Reproduction… passing on the genetic code Unit 8 Ch. 18.
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Transcript of Reproduction… passing on the genetic code Unit 8 Ch. 18.
Reproduction…passing on the genetic code
Unit 8 Ch. 18
Two Types of Reproduction
Asexual (without sex) • one parent• Offspring genetically
identical to parent – clone – no variation
Sexual • Two parents• Variation in offspring
Asexual Reproduction
1. Splitting or Binary Fission• DNA replicates, cell divides into 2
identical cells
• More complex in unicellular eukaryotes – involves mitosis and cell division:– e.g., Amoeba, Euglena, Paramecium
2. Budding• Small piece breaks off and grows into
complete organism.
Hydra
yeast
In plants – called vegetative reproduction.
Tuberous roots
rhizome
corm
True bulbs
tuber
creeper
Side stems called runners or creepers that grow roots and leaves forming new plants that grow independently.
Artificial vegetative reproduction(vegetative propagation)
Cuttings from roots, stems, leaves can produce new plants.
3. Fragmentation and Regeneration• Fragmentation - Small piece or fragment
will grow into whole new adult
• Regeneration refers to ability to regrow missing part
Sea StarsPlanaria
4. Spores• Algae, fungi, ferns, bacteria
– DNA, cytoplasm, protective coat– Doesn’t fuse with another cell– Adapted for dispersal and surviving
unfavorable conditions
Clostridium botulinum
Fern sori
Spore prints
5. Parthenogenesis• Eggs develop without fertilization: complex
organisms including aphids, honeybees, some lizards
Asexual Reproduction - Advantages
• Rapid
• Doesn’t require partner
• Less energy
• Well adapted individuals spread quickly
Sexual Reproduction
• involves an exchange of genetic information – two gametes undergo fertilization.
1.Conjugation
• genetic material is exchanged through conjugation tubes
• Algae, bacteria, fungi
Spirogyra Bacteria
Flower is reproductive organ
pistil
Pistil - female
• Stigma – sticky to trap pollen
• Style – long narrow – sperm travels through
• Ovary – swollen base that contains the ovules where eggs are produced
Stamen – Male• Most flowers have both male and female
parts– Anther produces pollen that contains sperm
- Filament – supports anther
pollen
Some flowers are only male or female
2. Plants – alternation of generation – between n and 2n
• Alternation of Generation
Angiosperm Life CycleAlternation of Generation
Alternation of Generation
• In anthers and ovules of diploid sporophytes are cells that undergo meiosis to produce haploid spores
• Spores divide by mitosis to produce male and female gametophytes.
• Cells in gametophytes divide by mitosis to produce sperm and eggs
• Male gametophyte = pollen grain & pollen tube
• Female gametophyte = embryo sac within ovule
• In flowering plants there is an alternation of generation between a diploid sporophyte generation and a haploid gametophyte generation.
Double Fertilization
Double Fertilization
• 1 sperm nucleus + egg 2n zygote» (forms embryo)
• 1 sperm nucleus + 2 polar nuclei 3 n endosperm (food for embryo)
Double Fertilization• The pollen lands on the stigma. • A pollen tube grows through the style to the
ovule. • 2 haploid sperm nuclei travel through the style to
the ovule. • 1 sperm nucleus fertilizes the n (haploid) egg to
form a 2n (diploid) zygote that develops into the embryo.
• 1 sperm nucleus fertilizes 2 polar bodies (or nuclei) to form a 3n (triploid) endosperm that nourishes the embryo.
• Seed develops after fertilization
• Ovule forms the seed coat
Seed coat
2n embryo
Fruit is the ripened ovary
Sexual Reproduction - Animals
• No alternation of generation
• Gametes produced in ovaries and testes
Sexual Reproduction – Animals
• Hermaphrodites – both male and female - still exchange gametes with another individual
Sexual Reproduction
• External fertilization– Aquatic environments– Large numbers of gametes released– Synchronized release of gametes ensured by
mating behaviors
3. Animals
• Internal fertilization– Many male, few female gametes– Mating behaviors (courtship, estrous cycles)– Parental care– Fewer offspring
(Fallopian tube)
• Eggs are produced in the ovaries
• Released midway through menstrual cycle = ovulation
• Travel through oviducts to uterus
• Uterine lining builds up tissue to support pregnancy – shed through cervix and vagina as menstrual flow
• Fertilization takes place in oviducts
*Accessory glands
prostate, seminal vesicle, bulbourethral
•Sperm are produced in the testes and stored in the epididymis•They travel through the vas deferens which joins the urethra in the penis where they are discharged•The accessory glands supply seminal fluid which along with the sperm comprises semen. •During intercourse, sperm travel through vagina, cervix, uterus, and into oviducts to fuse with egg (fertilization)
Human Menstrual Cycle
Menstrual Cycle
• Hormonally controlled
• Ovulation - Egg matures and is released
• 4 phases - approximately 28 days– Thickening of uterine lining– Ovulation (release of mature egg from follicle)– Passage of egg into uterus – Loss of egg and lining or “menstruation”
• If sperm are present, fertilization takes place in the oviducts
• Resulting zygote travels to uterus and implants in uterine wall for development