Lecture 2 Sexual Production: What Is It and Why? Flashcards
What is sexual reproduction?
Perpetuation of the species
Requires male and female gametes (halving of chromosomes) then subsequent fertilisation
What are the advantages of sexual reproduction?
Hybrid vigour
Genetic variation and evolutionary flexibility
Maximise individual and species survival
Ability to respond rapidly to changes
What are the disadvantages of sexual reproduction?
Requires both male and female (sometimes not both available in the population)
What are some possible solutions if both sexes are not present in the population?
Parthenogenesis, gynogenesis, hybridogenesis
What is parthenogenesis?
Within the female, cells duplicate without to make a replicate of itself with no male genetic material. Either by moving from female egg cell (2n) to diploid egg (2n) without division so diploid thus no need for fertilisation. Or normal oocyte (n) is fertilised with another oocyte (n) to form diploid zygote
/main solution we learn about, only female!
What is gynogenesis?
Female produces eggs with the full complement of chromosomes (2n) but relied sperm from any other species to activate zone pellucida causing growth of ovum but only retains genetic material of ovum
/’gyno-‘ means women, so out of gynogenesis and hybridogenesis, gynogenesis is more reliant of women
What is hybridogenesis?
Female produces haploid eggs which are fertilised by a male that must be from a closely related species causing development. So the hybrid organism will have genetic material from both male and female species. However during gametogenesis, the hybrid eliminates genetic material from male and only retains the original female to form ovum.
Which animals are amniotes?
Mammals, reptiles, birds
Which animals are anamniotes?
Amphibians, fish
What are amniotes?
Developing embryos have an amniotic membrane, a specialised formation of extra embryonic membrane which surrounds the developing embryo and fills with cushioning amniotic fluid. Internal fertilisation. Amniotes bypass the aquatic larval stage due to fluid around amnion providing nutrition. Reptiles and birds lay cleidoic eggs on land, the egg contains all the food the embryo needs to develop into a hatchling. Mammals have evolved to live birth.
What are anamniotes?
Developing embryos do not have amniotic membrane. Secondary egg cells are laid into water, where fertilisation takes place externally
How are vertebrates categorised into modes of sexual reproduction?
Vertebrate group (taxa): mammals, reptiles, birds are amniotes. Amphibians, fish are anamniotes Environmental conditions
What is oviparity?
Oviparous animals lay eggs only
All birds, most fishes, amphibians and reptiles
What is viviparity?
Viviparous animals give birth to live young.
There is a continuum of minimal to invasive embryo dependence on the mother
Ovoviviparity: embryo develops inside mother but does not rely on her for nourishment
Viviparity: embryo develops inside mother and dependent on her for nourishment.
What is genotypic sex determination?
Determined at fertilisation because male and females have different chromosomal karyotypes. Leads to formation of separate sex-specific reproductive tracts.
