1. Sexual Reproduction
Science 9, 2016

2. Introduction Usually involves two individuals
Doesn’t always have to involve a male and a female
Occurs in species we may not think of having definite male and female individuals (plants and coral)
Scientific Definition
Is the union of two sex cells (gametes) to produce a new individual

3. Sex Cells
Gametes from females are called eggs
Gametes from males are called sperm
Union of the sperm cell with the egg cell is called fertilization

4. Meiosis Cell division process that produces gametes
Divided into two processes
Meiosis I: Chromosomes are duplicated and then cell divides
Meiosis II: Cell divides again without chromosomes being duplicated
Result of meiosis is four daughter cells with half the number of chromosomes of the parent

6. Sexual Reproduction in Animals
Most animals reproduce sexually
Joining of the two gametes creates a new single cell known called a zygote
Zygote has a full set of chromosomes and is the first cell of a new individual
Zygote then divides into two cells, beginning a process called cleavage
New multicellular life form (embryo) develops through continued mitotic division

7. Development of the Embryo
Offspring will show some traits of male parent and some of female parent
Although it may look more like one parent, it will not be identical to either parent
Depending on the species, the embryo may develop differently
For most mammals it happens inside the female
For most other animals, it occurs in an egg

9. Critical Role of Meiosis
During sexual reproduction, the male and female gametes unite to form a zygote
Gametes are haploid
They have half the number of chromosomes of a normal cell
If the gametes were diploid (like every other cell) then the zygote would inherit twice as many chromosomes as it needs
Incorrect number of chromosomes can cause problems with normal cell function and growth

10. Hermaphrodites Can produce both male and female gametes
Usually mate with other individuals, but can fertilize themselves in times of environmental stress
Example:
Common garden worms and slugs

11. Sequential Hermaphrodites
Born one sex but then become the opposite sex
Finding Nemo:
Clownfish travel in packs that consist of a large reproductive female, a smaller reproductive male, and numerous small, non reproductive males
If the female dies or leaves, the reproductive male becomes a female and the largest of the non-reproductive male becomes the new reproductive male

12. Sexual Reproduction in Plants
Ovules contain the female gametes of a plant and are found in the pistil (female part of plant)
Pollen contains the male gametes of the plant and is found on the stamen (male structure of plant)
Most plants produce both female and male gametes
However, some produce only male gametes and others only female

14. Pollination
Pollination occurs when pollen is transferred from the anther of the stamen to the stigma of the pistil
Self pollination: when the transfer is within the same plant
Cross pollination: when the pollen of one plant is carried to the stigma of another by wind, water or animals like bees
A gamete in the pollen grain and a gamete in an ovule join and a zygote is formed
Zygote undergoes many cell divisions to produce an embryo
Embryo is produced inside a protective covering called a seed

15. Advantages of Sexual Reproduction
Offspring produced through sexual reproduction show variation because they have a mix of traits from both parents
Variation helps a species survive by giving it the ability to adapt to a changing environment

16. Disadvantages of Sexual Reproduction
Requires a great deal amount of energy
Flowering plants produce lots of pollen to be blow by the wind
The embryo requires nurturing
Limits the number of offspring