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