cycle 7 Flashcards
what is sex?
sex is the exchange of genetic material.
How does sex work in sexual organisms
In sexually reproducing organisms, gametes fuse to generate new combinations of alleles in the off-spring
- typical of animals and plants, most eukaryotes
- for example in humans through sex and combination there are more than 10^600 allele combination, which is why no two humans are identical
how does sex work in asexual organisms?
In asexually reproducing organisms, sex can happen by acquiring DNA from another organism or their environment
- typical in bacteria and archaea
what is the name of sexual reproduction with two organisms?
Individuals have separate sexes and need a pair= dioecious (ie. two house)
E.g humans, lions
what is the name of sexual reproduction with one organism?
Individuals are both sexes = monoecious (one house)
= hermaphrodites (animals)
what is typical of sex in plants?
- plants are monoecious and each individual develops the reproductive tissue of both sexes
what is atypical of sex in animals?
- hermaphrodites
- Simultaneous: simultaneously male and female
- E.g earthworms, individuals have ovaries and testes
- Sequential: starts as one sex and develops into another
- E.g bluehead wrasse, starts as female (yellow), if the dominant male dies, a female will become male
E.g clownfish male can become female
When sex changes occur how does an individual know when it should be female and when it should be male?
= size advantage model
- in protogyny start as female, since the small size has more eggs, but when size grow more reproductive success as male, so you transition
- protandry first male then female
(Gamete production is lower when a smaller female, but with time egg production ability gets bigger when female so you change.)
explain the rarer types of sex occurring in ekaryotes? What type of species?
- Usually single celled eukaryotes called protist
- Have different mating types(at least 2+)
- Gametes of different mating types fuse
- Exchange nuclei between mating types
Which type of reproduction does not involve sex?
- asexual reproduction
- the new individuals are clones and are genetically identical, this means there has been no sex and no exchange of genetic material
- Ex. pieces of potato plant, tuber can be planted and new individuals will grow
- Ex. strawberries produce runners that produce new roots and new individuals plants can grow that are exact copies
What is asexual reproduction in animals?
- pathogenesis
Methods
1) offspring can develop from unfertilized diploid egg (are clones)
2) meiosis can occur in DNA of haploid egg that will replicate and go from haploid to diploid egg (not clones) - ex. hammerhead sharks
How does asexual reproduction work in unicellular organisms?
- divide to reproduce
~occurs in bacteria and archaea via binary fission
~or in unicellular eukaryotes where they divide by mitosis - produces clones
how does sex in bacteria and archaea work?
- They reproduce asexually, but they can undergo genetic exchange between individuals: = SEX
- eg. bacterial conjugation occurs by transferring plasmids (circular bits of chromosomes inside cell) through conjugation into another cell), you can can also have DNA from other organism go into cell),or have DNA from virus grab DNA from bacteria and transfer DNA into another cell.
What are the limitations of sex?
sex is costly, sex is risky, sex is inefficient
why is sex risky?
- Finding a mate is time-consuming, takes resources
- In search exposed to predation, at higher risk of sexually transmitted disease
why is sex costly?
- Only ½ of genetic material is inherited
- For every generation, sexual individuals pass on 2 times less of their genetic material
- Two fold cost of sex
Why is sex inefficnet?
- Producing males reduces reproductive output
- Only females “grow” new off-spring, so males(only bring sperm) do not add to the population
- Asexual populations grow faster
So if sex is risky, costly and inefficient why did sex evolve?
- must of been evolutionary benefits, sex introduces greater population variation, which in turn means there can be greater adaptability (ie. can adapt quicker to new environments), and make better combination of alleles)
How does sex generate variation?
- sex generates the variation not possible through asexual reproduction
- get gene exchange, independent assortment of chromosomes, recombination, fusions of maternal and paternal chromosomes (get the new combination of alleles)
- thus offspring are genetically distinct from both parents
What is the lottery model?
- sexual populations have greater diversity of offspring increased probability of some offspring surviving/having favourable phenotypes
What are the advantages of sex and alleles?
- by lottery sex can bring beneficial alleles of different genes together
- Sex makes it easier to remove “bad” allele. If by lottery independent assortment brings all the bad alleles together this result in a very low fitness that is easily selected against and removed
what is the summary explanation for why there is sex?
- life started out through asexual division
- most life forms engage in some form of sex, in many different ways, so it must be a good thing
- the benefits must have outweighed the costs for sex to have evolved
- generates diversity – better chance at lottery
- makes new and improved combinations of alleles
- generates genotypes of higher fitness more quickly
- makes it easier to remove “bad” alleles
Do asexual organism have the ability to bring beneficial alleles together?
- to start all organisms have decent fitness, but have unique genetic variations:
- beneficial variants (1,2,3) cannot be combined together in asexual reproduction… = clonal interference
- unless there is sex: you can Exchange 1 and 2, Exchange again 1+2 hybrid and 3 then generate offspring that have most beneficial combination
What is sexual selection in animals?
- Struggle for mates
- Traits favoured are those that increase mating success, increase individual fitness
- Can result in exaggerated traits that can reduce survival
Ex. lions big with big mane
what is intersexual selection?
- one sex chooses= mate choice
- animals it is usually females that chooses mates based on display and physical traits from males
- males compete to gain female’s attention
What are examples of traits that have evolved due to intersexual selection?
what are the displays/ornamentation animals can have?
- elaborate courtship displays/calls
- Ornamentation
- Ex. peahens vs peacocks, the male peacocks have very elaborate feathers. Cumbersome since not as agile
- Bowerbirds: make display nests. Cumbersome because time consuming and only built to attract woman
- Peacock spider: have mating dance
Which sex chooses?
- Sex that invest more parental care is usually the chooser
- sex that has relatively fewer contributions to the next generation is choosier
- Why? must be selective to ensure quality of off-spring
- Thus females are usually the “choosier” sex
what is intrasexual selection?
- individuals of one sex compete amongst themselves for mates of the opposite sex
- Ex. fighting of elk (antlers bonking) or stag beetles
what are the results of intrasexual selection?
- Males monopolize access to females
- Do this by outcompeting rivals or controlling a resource that is important to females, eg. food, territory, thus enabling direct control of females
- Ex. bowerbirds have intraselection as well since they are trying to outperform and outcompete other males
How do females have intraselction?
- Females can compete with each other too
for territory, for access to mates, for resources - Nature of competition different
what is sperm competition?
- A more discrete type if competition
- swimming speed – fastest sperm to get to the egg
- scrapers - scrape out sperm deposited by other males
Ex. dragonflies, male can mate with females again and scrape out other men’s sperm. Now only his sperm is there - mating plugs - after mating, leave a plug to prevent other males from mating
Ex. moths
What are the results of the mating game?
- male of highest fitness wins the mating game and produces the most offspring
- Male lowest fitness loses the game and has no offspring
- Males have higher potential fitness
- Females, have minimal deviation from mean with highest fitness only having slightly more offspring. This is because females are removed from the mating game when rearing offspring. So the other females of lower fitness have opportunities to mate
- Average fitness is the same for both sexes
- males and females have difference in choice and strategy
conclusion on males from mating game
- reproduction is mainly limited by access to females
- individual fitness can vary widely
- higher potential fitness
conclusions on female from the mating game
- have limited gametes, must spend time growing and rearing offspring
- must choose mates wisely(limited opportunities) to maximize the quality of their offspring
- individual fitness often closer to the mean
What are the benefits of being choosy with reproduction?
Direct benefits
- attractive individuals are good parents (ie. more chance offspring survives)
- can gain food, territory, protection for offspring
E.g giving nuptial gift of fly for female to eat
Indirect benefits
- attractive individuals have good alleles (lower chance of parasites)
- improve survival or attractiveness of offspring
what is sexual dimorphism?
- when sexual selection gets very strong
- different sexes have distinct differences in size or appearance
- oftentimes males will get bigger and brighter in colour
why are males usually more affected by sexual dimorphism?
- dimorphism is impacted by the relative role in parental care
- males will oftentimes have lower parental investment
why do females usually provide the most parental care? And what are the results?
- when rearing offspring females become unavailable for reproduction, (less opportunities)
- male competition for females is high
- males under stronger sexual selection
- ex. grizzly bear
What happens when males provide the most parental care?
- availability of males is limited, males can be choosy
- females under stronger sexual selection
(will become more showy) - Ex. male seahorse, females deposit fertilized eggs in male pouch, and he is the one that gives birth to the babies,
- ex. red phalaropes (females big and red, since they defend territory while the males care for offspring)
What happens when both sexes invest heavily in parental care?
- this is biparental care
- males and females removed from seeking additional mating opportunities (spend time caring for offspring)
- both sexes compete for mates, both sexes choosy
- sexual selection acts on both sexes, little to no dimorphism
- Ex. humans and emperor penguins
IS there sexual dimorphism in humans? what is selected for?
- still some sexual dimorphism
- What traits are selected? Is it beauty, intelligence, wealth, parenting skills? Difference in choices long term vs short term?
