What have we learned?• We know that when a cell undergoes mitosis and

cell division two new identical cells are produced• We know that in asexual reproduction, one

parent divides mitotically to produce two identical offspring.

• We have seen variation in our classroom – everyone has different characteristics... Mitosis does not seem to fit. Perhaps another process is responsible for producing variation???

Basics – Sexual Reproduciton

• Sexual Reproduction – the reproductive process involving two sexes, resulting in offspring genetically different from both parents.

• Specialized organs make specialized cells called Gametes.

• Ex: Sperm and Eggs

Sexual Reproduction

• Sexual reproduction involves two stages:

1.Meiosis- the special cell division that makes haploid gametes

2.Fertilization- the fusion of two gametes to form a diploid zygote – this zygote is the first body cell of a new organism!

Sexual Reproduction – Zygote

Homologous Pairs

• Human body cells have 46 chromosomes – these can be arranged into 23 pairs of chromosomes that resemble each other in size and shape.

• These matching pairs are called Homologous Pairs.

Diploid and Haploid Cells• Human body cells (skin cells,

intestine lining cells) are referred to as diploid cells – meaning double, ex: zygote

• The human diploid number is 46• Human Gametes (sperm and

egg) have 23 chromosomes and are called Haploid – meaning half

Meiosis• During reproduction – Human gametes must

have one half the number of chromosomes (23 – Haploid).

• Two Haploid gametes (sperm and egg) will combine during fertilization to form a diploid zygote (46 chromosomes).

• Meiosis – ensures that each gamete contains only one-half set of chromosomes – 23 chromosomes.

Meiosis

• Meiosis also ensures that each Haploid gamete has a different combination of chromosomes.

• This difference in each Haploid gametes allows parents to produce offspring that are different from themselves.

• How do these chromosomes become different?

Meiosis – Crossing Over

• During the early stages of Meiosis – Chromosomes come together, during this time an event called Crossing Over occurs.

• Here DNA will be exchanged between paired homologous chromosomes.

Crossing Over

Understanding Meiosis

• http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related

• http://www.youtube.com/watch?v=Ba9LXKH2ztU – difference between mitosis and meiosis

• http://www.youtube.com/watch?v=iCL6d0OwKt8&feature=related – Square Dance!

Sperms and Eggs

• Sexually reproducing animals create gametes in organs called gonads – testes and ovaries.

• Testes create Sperm.• Ovaries create Eggs.

• Unlike sperm - only one haploid egg is produced through meiosis.

Fertilization

• This is the final step of sexual reproduction.• 2 haploid gametes will fuse together and form

1 diploid zygote.

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/evolution/reproductionrev2.shtml

What can we conclude about Sexual Reproduction?

• It produces variation• Meiosis is the first step in Sexual Reproduction

and it creates GAMATES! • Specialized organs create specialized

reproductive cells called – Gametes• Only haploid cells can join during fertilization to

create a diploid zygote.• What would be some advantages and

disadvantages for Sexual Reproduction?

Advantages and Disadvantages for Sexual Reproduction

• Advantages:• Produces Variation• More likely to survive when environment

changes – natural selection• Disadvantages:• Two parents are required – energy to find

mate • Longer process • Smaller number of offspring produced at a

time

Check your Understanding!

• In your textbook answer the following questions:

• Page 50• 2, 3, 4, and 5

Sexual Reproduction in Animals

• Animals follow the same CYCLE to reproduce:• Meiosis produces Gametes• A male gamete combines with a female

gamete• A zygote is produced and forms into an

embryo• The embryo develops and grows through

Mitosis and Cell Division into mature offspring

Life Cycle

Success! • For sexual reproduction to be successful, 2

requirements must be met:1. Both male and female gametes must arrive

at the same place and time to fertilize2. The Zygote must receive adequate food,

moisture, warmth, and protection to develop

External Fertilization • Most sea life reproduce through external

fertilization.• Free-swimming animals (ex: fish) and stationary

organisms (ex: coral) release their eggs and sperms directly into the water.

• Stationary organisms will rely on water currents to bring gametes together.

• Animals like fish, will lay eggs in a cluster, and the male will release sperm directly onto the egg cluster.

• http://videos.howstuffworks.com/hsw/17035-science-of-the-sea-reproduction-video.htm

Internal Fertilization

• Most organisms on land reproduce through internal fertilization.

• Specialized structures are often used by the male to transfer sperm directly into the female.

Sexual Reproduction – Plants!• Cycle that allows plants to reproduce sexually

is the same as in animals. • Seeds are the products of sexual reproduction

in most plants.• Seed – contains an embryo, a food supply, and

a seed coat, which protects the seed from drying out.

Plants!

• Seed-producing plants can be divided into 2 groups:

1.Angiosperms – enclosed seed2.Gymnosperms – naked seed

Angiosperms• Flowering plants• Seeds form inside the flower• When mature, the seeds are enclosed in

a shell, such as a pod or a case. • Some have showy flowers – such as a

lily.• Others produce very tiny

flowers – such as grasses.

Angiosperms

• Flowers contain the reproductive organs.

• The female reproductive organ is called the pistil.

• The male reproductive organ is called the stamen.

Pistil

• Includes:• Stigma – sticky lip of the pistil that captures

pollen grains• Style – stalk that supports the stigma• Ovary – swollen base containing ovules• Ovules – sacs containing female gametes

Stamen• Includes:• Anther – where the pollen is produced and

stored• Pollen Grains – cases containing male gametes• Filament – stalk the supports the anther

Pollination

• Pollination –seeds begin to develop when the pollen grains reach the stigma of the pistil.

• Self- Pollination - both male and female gametes come from the same flower

• Cross – Pollination - brings together gametes from different parent plants.

• The 2 most common helpers for cross-pollination are the wind and insects

Pollination

• Pollination is not enough to ensure fertilization.

• The pollen grains must grow a pollen tube – which will grow and reach the ovule inside the pistil.

Seed Matured• When the sperm reaches the

egg it creates a zygote.• The zygote will undergo

Mitosis and create a many celled embryo with a miniature leaf, root and stem, and a case that surrounds it and stores food.

• As the seed matures it forms a fruit – such as a pod or a case, around the seed.

Seed Dispersal

• This increases the likelihood that offspring will survive – as they will not be competing with the parent for water, soil, and sunlight.

• Animals, wind, and running water help with the dispersal of seeds.

• http://www.youtube.com/watch?v=sr4Khc7BUzA

Gymnosperms• Gymnosperms produce their seeds inside cones

– cones are the reproductive organs.• Some species will produce female and male

cones on separate tress – while others produce both cones on the same tree.

• http://www.youtube.com/watch?v=p0PctCgj66Q

Check your Understanding!

Answer the following questions:Page 591, 4 Page 712a c, 3