B12. (Comb) Types of reproduction and DNA

Question 1

What is a gamete?

Answer 1

A gamete is a sex cell produced in the sex organs by meiosis (e.g. sperm cell, egg cell are gametes).

Question 2

How many chromosomes do human sex cells contain in their nucleus?

Answer 2

They contain half the number of chromosomes compared to a normal body cell i.e. 23 chromosomes

Question 3

Describe the structure of DNA

Answer 3

Deoxyribonucleic acid (=DNA) is the molecule in the nucleus that carries our genetic code. DNA is a double stranded, double helix molecule.

Question 4

What is a chromosome?

Answer 4

A chromosome is a length of DNA. Chromosomes are arranged into pairs in the nucleus.

Question 5

A gene is….

Answer 5

Genes are small sections of chromosomes (DNA) that code for a particular sequence of amino acids to make a specific protein.

Question 6

What is an allele?

Answer 6

An allele is a different/alternate form of a gene.

For example: Gene is eye colour, the alleles could be brown, blue, green, etc.

Question 7

Homozygous alleles are…

Answer 7

alleles that are the same e.g. BB or tt

Question 8

Heterozygous alleles are…

Answer 8

alleles that are the different e.g. Bb or Tt

Question 9

When are dominant alleles expressed?

Answer 9

Dominant alleles are alleles that are always expressed if they are present - even if only one copy is present e.g. Bb, BB.

Question 10

When are recessive alleles expressed?

Answer 10

Recessive alleles are only expressed if there are 2 recessive alleles present e.g. bb (therefore no dominant allele is present).

Question 11

What is meant by the term ‘genotype’?

Answer 11

The genetic makeup (alleles) of an individual. e.g., BB, Tt, ss.

Question 12

What is meant by the term ‘phenotype’?

Answer 12

This describes the physical and biological characteristics expressed in an individual as determined by their genotype. e.g. Brown eyes, Tall, curly hair.

Question 13

List the 2 types of reproduction

Answer 13

• Sexual reproduction

- Asexual reproduction

Question 14

How many parents are involved in sexual reproduction?

Answer 14

Two parents - a male and a female

Question 15

Which type of reproduction requires gametes e.g. sperm cell, egg cell?

Answer 15

Sexual reproduction

Question 16

Why does asexual reproduction not require gametes?

Answer 16

Because in asexual reproduction only ONE parent is involved. There is no fusion of gametes.

Question 17

Describe the offspring in asexual reproduction

Answer 17

They are all genetically identical to each other and the parent. They are clones.

Question 18

Compare mitosis and meiosis in terms of number of divisions.

Answer 18

In mitosis there is one division, in meiosis there are two divisions.

Question 19

What are the products of meiosis?

Answer 19

Four genetically different sex cells.

Question 20

Name an advantage of sexual reproduction.

Answer 20

1) Produces variation in the offspring.
2) If the environment changes variation gives a survival advantage.
3) Natural selection can be speeded up by humans in selective breeding to increase food production.

Question 21

Name an advantage of asexual reproduction.

Answer 21

1) Only one parent needed
2) More time and energy efficient as do not need to find a mate.
3) Faster than sexual reproduction.
4) Many identical offspring can be produced when conditions are favourable.

Question 22

What are the sex cells of a plant?

Answer 22

Male sex cell = pollen grain

Female sex cell = ovule

Question 23

In which type of reproduction is there variation in the offspring?

Answer 23

Sexual reproduction - because there is fusion of gametes.