ppt file

1. Concept and Basics of Genetics
&
Practical application in Nursing

2. Genetics
• The process of transmission of characters from
one generation to next generation is called the
inheritance or heredity.

3. Branches of Genetics
1. Cytogenetics
2. Molecular genetics
3. Biochemical genetics
4. Cancer genetics
5. Immunogenetics
6. Developmental genetics
7. Behavioral genetics
8. Population genetics

4. Importance of genetics in Medicine
• ≈50% of first trimester abortion are due to
chromosomal abnormalities
• Congenital malformation: ≈2-3% of newborns.
• 2% infants are born with single gene disorder
• More than half of childhood blindness,
deafness and mental retardation are due to
genetic disorders.

5. 5
Genetic Information
• Gene – basic unit of genetic
information. Genes determine the
inherited characters.
• Genome – the collection of
genetic information.
• Chromosomes – storage units of
genes.
• DNA - is a nucleic acid that
contains the genetic instructions
specifying the biological
development of all cellular forms
of life

6. 6
Chromosome Logical Structure
• Locus – location of a gene/marker
on the chromosome.
• Allele – one variant form of a
gene/marker at a particular locus.
Locus1
Possible Alleles: A1,A2
Locus2
Possible Alleles: B1,B2,B3

7. 7
Human Genome
Most human cells
contain 46 chromosomes:
• 2 sex chromosomes (X,Y):
XY – in males.
XX – in females.
• 22 pairs of chromosomes
named autosomes.

8. 8
Genotypes Phenotypes
• At each locus (except for sex chromosomes)
there are 2 genes. These constitute the
individual’s genotype at the locus.
• The expression of a genotype is termed a
phenotype. For example, hair color, weight,
or the presence or absence of a disease.

9. 9
Genotypes Phenotypes (example)
• Eb- dominant allele.
• Ew- recessive allele.
genotypes
phenotypes

10. 10
Dominant vs. Recessive
A dominant allele is expressed even if it is
paired with a recessive allele.
A recessive allele is only visible when
paired with another recessive allele.

11. 11
Two members of a gene pair segregate from each other into
the gametes, so half the gametes carry one member of the
pair and the other half carry the other member of the pair.
Mendel’s 1st Law
Y / y y / y
½ y/y
½ Y/y
½ y
½ Y
all yGamete
production
Gamete
production

12. 12
Mendel’s 2nd Law
• Different gene pairs assort independently
in gamete formation.
Gene pairs on SEPARATE CHROMOSOMES
assort independently at meiosis.
This “law” is true only in some cases.

13. DNA
• 1953 - James Watson, Francis
Crick, Rosalind Franklin &
Maurice Wilkins
• Lead to understanding of
mutation and relationship
between DNA and proteins at
a molecular level
• 1959 – “Central Dogma”
– DNARNAprotein

14. Genetic Concepts
• Chromosome –
– double stranded DNA
molecule packaged by
histone & scaffold proteins
DNA double helix
nucleosome
30nm fiber
condensed chromosome

15. Genetic Concepts
• Chromosome numbers
– Constant for an organism
– n - haploid number
– 2n – diploid number
• Karyotype

16. Genetic Concepts
Y

17. Genetic Concepts
• Chromosome numbers
Each individual inherits 23 chromosomes from
father and 23 from mother.
Humans: 2n= 46 chromosomes
Humans 23 paternal, 23 maternal
Humans n = ____
Each maternal & paternal pair represent
homologous chromosomes - called homologs

18. Genetic Concepts
(a) Chromosomal composition found
in most female human cells
(46 chromosomes)
(b) Chromosomal composition
found in a human gamete
(23 chromosomes)
1 2 3 4 5 6 7
XX
8
9 10 11 12 13 14 15
17 18 19 20 21 22
16
1 2 3 4 5 6 7
X
8
9 10 11 12 13 14 15
17 18 19 20 21 22
16
Diploid Haploid

19. Genetic Concepts
• Homologous Chromosomes
– Share centromere position
– Share overall size
– Contain identical gene sets at matching positions (loci)
gene for color
gene for shape

20. Genetic Concepts
• Gene – sequence of DNA which is transcribed
into RNA
– rRNA, tRNA or mRNA
• Locus – the position on a chromosome of a
particular DNA sequence (gene)
G Locus – gene for color
W Locus – gene for shape

21. Genetic Concepts
• DNA is mutable
• A variation in DNA sequence at a locus is
called an allele
– Diploid organisms contain 2 alleles of each locus
(gene)
• Alleles can be identical – homozygous
• Alleles can be different – heterozygous
• If only one allele is present – hemizygous
– Case in males for genes on X and Y chromosomes

22. Genetic Concepts
Allele – G vs g; W vs w
At the G locus either the G or g allele may be present on a given
homologue of a homologous pair of chromosomes

23. Genetic Concepts
• Genome
– Collection of all genetic material of organism
• Genotype
– Set of alleles present in the genome of an organism
• Phenotype
– Result of Gene Expression
– Genes (DNA) are transcribed into RNA
– mRNA is translated into protein, tRNA & rRNA work in
translation process
– Biochemical properties of proteins, tRNAs & rRNAs
determine physical characteristics of organism

24. DNA
Gene
Transcription
Translation
RNA (messenger RNA)
Protein
(sequence of
amino acids)
Functioning of proteins within living
cells influences an organism’s traits.
Gene
Expression

25. Wing cells
Lots of pigment made Little pigment made
Pigment
molecule
(b) Cellular level
Pigmentation gene,
dark allele
Pigmentation gene,
light allele
Transcription
and translation
Highly functional
pigmentation enzyme
Poorly functional
pigmentation enzyme
(a) Molecular level
Mutation & Phenotypic Variation

26. 26
Medical Genetics
When studying rare disorders, 6 general
patterns of inheritance are observed:
• Autosomal recessive
• Autosomal dominant
• X-linked recessive
• X-linked dominant
• Codominant
• Mitochondrial

27. 27
Medical Genetics (cont.)
Autosomal recessive
• The disease appears
in male and female
children of
unaffected parents.
• e.g., cystic fibrosis

28. 28
Medical Genetics (cont.)
Autosomal dominant
• Affected males and
females appear in each
generation of the
pedigree.
• Affected mothers and
fathers transmit the
phenotype to both sons
and daughters.
• e.g., Huntington disease.

29. 29
Medical Genetics (cont.)
X-linked recessive
• Many more males than
females show the disorder.
• All the daughters of an
affected male are
“carriers”.
• None of the sons of an
affected male show the
disorder or are carriers.
• e.g., hemophilia

30. 30
Medical Genetics (cont.)
X-linked dominant
• Affected males pass the
disorder to all daughters
but to none of their sons.
• Affected heterozygous
females married to
unaffected males pass the
condition to half their sons
and daughters
• e.g. fragile X syndrome

31. 31
Medical Genetics (cont.)
Codominant inheritance
• Two different versions
(alleles) of a gene can be
expressed, and each
version makes a slightly
different protein
• Both alleles influence the
genetic trait or determine
the characteristics of the
genetic condition.
• E.g. ABO locus

32. 32
Medical Genetics (cont.)
Mitochondrial inheritance
• This type of inheritance
applies to genes in
mitochondrial DNA
• Mitochondrial disorders
can appear in every
generation of a family and
can affect both males and
females, but fathers do not
pass mitochondrial traits
to their children.
• E.g. Leber's hereditary
optic neuropathy (LHON)