Reproductive Strategies
- Created by: Emily Cartwright
- Created on: 26-05-14 18:32
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- Reproductive Strategies
- Asexual Reproduction
- 1 parent
- Genetically identical offspring
- Involves mitosis
- Diploid somatic cells produced
- Advantages
- It produces clones - if one is successful, they are all successful
- It requires less energy as a mate is not needed
- It is fast and can produce rapid population growth
- It allows species to colonise a stable environment and is a good strategy when environmental conditions are favourable
- Disadvantages
- Lack of genetic variation within the population leaves all the individuals susceptible to environmental changes or new diseases entering the population
- Sexual Reproduction
- 2 parents
- Genetically different offspring
- Involved meiosis
- Haploid gamete cells produced
- Advantages
- It produces genetic variation in a population
- It is a good strategy when environmental conditions are changeable
- Some offspring will survive unfavorable conditions, which allows the species to adapt by natural selection
- It can involve the production of a resistant phase in a life cycle, such as seeds which can be dispersed far away, reducing competition between parent and offspring
- Disadvantages
- It is slow
- It requires a lot of energy and a large % of gametes are wasted
- Gametes
- These are specialised cells and develop differently from normal body cells that divide by mitosis
- In normal body cells, chromosomes exist in homologous pairs (one from the male and one from the female)
- During fertilisation, the haploid sperm fuses with the haploid egg to produce a diploid fertilised egg
- The zygote formed then divides many times by mitosis to grow into a new individual
- These are specialised cells and develop differently from normal body cells that divide by mitosis
- Reproductive strategies in vertebrae
- All vertebrae reproduce sexually, however different groups of vertebrates have different strategies in terms of;
- How fertilisation occurs
- The development of the embryo
- The degree of parental care given to the offspring
- As vertebrates evolved from water to land the following changes occured;
- A change from external fertilisation to internal fertilisation
- A reduction in the number of gametes produced
- A reduction in the number of offspring produced
- An increase in the degree of parental care given to the offspring
- Fish
- Fish live in aquatic environments and exhibit external fertilisation
- Gametes are released into the water. Water provides a medium in which the sperm can swim
- Large numbers of gametes are produced because the chance of fertilisation is low - many gametes are eaten or carried away by the current
- If fertilisation does occur, the embryo is entirely dependent on the yolk supply for it's development
- Amphibians
- Although amphibians have colonised to land, they must return to water in order to reproduce
- Amphibians exhibit external fertilisation
- They 'couple' during reproduction to increase the chance of fertilisation as the sperm and ova are released in close proximity
- Amphibians do not produce as many gametes, because fewer are wasted
- Most amphibians show no parental care and therefore produce large numbers of embryos which are entirley dependent on the yolk for their development
- Reptiles and Birds
- Both of these groups have successfully colonised to land and do not need to return to water to reproduce
- They both exhibit internal reproduction
- Fusion of gametes occurs within the female's body
- This greatly increases the chance of fertilisation and therefore fewer gametes are produced
- Reptiles produce large numbers of eggs and show little parental care
- Birds lay fewer eggs and show a large amount of parental care which increases the chances of offspring reaching their reproductive age
- Mammals
- Exhibit internal fertilisation
- Low numbers of gametes are produced as the chances of internal fertilisation are high
- In placental animals (humans), the embryo gains nourishment from it's mother's blood via the placenta
- The embryo develops inside the mother's uterus and is protected from predators or adverse weather
- The young of mammals are born relatively well developed
- Mammals show a high degree of parental care which increases the of offspring reaching sexual maturity. Therefore, there are low numbers of offspring produced
- Insects
- Insects have developed many strategies to colonise terrestrial habitats and one of these is the use of internal fertilisation
- Most species lay eggs covered with a waterproof layer
- The life cycle of insects differ. species either show complete or incomplete metamorphosis
- Complete metamorphosis
- The adults produce eggs which develop into larvae
- Larvae are structurally different from the adult and are designed for feeding
- Next comes the pupal phase. During this, complete reorganisation of the tissues takes place
- Finally, the adult emerge, it designed for reproduction
- Next comes the pupal phase. During this, complete reorganisation of the tissues takes place
- Larvae are structurally different from the adult and are designed for feeding
- The adults produce eggs which develop into larvae
- Incomplete metamorphosis
- The adults produce eggs which develop into nymphs
- The nymphs resemble the adult and progress through a series of moults to become fully grown
- There is no pupa stage
- The nymphs resemble the adult and progress through a series of moults to become fully grown
- The adults produce eggs which develop into nymphs
- Complete metamorphosis
- Insects have developed many strategies to colonise terrestrial habitats and one of these is the use of internal fertilisation
- All vertebrae reproduce sexually, however different groups of vertebrates have different strategies in terms of;
- Asexual Reproduction
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