Unit A Section 3.1

Question 1

How many genes can a human have?

Answer 1

They estimated that humans have about 30 000 genes.

Question 2

What are blueprints?

Answer 2

Every multicellular organism on Earth contains a blueprint for making a copy of itself in each of its body cells.

Question 3

What could store so much information, and pass it on from generation to generation?

Answer 3

deoxyribonucleic acid,

Question 4

What is deoxyribonucleic acid?

Answer 4

• a large molecule first found in cells’ nuclei is responsible for storing such information and passing it on.
• DNA for short is the inherited material responsible for the variation.
• DNA was first identified in 1869
• Because every organism has so many physical and chemical characteristics, there is a lot of DNA in a cell.

Question 5

Who can have deoxyribonucleic acid?

Answer 5

-All living organisms contain DNA in their cells.
the cells of mammals and plants contain a nucleus,

• DNA is found in the nucleus.
• bacteria to plants and animals—scientists found DNA in all of them

Question 6

How could the blueprints for so many different organisms be passed on by what seemed to be exactly the same molecule?

Answer 6

the same chemical building blocks could carry such a wide range of instructions needed for the diversity we observe in the living world.

Question 7

What is the structure of a DNA molecule?

Answer 7

• The DNA molecule can be compared to a ladder that has been twisted into a continuous spiral.
• Each individual rung pairs up just two of the following four chemicals: guanine (orange), cytosine (blue), adenine (green), and thiamine (violet), or G, C, A, and T, for short

Question 8

What are the four DNA chemicals?

Answer 8

• guanine (orange),
• cytosine (blue),
• adenine (green),
• and thiamine (violet),
• or G, C, A, and T, for short

Question 9

What is a genetic code:

Answer 9

• is based on arranging the four chemical “letters” into “words,” or instructions, that describe how to make any particular organism.
• Paired chemicals make up the “rungs” of the DNA “ladder” and form the genetic code

Question 10

How can such a large amount of DNA into their cells?

Answer 10

• organisms arrange their DNA into packages.

- These packages are called chromosomes.

Question 11

Where are the chromosome located?

Answer 11

• the chromosomes are located inside the cell nucleus
• All of our nuclei, except for those in the gametes, must have a complete set of chromosomes.
• One chromosome contains only part of the instructions for making a human.

Question 12

How many chromosomes does each human nucleus cell contain?

Answer 12

• Each human cell nucleus, for example, contains 46 chromosomes.
• For dogs, a complete set has 78 chromosomes
• for cats, the number is 38.

Question 13

How are the chromosomes organized?

Answer 13

• In most familiar organisms, the chromosomes are organized into pairs.
• body cells of a human contain 23 pairs of chromosomes
• a dog’s body cells contain 39 pairs
• a cat’s body cells contain 19 pairs
• chromosome number varies from one species to another
• the composition of the chromosomes varies as well

Question 14

What are genes?

Answer 14

• genes are responsible for the inheritance of an organism’s characteristic features.
• A single gene is an uninterrupted segment of DNA, which contains coded instructions.

Question 15

Where are genes located?

Answer 15

• Genes are located on the chromosomes.

- Each chromosome contains numerous gene locations

Question 16

How are genes organized?

Answer 16

Like chromosomes, genes come in pairs.

Both genes in a pair carry DNA instructions for the same thing

For example, the two leg-length genes occupy matching locations on the two chromosomes.

The DNA code may not be exactly the same in both locations.

Question 17

What are alleles?

Answer 17

They are possible forms where most genes in most species exist that differ as to their exact DNA sequence.

Question 18

How are genes inherited?

Answer 18

• more than one gene pair may be involved in determining the individual details
• there could be one gene pair for hair length, a second gene pair for waviness, and another gene pair for texture
• there may be several possible alleles for each gene pair. For coat color alone, there must be ten or more possible alleles, all in just one species!