Flashcards in The Reproductive System Deck (23):
What the different modes of reproduction?
What is asexual reproduction?
Offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes and almost never changes the number of chromosomes.
What are the 3 different mechanisms of asexual reproduction?
1) Fission= Whole Cell division used by prokaryotes
2) Budding=outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals. Budding occurs commonly in some invertebrate animals such as corals and hydras. Breaks away from main body
3) Fragmentation= breaking of the body into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow.
4) Parthenogenesis: Some animals produce offspring via an egg but WITHOUT fertilisation- egg develops into a complete individual without being fertilized
What is sexual reproduction?
Combination of (usually haploid, or having a single set of unpaired chromosomes) reproductive cells from two individuals to form a third (usually diploid, or having a pair of each type of chromosome) unique offspring.
What are some different reproductive strategies to enhance evolutionary fitness in animals for sexual reproduction?
1) Synchronise release of games= Increase chance of fertilisation
2) Allow competition to determine sexual selection
What are the advantages and disadvantages of sexual reproduction compared to asexaul reproduction?
1) Sexual- Generates diversity= Offspring will have new set of genes which could allow it to compete better
2) Have 2 parents= Could provide more care for offspring
1) Slower reproduction rate
2) Have to find a suitable mate
ADV of Asexual:
1) Can reproduce much more= Only need favourable conditions to colonise
2) No fertilisation needed
3) Can quickly colonise= Each individual able to reproduce
4) All are identical= If parents are successful, their offspring will also be successful
DIS of asexual:
1) All are same= No genetic diversity= Little variation
What does fertilisation require?
Internal or External aquatic medium
External: Sperm will have to swim out, ovum attracts sperm towards it
What is external fertilisation?
A sperm cell unites with an egg cell in the open, rather than inside a specialized organ within the body of a parent. Releasing eggs and sperm into water is called spawning.
What is the risks and benefits of external fertilisation?
-Results in the production of a large number of offspring
-Easier to find mates as the gametes released can drift (wind, water etc).
-More genetic variation
-Environmental hazards such as predators reduce the change of surviving into adulthood.
-Large amounts of gametes go unfertilised and wasted= Need to produce many to increase probability of success
-Not guaranteed that sperm will come in contact with eggs
-Greater chance of desiccation of gametes/zygotes.
What is internal fertilisation?
-Union of an egg cell with a sperm during sexual reproduction inside the body of a parent.
-For this to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract.
What are the benefits and risks of internal fertilisation?
-Increase chance gametes meet
-greater chance of successful fertilisation
-More protection against outside environments and predators, and therefore a higher chance of surviving until birth.
-More selective of their mates
-Less chance of desiccation of gametes
-Harder to bring both male and female into intimate contact
-Limited amount of offspring being produced at any given time.
-Higher risk of sexually transmitted diseases being passed on.
What are the 3 modes of internal fertilisation? (NAMES ONLY)
What is Oviparous?
Producing eggs that lay outside the body
Examples: Spiders, reptiles, birds
Monotremes= Mammals but lays eggs e.g. Platypus
What is Viviparous?
Giving birth to living young that develop within the mother's body rather than hatching from eggs. They are attached to placenta
Examples: Humans, all mammals apart from monotremes
What is Ovoviviparous?
Producing eggs that are hatched within the body, so that the young are born alive but without placental attachment
Examples: Fish, lizards and sharks
Nutrients come from egg NOT mother
What are some examples of strategies to ensure survival and competition?
!) Snails and 'love darts'= Slow, one of snails shoot calcerous dart into into the other to increase survival of the sperm= Form of COURTSHIP, not actual mating mechanism
2) Sea urchin parties= Mate in large numbers
3) Larger brained species have longer gestations (Carrying of embryo) and fewer offpsring= Offspring will get maximum care needed
What are the different mating systems?
1) Monogamy: Only have one partner at a time, less than 10% of mammals, most common in birds
2) Promiscuous: No pair bonds, e.g. chimpanzees
3) Polyandry: One female, lots of males= VERY rare e.g. mole rats
4) Polygyny: Most common system in mammals (80%), intense male competition, one male will mate with more than one female
What is sexual dimorphism?
Difference in morphology between male and female members of the same species
Difference in size, colour to increase mating success e.g. increasing chances of attracting a mate, supporting production of eggs
What is hermaphroditism?
The condition of having both male and female reproductive organs
Variation on sexual reproduction= Both partners can act as 'female' or 'male'
What are the 2 forms of hermaphroditism?
1) Simultaneous hermaphroditism: An adult organism that has both male and female sexual organs at the same time= Could self fertilise but most do not, occurs in habitats where it is hard to find another member of the species
Example: Sponges, sea anemones, tapeworms, snails, and earthworms
2) Sequential hermaphroditism: Change from one gender or the other depending on the circumstances, individual changes sex at some point in its life
1) Protogynous: First female than male , Fish- 75% of all fish species, e.g. wrasse
2) Protandrous: First male than female e.g. Clownfish
How does sex determination and differentiation work?
1) Start off with Ovum= Only have X sex chromosome
2) Can either be fertilised by sperm with Y OR sperm with X chromosome
3 levels of difference between males and females:
1) Genetic= Embryo with XY sex chromosome OR embryo with XX sex chromosome
2) Gonadal: Tests or Ovaries present
3) Phenotypic: Apparent anatomic sex but some can be untrue
What is congenital adrenal hyperplasia?
Autosomal recessive disease
-Inherited enzyme problem in biosynthesis of cortisol
-Deficiency of 21β-hydroxylase leads to reduction in cortisol and build up of androgen steroid precursors from adrenals (including ultimately testosterone).
-High levels of testosterone= Masculinise features even though they are genetically female