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HSC BIOLOGY MODULE 5 STUDY NOTES: HEREDITY

BY JENNIFER AZZI INQUIRY QUESTION 1 HOW DOES REPRODUCTION ENSURE THE CONTINUITY OF A SPECIES? 1. ASEXUAL REPRODUCTION The mechanisms of reproduction are the range of biological processes by which new individual organisms are produced from their parents. PLANTS Vegetative Propagation ● It is any form of asexual reproduction in plants, in which new plants are produced from the vegetative parts of the plants, i.e. roots, stems or buds. ● Vegetative propagation in plants can occur both by naturally or also can be artificially induced by horticulturists. Runners ● Stem-like growths extending from a mother plant’s growing point, such as a strawberry’s crown ● Can’t survive unless attached to the mother plant ● Connects the mother plant to a newly formed daughter plant Rhizomes ● Modified stems running underground horizontally ● Strike new roots out if their nodes, down into the soil ● Shoot new stems up to the surface out of their nodes ○ Represents a form of plant reproduction ● Also, store nutrients Suckers ● Plant growth that develops from the rootstock of a plant that has undergone grafting ● Does not originate from a seed, but from the base of the root of the plant at a certain distance away from the plant Tubers ● Part of the plant that grows beneath the soil's surface ● E.g. Potatoes

● Stores valuable nutrients and water ○ Used during periods of drought or during the winter months Apomixis ● Some plants produce offspring from special generative tissues without involving fertilisation or the production of species ● Generative tissue may be in the form of gametes such as unfertilised ovules or nonreproductive tissue such as leaf tissue ○ Can produce plantlets that can grow into individuals that are genetically identical to their parents.

FUNGI ● Spores are not gametes ● Spores allow fungi to reproduce through unfavourable conditions. ● Mycelium → made up of hyphae (little root looking things of a mushroom). ● Fungi are generally haploid organisms→ half the amount of genetic information. ● Almost all fungi reproduce asexually by producing spores. An asexual fungal spore (mitospore) is a haploid cell produced by mitosis from a haploid parent cell. ○ It is genetically identical to the parent cell. Fungal spores can develop into new haploid individuals without being fertilized → benefit of asexual reproduction ● Spores may be dispersed by moving water, wind, or other organisms. Some fungi even have “cannons” that “shoot” the spores far from the parent organism. This helps to ensure that the offspring will not have to compete with the parent for space or other resources. ○ Being dispersed is the mechanism that allows for the continuity of the species. ○ By being lightweight they can easily move to different environments and therefore there is a lack of competition for resources allowing more to survive. BACTERIA & PROTISTS Binary Fission ● Protists are unicellular eukaryotes that reproduce sexually be a type of binary fission ○ Thus have membrane bound organelle ● This involves mitosis and the formation of a spindle within the cytoplasm of the cells to distribute chromosomes equally. ○ Spindle → collection of fibres that assist in splitting the cell. ● The circular chromosome makes an identical copy of itself and the 2 chromosomes move to opposite ends of the cell ● A cell wall forms across the middle of the bacterium and eventually separates into 2 separate cells ● Example → Amoeba ○ Divides after it grows to a certain size. Budding (also occurs in fungi e.g. yeast) ● Two nuclei are formed during mitosis and they move away from each other and a bulge (bud) will develop on one side ● The bud contains one of the nuclei and some of the cytoplasm of the original cell ● Bud will pinch off and become separated from the parent cell or the buds can stick together forming chains of buds, each one, however, is a separate organism

2. SEXUAL REPRODUCTION ANIMALS Mammals (Placental) ● The older males that are from 40 to 50 years of age are the most likely to breed with the females. The females are ready to breed when they are about 14 years of age. ● This old age of the male elephants is due to the aggression among the males for the rights to mate, a match which requires strengths that the younger elephants do not possess. ● Female elephants usually mate with a few males, choosing their mate based on strength, dominance, and rank within his herd. This allows the calf to inherit these traits. ● During mating, the male elephant releases billions of sperms in the female elephant to be fertilized with an egg. Once fertilised, the gestation period for elephants is the longest as it is 22 months → internal fertilisation Marsupials ● Mating usually takes place during the rainy season of the year, when vegetation is plentiful, but can occur all year around if the conditions are right (i.e no droughts) ● Sperm fertilises the egg internally, but the mother is able to delay the attachment of the embryo to the fetus. This means she is able to control when she will be pregnant. ● The gestation period is usually about 35 days after conception, and the joey climbs into the pouch, underdeveloped at about 0.85 g, hairless and blind. ● Depending on the species of Kangaroo, the joey will live in the pouch of the mother for 1 year to 1 ½ years, surviving off her milk. ● However, they begin to leave the pouch for short periods to explore at 9 months old but come back for milk. Reptiles ● Reptiles undergo internal fertilisation in order to produce offspring. ● This occurs when the male reptile places their penis or hemipenis into the female's cloaca. ● The sperm is then released by the males penis or hemipenis and travels into the eggs within the female's cloaca for fertilization. ● Usually, reptiles lay eggs on the ground and attempt to protect them from predation by hiding them in burrows or holes in the ground. The number of eggs a reptile produces varies from species to species. ● Once the eggs are laid, parent reptiles normally provide their eggs with minimal to no

care, and thus once the offspring hatch they can move around freely. Amphibians ● Gametes are released in freshwater → external fertilisation. ● Mass produce because many tadpoles are eaten and therefore many do not reach adulthood. Birds ● Birds reproduce by internal fertilization. The egg is fertilized inside the female. ● The male brings his sperm to the female cloaca. The sperm fertilizes the egg. ● Birds Incubate (keep warm) the eggs because the embryo will only develop at a temperature close to the bird's body temperature.

PLANTS

Gymnosperms → Have a naked seed (cones). Female cones develop 2 ovules on the upper surface of each cone scale. Each ovule contains haploid megaspores. Male cones produce microspores by meiosis and develop into pollen grains. Each winged pollen grain is a four-celled male gametophyte. The female gametophyte grows to produce two archegonia each containing an egg. During pollination, a wing-borne pollen grain falls near the opening in one of the ovules of the female cone. Each male gametophyte forms a pollen tube that penetrates the tissue of the female gametophyte. A sperm cell from the male gametophyte then fertilises the egg. The zygote develops into an embryo and a mature seed is produced. Angiosperms → Have a seed that is protected and develops inside an ovary (flowers). Male gametes travel from the anther to the embryo sac within the female reproductive organ. A pollen grain, containing a tube cell and generative cell, must land on the stigma where it will begin to germinate. The tube cell forms a long structure down the style, and into the ovary. The generative cell travels behind the tube cell nucleus. Once near the ovary, it divides by mitosis to produce two haploid sperm cells. The pollen tube reaches the micropyle and releases the sperm cells into the embryo sac. One of the sperm cells fertilises the egg cell, producing a diploid zygote which will become the embryo. The other sperm cell fuses with both of the central nuclei forming a triploid cell which develops into an endosperm and serves as the embryo’s food supply during early development. Alternation of Generations ● Plants alternate between two different forms in the process of alternation of generations ● The gametophyte (first form haploid: half genetic info) produces male and female gametes, by mitosis which fuse to form a zygote, which in turn gives rise to a diploid sporophyte (second form - diploid: full set of genetic info)which generates haploid spores, each of which again gives rise to a gametophyte. Pollination, Fertilisation and Seed Dispersal Sexual reproduction relies on the fusion of the male and female gametes which is difficult when the plants can’t move. Thus, there are a range of strategies to ensure this occurs, including; ● Relying on external agents to carry the gametes from one parent to another, commonly called pollinating agents. ● Relying on external agents to disperse their seeds wind water and animals. FUNGI

● To locate a fungus of the opposite mating type, hyphae will release pheromones (scent) ● The pheromones will not bind to the hyphae with the same mating type → Protect against sexual reproduction with a genetic twin → this ensures the continuity of a species through variation. ● Hyphae from two different mating types make contact and connect → after pheromones are released to attract each other. 1. Plasmogamy: The cytoplasms of the two different mycelia fuse → form together under cells. 2. Karyogamy: The two nuclei pair up and form a binucleated cell (dikaryon/heterokaryon). The nuclei then fuse and form a diploid nucleus. ○ Multiple nuclei fuse from each side. 3. Meiosis: The diploid nucleus gives rise to haploid nuclei forming haploid spores.

3. INTERNAL AND EXTERNAL FERTILISATION Features of Internal and External Fertilisation

Examples of organisms Fertilisation takes place inside or outside of the mother’s body Fertilised eggs (zygote) released into water or stay inside the mother Sperm sprayed on to the eggs or sperm placed inside mother Few or very many eggs produced Young develop inside or outside mother’s body Most or some of the eggs get fertilised Most or few of the offspring (babies) survive Eggs or offspring (babies) looked after, or not looked after by parents Parents build a nest or no nest

Internal Fertilisation Humans

External Fertilisation Fish, coral and frogs

Inside

Outside

Stays inside the mother

Released into water

Placed inside mother

Sprayed onto the eggs

Few

Many

Inside

Outside

Most

Some

Most

Few

Looked after by parents

Little to no parental care

Nest

No nest

Advantages and Disadvantages of Internal Fertilisation

Advantages and Disadvantages of External Fertilisation

4. PREGNANCY AND BIRTH IN MAMMALS Sex hormones ● Androgens ○ Commonly referred to as male hormones. ○ Control the development and functioning of male sex organs and secondary sex characteristics. ○ Testosterone is the main male hormone and its role is in spermatogenesis (production of sperm) ● Oestrogens ○ The main group of female hormones. ○ Control the development and functioning of the female reproductive system. ○ Also found in males ● Progestogens ○ A second group of female hormones. ○ Is the most common and plays a primary role in pregnancy. Hormones ● Hormones control male and female reproductive system ● In both sexes, the hypothalamus monitors and causes the release of hormones from the pituitary gland. ● Gonads → in testes(males) and ovaries. ○ Gonadotropin-releasing hormone (GnRH) is sent by the hypothalamus when the reproductive hormone is required. ● This causes the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary into the blood. ○ Whilst these are mainly in women, they are also in men. ● FSH stimulates the ovarian follicle, causing an egg to grow. It also produces estrogen in the follicle. ● A rise in estrogen tells your pituitary gland to stop producing FSH and to start making more LH. ● The shift to LH causes the egg to be released from the ovary, a process called ovulation. Female Reproductive cycle

Stages in the ovarian and menstrual cycle Stage

Time Span

Events

Menstruation

1-4

Uterine bleeding, accompanied by shedding of the endometrium

Pre Ovulation

5-12

Endometrial reparo begins; Development of ovarian follicle; uterine lining gradually thickens

Ovulation

13-15

Rupture of a mature follicle, releasing the egg

Secretion

16-20

Secretion of watery mucus by glands of endometrium, cervix and uterine tubes’ movement and breakdown of unfertilised egg

Pre Menstruation

21-28

Degeneration of corpus leutem; deterioration of endometrium

Sperm Production in males

Fertilisation → The fusion of male and female gametes to form a zygote. ● Gametogenesis is the name of the gamete formation process. (spermatogenesis producing sperm and oogenesis - formation of mature egg cells). ● The fertilisation process and fusion of gametes occurs in the fallopian tube of female’s body ● The zygote will develop into a living organism that has mixed genetic information from the parents. ● Fertilisation involved multiple stages that MUST be fulfilled for successful fertilisation and zygote formation and thus producing a new offspring. ● The gametes must be from the same species in order for successful fertilisation. ● Continuity of a species ○ Mixed genetic information from parents ○ Genetic variation ○ Can reproduce when they are from the same species ● Zygote → cleavage → morula → blastocyst (all occurs via mitosis to form cells which later become specialised to form the embryo) ● Stages of fertilisation ○ Formation and maturation of gametes ○ Spermatozoa must journey into the oviduct ○ Spermatozoa must make contact and fuse with the egg cells.

Implantation ● The process of adhering the fertilised egg to stick to the walls of the reproductive tract, providing the most suitable environment for zygote development. ● HCG → high levels of the hormone determine if one is pregnant in a pregnancy test. ○ Purpose of HCG is to stop FSH and LH from forming follicles and releasing eggs. ■ This is why your period stops. ○ It also instructs the corpus luteum to keep producing oestrogen and progesterone to ripen the endometrium for implantation ● This implantation process onto the walls establishes blastocyst access to nutrients to develop into an embryo ● Placenta develops to nourish the growing blastocyst ● When the blastocyst has differentiated into a number of cell types it is called the embryo ● Placenta now takes over from the blastocyst as starts secreting the hormones. Roles of hormones ● Estrogen ○ Helps the uterus grow, maintains the uterine lining, steps up blood circulation and activates and regulates the production of other key hormones. ● Progesterone ○ Promotes correct fetal development, prevents the muscles of the womb contracting until the onset of labour, strengthening the muscles of the pelvic wall in preparation for labour ● Relaxin ○ Relaxes the ligaments in the pelvis and softens and widens the cervix ● Lactogen ○ Tell fetus to grow, breasts to lactate, body to store glucose for the fetus. Hormonal Control of birth ● Oxytocin ○ Released to stimulate uterine muscles to increase the strength and frequency of dilation and contraction of the cervix. This allows the parent to deliver the offspring by pushing out placenta. ○ The hypothalamus produces oxytocin and stores it in the pituitary gland, situated below the hypothalamus. ○ Upon stimulation of hypothalamus neuron cells, the pituitary gland will secrete oxytocin into the bloodstream. ● Endorphin hormones ○ Released to increase concentration and relief pain to focus on the delivery of offspring. ○ The levels of endorphin peaks as the strength and frequency of cervix dilations and contractions increase to combat pain. ● Adrenaline hormones ○ Released during giving birth. This is due to the body’s response to fear and pain. ○ Adrenaline provides energy for the parent to continue delivering the offspring by producing stronger dilation and contractions of the cervix. ○ May cause the opposite response which is decreasing cervix contractions due to fear.

5. MANIPULATION OF PLANT AND ANIMAL REPRODUCTION Selective Breeding or Artificial Selection ● Used to produce animals and plants with more useful or more attractive characteristics ● Historically, they chose those animals or plants that expressed the characteristics they wanted to conserve and selectively bred them together hoping that their offspring would show even more of these characteristics. ● Selective breeding only uses the genetic pool of the species, current technology allows us to introduce new DNA combinations. Gene Linkage ● Is a disadvantage of selective breeding ● When selecting a desired trait that other traits may inadvertently be selected as well. ● For example, the gene that codes for weak stems may also be carried with the gene for ripened heads Hybridisation ● The crossing of different varieties within in species to produce new varieties with different combinations of characteristics is one kind of hybridisation. ● In general, Hybrid plants are more vigorous, higher yielding and may be more disease resistance by the outcome of hybridisation is not always an improvement. ● When a hybrid offspring are produced artificially, they are designed to be cultivated or farming and may not be suited to the conditions in the wild. Heirloom Plants ● A traditionally cultivated plant that is maintained by small scale gardeners and farmers. ● These may have been commonly grown during earlier periods in human history but are not used in modern large scale agriculture. ● In modern agriculture, most food crops are now grown using limited varieties in large, monoculture plots to keep the production of a consistent standard. Genetic Engineering ● Can allow the exchange of genes between organisms that are sexually incompatible and normally cannot interbreed. ● New forms of plants and animals developed in this way are referred to as genetically modified individuals (GMOs)

INQUIRY QUESTION 2 HOW IMPORTANT IS IT FOR GENETIC MATERIAL TO BE REPLICATED EXACTLY? 1. DNA HISTORY & STRUCTURE History of DNA ● Rosalin Franklin ○ Invented photograph 51 ● Watson & Crick ○ Did not produce a piece of evidence ○ One of them was a zoologist ○ Received a Nobel prize ● Wilkins ○ Saw Rosalin as an assistant rather than a fellow scholar ○ He took her photo and gave it to Watson and crick without her consent. They used this to make their model and published their findings. She published her findings a year later but died before she could be recognised for her findings. What is DNA, where is it located and why is it important? ● DNA is the hereditary material in humans and almost all other organisms ● Located in the cell nucleus ○ Some can be found in the mitochondria → mitochondrial DNA ● The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). ● The order, or sequence, of these bases determines the information available for building and maintaining an organism ● DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Nitrogenous Base

Purine or pyrimidine

Complementary base

Purine or pyrimidine

Adenine (A)

Purine

Thymine (T)

Pyrimidine

Guanine (G)

Purine

Cytosine (C)

Pyrimidine

Cytosine (C)

Pyrimidine

Guanine (G)

Purine

Thymine (T)