertilisation, sperm must be deposited in the vagina within 24-72 hours after ovulation. ● Once deposited in the vagina, sperm swim through the cervix and into the uterus, and then up into the fallopian tubes where the ovum resides. ● movement of sperm is helped by muscular contraction of the uterus walls and the fallopian tubes. Fertilisation occurs in the fallopian tube. ● Only one sperm will fertilise the ovum by penetrating its cell membrane and depositing the male genetic material into the female cell, where the two nuclei fuse. ● The zygote immediately becomes resistant to penetration. After fertilisation, the zygote remains in the fallopian tube for about 72 hours and develops rapidly. Features of implantation in mammals: ● Between five to seven days after fertilisation, blastocyst reaches the uterus and embeds itself in the thickened endometrium. if the embryo survives it is the beginning of a pregnancy. ● If the blastocyst implants successfully in the uterus, the cells go on multiplying by cell division and moving around into new locations to form two distinct structures: 1. Three or four blastocyst cells develop into the inner cell mass, which over the next few weeks will form into a human embryo with a head, beating heart and tiny limbs. Some also develop into fetal membranes that form a fluid-filled protective ‘bag’ around the embryo. 2. The remaining 100 or so blastocyst cells from the trophoblast, provides the baby’s contribution to the placenta. first stage of development of the placenta is when the trophoblast cells burrow into the endometrium. Hormonal Control of pregnancy:

● A wide range of hormones are involved and their roles have been described below: Human Chorionic Gonadotropin: ■ mainly responsible for the early pregnancy symptoms eg. missed menstruation to nausea, vomiting fatigue. ○ Progesterone ■ This hormone maintains the functionality of placenta and prevents sudden movement and contraction of the uterus.

○ Estrogen ■ ovarian hormone that is controlled by luteinising (hormone that triggers ovulation and develops in the corpus luteum). ■ An important role of estrogen is to facilitate the maturation of lungs, kidneys, adrenal gland, liver and bone density of the unborn baby. Besides this, it also aids the flow of blood to fetus. Estrogen also protects the female baby from the masculine effects of androgen. ○ Other Hormones ■ Human chorionic somatomammotropin hormone (HCS) also known as Human placental lactogen (HPL) hormone facilitates fetal development and formation of lactation glands. ■ Oxytocin facilitates the delivery process by helping in the contraction of the uterus and also stimulates the mammary glands to produce milk. ■ Calcitonin is useful in calcium metabolism and prevents bone calcium from entering the blood system. ■ Prolactin and oxytocin help the woman to get rid of post-pregnancy problems. ➔ Impact of scientific knowledge on the manipulation of plant and animal reproduction in agriculture: ● Scientific knowledge helps us to explore different dimensions of all fields of science and thus enriches us with the basic ideas that are required to conduct extensive researches. ● Manipulation of plant and animal reproduction processes is a very serious matter because it involves a lot of technique and since many processes take place inside both animals and plants, careful measures need to be taken before conducting such techniques that result in manipulation. ● Suppose a person is thinking of applying artificial vegetative reproduction techniques to promote the production of a specific plant in less time. Suppose the targeted plant

he selected is Rose and the technique he was trying to use was Layering. Layering techniques are more efficient for plants having longer branches and rose plants do not have that feature thus for those, cutting is a more effective method to adopt artificial vegetative propagation methods. Thus, if a person is devoid of this knowledge, his experiments will keep failing. ● Cross-breeding is a widely used technique used in case of both plants and animals. But before a cross-breed is done, it is a must to go through reproductive processes of the samples that will be bred because, at times, breeding might lead to incompatibility and result in no product. ● Scientific knowledge will also help us to predict possible outcomes from manipulation techniques. Not always precise but it helps to be prepared for any misalignment during the processes.

Cell replication ● Model the processes involved in cell replication, including but not limited to: ➔ Mitosis and meiosis Definition: ● The biological process in which one mother cell is divided into two identical daughter cells having the same number of chromosomes. ● Also known as “Equational Division” because of the equality in the number of chromosomes in mother and daughter cells; “Karyokinesis” relating to the fact of the occurring nuclear division. Process: ● The principal phases of Mitosis cell division are preceded by a major phase known as Interphase which has a collection of subphases. These subphases are necessary for a cell to prepare beforehand it actually goes under division. Interphase: ● It is a segment of the cell cycle before Mitosis where a cell prepares itself for division. There are 3 sub-phases which altogether build up the Interphase stage. They are: ○ G1 (first gap) – Cells synthesize a number of materials that are required for completing replication in the following steps including some enzymes, regulators and nutrients.

○ S (synthesis) – In this sub-phase, DNA packed in chromosomes are replicated so that complete set of information is passed on from the mother cell to the daughter cells which will be generated during Mitosis. ○ G2 (second gap) – Immediate phase after DNA Replication where cells synthesize materials required for the formation of spindle fibre during the different phases of Mitosis. ○ Phases of Mitosis: ● The 5 phases of Mitosis cell division are: Prophase/Early Prophase: ■ Condensation of chromosomes begins. ■ Formation of a spindle-shaped apparatus made from microtubules initiates which is often called Mitotic Spindle. The spindle fibres attach to the condensed chromosomes and help in their movement and distribution during the latter phases of cell division. ■ Nucleolus, the part of the cell where ribosomes are produced disappears. Prometaphase/Late Prophase: ○ Chromosomes attain a fully condensed and compact structure; the nuclear membrane disappears. ○ A complete spindle apparatus is formed and the microtubules within it gradually start attaching with the condensed chromosomes. ○ Microtubules bind to the chromosomes with the help of a specialized protein present in the centromere of each sister chromatid known as Kinetochore. ○ Microtubules that attach to kinetochores are known as Kinetochore Microtubules and those who are devoid of attachment with Kinetochores help in stabilizing the spindle apparatus by adhering to the microtubules near the poles of the spindle. ○ In animal cells, more microtubules extend from the microtubule-organizing centre centrosome towards the edge of the cells forming a structure called Aster.

Metaphase: ○ The chromosomes attached to the microtubules are aligned in the middle of the spindle apparatus. ○ Each kinetochore from two sister chromatids is attached with the microtubules facing towards the opposite poles. Anaphase: ○ The sister chromatids are separated into two individual chromosomes. ○ After separation, the microtubules facilitate the movement of the separated chromatids. The centromere moves ahead facing the poles and the arms follow. ○ Basing on the position of centromere, different shapes of chromosomes are seen in this phase. Some of the notable ones are: ■ Metacentric: Centromere is positioned at the centre of the chromosome causing the length of both the arms to be equal. The chromosomes look like the English alphabet “V”. ■ Sub-metacentric: The arms of the chromosomes are of unequal length and the centromere lies nearly at the centre. Chromosomes look a lot like “J” and sometimes, “L”. ■ Acrocentric: Centromeres are positioned nearly at one end and the length of the arm beyond the centromere is quite small. ■ Telocentric: Centromere is located at one end resembling a rod-like structure. Telophase: ○ The nuclear membrane and the nucleolus start regenerating from the left-over parts of the mother cell.

○ The separated chromosomes and other organelles start organizing. ○ This is the stage where the daughter cell formation is “nearly” complete Cytokinesis: ○ It is the process of division of cell’s cytoplasm. ○ In animal cells, two proteins known as Actin and Myosin facilitate the formation of the cell by creating a cleavage furrow. ○ In-plant cells, cell plate is formed which separated the almost created cell into two separate daughter cells completing division.

Meiosis: Definition: ● The process of cell division in which one mother cell divides into four daughter cells having half the number of chromosomes in the mother cell. ● Also known as “Reductional Division” since the number of chromosomes reduces to half, the preparatory steps for meiosis cell division are similar to that of mitosis. Meiosis is rather divided primarily into two phases which are a) Meiosis I and b) Meiosis II both of which have sub-phases. ● In case of meiosis, the chromosomes divide once while the nucleus undergoes division twice.

Meiosis I: ● Similar to Mitosis, before Meiosis I starts, the cell undergoes Interphase where it grows in G1 subphase, chromosomes replicate in S phase and synthesize necessary chemicals for carrying out different sub-phases under Meiosis I and Meiosis II. ● There are 4 sub-phases under Meiosis I which are as follows: Prophase I: ■ Leptotene: This is a comparatively short stage where progressive condensation of chromosome fibres take place.

■ Zygotene: Homologous chromosomes are formed and they pair up with another homologous chromosome by a process called synapsis. The paired chromosomes are called bivalent or tetrad. ■ Pachytene: Two non-sister chromatids form a physical linkage, the site of which is known as Chiasmata. In this region, the non-sister chromatids sometimes exchange their parts in a process called Crossing Over. ■ Diplotene: The synapsis becomes weak and the linkage of the chromatids starts to break causing separation. The chiasmata remain intact until Anaphase I. ■ Diakinesis: Condensation of chromosomes continues; nuclear membrane and nucleolus disappear and formation of spindle apparatus begins. Four parts of the tetrads and the chiasmata are prominently visible in this sub-stage. Metaphase I: ■ Homologous chromosomes arrange in the equatorial region in the completely formed spindle apparatus. ■ Similar to mitosis, kinetochores act as the bridge between chromosomes and the microtubules of the spindle apparatus. Anaphase I: ■ Homologous chromosomes are pulled towards the poles of the spindle apparatus by the shortening of the kinetochore microtubules. ■ The connection between the sister chromatids degrades near the arms but remains unharmed in the centromere. Telophase I: ■ The homologous chromosomes reach the pole of the spindle apparatus. ■ The spindle apparatus starts degrading while the nuclear membrane and nucleolus start reappearing. ■ Cytokinesis takes place and the animal cells are surrounded by a cell membrane whereas the plant cells are surrounded by a cell plate. Two complete daughter cells are formed. ■ Cells enter a phase known as Interkinesis or Interphase II. No DNA replication occurs in this phase. Meiosis II: Prophase II: ● Chromosomes start to condense and nucleolus and nuclear membrane disappear. ● Spindle fibre formation is seen and the microtubules start attaching to the kinetochores. Metaphase II:

● Chromosomes arrange in the equatorial plane of the spindle apparatus. ● The metaphase II equatorial plate is rotated at 90 degrees. Anaphase II: ● Kinetochore microtubules contract and the separated sister chromatids start moving towards the opposite poles Telophase II: ● Decondensation of chromosomes occurs. The nucleolus and nuclear membrane reappear and the spindle apparatus dissociates. ● Cytokinesis happens again which ends the meiosis II phase creating four complete haploid daughter cells surrounded by cell membrane in case of animal cells and cell wall/cell plate in case of plant cells. ➔ DNA replication using the Watson/Crick DNA model, including nucleotide composition, pairing and bonding The DNA molecule is composed of the following chemical components: Sugar: ● A 5-carbon sugar known as Ribose sugar is present in nucleic acid in two different forms. In DNA, the sugar is known as Deoxyribose sugar because oxygen from carbon at second position is missing. Nitrogenous Bases: ● These are nitrogencontaining compounds having basic properties. There are 5 t...