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 Stars Planaria

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 Cycle 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

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