Biology Notes - Module 5 ~ Heredity PDF

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Summary notes on the year 12 module 5 biology course...

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Module 5 Heredity

5.1 Reproduction ➔ How does reproduction ensure the continuity of a species?

5.1.1 ➔ 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

THE PURPOSE OF LIFE: REPRODUCTION?

❖ All life forms in the history of life on earth can reproduce ❖ They all pass on their genetic material in some form/way ❖ Through reproduction, an organism’s genetic material can continue to exist in the world for centuries after their individual death

❖ Reproduction methods vary between species ❖ Each species has specific adaptations for creating offspring including: ➢ Devoting energy/resources ASEXUAL REPRODUCTION

❖ Some organisms do not need a partner to reproduce (asexual reproduction) ❖ Asexual reproduction is essentually cloning ➢ Offspring are produced from only one parent cell

❖ Asexual reproduction is the making of a new individual without the use of sex cells or gametes ❖ One parent required for the mitotic cell divisions to occur ❖ The offspring can then have an identical genetic make up to the parent ➢ This results in similar appearance/function

❖ Variation is introduced through mutation MECHANISMS OF ASEXUAL REPRODUCTION

❖ Types of asexual reproduction include: ➢ Binary fission ■ Eg. Bacteria ➢ Budding ■ Eg. Hydra and coral ➢ Spore formation ■ Eg. moss, fungi and ferns ➢ Vegetative propagation ■ Eg. plant cuttings like roses ➢ Regeneration ■ Eg. starfish and earthworms ➢ Parthenogenesis ■ Eg. Binoe’s gecko (Heteronotia binoei) Binary Fission: ❖ The process in which bacteria (single cell) divides into two identical daughter cells.

Laboratory Press (2007) Binary fission in bacteria.

❖ Begins when the DNA of the bacterium divides into two (replicates) ➢ Bacterial cell then elongates and splits into two daughter cells each with identical DNA to the parent cell ❖ Each daughter cell is a clone of the parent cell. ❖ When conditions are favourable (right temperature / nutrients available) some bacteria can divide every 20 minutes ➢ Eg. Escherichia coli ❖ In just 7 hours one bacterium can generate 2,097,152 bacteria ➢ After one hour the number of bacteria will have risen to a colossal 16,777,216 ➢ This is why we can get easily sick when pathogenic microbes invade our bodies Budding:

❖ When a new organism develops from an outgrowth/bud due to cell division at a particular site ❖ Similar to plants many animals can reproduce asexually ➢ Eg. Starfish can grow from the arm of a parent starfish while hydra

Spore formation:

❖ When conditions are correct an organism will release its spores ➢ They are then considered entirely separate and autonomous organisms

❖ If an environment is suitable spores will then develop into fully grown organisms ➢ They will eventually grow their own spores, repeating the cycle

❖ Asexual spore production in fungi ➢ Mycelium branches out into a network structure of fine ‘threads’ called hyphae ➢ The ends of this hyphae have ends which are capable of spore formation ➢ Asexual spores are usually produced when ambient environment conditions are favourable via mitosis, spores are usually carried by the wind and then germinate

Parthenogenesis:

❖ A complicated form of asexual reproduction ❖ Occurs in: ➢ Bees

Parthenogenesis in aphids:

➢ Wasps ➢ Scorpions ➢ Crayfish

❖ Occurs when unfertilised eggs develop into offspring

❖ When no males are present, reproduction can occur

❖ Best known to occur in komodo dragons and geckos

❖ Parthenogenesis is an advantage for the continuity of a species as it does not require any males for the reproduction to occur

❖ Also beneficial as females do not have to expend energy looking for a mate ❖ Limits the genetic diversity within a species

SEXUAL REPRODUCTION

❖ Produces offspring that are genetically different and possibly better adapted to new and changing environmental conditions than the parents

❖ Sexual reproduction is often a more energetically expensive process ➢ Gives the species a better chance at surviving in ever-changing environments

❖ Requires male and female gametes ❖ Male gametes: ➢ Sperm

❖ Female gametes:

➢ Eggs/ova

❖ The goal of sexual reproduction is for a species to pass their genes onto their offspring ➢ Ensures the survival of the species

❖ Fertilisation involves the fusion of haploid male/female gametes to produce a diploid zygote ❖ The union of gametes can occur outside the body or inside the body ➢ External fertilisation ➢ Internal fertilisation

ANIMALS: ADVANTAGES OF EXTERNAL AND INTERNAL FERTILISATION ❖ Organisms have evolved from aquatic environments moving onto the land in which the evolution of reproductive adaptations has ensured the survival of species

❖ Organisms have continued to evolve and become more specialised in their reproductive adaptations and can now surviving in harsh arid Australian conditions with extremes of drought and fire EXTERNAL FERTILISATION

❖ Takes place outside the body ❖ Most aquatic animals have this character ❖ Gametes are shed directly into water ❖ After fertilisation occurs fertilised eggs develop (according to that organism’s life cycle) into adults

❖ Involves little energy investment from parents ❖ Millions of gametes have to be produced ➢ Due to low success rate, ensures that fertilisation will occur

❖ External fertilisation can occur in: ➢ Bony Fish ■ Most females of the bony fish species produce eggs in large quantities and then release them into the water ■ Generally followed by males releasing their sperm into the area of water containing the eggs ■ The union of gametes then occurs

■ Gametes (sperm/eggs) disperse quickly so the release of large numbers of gametes from the females and males must occur almost simultaneously ■ Many of the resulting offspring succumb to microbial infections/predation, and few grow to maturity ➢ Amphibians ■ Amphibians invaded the land without fully adapting to the terrestrial environment ● Life cycle is still tied to the water ■ Gametes from males and females are released through the cloaca ■ In frogs/toads the male grasps the female and releases fluid containing sperm onto the eggs as they are released into the water INTERNAL FERTILISATION

❖ When vertebrates invaded the land it posed the danger of dehydration ❖ Gametes could not simply be released near each other as they would quickly dry up and perish ➢ Led to the evolution of internal fertilisation/copulation

❖ Male gametes are inserted into the female reproductive tract via a penis/similar structure

❖ Allows the gametes to unite in a moist environment even though the animal is on land

❖ Internal fertilisation is beneficial as it is protected from: ➢ Dehydration ➢ External elements ➢ Predation ➢ Dispersal/loss of the gametes

❖ Internal fertilisation can occur in: ➢ Cartilaginous fish ■ The male releases the sperm into the female through a modified pelvic fin ➢ Turtles (reptiles) ■ Most reptiles fertilise the eggs internally then eggs are deposited externally for

development ■ Males use a tubular organ (penis) to penetrate far into the female reproductive tract ➢ Wolves (mammals) ■ Some mammals are seasonal breeders (reproducing once a year) ■ The female reproductive system involves the periodic release of a mature egg from the ovary ■ For fertilisation to occur sperm must be inserted in the female's reproductive tract PARENTAL CARE ❖ Varies between aquatic/terrestrial organisms ❖ Many aquatic species leave fertilised egg to develop in the open sea, despite dangers ➢ Less energy is put in to caring for offspring ➢ Survival rate is much lower ■ More eggs are produced to compensate for this ❖ Mammals generally give birth to live young (Viviparous) ❖ Oviparous animals will devote varying amounts of energy to caring for their eggs ➢ Some brood their eggs until they hatch to increase the survival rate of their eggs or guard the nest until they hatch

REPRODUCTION - AUSTRALIAN SPECIES

❖ Australian species have variations in their reproductive structures/mechanisms ❖ If an environment changes the most suited species will survive/reproduce ➢ Leading to the continuity of the species

❖ As the Australian environment becomes hotter/drier, animals with suited reproductive systems will survive and increase in numbers Adaptations for colonisation and survival:

❖ Reproductive adaptations are needed to survive for survival in the Australian environment ❖ Australia's harsh environmental conditions make it difficult for effective fertilisation and development to occur unless they possess suitable adaptations

❖ Reproducing in times which are favourable to the organism (climate, resources etc) can increase the chances of survival/continuation of a species

PLANTS: ASEXUAL AND SEXUAL REPRODUCTION SEXUAL REPRODUCTION IN FLOWERING PLANTS ❖ Flowers are the reproductive organs in angiosperm plants ❖ Different parts in flowers have different reproductive functions

POLLINATION AND FERTILISATION ❖ Before the egg/sperm fuse in fertilisation, the pollen ( contains male gametes) must be transferred from male anthers to female stigma ❖ Plants rarely self pollinate ❖ The stigma of one plant often receives pollen from other plants in cross-pollination ❖ After pollination: ➢ Sperm nuclei can enter the ovule and fertilisation can occur

❖ In angiosperms there is double fertilization ➢ One to produce the embryo, the other produces the endosperm nucleus

MECHANISMS FOR POLLINATION ❖ Pollen can be carried by wind/animals ➢ May originate from same flower ❖ Self pollination: ➢ When pollen from a flower’s anther pollinates a flower’s stigma from a different plant ❖ In most species pollen is produced at a different time from when the stigma can receive it ➢ Prevents plants being pollinated with their own pollen ❖ Flowers are mostly pollinated by other plants in the same species Wind pollination: ❖ Pollen is shed and blown out, occasionally reaching the ovules of the same plant species ❖ Plants of the same species must grow relatively close to each other for wind pollination to occur/operate efficiently ❖ Most wind blown pollen travels less than 100m ❖ Many angiosperms are wind pollinated ➢ The flowers of these plants are small,green,odourless or absent of petals and are often grouped together in large numbers and hang down, shedding pollen freely ❖ Wind pollination is inefficient so large quantities of pollen are produced ❖ Different pollen grain structure ensure compatibility with the same species ❖ Wind-pollinated species do not depend on the presence of a pollinator for species survival ❖ Stigmas are usually very large and spread out to receive pollen carried by wind Animal pollination: ❖ More effective in transferring pollen ❖ The relationship between animals and plants reduces wastage of pollen by ensuring it is deposited on the correct flower ❖ Animals which act as pollinators search flowers for nectar and pollen ❖ Flower scent, colours, markings, shapes and nectaries are important to attract animals Bird pollination:

❖ Plants must produce large amounts of nectar ➢ If the birds don't find enough food to maintain themselves, they will not continue to visit that plant ❖ Flowers that produce large amounts of nectar have no advantage in being visited by insects as insects can obtain energy at a single flower and would not cross-pollinate the flower. ❖ Bird pollinated flowers produce significantly less pollen than wind pollinated plants ❖ The red colour in flowers sends signals to birds about the abundance of nectar ➢ Birds are often attracted to bright flowers Insect pollination: ❖ The most common insect pollinators are bees ➢ Bees locate food by odour and then orient themselves on the flower by shape, colour and texture ➢ Bees generally visit blue/yellow flowers ❖ Flower shape can restrict pollen access ➢ Certain behaviours needed to access pollen

SEED DISPERSAL ❖ Seed dispersal: The movement of the seed from the parent plant ❖ After pollination/fertilisation of the flower the seed develops ❖ Plants who spread/disperse seeds over a wide distance have an advantage ➢ Prevents overcrowding from occurring within same species ➢ Increases chances of survival during environmental change ■ Eg. Fire and disease ❖ Seeds are dispersed by wind or animals ➢ Eg. Insects, birds, mammals are designed to disperse in many ways ❖ Australian plants have evolved many adaptations to be able to disperse their seeds effectively

ASEXUAL REPRODUCTION IN AUSTRALIAN PLANTS ❖ Plants that reproduce asexually clone new individuals from portions of the root, stem, leaves or ovules ❖ Asexually produced plants are genetically identical to the parent ❖ Different types of asexual reproduction in plants include: ➢ Vegetative reproduction ■ New plants are cloned from parts of adults (Eg. runners, rhizomes, suckers) ➢ Budding ■ Unusual form of asexual reproduction in plants ■ Development of a new individual as an outgrowth from parent plant ■ Eg. Kalanchoe produces buds along leaf margins which break off an form new plants ➢ Apomixis ■ Embryos in seeds may be produced asexually from parent plant ■ Produced to give rise to individuals which are genetically identical to parents ■ Plants have the advantage of seed dispersal (usually only in sexual reproduction) and rapid multiplication of plants ➢ Totipotency ■ An entire plant can be generated from a single plant cell

Plants adaptations for reproductive success ❖ Self pollination expends less energy in the production of pollinator attractants ➢ Can grow in area where the chance of insects/animals might visiting them is low ➢ These plants contain a high proportion of individual plants which are well adapted to their habitats ❖ In cross pollinators, insects, birds and mammals have become an effective way of transferring pollen to the stigma ➢ As flowers become specialised, their relationships with insects and animals do too ❖ Many features of flowering plants correlate with successful growth under arid/semiarid conditions ❖ Pollen transfer between flowers of separate plants ensure cross pollination

➢ May have been important in the early success of angiosperms

5.1.2 ➔ Analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals

MALE REPRODUCTIVE SYSTEM THE MALE REPRODUCTIVE ORGANS ❖ Involved in gamete production, storage and transfer to female

❖ Male gametes are called sperm ➢ Made in the testes ➢ Hang from the body in the scrotum to maintain a cooler temperature (3º cooler) ■ Essential for successful sperm production ❖ Testes are made up of small, thin tubes known as seminiferous tubules ❖ From the testes, newly made sperm travel to the epididymis where they are stored until matured ➢ Located in the scrotum of the testes ❖ Once sperm are matured they leave the epididymis via the vas deferens ❖ In the vas deferens fluid from the seminal vesicle and prostate gland is added to the sperm. ❖ The prostate gland secretes liquid that is added to sperm cells (forms semen) ➢ The secreted fluid is alkaline and contains enzymes ➢ Helps keep sperm cells alive in female reproductive tract ❖ The seminal vesicles secrete liquid which is added to sperm cells to form semen ➢ Includes proteins, enzymes, sugar and vitamins ➢ Provides an energy source for sperm cells ❖ The penis swells during sexual arousal ➢ Semen is ejaculated into the vagina, containing sperm cells HORMONAL CONTROL OF THE REPRODUCTIVE SYSTEM ❖ Hormones secreted from the hypothalamus, anterior pituitary and testes control the male reproductive system ➢ Hypothalamus ■ Releases gonadotropin releasing hormone (GnRH) ● Triggers the production of gonadotropins, LH and FSH hormones from the pituitary gland ● LH promotes development of interstitial cells of the testes (secrete testosterone) ● FSH stimulates the supporting cells of the seminiferous tubules

● FSH and LH stimulate spermatogenesis ■ Controls the changes during puberty which lead to a functional reproductive adult ❖ Male sex hormones are called androgens ➢ Testosterone is the most abundant ❖ Testosterone is secreted in a fetus until birth, then not until puberty, after this it is continuously secreted ❖ Testosterone is also responsible for secondary male characteristics such as: ➢ Deep voice, body hair and thickening of the skin ❖ A negative feedback system involving the hypothalamus regulates the quantity of testosterone ❖ As blood concentration increases, the hypothalamus becomes inhibited and stimulation of the anterior pituitary gland decreases ❖ As amount of LH drops in response, amount of testosterone reduces

FEMALE REPRODUCTIVE SYSTEM The reproductive system is involved

❖

in receiving sperm (gametes), female gamete production (ova) and fertilisation ❖ Cares for the young until birth ❖ Ova are produced in the ovaries ❖ Females are born with all the ova they will ever have (12 million) ➢ Unlike males who produce sperm continuously ❖ Female gametes begin development as primordial follicles in the ovaries

❖ Primordial follicle is made up of an oocyte (undeveloped ovum) and protected layer of granulosa cells ❖ During ovulation the mature follicle ruptures and releases the oocyte as well as the protective layer of cells in the fallopian tube ➢ Females release approx 400 oocytes in their lifetimes ❖ Once a girl reaches puberty, the ova progressively mature and are eventually released from the ovaries (ovulation) ➢ Ovulation occurs every 28 days ❖ Mature ovum travels down the fallopian tubes. ❖ If sexual itnercourse has happened in the past 5 days and there is sperm in the fallopian tube, fertilization will occur there ❖ If there is no sperm in the fallopian tube, the ovum continues into the uterus

ovar y

Fallopi an tube

cervix MENSTRUATION

Uterus

Vagina

❖ Uterus walls contain many blood vessels/glands ➢ Prepare the uterus for pregnancy ❖ If no pregnancy occurs the uterine lining breaks down ❖ The lining and ovum are passed through the cervix/vagina as menstruation (periods) ❖ The cervix is the passageway between the vagina and the uterus ❖ The vagina is the elastic tube that connects uterus to the outside

the

❖ During childbirth the cervix dilates to allow the baby to exit the uterus ❖ Semen enters the female reproductive system through the vagina MENSTRUATION + OVULATION ❖ Menarche (first period) generally occurs between the ages of 11 -14 ❖ Periods generally lasts for 4-6 days ❖ During this time stomach cramps and mood swings can occur ❖ Girls are born with approx 400,000 eggs/ova ❖ During puberty approx 400 eggs mature and are released in the menstrual cycle ❖ Each month the uterus lining prepares for a fertilised egg ➢ If the egg is not fertilised he lining is shed through the vagina as a menstruation ❖ The FSH and LH hormones are the important sex hormones ➢ FSH → Follicle stimulating hormone ➢ LH → Luteinizing Hormone

THE HORMONES INVOLVED IN FEMALE REPRODUCTION ❖ FSH and LH cause ova to develop in females (sperm development in boys) ❖ Oestrogen and progesterone are made in the ovaries ➢ Regulate the uterine lining during the menstrual cycle ❖ An increase in FSH and LH causes ovulation to occur along with uterine

lining growth

KEY EVENTS IN THE MENSTRUAL CYCLE ❖ Four key events in the menstrual cycle ➢ Follicular phase ■ Follicle stimulating hormone is secreted from the anterior pituitary gland and then stimulates the growth of ovarian follicles ■ Dominant follicle then produces estrogen which inhibits FSH secretion (negative feedback loop) and prevents other follicles ...