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