genetics

1. GENETICS
Topics:
Heritable Traits in Man
The Pedigree Chart
Application of Pedigree
Analysis

3. Handedness - is due to a
single gene with right
handedness dominant
and left handedness
recessive. However,
other scientists have
reported that the
interaction of two genes
is responsible for this
trait.

4. Naturally Curly Hair -
early curly hair was
dominant and straight
hair was recessive.

5. Allergies - allergic reactions
are induced by things a
person comes in contact
with, such as dust, particular
foods, and pollen, the
tendency to have allergies is
inherited. If a parent has
allergies, there is a one in
four (25%) chance that their
child will also have allergy
problems. This risk
increases if both parents
have allergies.

6. Colorblindness - due to a
recessive allele located on the X
chromosome. Women have two
X chromosomes, one of which
usually carries the allele for
normal color vision. Therefore,
few women are colorblind. Men
only have one X chromosome,
so if they carry the allele for
colorblindness, they will exhibit
this trait. Thus, colorblindness
is seen more frequently in men
than in women.

7. Hairline shape -
is reportedly due
to a single gene
with a widow’s
peak dominant
and a straight
hairline recessive.
Widow’s Peak Hairline
Straight Hairline

8. Tongue Rolling –
a dominant allele, R, gives
some people the ability to
roll their tongues into a
“U” shape when it is
extended. People with the
recessive alleles, rr,
cannot roll their tongues.

10. Pedigree
•The term 'pedigree' refers to the record of an
organism's ancestry.
•Is a pictorial representation of a family history,
essentially a family tree that outlines the inheritance
of one or more characteristics.
•Pedigree charts are diagrams which are constructed
to show biological relationships - how a trait can
pass from generation to generation.
•From a pedigree, you can determine if a trait is
dominant or recessive, if it is sex-linked, and
probability of it affecting future generations.
•To build such a chart to see the flow of genotypes,
symbols and rules must be followed.

12. Mitochondrial Genes
•Mitochondria are only
inherited from the mother.
•If a female has a
mitochondrial trait, all of
her offspring inherit it.
•If a male has a
mitochondrial trait, none of
his offspring inherit it.

13. Genetic conditions caused by a mutation in a
single gene follow predictable patterns of inheritance
within families. Single gene inheritance is also referred to
as Mendelian inheritance as they follow transmission
patterns he observed in his research on peas. There are
four types of Mendelian inheritance patterns:
Single Gene or
Mendelian

14. •Autosomal: the gene responsible for the phenotype
is located on one of the 22 pairs of autosomes (non-
sex determining chromosomes).
•X-linked: the gene that encodes for the trait is
located on the X chromosome.
•Dominant: conditions that are manifest in
heterozygotes (individuals with just one copy of the
mutant allele).
•Recessive: conditions are only manifest in
individuals who have two copies of the mutant allele
(are homozygous).

16. Autosomal Dominant
Dominant conditions are expressed in individuals
who have just one copy of the mutant allele. Affected
males and females have an equal probability of passing
on the trait to offspring. Affected individual's have one
normal copy of the gene and one mutant copy of the
gene, thus each offspring has a 50% chance on inheriting
the mutant allele. As shown in this pedigree,
approximately half of the children of affected parents
inherit the condition and half do not.

17. Autosomal Dominant
Conditions:
• Huntington Disease
• acondroplasia (short-
limbed dwarfism)
• polycystic kidney
disease
The pedigree illustrates the transmission
of an autosomal dominant trait

18. Autosomal Recessive
Recessive conditions are clinically manifest
only when an individual has two copies of the mutant
allele. When just one copy of the mutant allele is
present, an individual is a carrier of the mutation, but
does not develop the condition. Females and males are
affected equally by traits transmitted by autosomal
recessive inheritance. When two carriers mate, each
child has a 25% chance of being homozygous wild-
type (unaffected); a 25% chance of being homozygous
mutant (affected); or a 50% chance of being
heterozygous (unaffected carrier).

19. Affected individuals are
indicated by solid black
symbols and unaffected
carriers are indicated by
the half black
symbols.Autosomal
recessive diseases:
• Cystic fibrosis
• Tay-Sachs
• hemochromatosis
• phenylketonuria
(PKU)

20. X-linked Recessive
X-linked recessive traits are not clinically
manifest when there is a normal copy of the gene. All X-
linked recessive traits are fully evident in males because
they only have one copy of the X chromosome, thus do
not have a normal copy of the gene to compensate for
the mutant copy. For that same reason, women are rarely
affected by X-linked recessive diseases, however they
are affected when they have two copies of the mutant
allele. Because the gene is on the X chromosome there is
no father to son transmission, but there is father to
daughter and mother to daughter and son transmission. If
a man is affected with an X-linked recessive condition,
all his daughter will inherit one copy of the mutant allele
from him.

21. X-linked Recessive
Disorders:
• Duchenne muscular
dystrophy
• hemophilia A
• X-linked severe combined
immune disorder (SCID)
• some forms of congenital
deafness

22. X-linked Dominant
Because the gene is located on the X
chromosome, there is no transmission from father to
son, but there can be transmission from father to
daughter (all daughters of an affected male will be
affected since the father has only one X chromosome to
transmit). Children of an affected woman have a 50%
chance of inheriting the X chromosome with the mutant
allele. X-linked dominant disorders are clinically
manifest when only one copy of the mutant allele is
present.

23. X-linked Dominant
Disorders
• some forms of retinitis
pigmentosa
• Chondrodysplasia
Punctata
• hypophosphatemic
rickets

24. Application of Pedigree
Analysis

25. Huntington disease

26. Albinism

27. Cystic fibrosis
The roman numerals indicate the generation (I, II or III) and the numbers
show birth order of children (1, 2, 3, 4 etc.)

28. ① Assuming this is a recessive
gene, we know that II-3 and III-4
must be “aa.”
② Therefore both parents of these
offspring must have given an “a”
allele.
③ So, I-1, I-2, II-4 and II-5 must
each have one “a” in their
genotypes.
④ Since I-1, I-2, II-4 and II-5 don’t
have the disease, their other
allele must be “A.”
⑤ All the rest of the people could
be either AA or Aa.