Transcript Unit A Section 2.0

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 & NonHeritable 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 nonflowering 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