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

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

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 HeritableNon-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 DiscreteContinuous

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

Spore Production Many fungi, green algae, moulds, and non- flowering plants reproduce through spores

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

Sexual Reproduction in Plants Flowers contain the parts of a plant involved in reproduction

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

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