Sex determination Genetic disorders Mendelian disorders Chromosomal disorders

1. BASIC
MOLECULAR BIOLOGY
AND GENETICS FOR
AYURVEDA
UNIT-I BASIC GENETICS
Sex determination in human and other organisms, genetic disorders and human
diseases, chromosomal disorders
Devika M
BSc Ayurveda Biology
2nd year

2. LIST OF CONTENTS
• Sex determination
• Genetic disorders
• Mendelian disorders
• Chromosomal disorders

3. SEX DETERMINATION
Sex-determining mechanisms include chromosomal, genic, and environmental sex-
determining systems.
On the basis of fertilization , sex determination is of three types :
Progamic :- Sex determination before fertilization.
Eg- Male honey bee (Drone)
Syngamic :- Sex determination during fertilization.
Eg- Humans, Most of the plants & animals
Epigamic :- Sex determination after fertilization.
Eg- Female honey bee , Crocodile , turtle etc

4. XX- XY SYSTEM
Present in humans, fruit fly, coccinia, melandrium
ncbi.nlm.nih.gov

5. • The SRY gene on the male Y chromosome
regulates sex determination in mammals,
activates a testis-forming pathway.
• srY gene codes for a protein called testis
determining factor.
• If embryo inherit Y chromosome, primitive
gonads develop into testis
• If embryo does not inherit Y chromosome
and the srY gene, primary gonads develop
into ovaries.
ncbi.nlm.nih.gov

6. XX- XO SYSTEM
• Grasshopper is an example of XO
type of sex determination in
which the males have only one X-
chromosome besides the
autosomes, whereas females
have a pair of X-chromosomes
• Grasshopper, cockroach,
Vallisneria ncbi.nlm.nih.gov

7. ZZ- ZW SYSTEM
• Female heterogamety : two different
types of gametes in terms of the sex
chromosomes, are produced by
females
• In birds, sex is determined by
chromosomes known as the Z and W,
and females are the heterogametic
sex.
• Bird, fish, Fragaria
vedantu.co
m

8. HAPLOID- DIPLOID MECHANISM
• Haplodiploidy is present in honeybees
• Honey bees lack sex chromosomes
• Sex is normally determined by the
fertilization or non-fertilization of eggs,
rather than the presence or absence of sex
chromosomes.
• Males develop from unfertilized eggs and
are haploid, and females develop from
fertilized eggs and are diploid.
vedantu.com

9. SEX DETERMINATION AND ENVIRONMENT
• egg incubation temperature.
• In the alligator snapping turtle, Macroclemys temminckii,
incubation of eggs below 22°C or above 28°C gives rise
to females, while incubation at intermediate
temperatures produces predominantly males.
• In the European pond turtle, Trachemys scripta,
incubation temperatures above 30°C produce all
females, whereas incubation temperatures below 25°C
produce all males. At 28.5°C, equal numbers of males
and females are produced.

10. GENETIC DISORDERS : A genetic disorder is a disease caused in whole
or in part by a change in the DNA sequence away from the normal
sequence.
• MENDELIAN DISORDERS
o Caused due to alternation or
mutation in the single gene
o These disorders are transmitted
to offspring on the same line.
o The pattern of inheritance of such
disorders can be traced in a
family by pedigree analysis
• CHROMOSOMAL DISORDERS
o Caused due to absence or excess or
abnormal arrangement of one or
more chromosomes.
o Non-inheritable.
o Pedigree analysis of a family does
not help in tracing the pattern of
inheritance.

11. topperlearning.com

12. CHROMOSOMAL DISORDERS
Autosomal disorder
Sex chromosomal disorder
• Autosomal disorder : Caused due to absence or excess or abnormal
arrangement of one or more in autosomal chromosomes.
• Down's Syndrome
• Edward's Syndrome
• Sex chromosomal disorder : Caused due to absence or excess or abnormal
arrangement of one or more in sex chromosomes.
• Turner's Syndrome
• Klinefelter's Syndrome

13. AUTOSOMAL DISORDERS

14. DOWN'S SYNDROME
• abnormal cell division results in extra genetic
material from chromosome 21
• 21-trisomy
• 47 (45+XY in males and 45+XX in females) instead
of 46.
• Rounded face, broad forehead
• Permanently opened mouth with protruding
tongue.
• Gonads and genitalia are undeveloped. Google
images

15. EDWARD'S SYNDROME
• This syndrome is due to an extra chromosome
number 18.
• It occurs more often in females than in males.
• The affected person keeps the fingers tightly
clenched against the palm of the hand.
• Other symptoms are small jaws, deformed ears,
small mouth, nose and fingers, small sternum
and pelvis.
• The patient is mentally retarded and dies within
6 months after birth.
Google
images

16. SEX CHROMOSOMAL DISORDER

17. TURNER'S SYNDROME
• It is due to monosomy (2n - 1)
• 2n- 1 = 45 chromosomes (44 +XO)
instead of 46.
• Symptoms include short stature, delayed
puberty, infertility, heart defects and
certain learning disabilities.
• Sterile females with rudimentary ovaries
filled with connective tissue, have
undeveloped breasts, small uterus. Google images

18. KLINEFELTER'S SYNDROME
• Trisomy of sex (X) chromosome
• The individual has 47 chromosomes (44+XXY).
• Klinefelter's syndrome isn't inherited, but rather occurs
only as a result of a random genetic error after
conception.
• low testosterone and reduced muscle mass, less facial
hair and body hair
• Feminine pitched voice and enlarged breasts
(gynaecomastia).
Google images

19. MENDELIAN GENETIC DISORDER
Mendelian disorders are mainly determined by alteration or mutation in the single
gene.
Google images

20. AUTOSOMAL DOMINANT
ACHONDROPLASIA
• The normal allele is recessive and the abnormal
allele is dominant.
• Achondroplasia may be considered as an
example which leads to a type of Dwarfism in
the affected individuals
• In this condition normal people have genotype
d/d, affected individual with mild disease have
D/d and severly affected have D/D which is
often lethal. So most of the surviving cases of
achondroplasia are heterozygotes
NCERT

21. AUTOSOMAL DOMINANT
SICKLE CELL ANAEMIA
• autosomal recessive disorder in which the affected individuals produces an altered from
of hemoglobin.
• Normal people carry the Hba allele and make hemoglobin A. Individuals affected with
sickle cell anemia are homozygous for the Hbs allele and produce only hemoglobin S.
• This causes their RBC to deform into a sickle shape under conditions of low oxygen
concentration.
• This defect caused by the substitution of glutamic acid by valine at the sixth position
of the beta globin chain of the haemoglobin molecule.

23. X- LINKED DOMINANT
HYPOPHOSPHATEMIA
• Hypophosphatemia is a type of vitamin D resistant
rickets. It is an inherited disorder characterized by low
levels of phosphate in the blood
• The affected males pass on the mutated dominant gene
to all their daughters but to none of their sons
• In case of affected female married to unaffected male
the condition is passed on to half of their sons and
daughters
Google images

25. X- LINKED RECESSIVE
HAEMOPHILLIA
o It is sex-linked recessive disease which is also
known as bleeder's disease.
o The patient will continue to bleed even from a
minor cut
o There is absence of antihaemophiliac globulin or
factor VIII (haemophilia-A) and plasma
thromboplastin factor IX (haemophilia-B.
Christmas disease) essential for it.
o It is due to the presence of a recessive sex linked
gene h, carried by X- chromosome.
o In the X-linked recessive inheritance in the mother
(XX) the affected gene remains on one X
chromosome, as a result she becomes the carrier
and usually only males (XY) are affected by the
disorder

26. REFERENCES
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4077654/
• https://www.nature.com/scitable/topicpage/genetic-mechanisms-of-sex-
determination-314/
• https://youtu.be/VKQLtgBWQ9Q
• https://www.nature.com/scitable/topicpage/sex-determination-in-honeybees-
2591764/
• NCERT class XII
• https://my.clevelandclinic.org/health/body/23078-autosomal-dominant--autosomal-
recessive
• https://ncert.nic.in/textbook/pdf/kebt108.pdf