Reproduction

Question 1

What is a chromosome?

Answer 1

A large molecule of DNA

Question 2

What is a gene?

Answer 2

A small section of DNA that codes for a particular sequence of amino acids that make a specific protein

Question 3

What is the genome of an organism?

Answer 3

The entire genetic material of an organism (including all of the chromosomes and the mitochondria).

Question 4

How many chromosomes do humans have?

Answer 4

46 (23 pairs) in most cells. Gametes have half of this number (23).

Question 5

Describe the structure of DNA.

Answer 5

DNA is a polymer made up of two strands, which form a double helix.

Question 6

How many bases code for a particular amino acid?

Answer 6

3

Question 7

Describe the importance of the order of bases in DNA.

Answer 7

The order of bases controls the order in which amino acids are assembled into a protein.

Question 8

What is involved in sexual reproduction?

Answer 8

The joining of male and female gametes, which results in a mixing of genetic information.

Question 9

What is involved in asexual reproduction?

Answer 9

1 parent (no gametes). There is no mixing of genetic information, leading to genetically identical offspring (clones).

Question 10

What are gametes?

Answer 10

Sex cells (eggs and sperm cells) which have half the number of chromosomes as an ordinary cell.

Question 11

Why do body cells divide?

Answer 11

• Replace worn-out cells
• Repair damaged tissues
• For growth of the organism

Question 12

Which process allows division of body cells?

Answer 12

Mitosis

Question 13

What must happen before mitosis can occur?

Answer 13

The DNA doubles (DNA replication)

Question 14

Outline the 3 main stages of mitosis.

Answer 14

1 - DNA replicates to produce 2 copies of each chromosome and sub-cellular structures increase in number;
2 - one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides;
3 - the cytoplasm and the cell membrane also divide to form 2 identical daughter cells

Question 15

Compare the cells that are produced (daughter cells) by mitosis to the parent cell.

Answer 15

They are genetically identical as the DNA is copied

Question 16

Which cells undergo meiosis and what do they form?

Answer 16

Cells in the reproductive organs divide by osmosis to form the gametes (egg cells and sperm cells)

Question 17

What happens when a cell divides by meiosis to form gametes?

Answer 17

The genetic material is copied and then the cell divides twice to form 4 genetically different cells, each with one set of chromosomes

Question 18

Why do gametes have just 23 chromosomes instead of 46?

Answer 18

Two gametes join at fertilization to restore the number of chromosomes to 46.

Question 19

How is mitosis different to meiosis?

Answer 19

In mitosis, cells divide once to produce two genetically identical daughter cells. The cells produced in mitosis each have 2 sets of chromosomes. In meiosis, cells divide twice to produce 4 genetically different daughter cells. The cells produced in meiosis each have one set of chromosomes.

Question 20

What is an allele?

Answer 20

A different form of a gene (the combination of alleles inherited determines characteristics).

Question 21

What are dominant alleles?

Answer 21

A form of the gene that controls the characteristic even if it is only present on 1 chromosome

Question 22

What are recessive alleles?

Answer 22

A form of the gene that only controls the characteristic if it is present on both chromosomes

Question 23

What is a homozygote?

Answer 23

An individual with two identical alleles for a characteristic e.g. BB or bb

Question 24

What is a heterozygote?

Answer 24

An individual with different alleles for a characteristic e.g. Bb

Question 25

What is a genotype?

Answer 25

This describes the alleles that are present for a particular characteristic e.g. Bb

Question 26

What is a phenotype?

Answer 26

This describes the physical appearance of an individual for a particular characteristic e.g. brown fur

Question 27

What is polydactyly?

Answer 27

More digits (fingers or toes) than normal

Question 28

How is polydactyly inherited?

Answer 28

The allele is dominant. If a parent has polydactyly there is a 50% that offspring will have polydactyly.

Question 29

What is cystic fibrosis?

Answer 29

A disorder of the cell membranes of cells lining the airways and pancreas. They have thick mucus so they get frequent lung infections and cannot digest food properly.

Question 30

How is cystic fibrosis inherited?

Answer 30

The allele is recessive. If both parents are carriers there is a 25% chance that the offspring will have CF.

Question 31

How can embryos or foetuses be screened for genetic disorders?

Answer 31

Cells have to be collected from the developing embryo/foetus.

Question 32

Give some reasons why some people may be concerned about embryo screening.

Answer 32

• Risk of miscarriage
• false positive or false negative results
• could result in termination
• expensive.

Question 33

How is sex determined in humans?

Answer 33

By the sex chromosomes (22 pairs of chromosomes control general body characteristics but one pair of chromosomes control the sex).

Question 34

What are the female and male sex chromosomes?

Answer 34

Female - XX (homozygous); Male (XY - heterozygous)

Question 35

What is variation?

Answer 35

The differences in characteristics of individuals in a population (e.g. hair colour in humans)

Question 36

What causes variation?

Answer 36

Genetic causes, environmental cause or a combination of both genes and the environment.

Question 37

What causes variation in genes?

Answer 37

Mutations - a change in the DNA code (many mutations have no effect, some influence phenotype and very few will determine phenotype).

Question 38

What is a Zygote

Answer 38

A fertilised egg cell