makkah

Topics: Mother, Family, Parent Pages: 8 (682 words) Published: October 17, 2014
THE STEPS WHEN INTERPRETING
A PEDIGREE CHART


Determine if the pedigree chart shows an autosomal or Xlinked disease.

 If most of the males in the pedigree are
affected, then the disorder is X-linked
 If it is a 50/50 ratio between men and
women the disorder is autosomal.

INTERPRETING A PEDIGREE
CHART


Determine whether the disorder is dominant or
recessive.

 If the disorder is dominant, one of the
parents must have the disorder.
 If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous.

Pedigree showing transmission and
expression of a mitochondrial trait. Note
that transmission occurs only through
females.

Rules of Inheritance
Autosomal Recessive
•Appears in both sexes with equal frequency

Trait tend to skip generations
• Affected offspring are usually born to
unaffected parents

When both parents are hetrozygout,
approx. 1/4 of the progeny will be affected

Appears more frequently among the
children of consanguine marriages

Rules of Inheritance
Autosomal Dominant

Appears in both sexes with equal frequency
• Both sexes transmit the trait to their offspring

Does not skip generations
• Affected offspring must have an affected parent
unless they posses a new mutation
• When one parent is affected (het.) and the other
parent is unaffected, approx. 1/2 of the offspring
will be affected
• Unaffected parents do not transmit the trait

Rules of Inheritance






X-Linked Dominant
Both males and females are affected; often more
females than males are affected
Does not skip generations.
• Affected sons must have an affected mother;

affected daughters must have either an
affected mother or an affected father
Affected fathers will pass the trait on to all their
daughters
Affected mothers if heterozygous will pass the
trait on to 1/2 of their sons and 1/2 of their
daughters

Rules of Inheritance







X-Linked Recessive
More males than females are affected
Affected sons are usually born to unaffected
mothers, thus the trait skips generations
Approximately 1/2 of carrier mothers’ sons are
affected
It is never passed from father to son
All daughters of affected fathers are carriers

Rules of Inheritance








Y-Linked Dominant
Only males are affected
It is passed from father to all sons
It does not skip generations
Mitochondrial
Trait is inherited from mother only
All children of a mother are at risk to be
affected or carriers

Example

Example 1

X-linked recessive
Hemophilia
Only males are affected and sons do not share the
phenotype of their father - Thus X-linked
Expression of hemophilia skips generations:
RECESSIVE

Example 2

X-Linked Dominant
Every Generation: Dominant
Father passes on to only daughters
Mothers passes on to 1/2 of offspring

Example 3

Autosomal Recessive
Affected individual from
unaffected parents
Skip generations

Example 4

Autosomal recessive
Expressed in both sexes at approximately
equal frequency: AUTOSOMAL
Not expressed Autosomal Recessive in every
generation: RECESSIVE

Example 5

Autosomal Dominant
In every generation:
DOMINANT
Equal in Males and Females:

Example 6

Autosomal Dominant
Appears equally In both sexes
so autosomal
In every generation so

Example 7

Y-Linked
Only males are affected
All sons of affected
father

Example 8

X-Linked Dominant
Every generation: DOMINANT
Daughters of affected males are affected
Half offspring from mothers should get it

Example 9

Autosomal Dominant
In every generation: DOMINANT
Both Male and female affected:

Example 10

Mitochondrial
All children at risk
Father doesn’t pass it along to
any children

Example 11

Autosomal
Recessive
Consanguinity

Example 12

Mitochondrial
Inheritance

Example 13

Autosomal dominant
In every generation: DOMINANT
In males and...
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