Lecture 4: Mendelian Inheritance in humans Flashcards
Mendelian or monogenic disease=
If on gene is involved to cause a disease
Multifactural disease=
if many genes are involved in causing the disease
Are all mendelian characters diseases?
no
how many mendelian characters are in man?
Over 6000
White square
MALE (unaffected)
black square
Male (affected)
white circle
FEMALE (unaffected)
Black circle
Female (affected)
Diamond white
Sex Unknown, unaffected
Square with DOT in it
male carrier
square line through
male dead
two lines between square and circle
Consanguineous ‘marriage’
Consanguineous
relating to or denoting people descended from the same ancestor.
Autosomal dominant
Autosomal recessive are caused by..
a gene on chromosomes 1 to 22
x-linked recessive
x-linked dominant
y-linked are caused by
a gene on the sex chromosomes
if a disease is recessive then…
an affected individual has USUALLY inherited the disease from both parents
Characters of autosomal dominant disease..
- affecte person usually has at least one affected parent
- affects either sex
- transmitted by either sex
- child of an unaffected X affected mating as 50% chance of disease
autosomal refers to…
disease from numbered chromosome (not sex chromosomes) no. 1-22
Autosomal dominant diseases/phenotypes (humans)
- Achondroplasia - form of dwarfism
- polydactyly - extra fingers or toes
- Hairy mid-digit
- Widows peak
Characteristics of autosomal recessive disorder
- affecteds usually have unaffected parents
- Parents are usually carriers
- Affects either sex
- increased incidence of inbreeding
- carriers and non-carriers are indistinguishable
- 2 carriers mate their offspring have a 1/4 chance of being affected
Examples of autosomal recessive disorders
- Albinism
- Sickle cell anaemia
- Cystic fibrosis
- Attached ear lobes
Cystic fibrosis median survival
31 years
CF what doe sit affect?
Lungs, increased mucus secretion
most common autosomal recessive disease in Europeans?
CF
CF affecteds have..
two inactive copies of the CFTR gene
CFTR…
Cystic Fibrosis Transmembrane conductance Regulator
CF: the delta508 mutation results in
3bp deletion and a non-functional protein
CF: heterozygotes may have (or had) a
selective advantage through resistant to cholera, typhoid or other diseases.
Characteristics of x-linked recessive disorders
- affects mainly males
- probability of male offspring of female carrier being affected is 0.5
- females only affected if father affected and mother carrier.
- affected miles are usually born to be parents with no symptoms, although the mother often has affected male relatives
examples of x-linked recessive disorders
- duchenne muscular dystrophy
- red-green colour blindness
- haemophilia
Characteristics of x-linked dominant disorders
- affects either sex
- the child of an affected female has a 50% chance of being affected
- all female children of affected males are affected
- -no male children of accepted males are affected
X-inactivation (lyonization)
females XX males XY. to compensate. In each cell of females one X is randomly inactivated. Occurs early in development and daughter cells have the same X inactivated.
Characteristics of Y-linkage
Affects only males
All sons of an affected man are affected
Examples of Y-linkage - very few
maleness
Hairy ear rims - possibly
Mendelian disorders are usually..
rare - affected/carriers reduced fitness
Mendel’s pea traits were
dominant
