This document discusses chromosomes, genes, and chromosomal abnormalities. It provides details on: - The human XX/XY sex determination system and SRY gene determining male characteristics. - Types of chromosomal abnormalities including aneuploidy (trisomy, monosomy), structural abnormalities (deletions, duplications, inversions, translocations), and conditions resulting from these abnormalities like Down syndrome and Klinefelter syndrome. - Components of genes like exons, introns, loci, alleles, and regulatory sequences; and processes like transcription, splicing, and translation.

1. Chromosome, Aberrations, Gene

2. Chromosome

3. Types of chromosomes

4. Ultra structure of DNA

5. Sex determination
• The XX/XY sex-determination system is found in
humans.
• In this system, females have two of the same kind of sex
chromosome (XX), while males have two distinct sex
chromosomes (XY).
• The XY sex chromosomes are different in shape and size
from each other, unlike the autosomes, and are termed
allosomes.
• SRY gene on the Y chromosome determines male
characteristics.

6. Chromosomal abnormalities
• Normal Chromosomal Complement in the Male : 44, XY
• Normal Chromosomal complement in the Female : 44, XX
• Haploid : Refers to n = 23 (found in gametes)
• Diploid : Refers to normal chromosome number (2n=46)
• Euploid : Normal set of chromosomes (2n=46)
• Aneuploid : Any number which is not exactly a multiple of
‘n’(2n – 1 or 2n + 1)

7. CHROMOSOMAL ABNORMALITIES
Numerical Structural
(1)Aneuploidy
- Monosomy (2n – 1)
- Trisomy (2n + 1)
(1)Translocation
- reciprocal
- robertsonian
(2) Inversion
- paracentric
- pericentric
(3) Insertion
(4) Deletion
(5) Duplication
(6) Rings
(7) Isochromosomes

8. Numerical chromosomal abnormality
• Monosomy (2n – 1)
Turner syndrome 44XO
• Trisomy (2n + 1)
Down syndrome 45XY or 45 XX
Klinefelter syndrome 44XXY

9. Structural chromosomal abnormality
• Alteration in the morphology of the
chromosome
• Balanced – genetic material not lost
• Unbalanced – loss or gain of genetic material

10. Deletion
• Deletion refers to the loss of a segment
of a chromosome.
• Types
1. terminal : can be terminal (close to
the end of the chromosome on the
long arm or the short arm)
2. interstitial: it can be interstitial (within
the long arm or the short arm).

11. Duplication
A portion of the chromosome is duplicated, resulting in extra
genetic material.

12. Translocation
Reciprocal Robertsonian
Break occurs in two
nonhomologous
chromosomes, with mutual
exchange of genetic material
resulting in a derivative
chromosome.
Break points are located at
or close to the centromeres
of two acrocentric
chromosomes
Transfer of genetic material from one chromosome to another

13. (Reciprocal translocation) 46, XX,t(3;9)

16. • Inversions occur when there are two
breaks within the same chromosome
and the segment is inverted 180 degree
and rejoined
• No loss of genetic information, just a
reorganization
• Inversions are balanced rearrangements
Inversion

17. Inversion
Paracentric Pericentric
Does not include centromere Includes centromere

18. Ring chromosome
• A ring chromosome forms when the tips of the long and short arms
fuse together to form a ring . Usually there are small deletions of
the tips of both arms

19. Isochromosome
• Isochromosomes arise if the centromere splits Horizontal instead of
longitudinally .
• Isochromosomes are rare.

20. Genes
• Genes are the basic physical and functional units of heredity.
• Each gene is located on a particular region of a chromosome
and has a specific ordered sequence of nucleotides.
• A gene is a fundamental unit of genome that controls the
transmission of hereditary characters.
• Genes are linearly arranged on chromosomes at specific
points called loci
• A gene may be in two or more functional forms

22. • All modifications of the original gene are called alleles, which
occupy the same position on the two homologous chromosomes.
• If there are two alleles one is dominant another recessive

23. Locus

24. Locus of human insulin gene
• 11p15.5 is the locus for the human insulin
gene.
• 11 is the chromosome number
• p indicates the short arm of the chromosome
• 15.5 is the number assigned to a particular
region on a chromosome.
• When chromosomes are stained in the lab,
light and dark bands appear, and each band is
numbered. The higher the number, the farther
away the band is from the centromere.

26. Exons and Introns
• Eukaryotic genes have introns and exons.
• Exons contain nucleotides that are translated into amino acids of
proteins.
• Exons are separated from one another by intervening segments of
junk DNA called introns.
• Introns do not code for protein. They are removed when eukaryotic
mRNA is processed.
• Exons make up those segments of mRNA that are spliced back
together after the introns are removed; the intron-free mRNA is
used as a template to make proteins.

27. Splicing
• Exons are sequences of DNA that are expressed into protein.
• Introns are intervening sequences that are not translated into protein
DNA
Pre-mRNA
3
1
1 2 3
1 3
2
2
Spliced mRNA
C
C

29. Regulatory sequences
Regulatory sequences, play a role in determining when and
where the protein is made (and how much is made)
A human being has 20,000 to 25,000 genes located on 46
chromosomes (23 pairs). These genes are known, collectively, as
the human genome.
Gene components. Genes have promoter regions, which occur
upstream from the coding region. The exons and introns
represent the coding and noncoding regions of a gene,
respectively. The terminator sequence signals the point at which
transcription ends.