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