The Basics of Sexual Reproduction Variation or differences in characteristics among class members is not surprising because we all come from different.

• The Basics of Sexual Reproduction• Variation or differences in characteristics

among class members is not surprising because we all come from different families.

• certain characteristics can be found amongst members of the same family

• certain characteristics are different amongst members of same family

• Fraternal twins - sexual reproduction• Identical Twins - asexual reproduction• Gametes - Body has specialized organs

(testes/ovaries) that produce gametes (sex cells) used for reproduction

• Sexual Reproduction – gametes(1 n) from 2 parents combine during fertilization to form a zygote (2n)

Boy or Girl? The Y Chromosome “Decides”

• Sexual Reproduction – gametes(1 n) from 2 parents combine during fertilization to form a zygote (2n)

• Homologous Chromosome pairs - “matching” pairs of chromosomes

• receive one member of each pair from mother and another from father

• Human body – 46 chromosomes arranged in 23 pairs that resemble each other in shape and size

• Body cells = diploid (2n) - 2(23) = 46• Gametes = haploid (1n) - 1(23) = 23• In order for human chromosome # to remain 46,

gametes must have half of the chromosomes.

Boy or Girl? The Y Chromosome “Decides”

X chromosomeY chromosome

• Fertilization – only haploid gametes can combine to form a diploid zygote

• if both were diploid = 92 chromosomes• Mitosis – ensures that chromosome number does not

change• Meiosis – process to ensure that each gamete

contains only one set of chromosomes• Also ensures that each gamete has different

combination of chromosomes than were present before meiosis

• Because of non- identical nuclei, offspring are produced that are different from parents

• Crossing Over – exchange of genetic material between homologous chromosomes

– only in Prophase I and Metaphase I

• Formation of Sperm and Egg - sexually reproducing animals produce gametes in organs called gonads

• Male gonads (Testes) – produce male gametes called sperm

• Female gonads (Ovaries) – produce female gametes called eggs

• Fertilization – gametes come together to form a zygote

• Development – zygote starts to divide by mitosis and differentiate into all cells and tissues of the new organism.

Sexual Reproduction in Animals• Despite the variety amongst animal species, they still reproduce

sexually in relatively the same ways• meiosis produces gametes• male gamete (sperm) combines with female gamete (egg) =

FERTILIZATION• a zygote is produced and develops into an embryo• embryo develops by mitosis into an new organism (offspring)

For success 3 things must happen:• Fertilization occurs if both male and female gametes arrive in

same place at same time.• Fertilization occurs only if sperm meets an egg from the same

species. • Zygote must receive adequate food, moisture, warmth, and

protection to develop.

• Mating Patterns in Animal Kingdom• 2 members of a population come together to combine

gametes for fertilization• some only have one mating season/year (usually

offspring will hatch or be born in favourable conditions)• ie. fish called grunion mate when tide is high,

honeybees mate once in lifetime

Patterns of Fertilization:• moist environment is required so gametes don’t die• egg’s cell membrane needs to stay supple and sperm

need water to swim 1. External - sperm and egg meet outside the

organism’s bodies - (mostly aquatic) 2. Internal - sperm travels from male’s body into

female’s body to meet the egg – development of embryo can be internal or external

1. External Fertilization - mostly water-dwelling animals a) Coral & Sea anemone - adult anemones cannot move around

to mate with each other- release eggs and sperm directly in water (spawning)- rely on currents to bring gametes together- zygotes are free-swimming, self-feeding larvae which

travel distances before settling down and developing into adults

b)Fish - female lays cluster of eggs, male releases sperm directly over eggs (spawning)

c) Frogs - male frog embraces female who lays her eggs while male releases sperm over them (mating)

• New generation - young hatch from eggs of anemones, fish, frogs that do not look like the adult forms

• undergo many developmental changes to become adult forms (some remain in water, others move to land)

2. Internal Fertilization - Mostly land animals therefore they need specialized structures on male to transfer sperm inside female

a)Reptiles - males transfer sperm into female’s cloaca (chamber where female reproductive, urinary and digestive ducts leave body)

• most reptiles lay eggs with tough, leathery shells with a fluid-filled sac surrounding the embryo

b)Birds - few have specialized structures for transferring sperm, both males and females have cloaca

• fertilization by close contact where the sperm swim from male cloaca to female cloaca

• eggs laid with hard outer coverings – parent(s) incubate & protect

• most species of birds – parents invest a great deal of energy in feeding young

Differences In Development:

• Hermaphrodites- Animals that have both female and male reproductive organs

ie. Earthworms – during mating, each worm injects sperm into a reproductive pore on other worm’s body

- each organism lay fertilized eggs• Metamorphosis - some animals are born as miniature adults

while others pass through different stages of development:Incomplete metamorphosis (grasshoppers, crickets,

frogs) larval form has similarities to adultComplete metamorphosis (houseflies, butterflies) -

adult form does not look like earlier stages• Internal Development - some mothers retain and nourish

young before birth which ensures protected developmentie. Placental animals

• Mammals produce milk for nourishment of their young

• Marsupials – no placenta however, they do produce milk for their many babies who after birth crawl into the pouch.