B1 - You and your genes

Question 1

State the two types of cell

Answer 1

Eukaryotic (animals and plants)
&
prokaryotic

Question 2

What is the difference between a

eukaryotic and prokaryotic cell?

Answer 2

A eukaryotic cell contains a nucleus and
membrane-bound organelles. A
prokaryotic cell does not.

Question 3

How can the structure of eukaryotic cells

be observed?

Answer 3

Using a light microscope

Question 4

How is genetic information stored in a

eukaryotic cell?

Answer 4

Within the nucleus, arranged in

chromosomes

Question 5

How is genetic information stored in a

prokaryotic cell?

Answer 5

Found free within the cytoplasm as:

● Single large loop of circular DNA
● Plasmids

Question 6

What are plasmids?

Answer 6

● Small, circular loops of DNA found free in the
cytoplasm and separate from the main DNA

● Carry genes that provide genetic advantages
e.g. antibiotic resistance

Question 7

Define genome

Answer 7

The entire genetic material of an

organism

Question 8

What is a chromosome?

Answer 8

A long, coiled molecule of DNA that
carries genetic information in the form of
genes

Question 9

What is DNA?

Answer 9

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

Question 10

Define gene

Answer 10

A section of DNA that codes for a
specific sequence of amino acids which
undergo polymerisation to form a protein

Question 11

What are alleles?

Answer 11

Different versions of the same gene

Question 12

Define genotype

Answer 12

An organism’s genetic composition,

describes all alleles

Question 13

Define phenotype

Answer 13

An organism’s observable characteristics
due to interactions of the genotype and
environment (which can modify the
phenotype)

Question 14

What are the monomers of DNA?

Answer 14

Nucleotides

Question 15

What are DNA nucleotides made up of?

Answer 15

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

Question 16

Describe how nucleotides interact to

form a molecule of DNA

Answer 16

● Sugar and phosphate molecules join to form a
sugar-phosphate backbone in each DNA strand

● Base connected to each sugar

● Complementary base pairing: A pairs with T, C pairs with G

Question 17

Explain how a gene codes for a protein

Answer 17

● A sequence of three bases in a gene forms a triplet

● Each triplet codes for an amino acid

● The order of amino acids determines the structure
and function of protein formed

Question 18

Describe the differences between mRNA

and DNA

Answer 18

mRNA is single stranded whereas
DNA is double stranded

● mRNA uses U whereas DNA uses T

Question 19

What is protein synthesis?

Answer 19

The formation of a protein from a gene

Question 20

Outline protein synthesis

Answer 20

In the nucleus, DNA is used as a template to form mRNA

2. mRNA exits the nucleus, moving into the cytoplasm where
   it attaches to a ribosome
3. The ribosome joins amino acids in a specific order,
   dictated by mRNA to form a protein.

Question 21

Why does mRNA rather than DNA join to

a ribosome in the cytoplasm

Answer 21

DNA is too large to leave the nucleus so

cannot reach the ribosome

Question 22

What is a mutation?

Answer 22

A random change to the base sequence

of DNA which results in genetic variants

Question 23

State the three types of gene mutation

Answer 23

● Insertion
● Deletion
● Substitution

Question 24

Describe the effect of a gene mutation in

coding DNA

Answer 24

● If a mutation changes the sequence of amino acids,
protein structure and function may change

● If a mutation does not change the sequence of amino
acids, there is no effect on protein structure or
function

Question 25

What is non-coding DNA?

Answer 25

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

Question 26

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

Answer 26

Gene expression may be altered, affecting protein production and the resulting phenotype

Question 27

What are gametes?

Answer 27

Reproductive cells (e.g. egg and sperm cells) that contain a single copy of each chromosome

Question 28

Describe sexual reproduction in terms of | chromosome number

Answer 28

● Two gametes with a single copy of each chromosome fuse ● Resulting embryo has two chromosomes for each gene and two copies of each allele

Question 29

Define homozygous

Answer 29

Having two identical alleles of a gene | e.g. FF or ff

Question 30

Define heterozygous

Answer 30

Having two different alleles of a gene | e.g. Ff

Question 31

What is a dominant allele?

Answer 31

Describes an allele that is always expressed Represented with a capital letter e.g. F

Question 32

What is a recessive allele?

Answer 32

An allele that is only expressed in the absence of a dominant allele Represented with a small letter e.g. f

Question 33

What is the problem with single gene | crosses?

Answer 33

Most characteristics are controlled by | multiple alleles rather than just one

Question 34

What are sex chromosomes?

Answer 34

A pair of chromosomes that determines sex: ● Males have an X and a Y chromosome ● Females have two X chromosomes

Question 35

Why does the inheritance of a Y chromosome mean that an embryo develops into a male?

Answer 35

Testes development in an embryo is stimulated by a gene present on the Y chromosome

Question 36

Other than using a punnett square, how else can single gene inheritance be represented?

Answer 36

Using a family tree

Question 37

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

Answer 37

● 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 38

What is genome sequencing?

Answer 38

Finding out the order of nucleotides in the DNA of an organism, enabling the function and interaction of genes to be assessed

Question 39

Why is genome sequencing important?

Answer 39

● Allows the comparison of genomes of healthy individuals with patients who have a disease ● Potential disease-causing alleles are identified ● Individuals can then undergo genetic testing for these alleles

Question 40

Outline how genetic testing can be used | to improve healthcare (3)

Answer 40

● Enables awareness of potential risks and the introduction of lifestyle changes to reduce these associated risks ● Enables early treatment plans to begin ● Prediction of a patient’s reaction to certain drugs - ‘personalised medicine’

Question 41

Outline the drawbacks of using genetic | testing in healthcare

Answer 41

● Discrimination by employers, insurance firms etc. if a person is likely to develop a disease ● Person may develop anxiety, depression etc.

Question 42

Outline how genetic testing can be used | in family planning

Answer 42

● Parental carrier testing - parents tested for the presence of recessive disease-causing alleles ● Prenatal testing - egg fertilised In vitro, embryo tested for genetic disorders ● Fetus tested for genetic disorders via amniocentesis or chorionic villus sampling (CVS)

Question 43

Outline the drawbacks of using genetic | testing in family planning

Answer 43

● False-positive/false-negatives ● Ethical considerations - involves the destruction of embryos and potential terminations ● Amniocentesis and CVS carry a slight risk of miscarriage ● Could lead to ‘designer babies’

Question 44

What is genetic engineering?

Answer 44

● The changing of the genome of an organism by the insertion of a desired gene from another organism ● Enables the formation of an organism with beneficial characteristics

Question 45

Describe the process of genetic | engineering

Answer 45

1. Desired gene isolated using enzymes 2. Gene replicated 3. Gene placed into vector (e.g. plasmid, virus) 4. Vector mixed with and ‘taken up’ by target cells 5. Modified cells identified, selected and cultured

Question 46

Describe the benefits of genetic | engineering

Answer 46

● Increased crop yields for growing population e.g. herbicide-resistance, disease-resistance ● Useful in medicine e.g. insulin-producing bacteria, antithrombin in goat milk ● GM crops produce scarce resources e.g. GM golden rice produces beta-carotene (source of vitamin A in the body)

Question 47

Describe the risks of genetic engineering

Answer 47

● Long-term effects of consumption of GM crops unknown ● Negative environmental impacts e.g. reduction in biodiversity, impact on food chain, contamination of non-GM crops forming ‘superweeds’ ● Late-onset health problems in GM animals