6. Inheritance, Variation and Evolution (reproduction)

Question 1

What is sexual reproduction?

Answer 1

• a type of reproduction
• involves the production of gametes by meiosis
• a gamete from each parent fuses to form a zygote
• genetic information from each gamete is mixed so the resulting zygote is unique

Question 2

What are gametes in animals?

Answer 2

sex cells (sperm and egg cells) with 23 chromosomes

Question 3

What are the gametes for plants?

Answer 3

pollen and egg cells

Question 4

What does haploid mean?

Answer 4

half the number of chromosomes

Question 5

What is meiosis?

Answer 5

• A form of cell division involved in the formation of gametes in reproductive organs.
• The chromosome number is halved
• it involves two divisions

Question 6

What must occur prior to meiosis?

Answer 6

Interphase - copies of genetic information are made during this process

Question 7

What happens during the first stage of meiosis?

Answer 7

1. Chromosome pairs line up along the cell equator
2. The pair of chromosomes are separated and move to opposite poles of the cell
3. The chromosome number is halved

Question 8

What in the first stage of meiosis creates variation?

Answer 8

how the side to which each chromosome is pulled is random

Question 9

What happens during the second stage of meiosis?

Answer 9

4. Chromosomes line up along the cell equator
5. The chromatids are separated and move to opposite poles of the cell
6. Four unique haploid gametes are produced

Question 10

Why is meiosis important for sexual reproduction? (2)

Answer 10

• it increases genetic variation
• it ensures that the zygote formed at fertilisation is diploid

Question 11

Describe fertilisation and its resulting outcome

Answer 11

• gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis, which increases the number of cells
• as the embryo develops, cells differentiate

Question 12

What is the advantage of sexual reproduction? (2)

Answer 12

• It creates genetic variation in offspring, increasing the probability of a species adapting to and surviving environmental changes
• natural selection can be speeded up by humans in selective breeding to increase food production

Question 13

Describe the disadvantages of sexual reproduction? (2)

Answer 13

• two parents are required. so reproduction is difficult in endangered populations
• more time and energy is required so fewer offspring are produced

Question 14

What is asexual reproduction?

Answer 14

• a type of reproduction
• involves mitosis only
• produces genetically indentical offsprings known as daughter cells

Question 15

Describe the advantages of asexual reproduction? (3)

Answer 15

• only one parent is required
• lots of offsprings can be produced in a short amount of time, enabling the rapid colonisation of an area and reducing competition from other species
• requires less time and energy as do not need to mate

Question 16

Describe the disadvantages of asexual reproduction? (1)

Answer 16

No genetic variation (except from spontaneous mutations) reducing the probability of a species being able to adapt to an environmental change

Question 17

Describe the circumstances in which malarial parasites reproduce sexually and asexually

Answer 17

• sexual reproduction in the mosquito
• asexual reproduction in the human host

Question 18

Describe the circumstances in which fungi reproduce sexually and asexually

Answer 18

• asexual reproduction by spores
• sexual reproduction to give variation

Question 19

Describe the circumstances in which plants reproduce sexually and asexually

Answer 19

• sexual reproduction to produce seeds
• asexual reproduction by runners (eg. strawberry plants)

Question 20

What is DNA?

Answer 20

a double stranded polymer of nucleotides, wound to form a double helix

Question 21

Define genome

Answer 21

the entire genetic material of an organism

Question 22

Why is understanding the human genome important?

Answer 22

It has been studied and is important for the development of medicine in the future:
- searching for genes linked to different types of diseases
- understanding and treating inherited disorders
- tracing human migration patterns from the past

Question 23

What is a chromosome?

Answer 23

a longm, coiled molecule of DNA that carries genetic information in the form of genes

Question 24

How many chromosomes do human body cells have?

Answer 24

46 chromosomes (23 pairs)

Question 24

How many chromosomes do gametes have?

Answer 24

23 chromosomes

Question 25

Define gene

Answer 25

a small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein

Question 26

What are the monomers of DNA?

Answer 26

nucleotides