1. Basics of Genetics by Mrs. Sambharam K
Basics of Genetics by Mrs. Sambharam K.P( Asst Prof) Lokmangal Science and Entrepreneurship College, Wadala

2. Concept and Basics of Genetics

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

4. Branches of Genetics Cytogenetics Molecular genetics
Biochemical genetics
Cancer genetics
Immunogenetics
Developmental genetics
Behavioral genetics
Population genetics

5. 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.

6. 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 5

7. 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 6

8. 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. 7

9. 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. 8

10. Genotypes Phenotypes (example) Eb- dominant allele.
Ew- recessive allele. 9

11. 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. 10

12. Mendel’s 1st Law
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.
Y / y
y / y
Gamete production
all y
Gamete
production
½ y/y
½ y
½ Y/y
½ Y 11

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

14. DNA
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

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

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

17. Genetic Concepts Y

18. 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

19. Genetic Concepts Diploid Haploid1 2 3 4 5 6 7 8 1 2 3 4
5 6 7 8 9 10 11 12 13 14 15 16
(a) Chromosomal composition found in most female human cells
(46 chromosomes) X
(b) Chromosomal composition found in a human gamete (23 chromosomes) 22 XX
Diploid
Haploid

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

21. 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

22. 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

23. 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

24. Genetic Concepts Genome Genotype Phenotype
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

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

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

27. 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 26

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

29. 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. 28

30. 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 29

31. 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 30

32. 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 31

33. 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) 32