Transcript Sex linked inheritance and hereditary defects

Contents:
 Introduction to sex linked inheritance.
 Chromosome carries which type of genes?
 Three types of traits
 Characteristics of sex linkage.
 Types of sex linkage.
 Sex linked disorders.
Sex linked inheritance :
o Discovered by Morgan in 1910 in case of eye -colour in
Drosophila melanogester.
o Also known as sex linkage.
o It is the transmission of characters and their
determining genes along with sex determining genes ;
inherited together from one generation to another.
Y- Chromosome (male)carries fewer genes
along with TDF(testis
determining factor).
X-Chromosome – carries a
number of genes.
TRAITS:
SEX LINKED TRAITS- traits whose determining genes
are found on sex chromosome.
 SEX LIMITED TRAITS- autosomal traits which are
expressed in a particular sex. E.g: milk secretion in
mammalian females , pattern baldness in males.
 SEX INFLUENCED TRAITS- not due to particular genes
but are by by-products of sex hormone. E.g. low pitched
voice , beard , moustaches.
CHARACTERISTICS OF SEX
LINKAGE:
 It is criss cross inheritance.
 Mother passes alleles of sex-linked traits to both sons
and daughters.
 Majority of sex linked traits are recessive.
 More apparent in males than females.
 Females generally function as carriers.
Criss cross inheritance:
Father passes the traits
to grandson through his daughter (diagynic) while
mother transfers traits to her grand daughter through
her son (dia-andric).
Holandric: traits transferred from father to son, e.g.
hypertrichy, maleness.
Hologynic: trais transferred from mother to
daughter.
 These sex linked disorders are caused by recessive gene located
in X-chromosme and affect the males more than in females.
Haemophilia (John otto, 1803)
 Also known as bleeder’s disease as
patient will continue to bleed even
from a minor cut.
 Absence of antihaemophilic
globulin or factor 8 (haemophiliaA) and plasma thromboplastin
factor 9 (haemophilia-B).
 Royal disease-common in royal
families of Europe.
 Its frequency is 1 in 7000 in
human males and 1 in 10000000
in females.
Inheritance of haemophilia:
Colour blindness(horner,1876)
 Eye fails to distinguish red and
green colour as shown in fig.
 It is more common in males(8%) as
compared to female(0.4%)
 It shows criss-cross inheritance.
 Normal Vision is not affected.
Inheritance of colour blindness:
Night blindness:
 It is of two types:
Acquired- due to Vitamin A deficiency.
ii. Congenital- due to visual purple deficiency that
interferes with functions of retinal rods.
 It is inherited like red green colour blindness.
 Females become colour blind only if they receive two
genes for defect.
i.
Duchenne’s muscular dystrophy
(DMD):
 Mutated gene is the largest gene with 2400kbp in man
which is unable to produce a protein dystrophin.
 Due to its deficiency, calcium is not released from the
muscle cell. As a result muscle contraction does not
takes place.
 Deterioration of girdle muscles at an early age.
 Patient is unable to walk after the age of 12 followed by
cardiomyopathy , mental impairment and death by age
of 20 due to cardiac or respiratory failure.
Inheritance of DMD:
REFERENCES:
TRUEMAN’S elementary biology
Internet.org
Wikipedia