CB3: Genetics

Question 1

What is a zygote?

Answer 1

A single fertilised egg cell

Question 2

What is DNA?

Answer 2

Deoxyribonucleic acid. The material inside the nucleus of cells, carries the genetic information of a living being.

Question 3

Define genes

Answer 3

The basic unit of genetic material inherited from our parents. A gene is a section of DNA that controls part of a cell’s chemistry - particularly protein production

Question 4

Define chromosomes

Answer 4

The structure made of DNA that codes for all the characteristics of an organism.

Question 5

What is the difference between a diploid cell and a haploid cell?

Answer 5

A diploid cell contains 2 sets of 23 pairs of chromosomes (46 individual chromosomes) whereas a haploid cell only contains 23 chromosomes (half the amount)

Question 6

Under what circumstances must a cell be haploid?

Answer 6

When the cell is a gamete (sex cell) it is haploid because two gametes combine to make a diploid zygote

Question 7

What type of cell division produces:
a) diploid cells?
b) haploid cells?

Answer 7

a) Mitosis
b) Meiosis

Question 8

What is the difference between mitosis and meiosis?

Answer 8

Mitosis produces two diploid genetically identical cells whereas meiosis produces four genetically different cells. Mitosis is used during asexual reproduction whereas meiosis is used during sexual reproduction

Question 9

What are the steps in meiosis?

Answer 9

1. The gamete-making cell has two sets of chromosomes
2. The chromosomes replicate and the copies stay stuck to each other
3. The cell divides into 2 and then 2 again. Each of the four daughter cells ha a copy of 1 chromosome from each pair. They are haploid

Question 10

What is a double helix and what connects it?

Answer 10

The shape of a DNA molecule with two strands twisted together like a spiral. They are connected by weak hydrogen bonds between complementary base pairs

Question 11

What is a nucleotide and what is it made up of?

Answer 11

The monomer of DNA. Made up of a base, a phosphate group, and a sugar

Question 12

Define genome

Answer 12

The copy of all an organisms DNA

Question 13

What are the base pairs in DNA?

Answer 13

A-T
C=G

Question 14

What do the order of the bases affect?

Answer 14

Controls the order in which amino acids are joined up to make a specific protein or enzyme molecule

Question 15

Define alleles

Answer 15

Different versions of the same genes (eg eye colour). A body cell contains two copies of every gene

Question 16

What is the difference between heterozygous and homozygous?

Answer 16

Heterozygous: if the two copies of the gene are different
Homozygous: if the two copies of the gene are the same

Question 17

What is the difference between a dominant and a recessive allele?

Answer 17

A dominant allele will always be expressed no matter if the gene is heterozygous or homozygous, whereas a recessive allele will only be expressed in a homozygous gene. A dominant allele is written with a capital letter whereas a recessive gene is written with a lowercase letter

Question 18

What is a genotype?

Answer 18

All of the alleles in an organism

Question 19

What is a phenotype?

Answer 19

The alleles that have been expressed

Question 20

What are the two sex chromosomes and what are the combinations for males and females?

Answer 20

X and Y
Male: XY
Female: XX

Question 21

Define mutations

Answer 21

A random and spontaneous change in a gene or a chromosome. Most have no effect on the phenotype

Question 22

Define variation

Answer 22

The differences between organisms.

Question 23

Define natural selection and give another name for it

Answer 23

Organisms better suited for an environment are more likely to survive and pass on their genes. It is also called the survival of the fittest

Question 24

What are the causes of mutations?

Answer 24

• ionising radiation
• chemical mutagen such as tar from cigarette smoke

Question 25

State and define the two types of variation

Answer 25

Genetic variation: caused by inherited alleles during sexual reproduction
Environmental variation: caused by the environment giving acquired characteristics

Question 26

What are the two groups that variation can be grouped into?

Answer 26

Continuous variation: data that can be any value in a range
Discontinuous variation: data that can only take a limited set of values

Question 27

What is a normal distribution?

Answer 27

A bell shape curve on a graph