Embryonic abnormalities; Numerical and structural abnormalities

1. Embryonic Disorders
By- Isha Thapa Magar

2. Introduction
• Embryonic Disorders is defined as the
deformity or defect which arises or exists at or
before birth during the process of development
which may be result of genetic or environmental
factors.

3. Condt..
• Embryonic Disorders/Genetic disorders are
of following types:
1.Chromosomal abnormalities
2.Mendelian disorders
3.Multifactorial defects.

4. Contd…
• Chromosomal abnormalities is alterations in
normal number of chromosomes or structural
problems within chromosomes themselves.
• Both kinds of chromosome abnormalities may
result from an ovum or sperm cell with incorrect
number of chromosomes, or with a structurally
faulty chromosome uniting with a normal egg or
sperm during conception.
• Consequences in affected individual are often
severe, or even lethal.

5. Types
1. Numerical abnormalities.
i. Trisomy 21 (Down
syndrome).
ii. Trisomy 18 (Edward
syndrome).
iii.Trisomy 13 (Patau
syndrome).
iv.Klinefelter syndrome.
v. Turner syndrome.
2. Structural abnormalities.

6. 1.Numerical Chromosomal
abnormalities
• Aneuploidy is the result of numeric
chromosome errors.
• If the zygote has an extra chromosome,
condition is called trisomy.
• If the zygote is missing a chromosome, the
condition is called monosomy.

7. • If the zygote survives and develops into a
fetus, the chromosomal abnormality is
transmitted to all of its cells. The child that is
born will have symptoms related to the
presence of an extra chromosome or absence
of a chromosome.

8. i.Trisomy 21 (Down syndrome)

9. 2.Trisomy 18 (Edwards syndrome)

10. 3.Trisomy 13 (Patau syndrome)

11. 4.Turner syndrome (45,X)

12. 5.Klinefelter male, 47,XXY.

13. Structural Chromosomal abnormalities
• Occur when there is a change in structure or
components of a chromosome.
• Such as when part of a chromosome is
missing, a part of a chromosome is extra, or a
part has switched places with another part.

16. Mendelian Inheritance Disorder
- The disorders whose inheritance is in
accordance to the Mendels’ laws of
inheritance.
- They occur as a result of mutation.
- They are single gene disorders.

17. Mendel's laws of inheritance
Law of dominance and
uniformity
Some alleles are dominant
while others are recessive; an
organism with at least one
dominant allele will display
effect of dominant allele.
Law of segregation
During gamete formation, the alleles
for each gene segregate from each
other so that each gamete carries
only one allele for each gene.
Law of independent
assortment
Genes of different traits can
segregate independently during
formation of gametes.

18. Law of Dominance and unformity

19. Law of segregation

20. Law of independent Assortment

21. Types
1.Autosomal Dominant
2. Autosomal Recessive
3.X-linked Dominant
4. X-linked Recessive
5.Mitochondrial

22. 1.Autosomal Dominant:
 When affected gene is located on an autosome
and disorder gets expressed in both
homozygous and heterozygous condition, this
disorder is called autosomal dominant.
 Affected person has an affected parent and
occurs in every generation.

23.  Every affected child has at least one affected
parent.
 Male and female offspring are equally
affected.
 There are affected people in several
generations.
 There is a 50% risk of involvement of each
sibling of an affected person if the parent is
affected.
 Eg: Cardiomyopathy, skeletal dysplasia etc.

25. 2. Autosomal Recessive
• When the affected gene is located on an
autosome but the disorder gets expressed only in
homozygous condition, the disorder is called
autosomal recessive.
 Both parents of an affected person are either
carriers or affected themselves.
 Eg: Sickle-celled anaemia, phenylketonuria,
cystic fibrosis etc.

27. 3. X-linked dominant:
 When affected gene is located on X sex
chromosome and disorder gets expressed in
both homozygous and heterozygous condition,
disorder is called X-linked dominant.
 Females are more frequently affected but both
males as well as females can be affected in one
generation.
 Eg: vitamin D-resistant rickets.

29. 4. X-linked recessive:
 When affected gene is located on X sex
chromosome and disorder gets expressed only in
homozygous condition, disorder is called X-
linked recessive.
 Males are more frequently affected and female are
just carriers.
 The mother is usually a carrier, and she transmits
disease to 50% of her son.
 Eg: Haemophilia, colour blindness, muscular
dystrophy etc.

31. 5. Mitochondrial Disorder
 When affected gene is coming from
mitochondrial DNA it is called mitochondrial
disorder.
 It is transferred from one generation to other
only by females but can affect both males and
females.
 Appear in every generation.

32. Multifactorial Defects
Multifactorial inheritance means that many
factors are involved in causing a birth defect.
The factors are usually both genetic and
environmental, where a combination of genes
from both parents, in addition to unknown
environmental factors, produce the trait or
condition.
Often one gender (either males or females) is
affected more frequently than the other in
multifactorial traits.

33.  Multifactorial traits do recur in families, because they
are partly caused by genes.
 Chance of occurrence for a multifactorial trait, depends
upon how closely family member with trait is related
to individual.
 E.g. risk is higher if individual sibilings has the trait or
disease, than if first cousin has trait or disease.
 Family members share a certain percentage of genes in
common, depending upon their relationship.
 Eg. of multifactorial traits and diseases include: height,
neural tube defects, and hip dysplasia.