Topic 3: Genetics

Question 1

What is Sexual Reproduction?

Answer 1

Where genetic information from two organisms’ gametes is combined to produce offspring genetically different to either parent.

Question 2

What is Meiosis?

Answer 2

A type of cell division that produces gametes (haploid cells).

Question 3

What occurs during and before Meiosis?

Answer 3

• Interphase produces copies of genetic information
• Two stages of cell devision : results in production of 4 haploid gametes

Question 4

What are the characteristics of cells produced by Meiosis?

Answer 4

• 4 haploid gametes
• Each cell is genetically different from its parent and each other

Question 5

What are Chromosomes?

Answer 5

Molecules of DNA wrapped/coiled around proteins

Question 6

What are the 4 bases that make up DNA?

Answer 6

Adenine + Thymine
Cytosine + Guanine

Question 7

What is the structure of a DNA nucleotide?

Answer 7

• Phosphate-Sugar-Base molecule
• Hydrogen bonds between bases
• Coiled, double-helix shape

Question 8

What is a gene?

Answer 8

A section of DNA that codes for a protein

Question 9

What are the 5 steps in extracting DNA?

Answer 9

1) Add Salt: Clumps together DNA
2) Add Detergent: Breaks down cell + nuclear membranes to release DNA
3) Place in a Water Bath: Provides optimum temp. for Enzyme activity
4) Add protease enzymes: Breaks down proteins associated with DNA
5) Add ethanol: Causes DNA to precipitate + become visible

Question 10

What is Asexual Reproduction?

Answer 10

Where organisms reproduce by mitosis to produce genetically identical offspring.

Question 11

Advantages of Asexual Reproduction

Answer 11

• Only needs one parent (no time wasted on mating)
• Fast process
• Rapid population growth

Question 12

Disadvantages of Asexual Reproduction

Answer 12

• No genetic variation in the population
• All vulnerable to same diseases + infections

Question 13

Advantages of Sexual Reproduction

Answer 13

• Genetic variation in the offspring
• Better chance of survival

Question 14

Disadvantages of Sexual Reproduction

Answer 14

• Takes time to find a mate
• Takes long periods of time for offspring to grow after fertilisation (slow process)

Question 15

Describe the Process of Transcription

Answer 15

• RNA Polymerase binds to non-coding region of the DNA in front of a gene
• The enzyme moves along the gene and unzips the DNA
• It creates a complementary strand of mRNA from the template DNA
• This mRNA strand has the same bases as DNA except for Uracil which replaces Thymine

Question 16

Describe the Process of Translation

Answer 16

• mRNA strand travels out of the nucleus through nuclear pores into the cytoplasm
• It binds with a ribosome which reads the strand a codon at a time
• Each codon codes for a single amino acid
• tRNA molecules bring the corresponding amino acids to the ribosome and peptide bonds form between the amino acids
• This forms a growing polypeptide chain that will fold into a 3D shape of a protein when a codon from the mRNA strand signals stop

Question 17

Define Mutation

Answer 17

A rare random change to the DNA base sequence.

Question 18

What are the causes of mutations?

Answer 18

• Carcinogens
• Radiation (eg. X-ray, Gamma, UV)
• Random errors during DNA replication

Question 19

What are the 3 types of Mutation?

Answer 19

Substitution
Deletion
Insertion

Question 20

What is the effect of mutations in non-coding regions of the DNA?

Answer 20

They affect the binding of RNA polymerase during protein synthesis. This can result in making too much or too little of a protein.

Question 21

Define Phenotype

Answer 21

The characteristics of an individual as a result of their genes.

Question 22

What are Alleles?

Answer 22

Different versions of the same gene. Can be either dominant or recessive.

Question 23

Define Genotype

Answer 23

The combination of alleles that result in a particular characteristic/phenotype.

Question 24

What is meant by Homozygous and Heterozygous alleles?

Answer 24

Homozygous = Two alleles that are the same
Heterozygous = Two alleles that are different

Question 25

Who was Gregor Mendel?

Answer 25

An Austrian monk who carried out valuable research into the field of genetics and inheritance with the use of pea plants.

Question 26

What were Mendel’s conclusions?

Answer 26

1) Characteristics in plants are determined by “hereditary units” 2) Hereditary units are passed on from parents to children, with one unit from each parent 3) Hereditary units can be dominant or recessive (hereditary units are genes)

Question 27

What is codominance and co-dominant alleles?

Answer 27

• Alleles that are neither dominant nor recessive • When two alleles of the same type are expressed in a phenotype

Question 28

What is meant by Autosomal?

Answer 28

Genes that are carried on autosomes instead of chromosomes

Question 29

Define Variation

Answer 29

The differences that exist between members of a species

Question 30

How is genetic variation achieved?

Answer 30

• Arisal of new alleles through mutations • Combining alleles in sexual reproduction

Question 31

How is environmental variation achieved?

Answer 31

• Any difference caused by conditions from the environment an organism lives in • Known as acquired characteristics

Question 32

What were the aims of the Human Genome Project?

Answer 32

• To discover + identify all 20-25,000 genes • To find where each gene is located • To determine the sequence of the 3 million base pairs • To store this information within a database

Question 33

What were the outcomes of the Human Genome Project?

Answer 33

• **New genes discovered** (eg. Breast cancer gene) • **New drug targets** • **Preventative medicine** (identification of mutations associated with disease) • **Understanding Biology** (eg. Receptor proteins = sense of taste) • **Investigating evolution** (comparisons with other organisms)

Question 34

What are the potential disadvantages/ ethical considerations of the Human Genome Project?

Answer 34

• People may be put under pressure not to have children • Increases pressure for germ line therapy to prevent children inheriting genetic conditions • Embryo has no choice/can’t object • Can lead to employment discrimination • May lead to issues with insurance (eg. Medical insurance for those with breast cancer gene) • Data protection issues • Could create ‘designer babies’ with selected genes • Infringement on human rights (who gets tests?)