ABC of Genetics

1. Introduction to Genetics
for beginners
An Introduction to basic
genetic concepts and links to
health for individuals who
have had minimal experience
of genetics

2. 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

3. The structure of DNA, genes & chromosomes

4. 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)

5. Chromosom
es
p
Centromer
e
q
Chromosome
5

6. TheKaryotype
A normal male chromosome pattern would be
described as:
46,XY.
46 = total number of
chromosomes XY = sex
chromosome constitution (XY =
male, XX = female).
Any further description would refer to any abnormalities
or
variants found

7. Total Genes On Chromosome: 723
373 genes in region marked red, 20 are
shown
FZD2
AKAP1
0
ITGB4
KRTH
A8
WD1
SOST
MPP3
MLLT
6
breast cancer 1, early
onset
STAT3
BRCA
1
GFAP
NRXN
4
NSF
NGFR
CACN
B1
HOXB9
HTLVR
ABCA5
CDC6
ITGB3
Chromosome 17
source: Human Genome
Project
Genes are arranged in linear order
on chromosomes

8. Chromosome anomalies
• Cause their effects by altering the amounts of products
of the genes involved.
– Three copies ofgenes (trisomies)
=1.5times normal amount.
– One copy ofgenes (deletions)
=0.5 times normalamount.
– Altered amounts may cause anomalies directly or may alter the balance
ofgenes acting in apathway.

9. Classification of chromosomalanomalies
• 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

10. Most frequent numerical
anomalies in
liveborn
Autosomes
Down syndrome (trisomy 21:
47,XX,+21) Edwards syndrome
(trisomy 18: 47,XX,+18) Patau
syndrome (trisomy 13: 47,XX+13)
Sex chromosomes
Turner syndrome 45,X
Klinefelter syndrome
47,XXY
All chromosomes
Triploidy (69 chromosomes)

11. Summary of Chromosome
Anomalies
• Change in number
e.g. trisomy 21 Down syndrome;
Edwards’
syndrome; Turner syndrome.
Usually an isolated occurrence.
• Change in structure
e.g. deletions
May be inherited.
Trisomy
21

12. The DNA DoubleHelix

15. Disease-Associated
Mutations Alter
Protein Function

16. What is amutation?
• 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 DNAreplication / repair
• More likely to be recognised if effects are detrimental

17. Summary
• Human body cells contain 46 chromosomes in 23pairs –
one of each pair is inherited fromeach parent
• Chromosomes are made of DNA
• Eachchromosome contains genes in alinearorder
• Genes are codes for cells to make proteins
• Alterations in genes or chromosomes alter the protein
produced and can hence causedisease