Topic 13: Genomes, Genes And Alleles

Question 1

Define genome.

Answer 1

The sum total of an organism’s DNA and is expressed as the base sequence of the haploid set of chromosomes.

Question 2

Describe the Human Genome project.

Answer 2

Publically funded, international cooperative beginning in 1990-2003.

Aim was to sequence the human genome, store sequence in accessible databases and to map all human genes.

Question 3

Define genome sequence.

Answer 3

Identification of the precise order or sequence of bases in the DNA of the genome.

Question 4

How is the info gained from HGP used?

Answer 4

DIAGNOSIS: more accurate diagnosis of inherited disorders due to single genes.

TREATMENT: Identifies the products of genes, infer how mutant alleles produce undesirable effects of genetic disorders.

PREVENTION: Identifies genetic factors predisposing disabling conditions.

HUMAN BIOLOGY: better understanding of genetic control of normal human development.

HUMAN EVOLUTION: mitochondrial DNA sequence (mtDNA) - new insight to human evolution and human group migration

Question 5

What did the HGP unveil about genes?

Answer 5

99.9% of genome identical of two unrelated people. Differences occur in single nucleotide polymorphisms and short tandem repeats (forensic application in gel electrophoresis). 3 bil base pairs, 2100 genes. Some are protein coding, some have regulatory function and are non coding.

Question 6

Comparative genomics definition.

Answer 6

Sequencing of other species enabling scientists to see various features evolution and identify how genome of closely related species differ.

Question 7

How are bonds held together of DNA chains?

Answer 7

Weak hydrogen bonds between specific bases of nucleotides.

Question 8

How is DNA packaged into chromosomes?

Answer 8

DNA helix is 2m long. Prior to cell division, DNA coiled and packaged. Coiling of DNA around histone proteins. 8 histone proteins + DNA = chromatin fibre. Histones and DNA further coiled into nucleosomes which are also coiled and organised into chromosomes.

Question 9

What is a gene?

Answer 9

Inherited instruction carried on chromosome, specific segment of DNA carrying instruction encoded in base sequences for specific protein product.

Question 10

Differentiate DNA and RNA.

Answer 10

DNA

• deoxyribose sugar
• Thymine base
• double stranded
• forms double helix

RNA

• Ribose sugar
• Uracil base
• Usually single stranded
• No double helix formation

Question 11

How many H bonds between A and T?

Answer 11

2 H bonds

Question 12

How many H bonds between C and G?

Answer 12

3 H bonds.

Question 13

What is transcription?

Answer 13

Transcription is process where 5’ to 3’ strand of DNA (coding strand) is transcribed to mRNA. Occurs in nucleus.

Question 14

What is translation?

Answer 14

Translation is reading of mRNA in codons in ribosomes enabling tRNA to attach anticodons and deliver amino acid from codon, stringing together amino acids to produce protein products.

Question 15

What does the redundancy of the genetic code refer to?

Answer 15

Degeneracy of genetic code denotes how differences in bases comprising codes may still result in the same amino acids being coded for. For example, AGU and CGU have a difference in their first bases but code for the same amino acid.

Question 16

Describe the substitution mutation.

Answer 16

substitution of a single base occurs in DNA sequence. Thus, incorrect amino acid produced. Frame shift does not occur. Translation to different amino acid may occur unless code is redundant. If different amino acid is produced, this alters protein product which may be non functional. Sickle cell aenemia is an example of this.

Question 17

Describe the insertion/deletion mutation.

Answer 17

large scale movement (frame shift) resulting in completely new sequence of amino acids. Resulting protein product most likely biologically inactive. Most disruptive as all amino acid code is changed from mutation onwards and translate amino acids deviate from normal producing incorrect protein.

Question 18

State chargaff’s rule.

Answer 18

In DNA double helix, porterions of A and T are equal, and so are the proportions of C and G.

Question 19

Describe relationship between DNA, genes and chromosomes.

Answer 19

Chromosome is long molecule of DNA. Chromosomes divided in to subunits - genes - that code for specific protein product. Genes comprised of DNA and a series of linked genes forms chromosome.

Question 20

Gene mapping vs gene sequencing.

Answer 20

Gene mapping refers to exact location of gene on particular chromosome (loci) whereas gene sequencing référés to base order within gene.

Question 21

Difference between autosomes and sex chromosomes.

Answer 21

Carry different gene loci. Autosomes found in males and females of same species. Sex chromosomes not the same in males and females as they determine gender.