Unit A Section 2.0 Reproduction Passes Characteristics from Parents to Offspring.
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Transcript of Unit A Section 2.0 Reproduction Passes Characteristics from Parents to Offspring.
Unit A Section 2.0
Reproduction Passes Characteristics from Parents to Offspring
Goals for This Section
• Identify the difference between sexual and asexual reproduction
• Describe examples of sexual and asexual reproduction
• Describe types of variations within a species• Classify variations as discrete or continuous• Distinguish between heritable and non-heritable
characteristics
2.1 – A Closer Look at Variation
• Recall that variations can contribute to species survival
• Remember that variations are not always visible in nature
• To understand variation, scientists can study which characteristics are passed from one generation to the next
Gregor Mendel’s Studies
• One of the first scientists to study characteristics that are passed from parent to offspring was Gregor Mendel
• He was a monk who studied different types of variation in pea plants
http://kentsimmons.uwinnipeg.ca
• Mendel identified a number of characteristics that could be passed from one plant to its offspring
• He used cross-fertilization to test how these characteristics were passed on
http://www.scq.ubc.ca
Heritable & Non-Hertiable Characteristics
• Heritable characteristics are passed on from one generation to the next
• Non-hertiable characteristics cannot be passed on to other generations
Examples of Heritable & Non-Heritable Characteristics
Heritable Non-Heritable
Discrete & Continuous Variation
• Discrete variations are differences that have very few possible forms
• Continuous variations are differences that have a larger range of possible forms
Examples of Discrete & Continuous Variation
Discrete Continuous
Variation & the Environment
• A number of heritable characteristics rely partially on the environment
• For example, two identical plants will grow differently if given different amounts of sunlight, water, or fertilizer
• A lot of characteristics in humans also depend on the environment
• For instance, modern North Americans are generally taller than North Americans living in the 1800s due to better nutrition
• However, variations that have an environmental component are not completely heritable
2.2 – Asexual and Sexual Reproduction
• Reproduction produces new individuals for a species
• Depending on the type of reproduction, the resulting new individuals may be identical to the parents, or different from the parents
Asexual Reproduction
• Asexual reproduction involves only one parent
• Therefore, the offspring will be identical copies of the parent
Binary Fission
• Single-celled organisms reproduce through binary fission
Budding
• Some organisms such as yeast, hydra, and coral reproduce by budding
http://io.uwinnipeg.ca
Spore Production
• Many fungi, green algae, moulds, and non-flowering plants reproduce through spores
http://upload.wikimedia.org
Vegetative Reproduction
• Most plants carry out vegetative reproduction
Sexual Reproduction
• Sexual reproduction involves two individuals who each donate their genes to the offspring
• This requires the union of two specialized cells known as gametes
Sexual Reproduction in Animals
• Almost all animal species carry out sexual reproduction
• Sperm cells meet with egg cells (or ova) and they combine to form a zygote
• This zygote then begins to divide to form an embryo, which can develop into a new individual
http://z.about.com
http://www.csu.edu.au
Sexual Reproduction in Plants
• Flowers contain the parts of a plant involved in reproduction
http://www.troy.k12.ny.us
• Pollination occurs when pollen is transferred from the anther to the stigma
• Cross-pollination occurs when pollen from one plant reaches another
• Cross-fertilization occurs when a grain of pollen produces a tube that grows down into the ovary
http://cache.eb.com
After Pollination
• After the pollen grain gamete joins the ovule, a seed begins to form
• These seeds can remain dormant for many years, especially when left in a dry environment
• In some cases, a plant may self-fertilize, and the resulting offspring will be identical to the parent
Advantages & Disadvantages of Asexual Reproduction
Advantages & Disadvantages of Sexual Reproduction
Organisms that Reproduce both Sexually and Asexually
• Most plants can reproduce both sexually and asexually
• Aphids produce female young asexually during the summer and produce males and females (who produce sperm & eggs) when the temperature drops during the fall
• Sponges can also reproduce using both methods
http://www.richard-seaman.com