Module 5: Heredity Flashcards
heredity
how life (species and gene pool) continues as characteristics are passed down from one generation to the next
sexual reproduction
- the process in which new organisms are created by combining the genetic information from two individuals of different sex
- each parent provides haf the genetic material of the offspring in the form of a gamete (sperm for males and egg/ova for females) (haploid).
- the female and male gametes fuse to create a full set of chromosomes, thus allowing the offspring to inherent characteristics from both parents
reproduction
production of offspring
asexual reproduction
The process requires one parent organism to produce genetically identical offspring without exchanging genetic information with another organism.
difference between sexual and asexual
no. of parents:
–> (S) 2
–> (A) 1
genetics of the offspring :
–> (S) High variation (similar but not identical to parents)
–> (A) Low variation (identical cloned daughter cells to parent)
type of cell division:
–> (S) gamete production (meiosis), (eukaryotes)
–> (A) binary fission: (prokaryotes)
and cell replication (mitosis): (eukaryotes)
fertilisation:
–> (S) sperm fertilises the egg (fusion of gametes)
- internal/external
–> (A) no fusion of gametes
rate of offspring production:
–> (S) Slower/longer
–> (A) Quicker/shorter
advantages of sexual reproduction
> High gene diversity → allows organisms to adapt and survive environmental changes
> Not as susceptible to disease
> Successful in unstable condition
> ‘Selective advantage’ - able to outcompete other individuals and survive
advantages of asexual reproduction
> Energy efficient
> Only requires 1 parent
> No need to find a mate
> Shorter reproduction cycle
> Populate and repopulate species quickly
> Successful in stable conditions
> Every member can reproduce
> (for plants) - no need for pollen and vectors
disadvantages of sexual reproduction
> Longer reproduction cycle
> Time and energy consuming to find and court mate, produce gametes and mate
> Requires two parents
> Longer time to populate and repopulate
> Only females can reproduce
disadvantages of asexual reproduction
> Low genetic diversity
> Offspring may not survive environmental change due to low genetic variation
> Susceptible to disease
Inhibits the process of adaptation
reproductive success
determined by an organism’s ability to produce fertile offspring that survive to reproductive maturity to produce their own offspring
biological fitness
a measure of an individual’s reproductive success. it measures how well an organism can pass on its genes to the next generation. organisms with higher fitness are more likely to produce more offspring that can also survive and reproduce, thereby passing on their traits
types of asexual reproduction
binary fission, budding, fragmentation, spores, vegetative propagation
parthenogenesis
binary fission
binary fission results in the formation of two genetically identical organisms from a single-parent organism e.g. bacteria, protists
budding
budding is the uneven cell division (unicellular) or outgrowth in which a new organism grows on the parent before breaking away.
spore formation
a unicellular reproductive structure called sporangium that can make and disperse spores into the environment that germinate into new individuals
if an organism is well-adapted to its environment, what is advantageous?
to conserve its genome by performing asexual reproduction. Allows for rapid population growth
if an organism is exposed to changing environments, what is advantageous?
mutations that occur during DNA replication, translating to variation in species. facilitates adaptations.
what selection pressures make asexual reproduction more effective than sexual reproduction?
–> shortage of food and/or other resources because asexual uses less energy to produce offspring
–> small mating population and/or time restraints to find partner because only 1 organism needed for asexual reproduction
do fungi reproduce sexually or asexually and how?
asexual –> budding, spores
sexual –> fusion of hyphae in two fungi
budding in yeast (unicellular fungi)
- FORMATION OF BUD → A bud forms @ a specific site of the cell membrane on the parent protozoan.
- GROWTH OF BUD → The bud enlarges as it accumulates organelles and cytoplasm from the parent cell. However, these materials are unequally distributed between the two cells, causing the bud to be smaller. The cell wall enlarges to facilitate its growth.
- MITOSIS → Genetic material (DNA) is replicated and migrates to the daughter cell.
- CYTOKINESIS → Once the bud has grown sufficiently and has its nucleus and organelle, it may pinch off from the parent cell via cytokinesis. The bud can either remain attached to form a chain-like structure or detach from the parent.
spores in rhizopus (asexual)
- PRODUCTION OF SPORES → A structure called sporangia produces a large number of asexual spores. These spores, produced by mitosis, are haploid and contain a single set of chromosomes.
- SPORE RELEASE → Once the spores are fully formed, the sporangium breaks open and releases the spores into the environment.
- DISPERSAL → The spores are light and can be easily dispersed by air, water etc, allowing them to disseminate over long distances.
- GERMINATION → When a spore lands in a suitable environment (favourable moisture, temperature and nutrients) it germinates. It develops its hyphae then grows into a new mycelium.
when does sexual reproduction happen in fungi? what happens?
Unfavourable conditions will induce sexual reproduction in fungi.
- FUSION OF HYPHAE → The hyphae of two mating types fuse before forming a sexual reproductive fruiting body with a diploid structure. Its spores will have a combination of genetic material, resulting in the species having genetic variation.
spores
tiny, multicellular reproductive cells produced by fungi. they have an outer casing that protects them from drying out
do bacteria reproduce sexually or asexually and how?
asexually –> binary fission
binary fission in bacteria
- DNA REPLICATION → The circular genetic material in the parent cell (nucleoid and plasmids) is replicated. The chromosome begins to replicate at a point called the origin of replication.
- MOVING TO OPPOSITE POLES → Both copies of DNA move towards opposite poles ends of the cell.
- ELONGATION OF CELL
CYTOKINESIS → A range of proteins accumulate at the centre of the cell. A cleavage furrow begins to form. Cytokinesis pinches off the cytoplasm between two emerging cells. - CELL WALL FORMED → Cell wall is formed in the cleavage furrow
do protists reproduce sexually or asexually and how?
asexually –> binary fission, budding
binary fission in amoeba
- INTERPHASE (DNA REPLICATION)
- MITOSIS
Prophase - Chromosomes condense, nuclear membrane disassembles, spindles form in cytoplasm
Metaphase - Chromosomes line up in the middle of the cell, and spindle fibres attach to the centromere of each chromosome
Anaphase - Chromosomes split at the centromere and chromatids are pulled to the poles of the cell by spindle fibres
Telophase - Two nuclei form around chromatids, chromosomes return to normal form - CYTOKINESIS
Explain how binary fission ensures the continuity of species.
–> Binary fission results in the formation of two genetically identical organisms from a single-parent organism.
–> If conditions are stable, this method of asexual reproduction is efficient as it only requires the genome of one parent to pass favourable characteristics onto offspring. Also, they can populate/repopulate rapidly.
–> Mutations that arise during DNA replication can cause slight variation in daughter cells, allowing for possible adaptation to changing environments.
Explain how budding ensures the continuity of species.
–> Budding is the uneven cell division (unicellular) or outgrowth in which a new organism grows on the parent before breaking away.
–> Pass down genetic information most favourable to a specific environment. Efficient as it only needs one parent and can populate/repopulate quickly
Explain how spore formation ensures the continuity of species.
–> A unicellular reproductive structure called sporangium that can make and disperse spores into the environment that germinate into new individuals
–> The outer casing of the spore protects them from drying out
–> Lightweight, meaning they can be dispersed by wind. It expands the distribution of species, allowing them to colonise new environments.
–> Release in large quantities, increasing survival chances.
fertilisation in sexual reproduction
the process in which a male gamete fuses with a female female to create a fertilised egg called a zygote. the zygote undergoes mitosis (rapid cell division) and differentiation to produce a blastocyst then embryo.
internal fertilisation
involves the fusion of male and female gametes within a parent’s body. tends to occur between terrestrial animals.
external fertilisation
involves the fusion of male and female gametes outside a parent’s body. tends to occur between aquatic animals.
internal vs external fertilisation
Number of gametes produced (many/few):
(EF) Many - of both female and male gametes
(IF) Few - more male gamete than female
The environment in which this type of fertilisation usually occurs:
(EF) Aquatic
(IF) Terrestrial
How male gamete reaches the female gamete:
(EF) Sperm are released over the eggs
(IF) Sperm travels through the fallopian tube to the egg
Copulation aka intercourse (yes/no)
(EF) No
(IF) Yes
Chance of fertilisation and reason:
(EF) Low, because sperm are spread out in a big open area
(IF) High, gametes are protected from external environmental factors e.g. predators
Number of offspring/zygotes produced (low/high):
(EF) High
(IF) Low
Survival rate (low/high):
(EF) Low
(IF) High
Zygote development location:
(EF) Water
(IF) Fallopian tube
Parental investment:
(EF) No
(IF) Yes
Organisms involved:
(EF) Fish, frogs
(IF) Humans, kangaroos
advantages of external fertilisation
–> Low energy requirement to find a mate
–> A large number of offspring produced
–> No specialised structures required
–> Parental care is not essential
–> Offspring are spread widely = there less competition
advantages of internal fertilisation
–> Fertilisation is more likely to occur
–> Embryo protected from predators
–> Offspring more likely to survive
disadvantages of external fertilisation
–> Many gametes are unfertilised
–> Offspring are often not protected by parents; many die
Increased risk of predation due to environmental hazards
–> Offspring are mostly independent and must fend for themselves; more likely to die
disadvantages of internal fertilisation
–> Higher energy requirement to find a mate
–> Less offspring produced
–> More energy is required to raise offspring
–> Requires specialised structures
vegetative propagation
asexual reproduction method in plants where new plants row from parts like roots, stems or leaves without seeds.
Runners
e.g. cultivated strawberry plants and spinifex grass
runners are long, thin modified stems that grow along the soil’s surface
produce leaves, flowers and roots at every alternate node of the stem runner, so the runner can then be subdivided into new plants.
bulb
e.g. tulips, onions
a bulb is a shoot compressed into a shortened form.
fleshy storage leaves are attached to a stem plate, forming concentric circles around the growing tip.
new roots form from the lower part of the stem.
protect plant from adverse conditions and allow them to grow quickly when conditions are favourable.
tubers
e.g. potatoes
tubers are the swollen part of an underground stem or root modified to store food. Buds produced on stem tubers (called ‘eye’) give rise to new individuals.
cuttings
e.g. roses
cuttings are sections of a parent plant that are removed and grown as new individuals.
angiosperms
flowering plants
parts of flower and role.
male: (stamen)
–> anther: where pollen grains (male sperm cells) are formed.
–> filament: stalk that carries anther.
female: (carpal)
–> ovary: location of ovule production and fertilisation.
–> style: joins stigma to ovary.
–> stigma: sticky top surface of flower which pollen adhere to.
–> sepal: modified leaves, often green. protects the unopened bud.
–> petal: often modified to be brightly-coloured and scented to attract pollinators, increasing likelihood of pollination
pollination
the act of transferring pollen grains (male gametes) from the anther of a flower to the female stigma.
how does sexual fertilisation in flowers occur?
- pollen grains are transferred to the stigma of the flower. the pollen grain contains 2 male sex cells. the transfer of pollen could be done by a pollinator or wind and water dispersal.
- a pollen tube is created in the style from the stigma towards the ovary.
- two male sex cells travel down the pollen tube to the female ovule. it enters the ovary through an opening called the micropile.
- one male sex cell fertilises the ovule, developing it into a seed. the other male sex cell attaches to two cells in the embryo sac to form the endosperm. it provides starchy food for the seed to grow.
cross pollination.
Cross-pollination → pollen grains are transferred from the anther of one flow to the stigma of another flower of the same or different species.
benefits of cross pollination
greater variation in offspring
what are some strategies that plants possess that favour cross pollination?
e.g. the plant’s pollen matures at a different time to its stigma.
wind-pollinated flower
PETALS -
* small and inconspicuous, usually green or dull in colour
SCENT -
* none
NECTAR -
* none
ANTHERS -
* anthers protrude outside the flower so wind can easily blow it.
- abundant pollen grains produced
STIGMA -
* stigma protrudes from flower
*often long, feathery and sticky t o increase SA and trap air-borne pollen
POLLEN -
* very small and light grains; lots produced
bird-pollinated flower
PETALS -
* large and colourful, tubular shape
*sometimes no petals
SCENT -
* rarely; birds have little sense of smell
NECTAR -
* large amounts produced
ANTHERS -
* lower than stigma, colourful
*sometimes not enclosed by petals
STIGMA -
* higher than anther, colourful
*sometimes not enclosed by petals
POLLEN -
* sticky or powdery pollen; little produced
insect-pollinated flowers
PETALS -
* large and colourful, shaped to encourage specific pollinators
SCENT -
* present; insects are highly attracted to scents
NECTAR -
* produced at the base of petals so insect must enter flower to reach nectar
ANTHERS -
* enclosed within flower, lower than stigma
STIGMA -
* enclosed within flower, higher than anther
POLLEN -
* large and sticky grains; little produced
Ovulation
→ a part of the menstrual cycle when an ovary releases an egg/ovum
