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 mQS_FZ0&feature=related mQS_FZ0&feature=related ztU – difference between mitosis and meiosis ztU wKt8&feature=related – Square Dance! wKt8&feature=related

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. bitesize/science/aqa/evolution/rep roductionrev2.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 fertilize 2.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. reproduction-video.htm 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 seed 2.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.

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.

Check your Understanding! Answer the following questions: Page 59 1, 4 Page 71 2a c, 3