B2- Simple Inheritance in Animals and Plants

Question 1

Define dominant.

Answer 1

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

Question 2

Humans have how many pairs of chromosomes?

Answer 2

23 pairs.

Question 3

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

Suggest two reasons why.

Answer 3

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.)

Question 4

Define gene.

Answer 4

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

Question 5

Where are stem cells found?

Answer 5

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

Question 6

What is cystic fibrosis?

Answer 6

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 7

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

Answer 7

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

Question 8

What is mitosis?

Answer 8

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

Question 9

Define chromosome.

Answer 9

A chromosome is a strand of DNA.

Question 10

Describe the 3 steps of meiosis.

Answer 10

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

Question 11

Define recessive.

Answer 11

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

Question 12

Describe the 4 steps of mitosis.

Answer 12

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 13

What are gametes?

Answer 13

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

Question 14

What is polydactyly?

Answer 14

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

Question 15

Define allele.

Answer 15

Different forms of the same gene.

Question 16

Describe and explain some of the symptoms of cystic fibrosis.

Answer 16

• 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 17

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

Answer 17

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

Question 18

Why does meiosis produce variation?

Answer 18

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

Question 19

Define genotype.

Answer 19

The genetic make-up of an individual.

Question 20

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

Answer 20

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 21

What are stem cells?

Answer 21

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

Question 22

Define phenotype.

Answer 22

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