9A - Sexual and Asexual reproduction

What is genetic diversity?

The genetic diversity of a population refers to the amount of genetic variation

• that exists between individuals.

How is genetic diversity measured?

The populations genetic diversity is measured by a populations gene pool;

• Gene pool: the total number of individual alleles within a particular population

• A larger, or more diverse, gene pool contains a greater variety of different genes and alleles, meaning that the population will have a greater variety of genotypes and phenotypes.

Why is genetic diversity important?

Genetic diversity is important in protecting the longevity of a species by guarding against disadvantageous environmental changes, like new diseases or predators.

• The larger the gene pool, the greater that population’s resilience to environmental change.

sexual reproduction

a specific reproductive strategy that involves the fusion of two haploid gametes, a process known as fertilisation, to form a single, genetically unique, diploid zygote.

types of sexual reproduction: Oviparity

• eggs are released into the external environment

• The embryo develops from nutrients inside the yolk.

• The organism grows with little development inside the mother.

• For most birds and insects, fertilisation occurs inside the mother, while most fish will release unfertilised eggs into the water to be fertilised externally by free-flowing sperm (ovuliparity).

types of sexual reproduction: viviparity

• The embryo develops inside the mother’s body.

• is born after a period of gestation.

• Fertilisation occurs inside the mother, and the organism grows and receives nutrients inside the mother during gestation.

• For many sharks and snakes, the embryo will develop inside an egg that is retained in the mother’s uterus (ovoviviparity), while for most mammals, the embryo will develop inside a fluid-filled sac inside the mother’s uterus.

Sexual reproduction in plants: Angiosperms

Pollination occurs when pollen (male gamete) is collected by the stigma of the flower and fuses with the ovule (female gamete).

The embryo that develops will become a seed, which contains nutrients from which an immature plant can begin to grow into a new plant under the right conditions.

Biotic pollinators

living organisms such as insects or birds which are often attracted to the brightly coloured petals, inviting smell, and nutrient-rich nectar.

Abiotic pollinators

non-living methods such as wind or water. This method allows the plant to focus on maximising pollen dispersion rather than attracting pollinators. Such plants will often lack colourful petals and smells and will hang downwards to enable wind dispersion

Advantages of sexual reproduction

• Increases genetic diversity of a population by allowing for recombinant offspring.

• Improving disease resistance by promoting the presence of different alleles

• Combining the genetic material from two gametes reduces the chances of an offspring inheriting a genetic disorder that might be carried by one parent.

disadvantages of sexual reproduction

• The cost of male progeny

• The time, energy, and resources it takes to attract and find a mate

• The risk of transferable diseases associated with sexual intercourse

• The risk of losing offspring outside influences such as embryo damage.

Asexual reproduction

Some organisms can reproduce without the fusion of gametes and therefore do not require a mate.

• Offspring/daughter cells are clones of each other and of the parent

Binary fission

• Occurs in simple prokaryotic organisms such as bacteria, though similar form of binary fission also occurs in more complex, multicellular organisms.

• The development of a new organism by the parent organism splitting into two. Involving the equal division of the cytoplasm.

• Parent nucleus divides by mitosis

• Equal distribution of cytoplasm to produce two new daughter cells.

Budding

• The development of a new organism or parts of an organism from an outgrowth of the parent

• Unequal distribution of cytoplasm

• New organism may detach from the parent and grow to adult size.

• Can remain attached to parents.

Fragmentation

• Occurs in simple eukaryotes such as worms and sea stars, as well as many species of plants.

• Involves a parent organism breaking into separate fragments, each of which is capable of independently developing into new, separate organisms identical to the original

Vegetative propogation

• A type of asexual reproduction that allows a plant to reprodce without the need of seeds.

• Involves a vegetative section such as roots of leaves breaking away from the original plant.

• Independently growing into a new plant

Natural vegetative propogation

• occurs when a part of a plant naturally falls off or plants itself, and then the part grows into a plant.

  • Blubs, tubers, runners, rhizomes, corms

Artificial vegetative propogation

• Occurs when a person deliberately manipulates or ‘cuts and pastes’ a part of a plant to stimulate vegetative propagation.

  • Cutting, layering, grafting

Grafting

the stem of one plant is attached to the stem and roots of another. The two plants continue to divide normally, and their tissues gradually fuse.

• Stock: the ‘host’ part of the plant

• Scion: the pierce of the stem which is attached.

Sporogenesis

• Sporogenesis typically occurs in many plants, as well as fungi, algae, and moulds.

• It involves the formation of spores, which are small haploid units that form on the surface of the organism and are dispersed into the surroundings (often via water or air

Parthenogenesis

• A rarer form of asexual reproduction

• An embryo can develop from a female gamete alone, without the need for a male gamete to fertilise it.

• This process is sometimes referred to as a ‘virgin birth’ -> eggs produced via mitosis develop into a new organism that is identical to the female.

Advantages of sexual reproduction

• Asexually reproducing populations grow faster than sexually reproducing populations (exponential growth)

• offspring are identical clones of the parent. This is especially important for organisms that have adapted a phenotype that is fine-tuned to survive in a particular environment

• does not require an organism to find a mate to reproduce, meaning that the organism does not have to be mobile

• requires very little parental investment and removes the need to protect fragile offspring.

Disadvantages of asexual reproduction

Genetic diversity is low and asexually reproducing populations may suffer during rapid environmental change.