Week 6 Reproduction Biology PDF

NEW LECTURE - ANIAL DEVLEOPMENT AND REPRODUCTION - Learning outcomes - Understand how gametes are produced, find each other and what happens at fertilisation - Be able to envisage the early stages of development from fertilised egg to late gastrula - Understand how early devel...

NEW LECTURE - ANIAL DEVLEOPMENT AND REPRODUCTION - Learning outcomes - Understand how gametes are produced, find each other and what happens at fertilisation - Be able to envisage the early stages of development from fertilised egg to late gastrula - Understand how early development differs in protostomes and deuterostomes - Appreciate the processes involved in the production of an organised embryo from a single celled zygote - Blast = ball of cells in development - Blastula = ball of cells itself - Blastopore is a particulare structure - Blastocoel , coel is a cavity , so it's a cavity within ball of cells - FERTILISATION - Sexual reproduction - Male and female gametes- sperm and egg are - Produced by male and female gonads - Released through gonoducts -- vas deferns and oviducts - Meiosis - Reduces amount of genetic information in a cell by reducing chromsosmes by half from diplod to haploid - Mixes up combination of allels by recombination (pieces of DNA are broken and recombined to produce new combination of alleles) creating genetic diversity at the level of genes - The gonads are the only place in the animal body where meiosis occurs , function is solely to produce gametes - Recombination is important because it creates variation in population and allows evolution to happen , - To produce gametes - 6 stages in total , - Happens in germ cells - Purpose is sexual reproduction - Produces 4 haploid daughter cells - Genetic variation increases - Mitosis - DNA is duplicated in cell and divided equally between two cells - Organised series of evets called the cell cycle - Cell cycle triggered by presence of certain growth factors or other signals that indicate that the production of new cells is needed - Occurs in somatic cells -- fat cells, blood, skin - Necessary to replace dead cells, damaged cells or cells that have short life span - New cells, fix damaged cells, - 4 stages in total - Happens in somatic cells - Purpose is cellular proliferation - Produces 2 diploid daughter cells - Both - Start with a parent cell single - Produce new cells - Similar basic steps - - Meiosis and mitosis s - Cell division - Organisms grow and reproduce through cell division , in eukaryotic cells production of new cells occur as a result of them - Processes are similar but distinct - Gametogenesis - Occurs in primary sex organs, gonads - Production of gametes by primordial germ cells and it involves both mitosis and meiosis - Spermatogenesis (production of sperm) - Oogenesis (production of eggs) - Oogenesis - Primary oocyte (product of mitotic divisions -- end during gestation) - First meiotic division -- primary oocyte gives rise to secondary oocyte AND first polar body - Second meiotic division- secondary oocyte gives rise to ovum and second polar body - First polar body usually gives rise to two more polar bodies - Egg maturation - Huge increase in size - Increase I organelles - Increase in nutritive materials - Development of protective extracellular membranes - Spermatogenesis - Primary spermatocyte ( product of mitotic divisions) - First meiotic division -- primary spermatocyte gives rise to secondary spermatocytes - Second meiotic division -- secondary spermatocytes give rise to eprmatids - Spermatocyte - Loss of most of cytoplasm - Development of log flagellum -- tail - Formation of secretory acrosome at anterior of head section - - Eggs are full of nutrients and trying to ake it as nutrient rich as possible but its immobile while sperm which is tiny with masses of energy , directing that nucleus to et to the egg and insert inside egg. - - A sperm must - Find an egg - Find the right egg - Prevent other sperm from fertilising the right egg - This is easier when fertilisation is internal - - Needs quantity and proximity , chemical signalling for coral , - Egg is producing sugas, lipids , proteins on the surface that will help to attract the right sperm and repel the incorrect sperm - If chemicals don't match the sperm they will go off and try to find something else - - External vs internal - External -- outside body like corals and frogs, tend to have thicker membrnaes because they have to be protected from the salt water. - Internal -- inside body like sperm goes to female reproductive tract , much more protetcted so jelly coat is much thinner - Several options -- intromittent organ ( penis, claspers) pr spermatophore ( sperm packet) pr injected through body wall - - - Fertilisation -- fusion of egg and sperm - Step 1. - Egg activation - Inactive egg is activated by fusion of plasma membranes of egg and sperm - Resumes synthetic activity - Step 2. nuclear fusion - Pronuclei of egg and sperm fuse - Creates diploid zygote - Chemicals that dissolve the membranes so they can fuse together and sperm can insert its acrosomal processes. - Acrsomal processes have to go past the egg jelly coat so it can make contact with the actual egg plasma membrane and the nucleus from sperm can come out and go straight into the egg , where the tail falls out -- mitochondria falls away. - - Two different sources of genetic materia give you lots of information about evolutionary backgrounds of different speies , - Once nucleus is inside, put up barriers, have electric fence type barrier which is waves of calcium ions, calcium is positively charged and repeles the spem away from the egg and released when calcium is released next to the membrane and have a fertilisation membrane which is much slower and much longer lasting - The calcium fence is very expensive to do that , and cant last a long time but it is a very quick response , long enough until you get fertilisation membrane up. - While the calcium fence is occuirng , there is cortical granules that are ready to release themselves to insert into the membrane. - The psemr goes in , breaking the membrane which triggers the calcium release and then calcium release triggers cortical granules going in , - - Diploid zygote has a full set of chromosomes , one set from each parent - Recombination allows alleles to combine in new arrangements to produce a unique genotype - - Once fertilisation has occurred - Zgote must - Proliferate to make many cells - Eliminate unwanted cells - Differentiate the remaining cells to form different types of cells - Develop tissues, organs and body structures - - Blastula formulation ( cleavage - Exponential growth , cells grow extremely quickly - Super efficient - 2 types of cleavage , radila and spiral - Cleavage is extremely organsed , protosome is mouth first-spiral , deutrosomes -radial is the mouth forms second, anus is the other end of the digestive tube, they both form in the same place at the bottom - A diagram of the body parts Description automatically generated - - Different species have different amounts of yolk in their eggs and that contributes to their cleavage pattern. - Amphibians have bit of yolk. Fish repties and birds have ots of yolk. mammlas have very sparse yolk that's distributed euqlalay throughout egg , - Yolk will determine the pattern of cleavage , - BIRDS - Little blobl of blastula sitting on top of yolk because yolk dosent get cut up - - FROGS - Have bit of yolk , really concentrated in botto of egg compared to top. - First cleavage line isnt complete but the second line has already started. Creates a gradien of cleavage so the top divides much quicker than the bottom and you end up with smaller cells at the top and bigger cells at the bottom - Blastic seal is really asymmetrical , - Yolk is concentrated at the bottom and impedes the process of those cleavage furrows. - Pattern of blastic seal at top is important - **Meroblastic**- incomplete cleavage - **Teloecitha** -- lots of yolk concentrated at one end of egg - Division happens on top of the yolk , spread out like a sheet - Mammals - Rotational cleavage - Ends up with cells being slightly asymmetrical - Placenta : make a placenta so they hae to have part of the egg that's ready to implant into uterus wall , - Gastrulation - Rearrangement of cells in the blastula to form a gastrula - Blastula : no specialised tisses and no organs except for mammal internal cell mass and trophoblast - Gastrula : germ laers ( ectoderm, mesoderm , endoderm) , body cavities (archenteron, coelom), bilateral symmetry -  - Ectoderm : outside brain cells and skin cells , mesoderm : middle all of the ograns , endoderm inside liver bones, muscle, heart , blood cells - Mesoderm: lots of limb development , - Ecto is blue, meso is red and endo is yellow, - Deuterostome, - Blastopore is going to be your anus because it is formed first , and mouth forms second , - Protostome , mouth forms first - - For frogs, they have lots of yolk and lots of cells at the top , they differentiate it by at the border of the vegetal and animal pole , goes through involition because it turns inside out and you start to have bits going inside, make a hole and you sed yoru cells in to create your three different layers, - If reptile or bird you ave much flatter surface, do te same thing as frog , make nice ong streak and then you get a nice long streak and cells migrate over the streak to the inside and again , have ecto , endo and meso in middle , get clel so migrate to the top , go in and start to form. - - Gastrulation in mammals - Inner cell mass starts to create amniotic cavity , amniotic sac and amniotic fluid ,. - Called inner cell mass reorganises , - Epiblast -- ectoderm - Hypoblast = endoderm , migae around blastocoel - Inner cell mass becomes flattened - Formulation of the primitive streak , gastrulation pattern from hee is like birds and reptiles , - A cavity opens up , get invagination of blastula, so cells are more or less same , cells migrate into that hole or strea , which form the middle layer and you get the three layers. Tissues development Ectoderm - Outer layer - Body covering - Neural tissue - Sensory cells - Mesoderm - Middle layer - Gonads - Heart and blood vessels - Nephridia ( kidneys)\ digestive glands - Internal skeleton - Muscles - Inner layer - Lungs - Gut - Gut derivatives (ducts and tubes) - Determination - Fate of protostome cells are determine from onset of cleavage - Deuterostome cells remain totipotent unti later in development ( stem cells) -- indeterminate development - They can become anything right up until later in development - Pluripotent -- many opportunities to o and do different things, have potential to become anything so they're essentially stem cells Stem cells - Can become any cells - Fertilised egg is ultimate stem cell - As they start to divide and differentiate they always make a copy of themselves, - When they divide , one of the daughter ells is a copy of themselves where the other is often a differentiated cell that will goa nd becoe something else nad stop dividng - In neurons, you ave stem cells that make a copy of a stem cell plus a neuron and that neuron is then fixed, so stem is very powerful as it will keep on enerating a copy of itself , - Embryonic stem cells ae the ones that are inhe fertilised egg that can go on and becoe anything - All cells have the same DNA , when you become a skin cell, you switch on all the DNA parts that are going to make you a skn cell and switch off all the ones that will make you a neuron or a liver cell. - Use of stem cells in research - Transplantation - Diagnosis - Persoanlised medicine - Use of stem clel sin clinic ( patient treatment ) is still controversial and experimental - Portosome and deuttrostome - Cleavage , spiral vs radial - Development , determinate vs indeterminate - Blastopore mouth vs anus - Mesoderm li pof blastopore vs archenteron - Coelom -- schizocoel vs enterocoel Coelom development - If cells are touching each other or not , - Cells can trigger different geetic factors , its mechanical structures nad interaction sbetween cells and development hat can sart to trigger these things - Empty space versus a cell occupied space and te cavities in the embryo develop differenty if you are a protstome or a deutrostomes , - Neurulation - Purpose o for the nervous system - Have primitive streak with all three layers moving around , - Ectoderm is layer of cells of outside, to turn into brain, you start to divide the cells quicker in palces alongside a ridge so you end pu with a neural plate which is surrounded by two little ridges , cells continue to divide , ridges get bigger and then closes up and akes a tube, structure underneath called the notochord -- mesoderm structure which secretes factors , so proteins wll cause these cells to start to divide and create the tube. - Tube becomes your brain and spinal cord, - Forebrain is cortex , part that is really developed, big and folded and complicated , - Mid brain Cell development - Cells can either proliferate-mitosis or udergo apoptosis for cancer cells, tail in embryo , webbed fingers, neurons that haven't made the right connection 50% etc , - Surviving cells develop through a lineage of cell division by a process called differentiation - In deuterostomes, undifferentiated cells that have the capacity to form many different cells are called stem cells - Embryonic stem cells -- cells that make up the blastula can become any cell in the fully formed body - After gastrulation -- process of creating three cell layers , each cell can only become a cell in the tissues that the layer will go on to produce- mesodermal cells can still for vast array of cells. TWINS Monozygotic twins - Single egg fertilised by single sperm and at some stage in the first two weeks the developing embryo splits in two , - Two genetically identical babies develop - Can have monozygotic twins tat ahpepsn at different times in development - Depening on when the egg splits will determine hwo you and your twin live together in the uterus - If egg splits relaly early you end up with two separate eggs with two inner cell masses that are very separate , don't contact each other - Splitting happens later, have common corionic sac so outside membrane is shared but each embryo will have own amniotic sac , - Really eally late, embryo is far advanced , it splits off and end up with two embryos s Dizygotic twins - Two separate eggs fertilised by two different sperm , - Dizygotic twins share the same type of genetic relationship as non twin siblings - Fraternal Semi identical twins - Two sperm cells fuse with single egg, - Vey rare because of the calcium block and the inflatable block - Embryos don't usually survive but a few known cases Mirror split twins shared everything : amniotic sac, chorionic sac , in contact with each other in utero.