BIOC0005 - THE HUMAN GENOME EXAM QUESTIONS
AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
Describe the composition of the human nuclear genome.
One genome has 23 chromosomes.
22 autosomes
50 to 260 Mb DNA
23 chromosomes has 3x10e9 bp, therefore somatic cells have 6x10e9.
Chromosomes are arranged in order, with 1 being largest and 22 being smallest. Made
up of 2 arms: p is the shorter arm and q is the longer one.
Human genome encodes 21000 genes.
Describe the proportions of sequences in the human genome.
1.5% of the human genome codes for protein coding regions (exons).
25% of the human genome codes for introns.
43% of the human genome comprises repetitive DNA - 'non-functional'.
Other DNA: Regulatory regions of genes, Pseudogenes, RNA genes (not mRNA),
Fragments of genes
,How does the human genome encode so many genes?
Alternative splicing of mRNA provides additional proteins from a single transcript. Exons
will remain in order.
Exons exit from the nucleus, introns remain in the nucleus during splicing. Addition of
polyA tail.
Several genes are members of a gene family. How does this occur?
Arisen by gene duplication
Duplicated genes have acquired base changes
Gene products encode proteins with different properties.
Describe haemoglobin in terms of its gene family.
Part of the globin gene family, which encodes the protein chains for haemoglobin (2
alpha and 2 beta chains)
Alpha globin gene cluster is found on chromosome 16; transcribed in fetus and adult.
Beta globin gene cluster is found on chromosome 11; transcribed in adult.
Gene duplication allows for higher affinity of oxygen of foetal haemoglobin compared to
adult haemoglobin.
Describe the composition of the histone gene family.
Genes make up the histone - 2 H2A, 2 H2B, 2 H3 and 2 H4 make up the nucleosome
octamer. 1 H1 sits on nucleosome octamer, pulling DNA together, makes up the histone
octamer.
, 11 histone gene clusters, 60 histone genes distributed over 7 chromosomes. Although
duplicated, each member of a particular histone gene family encodes the identical
protein.
140 bp of DNA wraps twice around the histone octamer.
Lots of histone proteins are needed when DNA replicate; each histone connected by
linker DNA.
What are the different gene duplication outcomes?
If there is selective pressure on both genes, the genes stay similar (such as globin and
histone family members).
If there is selection pressure on just one gene, one copy mutates and loses function
(pseudogenes) or one copy acquires a new function.
The human genome contains repetitive DNA interspersed throughout the
genome. What are LINES?
Long interspersed nuclear elements (L1)
Comprise 20% of genome.
Human L1 elements are the only autonomously active family - have ability to copy
themselves and reinsert a copy at a different site in a human chromosome.
Individuals vary therefore in their L1 insertions. L1 elements are a 'dynamic' force that
gives plasticity to the genome.
Describe the genetic makeup of LINES.
AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
Describe the composition of the human nuclear genome.
One genome has 23 chromosomes.
22 autosomes
50 to 260 Mb DNA
23 chromosomes has 3x10e9 bp, therefore somatic cells have 6x10e9.
Chromosomes are arranged in order, with 1 being largest and 22 being smallest. Made
up of 2 arms: p is the shorter arm and q is the longer one.
Human genome encodes 21000 genes.
Describe the proportions of sequences in the human genome.
1.5% of the human genome codes for protein coding regions (exons).
25% of the human genome codes for introns.
43% of the human genome comprises repetitive DNA - 'non-functional'.
Other DNA: Regulatory regions of genes, Pseudogenes, RNA genes (not mRNA),
Fragments of genes
,How does the human genome encode so many genes?
Alternative splicing of mRNA provides additional proteins from a single transcript. Exons
will remain in order.
Exons exit from the nucleus, introns remain in the nucleus during splicing. Addition of
polyA tail.
Several genes are members of a gene family. How does this occur?
Arisen by gene duplication
Duplicated genes have acquired base changes
Gene products encode proteins with different properties.
Describe haemoglobin in terms of its gene family.
Part of the globin gene family, which encodes the protein chains for haemoglobin (2
alpha and 2 beta chains)
Alpha globin gene cluster is found on chromosome 16; transcribed in fetus and adult.
Beta globin gene cluster is found on chromosome 11; transcribed in adult.
Gene duplication allows for higher affinity of oxygen of foetal haemoglobin compared to
adult haemoglobin.
Describe the composition of the histone gene family.
Genes make up the histone - 2 H2A, 2 H2B, 2 H3 and 2 H4 make up the nucleosome
octamer. 1 H1 sits on nucleosome octamer, pulling DNA together, makes up the histone
octamer.
, 11 histone gene clusters, 60 histone genes distributed over 7 chromosomes. Although
duplicated, each member of a particular histone gene family encodes the identical
protein.
140 bp of DNA wraps twice around the histone octamer.
Lots of histone proteins are needed when DNA replicate; each histone connected by
linker DNA.
What are the different gene duplication outcomes?
If there is selective pressure on both genes, the genes stay similar (such as globin and
histone family members).
If there is selection pressure on just one gene, one copy mutates and loses function
(pseudogenes) or one copy acquires a new function.
The human genome contains repetitive DNA interspersed throughout the
genome. What are LINES?
Long interspersed nuclear elements (L1)
Comprise 20% of genome.
Human L1 elements are the only autonomously active family - have ability to copy
themselves and reinsert a copy at a different site in a human chromosome.
Individuals vary therefore in their L1 insertions. L1 elements are a 'dynamic' force that
gives plasticity to the genome.
Describe the genetic makeup of LINES.
