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Chapter 3
6th grade Science
Reproduction
• There are two types of reproduction
– Asexual – one parent passes inherited traits to its
offspring. Offspring are identical!
– Sexual Reproduction - two parents pass on
inherited traits to their offspring. Offspring are
not identical!
An organisms inherited traits and their environment
shape an individuals characteristics
Learned traits are not passed from parents to
offspring
Heredity
• The passing along of traits from parents to their offspring is
called ____________.
• Parents and offspring_______________ each other because
of the traits that they have in common.
• Parents and offspring are not _______________ but their
basic pattern is the same. Example: an oak tree will grow
from an acorn. A maple tree will not grow from an acorn.
• All organisms _______________ traits.
• ____________________ also affects characteristics of an
individual. Example: tree height
• Organisms also have traits that they did not _______ such as
talents - these traits are _____________ traits
Asexual Reproduction
• All species need to reproduce in order to survive
• The __________ that help a parent survive in its environment can
be passed to offspring so that they can live successfully and
reproduce.
• In __________________ reproduction, offspring come from a single
parent by mitosis.
• The offspring will have the same _______ as the parent.
• In asexual reproduction the offspring is ___________ to the parents
• There are three types of asexual reproduction:
– ______________ - a parent cell splits to produce two offspring (Example –
bacteria)
– ______________ - a cell in the parents body produces a small version of
itself. Many buds can come from a single parent
– _______________- when conditions are right a spore can produce many
spores at the same time. (Example – mold)
Sea Stars
• Some sea stars can reproduce asexually by
forming new individuals from body parts
• Some oyster fishers captured sea stars and
chopped them up to protect their oysters.
• Fishers threw the pieces of the sea stars back into
the water.
• Many of the sea stars grew into new individuals.
• The problem got worse because there were more
sea stars than before.
How are traits passed on?
• Instructions for an organisms traits are found
in the organism’s ________.
• DNA and proteins make up ___________
which are found in the _________of the cell.
• DNA is short for _______________.
• There are _______ chromosomes in every
human body cell
• You cannot see DNA under a microscope
because it is too small and thin.
DNA and GENES
• DNA is passed from one parent cell to its
offspring.
• In 1953, _____________________ used X-ray
photographs to describe the structure of DNA.
• They described DNA as a “twisted ladder” with
millions of rungs.
• The DNA of a chromosome is divided into
sections called ______.
• Each gene controls what substances the cell
makes and when it makes them.
Copying DNA
• The rungs of DNA are made up of four kinds of material
called ______
• Each rung is made up of two bases, these are called
_________.
• The DNA of all living things is made up of pairs of the
same four bases.
• The ______ of the pairs determines exactly what
instructions each gene gives to its organisms cells.
• The bases are known by the letters ___________
• The pairs are combinations of those letters
DNA Combinations
• TA-CG-GC-TA or TA-AT-GC-TA
• Those two combinations give the cell different
instructions.
• Two ________ fit together to form each ______
• Base ___ can only pair with base ____.
• Base ___ can only fit with base ____
• This pairing alllow DNA to make an copy of itself
when it divides through mitosis
DNA Copies Itself
• When a cell undergoes mitosis, the DNA
_______ and the base pairs come apart.
• Before a cell divides, the base pairs pull apart
• Extra bases float around inside the nucleus
• The extra bases join the bases that are still
attached
• Because each base only pairs with one other
kind of base, the two new complete strands of
DNA are identical
Deoxyribonucleic Acid Strand