Sexual Reproduction Mr. Mitcheltree
SpermPollen Sexual reproduction • 2 gametes “parents” - Many organisms produce both gametes (Ex: plants) and sexually reproduce themselves • Offspring genetically different from parent • Provides genetic variation within a species - Allows for evolution – “survival of the fittest genes” Ovule = male Egg = female
2n multicellular organism 2n Meiosis n 4 Haploid Gametes 23 chromosomes All X 2n Zygote fertilization Diploid 23 pairs = 46 Mitosis 1 of each homolog from each parent = 23 pairs All cells genetically identical – somatic stem cells specialize 2n Meiosis n 4 Haploid Gametes 23 chromosomes 1/2 X, 1/2 Y Diploid 23 pairs = 46
Allele = alternate form of a gene A = dominant a = recessive sex chromosomes – determine sex of the offspring - XX = female - XY = male XX Meiosis X 4 XX Gametes Fertilization XY Meiosis X XY 2 Y 2 Gametes
Disjunction Homologs separate and move randomly - crossing over may occur 2 homologous chromosome pairs carrying dominant and recessive genes Equator A A a A A a a a A a A A a a A A a a b B b B B B B b b b B B b b b b B B Diploid “Parent” Cell What else could have happened?
Equator A A A A A A A b A b b b b b b b 4 haploid gametes What else could have these been? a a a a a a a B B a B B B B B B Meiosis Overview
Chromatids in a tetrad crossing over – one cause of genetic change - mutation and variation: 1) Crossing Over 2) Independent Assortment 3) Random fertilization Chiasma
Random movement during disjunction and Crossing Over • Variation of offspring • In humans, 64 trillion combinations after fertilization • 1 in every 1,200 to 1,500 bases different • You have 50 - 100 new mutations from your parents – most neutral (silent)
Mitosis Meiosis • Sister Chromatids -Tetrads • Replicates Separate Ana - Homologs separate Ana I • 2 Diploid, genetically identical - 4 Haploid, genetically • daughter cells different gametes
Internal Fertilization : Mammals and birds Sperm and egg fuse inside the females body Mammals fertilization – copulatory organ Bird fertilization – a few with copulatory organ, most cloaca to cloaca Sperm can’t fly, it only swims!!!
Internal fertilization of reptiles Copulatory organs in most, cloaca in snakes Lizards Crocodiles and alligators Turtles Snakes
Internal Fertilization in Terrestrial Insects Why do they need internal fertilization?
Internal fertilization of fish: sharks, skates, rays and land based amphibians : salamanders – better chance of not having eggs in a marine/aquatic nest or free-floating eaten? Land salamander egg mass that came out of a female quite in proportion to her body size, then absorb water to swell up 20 times bigger. Male shark with claspers to transfer sperm packets
External fertilization in MOST amphibians – a gravid female Amplexus – a male squeezing eggs out of a female prior to sperm release Fertilized eggs undergoing oviparious development
External fertilization in MOST fish Release of Eggs and milt (sperm) Oviparous development
External fertilization of many marine (oceanic) and aquatic (fresh water) invertebrates Sponge dumping gametes Some jellyfish Non-parasitic mussels All oviparous = egg development outside of the body
Hermaphrodite – both male and female sex organs Typically don’t self-reproduce (a few parasites do) - reduced genetic diversity if they do self –repro.
Animal Development Oviparous – nutrition from yolk Viviparous – nutrition from placenta (female’s blood), live birth Ovoviviparous – nutrition from yolk, live birth
Site of meiosis Ovule = female gamete Pollen = male gamete Pollination Site of meiosis Fertilization
Fungi Reproduction spores are gametes Secondary mycelium – diploid Haploid spores formed by meiosis in fruiting body fertilization haploid Primary mycelium - haploid
Conjugation – exchanging DNA producing new genetic individuals in Protists
Bacteria genetic recombination
Horse Donkey A mule is the offspring of a male donkey and a female horse. Horses and donkeys are different species, with different numbers of chromosomes. Of the two F1 hybrids between these two species, a mule is easier to obtain than a hinny (the offspring of a male horse and a female donkey). All male mules and most female mules are infertile. Mule
Darwin’s Finches Diversification – speciation due to a lack of competition
Horse Evolution Speciation due to environmental change Why do giraffes have long necks?
- Evidence ofEvolution Speciation due to geographic isolation
- The Fossil Record 430 million years ago 66 million years ago 600 million years ago 1 billion years ago 3.5 billion years ago
The Genetic Basis of Evolution Thomas Morgan – genes on chromosomes
Chromatids in a tetrad crossing over – one cause of genetic change - mutation
- The DNA Connection DNA change allows for evolution according to modern theory 99.9% are neutral or bad, .1% makes an organism better adapted Copy Errors
Crash Course Biology Meiosis Study Island Review 6a