Download Pedigrees - SVHonBioLeas1

Pedigrees
Pedigree Analysis
• In humans, pedigree analysis is an
important tool for studying inherited
diseases
• Pedigree analysis uses family trees and
information about affected individuals to:
– figure out the genetic basis of a disease or
trait from its inheritance pattern
– predict the risk of disease in future offspring in
a family (genetic counseling)
Pedigree Symbols
= Males
Key:
= Females
Shading
= Has trait
No Shading = Normal (doesn’t have trait)
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Trends in Pedigrees
• In pedigrees, there are several basic
patterns of inheritance.
–autosomal, recessive
–autosomal, dominant
–X-linked, recessive
–X-linked, dominant (very rare)
• You should be able to recognize these
trends in pedigrees.
Autosomal recessive traits
• Trait is rare in pedigree
• Trait often skips
generations (hidden in
heterozygous carriers)
• Trait affects males and
females equally
Autosomal recessive diseases
Most common ones
• Cystic fibrosis
• Sickle cell anemia
• Phenylketonuria (PKU)
• Tay-Sachs disease
Autosomal dominant pedigrees
• Trait is common in the pedigree
• Trait is found in every generation
• Affected individuals transmit the trait to ~1/2 of their
children (regardless of sex)
Autosomal dominant traits
There are few
autosomal dominant
human diseases, but
some rare traits have
this inheritance
pattern
ex. achondroplasia
(a sketelal disorder
causing dwarfism)
X-linked recessive pedigrees
• Trait is rare in pedigree
• Trait skips generations
• Affected fathers DO NOT
pass to their sons
• Males are more often
affected than females
X-linked recessive traits
ex. Hemophilia in European royalty
X-linked dominant pedigrees
• Trait is common in pedigree
• Affected fathers pass to ALL of their daughters
• Males and females are equally likely to be affected
You can predict genotypes from a pedigree:
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Pedigree Tips
• If there are many colored in, it is dominant;
if there are few colored in, it is recessive.
• If there are mostly males colored it, it is
sex-linked; if there are about equal males
and females, it is autosomal.
• If there are carriers (females colored in ½
way), it is sex-linked.
Karyotypes
• Genes are found on
chromosomes(represented by banding).
• Chromosomes are found in the nucleus.
Chromosomes are found in pairs which
hold the same genes, but not necessarily
the same allele.
• Each cell in the human body has 46
chromosomes total (23 pairs); except for
the sex cells which are haploid and have
23 chromosomes.
Karyotypes
Karyotypes
• A karyotype is a picture of pairs
chromosomes arranged by
number, size, and type.
• Sex chromosomes determine an
individual’s sex. The remaining
chromosomes are called
autosomes.
Karyotypes
Karyotypes
• From a karyotype, we can
determine:
• The sex of the individual
• Whether or not there are any
chromosomal abnormalities such
as too many or too few
chromosomes.
Karyotypes
• To obtain a karyotype,
an amniocentisis is
performed during the
2nd trimester of
pregnancy.
• A sample of amniotic
fluid is removed from
the uterus and used to
create the karyotype.