Introduction to Genetics for beginners
An Introduction to basic genetic concepts and links to health for
individuals who have had minimal experience of genetics
DNA, genes & chromosomes
The objectives of this presentation are to:• Understand the role and structure of DNA, genes
and chromosomes.• Understand that proteins are encoded by genes• Be aware that alterations in genetic material can
cause disease
The structure of DNA, genes & chromosomes
Chromosomes
• Chromosomes are made of DNA. • Each contains genes in a linear
order.• Human body cells contain 46
chromosomes in 23 pairs – one of each pair inherited from each parent
• Chromosome pairs 1 – 22 are called autosomes.
• The 23rd pair are called sex chromosomes: XX is female, XY is male.Gene for sickle cell disease
(chromosome 11)
Gene for cystic fibrosis (chromosome 7)
Chromosomes
pp
CentromereCentromere
Chromosome 5Chromosome 5
The Karyotype
A normal male chromosome pattern would be described as:
46,XY.
46 = total number of chromosomesXY = sex chromosome constitution
(XY = male, XX = female).
Any further description would refer to any abnormalities orvariants found
Total Genes On Chromosome: 723373 genes in region marked red, 20 are shown
FZD2AKAP10ITGB4KRTHA8WD1SOST
MPP3
MLLT6
STAT3BRCA1 breast cancer 1, early onsetGFAPNRXN4NSF
NGFR
CACNB1HOXB9HTLVRABCA5CDC6ITGB3
Chromosome 17source: Human Genome Project
Genes are arranged in linear order on chromosomes
Chromosome anomalies
• Cause their effects by altering the amounts of products of the genes involved.
– Three copies of genes (trisomies) = 1.5 times normal amount.
– One copy of genes (deletions)= 0.5 times normal amount.
– Altered amounts may cause anomalies directly or may alter the balance of genes acting in a pathway.
Classification of chromosomal anomalies
• Numerical (usually due to de novo error in cell division)- monosomy- trisomy
• Structural (may be due to new error in cell division or inherited) - dosage changes (e.g. deletions) and rearrangements
Most frequent numerical anomalies in liveborn
AutosomesDown syndrome (trisomy 21: 47,XX,+21)
Edwards syndrome (trisomy 18: 47,XX,+18) Patau syndrome (trisomy 13: 47,XX+13)
Sex chromosomesTurner syndrome 45,X
Klinefelter syndrome 47,XXY
All chromosomesTriploidy (69 chromosomes)
Summary of Chromosome Anomalies
• Change in numbere.g. trisomy 21 Down syndrome;
Edwards’ syndrome; Turner syndrome.Usually an isolated occurrence.
• Change in structuree.g. deletionsMay be inherited.
Trisomy 21
The DNA Double Helix
Disease-Associated Mutations Alter Protein Function
What is a mutation?
• Mutation – an alteration or change in the genetic material
• In clinical use usually = “harmful”• Inherited• From exposure to mutagenic agents but more
arise spontaneously through errors in DNA replication / repair
• More likely to be recognised if effects are detrimental
Summary
• Human body cells contain 46 chromosomes in 23 pairs – one of each pair is inherited from each parent
• Chromosomes are made of DNA• Each chromosome contains genes in a linear
order• Genes are codes for cells to make proteins• Alterations in genes or chromosomes alter the
protein produced and can hence cause disease
Recommended
