SB3 Genetics

Question 1

What is sexual reproduction?

Answer 1

Sexual reproduction is where genetic information from 2 organisms is combined to produce genetically different offspring.

Question 2

Name the gametes involved in sexual reproduction in humans:

Answer 2

Sperm and egg cell

Question 3

True or false:

Gametes contain half the number of chromosomes of normal cells. They are diploid.

Answer 3

False.

Although gametes do contain 23 chromosomes, they are haploid not diploid. (Remember h=half=haploid)

Question 4

At fertilisation, a zygote is produced. Is this haploid or diploid?

Answer 4

Diploid

The zygote ends up with the full set of chromosomes. (23 from the egg and 23 from the sperm =46 chromosomes)

Question 5

What is produced in Meiosis?

Answer 5

4 haploid daughter cells
Gametes
Genetically different

Question 7

Explain why the daughter cells in meiosis are not genetically identical

Answer 7

Each daughter has half the chromosomes from each parent so daughter cells have different combinations of chromosomes so they are all genetically different.

Question 8

True or false:

Asexual reproduction is when cells divide by meiosis.

Answer 8

False
Asexual reproduction is when the cells divide by mitosis.
Sexual reproduction is when the cells divide by Meiosis.

Question 9

Describe the process of meiosis

Answer 9

The cell duplicates it’s DNA.
In the first division, the chromosomes line up in pairs at the centre of the cell.
The pairs are pulled apart.
2 cells are produced which have a mixture of the parents’ chromosomes.
In the second division, chromosomes line up again and are pulled apart.
4 haploid daughter cells are produced.

Question 13

State an advantage of sexual reproduction

Answer 13

It creates genetic variation within the population.

Question 14

State an advantage of Asexual reproduction

Answer 14

• Not time consuming/ lots of offspring are produced very quickly.
• Only one parent is needed so there is no need for a mate.

Question 15

State a disadvantage of sexual reproduction

Answer 15

• It is time consuming and needs more energy so organisms produce fewer offspring in their lifetime.
• 2 parents are needed which can be a problem if individuals are isolated

Question 16

State a disadvantage of asexual reproduction

Answer 16

There is no genetic variation between offspring in the population.

Question 17

What is the advantage of having genetic variation within a population?

Answer 17

If environmental conditions change it’s more likely that some of the individuals will have the characteristics to survive and then reproduce so the species will not become extinct.

Question 18

Which DNA bases pair up according to complimentary base pairing?

Answer 18

A and T (Adenine and Thymine)

C and G (Cytosine and Guanine)

Question 19

A DNA molecule is in the shape of:

Answer 19

A double helix

Question 20

What type of bonds are the complimentary base pairs joined together by?

Answer 20

Weak hydrogen bonds

Question 21

Where are the chromosomes of a cell found?

Answer 21

In the nucleus of a eukaryotic cell

Question 22

What is a gene?

Answer 22

A section of DNA on a chromosome that codes for a particular protein.

Question 23

The structure of DNA is made of nucleotides. What does this show?

Answer 23

DNA is a polymer.

Question 24

Describe the process of DNA extraction.

Answer 24

Mash some strawberries and put them in a beaker containing a solution of detergent and salt.
Mix
Filter the mixture.
Gently add some ice cold alcohol to the filtered mixture.
The DNA will appear as a stringy white precipitate.
Take this out with a glass rod.

Question 25

Why is a solution of detergent and salt used in DNA extraction?

Answer 25

Detergent = it breaks down the cell membrane to release the DNA
Salt = it makes the DNA stick together

Question 26

Why does the DNA appear as a solid white precipitate and not dissolve in the cold alcohol?

Answer 26

DNA is not soluble in cold alcohol.