Reproduction Flashcards
What is sexual reproduction
The creation of offspring by fusion of a male gamete and female gamete to form a zygote
Asexual Reproduction
Creation of offspring without the fusion of egg and sperm
4 types of asexual reproduction
Fission, Budding, Fragmentation, Parthenogenesis
What is fission and what animals use it
Adult organisms can simply split and divide into two individuals. These individuals can then move apart and continue living
- Cnidarians
What is Budding and what animals use it
Form of asexual reproduction where a bud forms that develops into an adult and breaks away from the main body
- Hydra
Fragmentation
This is an emergency form of reproduction where and adult undergoes physical trauma and regenerates after this - forming body from cinched head/tail.
- Planaria, Sea urchin/stars
Parthenogenesis
No fertilisation of female gamete. Offspring are identical to their mother (clones) as the egg alone is sufficient to develop into an adult organism
- Some lizards, hymenopterans, aphids, spiders, molluscs, fish
Clone
Group of genetically identical individuals from the same parent
What is an allele
Particular gene variant at a locus
What is phenotype determined by
The sum of an individuals alleles
What is a locus
A genes specific position along a chromosome
What are genes
Units of heredity that are made up of DNA segments
Diplod cell
2 copies of each chromosome
Haploid
1 copy of each chromosome
What is fertilization
Union of gametes
Why is meiosis required in sexual reproduction (not involving variation)
In sexual reproduction, meiosis is required to halve the amount of DNA in the gametes so that the amount of DNA after fertilisation is diploid, the required condition for all somatic ells
Two important changes in meiosis compared to mitotic reproduction
- Change in ploidy: go from diploid to haploid
- End up with 4 genetically different daugjter cells
3 aspects of fertilisation/meiosis that are responsible for variation
Independent assortment
Crossing over
Random fertilisation
What is independent assortment
Homologous pairs of chromosomes orient randomly at metaphase I of meiosis
In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs
What is crossing over
Recombining chromosomes, contributes to genetic variation by combining DNA from two parents into a single chromosome
What is random fertilisation
Any sperm can fuse with any ovum
How does variation arise in zygote
In humans, the fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations
Crossing over adds even more variation
Benefit of sexual reproduction
Increase genetic variation
Why is variation in heritable traits important
Allow adaptive evolution to occur
Why do sexually reproducing organisms have an advantage
When the environment changes rapidly, sexually reproducing organisms adapt faster than asexual organisms and thus outcompete them
Downside of asexual reproduction
Although asexual reproduction involves less energy to produce offspring, the species have a limited lifespan and will eventually die out. They eventually hit a change in their conditions that they cannot adapt to due to lack of variety between individuals
Monoecy/hermaphrodism
two sexes in the same individual
Dioecy
Specialised to produce only one type of gamete
Disadvantage of dioecy (3)
- Less efficient as only half of offspring can produce offspring (cost of males)
- Less efficient as energy wasted on mating (finding a mate, ensuring sperm finds egg,
- disastrous if isolated, features can be selected for (deer antlers) that may reduces survivor hood of males but is required to gain attention from females)
Disadvantage of Monoecy (loss of varation)
1/2 of animal species that undergo monoecious reproduction show between 20 and 80% selfing rates (own sperm fertilising own eggs)
- If a male and female gamete from an individual fuse, it will get a loss of variation
Disadvantage of Monoecy (energetically costly)
- Costly in terms of having to produce both male and female gametes (can be partially overcome by sequential hermaphrodism (switch dependant on size)
Main goal of sexual reproduction
bring egg and sperm together
Acrosome
Full of enzymes which are released when worm senses the jelly coat. The enzyme digests away the jelly coat, allowing the worm to bury into the surface of the egg
8 Step process of fertilisation
- Acrosome reaction to digest jelly
- Specificity via receptors on egg
- Binding triggers fusion of plasma membranes
- Need to avoid polyspermy: fast reaction via depolarization 1/10th of second
- Fusion also releases inositol triphosphate, causes Ca release in egg (wave)
- Ca wave triggers cortical vesicles to fuse with plasma membrane releasing enzymes
- Enzymes degrade receptors and harden vitelline membrane = slow block (10-60sec)
- Nucleus only is internalized and fuses with female.
what does external fertilisation need
- Need aquatic environment to allow sperm motility and prevent drying out of egg (and zygote)
Why does quantity assist in external fertilisation
More gametes released increases probability of gametes meeting and counters effect of predation
Protective mechanism involved in external fertilisation
Camouflage (fish eggs are white on the bottom and black on the top)
Guarding behaviour
How is timing involved in external fertilisation
Synchronisation of male and female gamete release is essential
- Environmental cues – day length, change in temperature, change in environment, usually indicating favourable season for breeding; tidal changes
Specific cues from individuals of the same species:
- In marine invertebrates (clams, sea urchins, sea cucumbers), pheromones may be involved.
- In fish and other aquatic animals with well-developed eyes, social stimulation or courtship behaviour is often important.
Benefits of internal fertilisation
- Safer for gametes
- Fewer gametes required (less costly)
- Synchronisation less of an issue
- Allowed the transition to a permanent land/terrestrial habitat (found in most terrestrial animals)
Behavioural adaptations of Internal fertilisation (3)
- Copulation (also called coitus) is the physical joining of male and female accessory sex organs to transfer sperm
- Multituse of behavioural mating strategies, usually stimulated by pheromones - chemical signals that females emit to signal sexual receptivity
- Requires a male and female to come close enough together for long enough to allow sperm transfer
Why do male and female have different mating strategies
Due to the nature of their gametes: Sperm are energetically inexpensive - egg is expensive
Why does mating behaviour originate
- Due to gamete anisogamy (unequal gamete size), female has fewer gametes (eggs), each of which is more costly to produce than a male gamete, so will try to choose the best male(s) – highly selective mating behaviour.
- Males can produce more gametes so will benefit from more mating’s – behaviour aimed at mating with as many females as possible (impress and collect females).
Monogamy
Both male and female maintain single partner throughout entire mating season
Advantage of monogamous behaviour
In species where the young are particularly vulnerable and may benefit from protection by both parents, monogamy may be an optimal strategy.
Why are birds monogamous
- Lay eggs that have to be kept warm (and protected)
- Chicks need to be fed and protected after hatching
- Too difficult for one parent so would evolve shared system that benefits both parents.
Advantage of internal fertilisation
Less cost of wasting gametes, easier to get synchronisation, lower danger of eggs being eaten/damaged
Challenge to overcome with internal fertilisation
Adaptations to allow adults to be bought together
Gonads/Primary sex organs
Where gametes are produced
Secondary sex organs
Function to ensure gametes meet
Oviduct
Area where sperm is collected, where the egg travels to be fertilised
Spermatheca
Insects - allows females to store sperm for up to a year
Advantage of spermatheca
Allow females to wait for the right time, when conditions are favourable and health is most optimal, to fertilise the egg
Ovary
Structures designed to grow the egg
Why can sperm not fertilise the egg at all times of the monthly cycle
Cervix is plugged with mucus under influence of the hormone testosterone
Vestibular gland
supply mucus that allows for intercourse.
Oocyte
Partially developed egg
Function of cilia in oviduct
Convey the egg to the uterus
What is the endometrium
Uterus lining that contains many blood vessels
What is the vagina
A muscular but elastic chamber that is the repository for sperm during copulation and serves as the birth canal
Function of seminal vesicle and accessory glands
Supply nutrients to allow sperm to activate, swim, and supply in the reproductive tract and regulate pH
Vas Deferens
Sperm travels along vas deferens, a duct which leads to the penis
Secondary sex organs in males
vas deferen, urethra,
Why are male primary gonads stored outside the main body
Temperature regulation
Function of uterus
Specialised part of oviduct to allow for internal embryo development
Intromittent organ
Structure that enters female reproductive tract and deposits sperm
Aedeagus
insect penis
How does female choice lead to rapid evolution of genitalia
Choose males with genitalia that best stimulate them during copulation of fit better - thus sons will have superior mate-attracting potential (by better female stimulation).
How does sperm competition lead to evolution of male genitalia
For females that display promiscuity, when the ejaculates of two or more males compete to fertilise an ovum.
Example of sperm competition
In dragon selection has favoured males with genitalia that remove rival sperm from the female.
Dragonfly penis adaptation
Dragonflies penis has a brush to brush out any sperm that is already present
Molluscs/sea slug copulation
- 2 penises which fertilise each other
- Sperm pumping takes about 10 minutes
- Then the sea slugs will separate
- They do not retract their penis, and their penis will break off inside the other individual
- Penis has spikes going backwards that prevent it from leaving the reproductive tract
- This prevents another sea slug from depositing their sperm
- Can keep having intercourse until they run out of penis
2nd male advantage
2nd male physically dislodges stored sperm via adaptation and or via fluid accompanying sperm
Sexual conflict
Sexual selection that only benefits males - Favours traits that increase the fitness of one sex even when it is costly to the other
Examples of sexual conflict in vertebrates
- In many reptiles, fish and felines, the male may have hooks or bards on or near his penis that attach to the female during copulation
- Dog penises also swell during copulation and are difficult to remove until completion
- Sharks have been known to severely bite females to hold them during copulation
Why do female birds only possess one gonad
- Adaptation for flight, get rid of excess weight
Do birds have an intromittent organ
No
How have birds evolved to copulate
Have evolved behavioural adaptations so they are able to bring the cloaca and can manage to mount each other and connect cloaca
How do male ducks reproduce
They evolved huge “ballistic” penises that are different from mammalian ones - being lymph filled and rapidly everted directly into the female ducks vagina
How have ducks evolved to counter forced mating
Can only let left handed corkscrew properly into vagina once the female relaxes and allows the entry of the penis - only happens with wanted & consenting sex
