GENE 1: Key terms and concepts

Question 1

What are genes?

Answer 1

Stretches of DNA that code for a functional molecule and determine the characteristics of the cell/organism, they are located as linear DNA on chromosomes in the nucleus, or circular DNA in the mitochondria (and one small chromosome)

Question 2

What ensures genes are transcribed into RNA?

Answer 2

DNA promoter sequences

Question 3

Name the messengers between DNA and a polypeptide chain

Answer 3

DNA -> Pre-mRNA -> mRNA

Question 4

What is the genome?

Answer 4

the complete genetic information for that organism so includes all the DNA in one set of chromosomes

Question 5

What % of the genome is made up of genes?

Answer 5

25%

Question 6

What % of the genome is made up of exons?

Answer 6

2%

Question 7

What makes up the non-genes of the genome?

Answer 7

repetitive and non-repetitive DNA, most of which has no known function

Question 8

What % of variation is there between DNA sequences between humans?

Answer 8

0.1% variation

Question 9

What is the transcriptome?

Answer 9

All of the RNA present in a cell or population of cells at a articular time (some definitions do or don’t include non-coding RNA)

Question 10

What is the complete set of exons known as?

Answer 10

Exome

Question 11

Why is the transcriptome highly variable?

Answer 11

It changes in different cells and in different cell types and at different times because different proteins need to be produced depending on what is required

Question 12

How can you compare the steady genome to the transcriptome? And what is the use of this?

Answer 12

To determine which parts of the genome are expressed in a sample and the relative amounts of each transcript present. Transcriptomic and genomic data can be generated by nucleotide sequencing and hybridisation techniques.

Question 13

What is the proteome?

Answer 13

Complete set of proteins expressed in a particular cell type at a particular time

Question 14

Why does the transcriptome not entirely correlate to the proteome?

Answer 14

the extent to which mRNA is translated varies with cell type and cellular conditions

Question 15

What does protein degradation depend on?

Answer 15

Cellular proteases and cellular conditions

Question 16

How many is haploid and diploid?

Answer 16

23 chromosomes is haploid and 46 chromosomes is diploid

Question 17

What is the genotype and phenotype?

Answer 17

Genotype: the genetic constitution of an individual and can refer to the overall constitution or that at a specific genetic locus
Phenotype: refers to the physical or biochemical appearance of an organism

Question 18

If two heterozygous individuals are bred, what are phenotype ratios and how many genotypes are there?

Answer 18

3:1 ratio of dominant to recessive alleles

3 genotypes: rr, rR, RR

Question 19

What is forward genetics?

Answer 19

The deduction of the underlying genotype from the phenotype

Question 20

What is reverse genetics?

Answer 20

Where the genotype is changed to inspect the difference in phenotype

Question 21

Why is determining the change in phenotype easier in some diseases than others?

Answer 21

Sickle cell anaemia for example is much easier to distinguish than diseases that require electrophoresis and peptide mapping to determine the difference

Question 22

What two types of analysis are used to complete molecular understanding of a disease

Answer 22

Genetic

Biochemical

Question 23

What does co-dominant alleles allow?

Answer 23

The expression of both alleles e.g. sickle cell trait

Question 24

What are monogenic inherited diseases caused by?

Answer 24

a mutation of just one gene, inherited according to mendelian rules

Question 25

List examples of monogenic diseases

Answer 25

Sickle Cell Disease
Cystic fibrosis
Werner’s syndrome
Permanent neonatal diabetes mellitus

Question 26

What can be used to distinguish diseases caused by dominant or recessive alleles?

Answer 26

Pedigree analysis

& the type of chromosome it was located on i.e. autosome, X or mitochondrial

Question 27

What are the 5 classes of monogenic diseases?

Answer 27

1. Autosomal Recessive
2. Autosomal Dominant
3. X-linked Recessive
4. X-linked Dominant
5. Mitochondrial

Question 28

What are Autosomal Recessive diseases?

Answer 28

Disease may not affect every generation and both parents of the affected individual are carriers. (e.g. SCD)

Question 29

What are Autosomal Dominant diseases?

Answer 29

Disease affects every generation and every affected individual has an affected parent (e.g. Huntington disease)

Question 30

What are X-linked Recessive diseases?

Answer 30

Males most often affected by the disease and affects every generation (e.g. Haemophilia A)

Question 31

What are X-linked Dominant diseases?

Answer 31

Females most often affected but disease can affect both sexes in a generation (e.g. Ornithine Transcarbamylase Deficiency)

Question 32

What are Mitochondrial diseases?

Answer 32

Disease passed on by females but affects both sexes in every generation (e.g. Leber’s hereditary optic neuropathy)

Question 33

What are polygenic diseases?

Answer 33

Depend on mutations of many genes and do not exhibit a Mendelian inheritance pattern

Question 34

Give examples of polygenic diseases

Answer 34

Heart disease
diabetes
obesity

Question 35

What type of analysis is required for polygenic diseases?

Answer 35

genomic analysis to identify the gene mutations responsible

Question 36

What is it called when environmental factors are also involved in increasing the risk of the disease?

Answer 36

Multifactorial disease

Question 37

What happens if random mutations occur in somatic cells vs germline/early embryo?

Answer 37

cancer which is not passed on vs disease that is passed on

Question 38

Why may identical twins have different genotypes?

Answer 38

Due to environmental and epigenetic factors that can affect genotype

Question 39

What environmental factors can directly cause mutagenesis?

Answer 39

• Chemical (pollutants)
• Physical (UV light)
• Biological (virus)
  These are random processes that might cause minor or major phenotypic changes.

Question 40

What is the epigenome?

Answer 40

The entire network of chemical modifications at a particular time that change the genome without altering the DNA sequence

Question 41

What is epigenetics?

Answer 41

study of changes to the DNA structure and gene expression but not the nucleotide sequence

Question 42

What can epigenetic changes lead to?

Answer 42

Changes in the transcriptome, proteome and phenotype, whilst the genome remains constant

Question 43

Are epigenetic changes permanent? What happens to the nuclei of the changed cells over time? What can this give rise to?

Answer 43

Not permanent. The nuclei of skin cells can be ‘reprogrammed’ when inserted into an enucleated egg, it can give rise to a new organism with all cell types (nuclear transfer experiment.)

Question 44

Describe the nuclear transfer experiment

Answer 44

Donor egg with nucleus removed, fused with a somatic cell of a different strain of sheep. Then implanted into a foster mother. Lamb born genetically identical to somatic cell donor

Question 45

Environmental factors such as diet can influence the ________ without changing gene expression.

Answer 45

phenotype

Question 46

What happens in phenylketonuria? How can it be avoided?

Answer 46

The gene encoding phenylalanine hydroxylase is mutated leading to phenylalanine accumulation causing damage to brain development and resulting in intellectual disabilities and seizures. If a child’s diet is changed to remove phenylalanine, the diseased phenotype can be avoided even if the genotype is unchanged since the harmful environmental factor has been removed.

Question 47

Give examples of environmental factors affecting gene expression

Answer 47

In bacteria, genes encoding tryptophan synthesis can be modulated as required. Therefore, when tryptophan is absent in the surrounding environment, these genes are upregulated. In mammals, a similar mechanism is the production of insulin only in the presence of glucose.