B2- Simple Inheritance in Animals and Plants

Question 1

Define chromosome.

Answer 1

A chromosome is a strand of DNA.

Question 2

What is mitosis?

Answer 2

Mitosis is the type of cell division that produces identical new cells.

Question 3

Describe the 4 steps of mitosis.

Answer 3

1. Chromosomes in a parent cell make identical copies of themselves.
2. The chromosomes line up along the centre.
3. They move apart.
4. Two identical daughter cells form with identical chromosomes to the parent cell.

Question 4

What are gametes?

Answer 4

Gametes are sex cells produced by meiosis, with only 1 set of chromosomes.

Question 5

Describe the 3 steps of meiosis.

Answer 5

1. Chromosomes in a parent cell replicate.
2. The pairs of chromosomes divide- 1st division.
3. Chromosomes divide- 2nd division.

Question 6

Why does meiosis produce variation?

Answer 6

There are lots of possible combinations of chromosomes, this makes variation. This is important for evolution.

Question 7

What are stem cells?

Answer 7

Stem cells are unspecialised/undifferentiated cells that can become specialised.

Question 8

Where are stem cells found?

Answer 8

Stem cells can be found in the human embryo and in adult bone marrow.

Question 9

Humans have how many pairs of chromosomes?

Answer 9

23 pairs.

Question 10

Sex is determined by the X and Y chromosomes- how so?

Answer 10

Human females have two X chromosomes. Human males have an X and a Y chromosome.

Question 11

Define allele.

Answer 11

Different forms of the same gene.

Question 12

Define phenotype.

Answer 12

Characteristics expressed by an individual= observable. Physical appearance of the characteristic.

Question 13

Define genotype.

Answer 13

The genetic make-up of an individual.

Question 14

Define dominant.

Answer 14

A dominant allele always shows, even if an individual only has one copy. Allele expressed with only one copy of allele.

Question 15

Define recessive.

Answer 15

A recessive allele only shows if the individual has two copies.

Question 16

What is polydactyly?

Answer 16

A genetic disorder where a baby is born with an extra finger or toe, caused by a dominant allele.

Question 17

What is cystic fibrosis?

Answer 17

Cystic fibrosis affects cell membranes and causes the production of thick, sticky mucus which can affect the lungs. It is caused by a recessive allele.

Question 18

Describe and explain some of the symptoms of cystic fibrosis.

Answer 18

• Not putting on weight ➡️ digestive enzymes blocked by mucus ➡️reduced absorption of broken down foods.
• Difficulty breathing ➡️mucus blocks trachea, bronchi and bronchioles.
• Infection➡️mucus too thick to be coughed up➡️pathogens sit in mucus and cause disease.

Question 19

What are the ethical issues with embryo screening of pregnant women and IVF?

Answer 19

Pregnant- Sample of cells from embryo➡️Risk of miscarriage and difficult decision if diseased.

IVF- Still ethical issues because its selecting ‘healthy’ embryos➡️Unhealthy embryos destroyed➡️Slippery slope.

Question 20

Define gene.

Answer 20

A gene is an instruction for making proteins to determine a characteristic.

Question 21

Why is it important that gametes have only 23 chromosomes? (2 marks)

Answer 21

When gametes fuse (1), chromosome number is restored to full number of 23 pairs (1).

Question 22

When Mendel published his work on genetics, other scientists at the time did not realise how important it was.

Suggest two reasons why.

Answer 22

1. They did not know about genetics or alleles.
2. Mendel only worked with pea plants.
   (3. Mendel was not considered to be a scientist.)