Genetics

Question 1

What is sexual reproduction?

Answer 1

• Type of reproduction
• Involves the production of gametes by meiosis
• A gamete from each parent fuses to form a zygote
• Genetic information from each gamete is mixed so the resulting zygote is unique

Question 2

What are gametes?

Answer 2

• Sex cells (sperm cells, egg cells)
• Haploid (half the number of chromosomes)

Question 3

Why is meiosis important for sexual reproduction?

Answer 3

• It increases genetic variation
• It ensures that the resultant zygote is diploid

Question 4

What is the advantage of sexual reproduction?

Answer 4

It creates genetic variation, increasing the probability of a species adapting to and surviving environmental changes.

Question 5

Describe the disadvantages of sexual reproduction

Answer 5

• Two parents are required. This makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
• More time and energy is required so fewer offspring are produced

Question 6

What is asexual reproduction?

Answer 6

• Type of reproduction
• Involves mitosis
• Produces genetically identical offspring known as daughter cells

Question 7

Describe the advantages of asexual reproduction

Answer 7

• Only one parent is required
• Lots of offspring can be produced in a short period of time, enabling the rapid colonisation of an area and reducing competition from other species
• Requires less energy

Question 8

What is the disadvantage of asexual reproduction?

Answer 8

No genetic variation (except from spontaneous mutations) reducing the probability of a species being able to adapt to environmental change

Question 9

What is DNA?

Answer 9

A double-stranded polymer of nucleotides, wound to form a double helix

Question 10

What are the monomers of DNA?

Answer 10

Nucleotides

Question 11

What are DNA nucleotides made up of?

Answer 11

• Common sugar
• Phosphate group
• One of four bases: A, T, C or G

Question 12

State the full names of the four bases found in nucleotides

Answer 12

• Adenine
• Thymine
• Cytosine
• Guanine

Question 13

Describe how nucleotides interact to form a molecule of DNA

Answer 13

• Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
• Base connected to each sugar
• Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds

Question 14

Describe the method used to extract DNA from fruit

Answer 14

1. Place a piece of fruit in a beaker and crush it
2. Add detergent and salt, mix
3. Filter the mixture and collect the liquid in a test tube
4. Pour chilled ethanol into the test tube
5. DNA precipitates forming a fibrous white solid
6. Use a glass rod to collect the DNA sample

Question 15

Why is detergent added to the crushed fruit?

Answer 15

It disrupts the cell membranes, releasing
DNA into solution

Question 16

Why is salt added to the crushed fruit?

Answer 16

Salt encourages the precipitation of DNA

Question 17

Why is chilled ethanol added rather water?

Answer 17

DNA is insoluble in ethanol, encouraging its precipitation

Question 18

What is protein synthesis?

Answer 18

The formation of a protein from a gene

Question 19

What are the two stages of protein synthesis?

Answer 19

1. Transcription
2. Translation

Question 20

What does transcription involve?

Answer 20

The formation of mRNA from a DNA
template

Question 21

Outline transcription

Answer 21

1. DNA double helix unwinds
2. RNA polymerase binds to a specific base sequence of non-coding
   DNA in front of a gene and moves along the DNA strand
3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
4. mRNA formation complete. mRNA detaches and leaves the nucleus.

Question 22

Describe the difference between mRNA and DNA

Answer 22

• mRNA is single stranded whereas
DNA is double stranded
• mRNA uses U whereas DNA uses T

Question 23

Why is mRNA used in translation rather than DNA?

Answer 23

DNA is too large to leave the nucleus so cannot reach the ribosome.

Question 24

What does translation involve?

Answer 24

A ribosome joins amino acids in a specific order dictated by mRNA to form a protein.

Question 25

Outline translation

Answer 25

1. mRNA attaches to a ribosome 2. Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule 3. A polypeptide chain is formed from the sequence of amino acids which join together

Question 26

How is a tRNA molecule adapted to its function?

Answer 26

Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries.

Question 27

What is a mutation?

Answer 27

A random change in the base sequence of DNA which results in genetic variants

Question 28

What is a mutation?

Answer 28

A random change in the base sequence of DNA which results in genetic variants

Question 29

Describe the effect of a gene mutation in coding DNA

Answer 29

• If a mutation changes the amino acid sequence, protein structure and function may change • If a mutation does not change amino acid sequence, there is no effect on protein structure or function

Question 30

What is non-coding DNA?

Answer 30

DNA which does not code for a protein but instead controls gene expression

Question 31

Describe the effect of a gene mutation in non-coding DNA

Answer 31

• A mutation may affect the ability of RNA polymerase to bind to non-coding DNA • This may affect protein production and the resulting phenotype of the organism

Question 32

Outline how the work of Mendel helped scientists to develop their understanding of genetics

Answer 32

• Mendel studied the inheritance of different phenotypes of pea plants • He established a correlation between parent and offspring phenotypes • He noted that inheritance was determined by 'units' passed on to descendants • Using gene crosses, he devised the terms 'dominant' and 'recessive'

Question 33

Why was Mendel's work initially overlooked?

Answer 33

Scientist's didn't understand Mendel's work as there was no knowledge of genes or DNA at the time.

Question 34

What is a chromosome

Answer 34

Molecule of DNA that carries genetic information in the form of genes

Question 35

Define gene

Answer 35

Section of DNA that codes for a specific sequence of amino acids that go under polymerisation to form a protein

Question 36

Alleles ?

Answer 36

Different versions of the same gene

Question 37

Why are men more likely to show the phenotype for a recessive sex-linked trait than women?

Answer 37

• Many genes are found on the X chromosome that have no counterpart on the Y chromosome • Women (XX) have two alleles for each sex-linked gene whereas men (XY) often only have one allele . only one recessive allele is required to produce the recessive phenotype in males

Question 38

Why are the majority of genes found on the X chromosome rather than the Y chromosome?

Answer 38

The X chromosome is bigger than the Y chromosome so more genes are carried on it.

Question 39

What is a mutation?

Answer 39

A random change to the base sequence in DNA which results in genetic variants

Question 40

What is the Human Genome Project?

Answer 40

• Scientific research project involving thousands of scientists across the globe which successfully mapped the entire human genome • Scientists now aim to identify the function of every gene in the human genome

Question 41

What are drawbacks associated with the discoveries of the Human Genome Project?

Answer 41

• Knowledge of predisposition to a disease can be stressful • Societal pressure influencing the decision to have children • Discrimination by employers, insurance firms etc.

Question 42

What is genetic variation?

Answer 42

• Variations in the genotypes of organisms of the same species due to the presence of different alleles • Creates differences in phenotypes

Question 43

What are the two causes of variation within a species?

Answer 43

• Genetics • Environment