Why have sex? Flashcards
(20 cards)
What is facultative asexual reproduction?
Switch to asexual reproduction
- when environment is constant
- parent survived, so if offspring inherits same genes, will also survive
Switch to sexual reproduction
- when environment varies and is changing
- offspring could benefit from new combination of genes that might be suited to new environment
What is evolutionary ratchet?
- individuals in asexual population eventually acquire deleterious mutations (high “genetic load”) that they can’t remove
- by chance, some individuals without those mutations die
- eventually, species goes extinct
- less severe if heterozygosity is maintained
- less of an issue for organelle genomes
- have many copies
What is heterosis?
The tendency of a crossbred individual to show qualities superior to those of both parents
What is the likely evolutionary timing of origin of sexual reproduction?
- 1.2 bya
- Bangiomorpha pubescens (similar to red algae)
- fossilized evidence of differential spore/gamete production
What is genetic load?
It’s the difference between the fitness of an average genotype in a population and the fitness of some refernce genotype, which may be either the best present in a population, or may be the theoretically optimal genotype.
What is uni-parental inheritance?
- The transmission of genotypes from one parental type to all progeny
- All the genes in offspring will originate form only the mother or only the father
What is maternal inheritance ?
Genetic material transmitted by the mother to her offspring
What is the role of polyploidy in asexual reproduction?
multiple additional copies of every locus/gene can give you a buffer zone against negative mutations
What are the basic principles of the deleterious mutation hypothesis?
- recombination itself promotes DNA repair
- recombination lets you make some offspring without mutation
- heterozygosity is good
What is the advantages and disadvantages of asexual reproduction
- clones
- 100% of your genes
- 1:1 production of offspring
- mutations occur that reduce fitness and eventually there is an accumulation of such mutations
- This would eventually lead to the species going extinct
Explain the mechanisms to ensure maternal inheritance of organelles
- don’t let it enter
- actively destroy
- abort embryos with bi parental mtDNA
- sperm mitochondria are over-replicated (more mutations) and overworked
- bi parental inheritance
- selfish elements within mitochondrial genome
- recombination among genetically distinct partners
Explain the mechanisms that ensure uni-parental inheritance of organelles
mat A is used as an example
- a homeobox domain
- determines which partner transmits mitochondria
- a hierarchy is presence within the domains
What is the mechanism of alternative meiosis by which asexual whip-tail lizards maintain high heterozygousity?
- start with a diploid gamete (one chromosome from mom one from dad)
- go through an extra replication stage so they end up with 8 chromatin (4 from mom and 4 from dad)
- double again (the same time that humans double)
- recombine
- pair up “like with like” chromosomes
- this leads to crossing over that doesn’t make for any new information on any chromosome
- mom pairs with mom copy and dad pairs with dad copy
- recombination actually does occur - can’t tell and recombination result in anything new
- split up chromosomes
What are the disadvantages of sexuality?
- you pass on less of your genes (relatedness)
- there is a much lower rate of production of offspring
- sex is costly in terms of time and resources
- sex is costly in terms of survival
What are ways to solve asexuality problems?
- prokaryotes use conjugation and transformation to transfer genes
- maintain polyploidy
- have unusual mechanisms for maintaining asexual reproduction (alternative meiosis)
Explain the role of conjugation/transformation in prokaryotic asexual reproduction
allow for the chance to replace/repair mutations … they have buffers against deleterious recessives due to polyploidy, but this is costly to maintain.
Why do we see two sexes?
- mitochondria and the co-evolution of mtDNA and nDNA
- need cytoplasm to come from one parent to reduce exposure to cytoplasmic parasites
What is the big idea of the mitochondria being maternally inherited?
- mitochondria do not play well with other mitochondria and other nuclei
- within one cell, you often have a high co-evolution of mitochondrial DNA and nuclear DNA within the cell because the two DNA types need to co-evolve and change in a way that they are “compatible” because a huge majority of proteins needed in the mitochondria come from the nucleus and then get transported over to the mitochondria
- there are also genes in the mitochondria that code for the mitochondria
- for all the proteins to work well together within the mitochondrial, the genes in the nucleus and in the mitochondria need to have co-evolved so that they are compatible enough with each other
How does mitochondrial inheritance work with slime molds?
- matA is the one that is responsible for transmitting the mitochondria
- the order of priority of who passes on the mitochondria goes depending on which organisms pair
- more than 2 sexes requires many more steps to make uniparental inheritance work
What is recombination load?
Where you have a reduction in fitness from sexual recombination
