PEDIGREE ANALYSIS

PEDIGREE ANALYSIS

14.   PEDIGREE ANALYSIS

There is a various organism in which cross is not possible to study the dominant/recessive or linkage. The opportunity to perform controlled crosses are not possible in human. However analysis of trait in existing population gives insight view of the nature of the gene/genes. Scientist have designed a new approach to study human genetics i.e. pedigree analysis. Pedigree analysis is also helpful in case when a species has long generation time.
14.1.    Symbols used in Pedigree analysis:

14.2.    Types of pedigree : 
On the basis of genes on linked to chromosomes, there are two types of pedigree.
(1)    Sex linked pedigree
(2)    Autosomal pedigree
(1)    Sex linked pedigree:- 
There are two types of sex linked pedigree.
(i)    X linked pedigree
(ii)    Y linked pedigree
(i)    X linked pedigree : There are two types of X linked pedigree on the basis of be dominant or recessive.
(a)    X linked dominant pedigree 
(b)    X linked recessive pedigree

14.2.1.    X linked dominant pedigree : 


(A)    In this pedigree each child of a mother affected with an X-linked dominant trait has a 50% chance of inheriting the mutation and their being to be affected with this disorder. [See Gen-I (1) is affected and inheriting the mutation with 50% chance, See Gen-II (2, 3, 4, 5)].
(B)    In case of father is affected, 100% of the daughters will be affected, since daughters inherit their X-Chromosomes from father and none of the son will be affected because they inherit their Y-Chromosomes. [See Gen-II (2) and Gen-III male and female].
(C)    Male and females both are affected. [See in Gen-II (2) and (5)].
(D)    Trait does not skip generation. (You can see effected individuals in all three generations, not any generation is skipped by trait). 
(E)    Affected mother in heterozygous condition pass the trait on ½ of their son and ½ their daughters. (See Gen-I and Gen-II).
(F)    Affected daughter must have either an affected mother or an affected father. [See Gen-I(1) and Gen-II(5) or Gen-II(2) and Gen-III 2.3].
(G)    Affected son must have affected mother. [See Gen-I(1) and Gen-II(2)].
Examples : (1)    Hypophosphatemic Rickets 
(2)    Incontinentia pigment
(3)    Focal dermal hypoplasia
(4)    Orofaciodigital syndrome
14.2.2.    X linked recessive pedigree : 

(A)    When the mother is a carrier each daughter has a chance of inheriting the gene alteration and inheriting the condition. [See the Gen-I (2) and Gen-II(2)].
(B)    When father carries X-linked condition. That means his son will not be affected and the condition his daughter will be a carrier. [See Gen-II(4) and Gen-III(5)].
(C)    Mainly males affected almost exclusively. (Analysis or see the complete pedigree).
(D)    Gene is transmitted from the female carrier to sons. [See Gen-II(2) and Gen-III(1)]
(E)    The affected male cannot transmit the condition to their sons. (Because male inherit Y-Chromosome to their sons).
(F)    Skip of generation from the disease. (See the Gen-I).

Examples :     

(1)    Haemophilia    A and B                

(2)    Duchenne muscular dystrophy

(3)    Colour blindness                    

(4)    Fabry disease

(5)    Glucose 6 phosphates deficiency            

(6)    Ocular albinism

(7)    Lesch-Nyhan syndrome

14.2.3.    Y linked pedigree : 


(A)    The concept of dominant, recessive doesn't apply because only one allele (Y) is ever-present in the male. Male with a single Y or X-linked allele is described as a hemizygous because only one allele is present in Y-linked. (Because of the single Y chromosome concept of dominant or recessive don't apply).
(B)    In this inheritance, the gene is present on Y-chromosome the only male have Y-chromosome. It can only be transmitted from father to son. That is also called Holandric Inheritance. [See in all generations].
(C)    In this trait only males are affected, that is passed from father to all sons. (See all generations).
(D)    Never skip generations.
(E)    In this Inheritance, the gene is present on the Y-chromosome. The only male has Y-chromosome. It can only be transmitted from father to son. That is also called Holandric Inheritance.
Examples :     

(1)    Retinis pigmentosa                    

(2)    Hairy Ears

(3)    ASMTY (acetylserotonin methyltransferase)    

(4)    TSPY (Testis-specific protein)

(5)    IL3RAY (Interleukin-3-Receptor)

(6)    TDF (Testis-determining factor)

(7)    ZFY (Zinc Finger protein)

(8)    SRY (Sex-determining region)

(9)    PRKY (Protein Kinase, Y-linked).        
14.2.4.    Autosomal Dominant Pedigree :- 

(A)    Affected children usually have an affected parents. (Female or Male) [See Gen-I(2) and Gen-II(2) or Gen-II(6.7) and Gen-II(7)].
(B)    Heterozygous are affected [See Gen-III(1)].
(C)    Two affected parents can produce an unaffected child, if the both affected parents are heterozygous. [See Gen-II (6.7) and see Gen-III 16].
(D)    Two unaffected parents will not have affected children. [See Gen-II (3.4) and Gen-III (4, 5)].
(E)    Both are affected with equal frequency.
(F)    Only one copy of diseased or mutated allele is sufficient for an individual to be susceptible to expressing the phenotype [See Gen-II (1) and Gen-II (1, 3)].
(G)    50% chance the offspring (heterozygote) inherit the disease allele. [See gen-II(1) and their off spring].
(H)    Also called ventricle inheritance because of the transmission from parent to offspring. [See pedigree]. 
Examples :     

(1)    Huntington disease                  

 (2)    Marfan syndrome    

(3)    Achondroplasia 

(4)    Familial Breast cancer

(5)    Noonan syndrome

(6)    Retinoblastoma
Autosomal Recessive Pedigree:- 

(A)    Both sex involved in this pedigree. [See Gen-II (1, 2)].
(B)    Skip of Generation. [See pedigree].
(C)    Both mutant alleles are required for an individual to be expressing the phenotype. [See Gen-II (2)].
(D)    In this trait, there is ¼(25%) chance that the offspring will inherit two copies of the disease allele and will therefore have the phenotype. [See in Gen-I (1, 2)].
(E)    Parents of an affected may not be affected but are carriers. [See Gen-I(1, 2) and Gen-II 2, 5].
(F)    In this trait, there is ½(50%) chance that the offspring will inherit two copies of the disease allele and will therefore have the phenotype. [See Gen-I (1, 2) inheriting 50-50% disease allele].
(G)    The proportion of affected males may be equal to the proportion affected female. [See the pedigree]. 
(H)    Male and Female both are unaffected carrier. [See Gen-I (1, 4)].
(I)    Observe more frequency in consanguineous matting or relationship. [See in generation IV]. 
(J)    Affected child have normal parents. [See Gen-II (2.5) and Gen-I (1.2)].
(K)    Heterozygous (Aa) have normal phenotype that is unaffected carrier. [Gen-I (1, 2), Gen-III (2)].
(L)    Close relatives (Consanguineous) who reproduce are more likely to have affected offspring. [See Gen-IV].
(M)    Male and Female both are affected with equal frequency. [See the pedigree].
Examples :

(1)    Cystic fibrosis             

(2)    Sickle cell anaemia

(3)    Tay-Sachs disease                

(4)    Congenital Deafness 

(5)    Diabetes Mellitus                   

(6)    Phenylketonuria 

(7)    Albinism


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