Sexual reproduction

6c&d: Sexual Reproduction

●Describe the three stages of sexual reproduction●Compare & contrast internal and external fertilization●Describe the process of fertilization in plants and animals●Describe the key events that occur during the stages of embryonic development

Sexual Reproduction

● Method of reproduction requiring genetic contribution from two parents and producing genetically unique offspring

● Three stages of sexual reproduction:

1)Mating – Process by which gametes arrive in the same place at the same time.

● Humans = intercourse● Plants = fertilization● Fish = spawning

2)Fertilization – Union of egg and sperm cells

3)Development – Growth and specialization into the organism

Mating● Timing is everything

– Many organisms mate during specific mating seasons to increase the chance of finding a suitable mate and increase the likelihood of offspring's survival.

● Ex. Many animals mate in the winter or early spring so offspring will be born when the weather is less harsh

● Ex. Marine and aquatic organisms may release eggs and sperm in sync with the moons cycle

Mating● Mate selection

– In order to produce the most successful offspring possible organisms may choose their mate based on:

● Ability to provide for the offspring ● Desirable genetic traits● Maximum genetic diversity

– Organisms may attempt to win a mate through mating displays or competition

● Colourful plumage● Mating dance/show● Chocolate and flowers

Fertilization

● There are three ways for the gametes to unite:

1)Internal Fertilization● Sperm are deposited inside the body of the female● Common in land-dwelling organisms● Embryo develops and is nourished inside mothers

body or inside a hard shelled egg

Fertilization

2) External Fertilization

● Sperm and egg meet outside of the parent bodies● Common in aquatic and marine organisms● Ex. Spawning fish

Fertilization

3) Pollination

● Type of internal fertilization found in plants● Plants may self-pollinate or cross-pollinate● Pollen contains the male gametes● May require pollinators (eg. birds, bugs, wind)

Flower Parts

● A – Stigma / Style

● B – Anther

● C – Petal

● D – Sepal

● E - Ovary

● F – Stem

● G – Ovules

● H – Filament

●

Pollination

1) Pollen grains carry the sperm cells of the plant to the sticky stigma of the female reproductive structure

2) A pollen tube grows from the pollen grain down the style to deliver sperm to the egg cells in the ovules

3) Fertilization occurs

4) Zygote develops and is nourished by stored nutrients inside a seed

5) Seed germinates and grows into a mature plant when conditions are optimal

Fertilization

Internal Fertilization

● Advantages

– More offspring survive due to protection and parental care

– Successful fertilization more likely● Disadvantages

– Requires more energy to find a mate

– Fewer offspring produced

– Large investment from female parent, may leave her vulnerable

External Fertilization

● Advantages

– Little energy needed to find a mate

– Many offspring produced

– Offspring not in competition with parents

● Disadvantages

– Many gametes do not survive or are not fertilized

– Zygotes and embryos are unprotected

– No parental care mean many offspring do not survive to adulthood

Embryonic Development

● After fertilization occurs the zygote begins the process of mitosis and divides rapidly

● Week 1 – Morula: cluster of cells

● Week 2 – Blastula: hollow ball of cells

● Week 3 – Gastrula: ball of cells organizes into layers which will later specialize

Embryonic Development

Embryonic Development

●Gastrulation – Layers of the gastrula differentiate into endoderm, mesoderm and ectoderm

Embryonic Development

Trimester Main Events Gestational age Size

First

Second

Third

Use text pg 218-219 to complete the table below