Pedigrees

1
Pedigrees Visual Maps for Chromosome Inheritance
2

• Please Do Now
• What are the three types of Mutations?
• In your own words, describe a Karyotype. (Hint
  Think back to Thursday/Fridays Chromosome Lab).
  What are two uses for a Karyotype?
• Explain why creating a visual map of genetic
  inheritance for a disease, that includes multiple
  generations would be useful.

3
A Closer Look at Chromosomal Mutations
There are 4 ways chromosomes can mutate and all
of them are associated with human disorders.
4
Chromosomes and Inheritance
Genes (traits) are carried on chromosomes. Knowle
dge of chromosome number and structure will
affect future advances in basic genetics, human
health, and evolution.
A normal human male karyotype.
5
Many Genetic Diseases are Autosomal Recessive
Traits
Sickle cell anemia is a recessive autosomal
disease common in areas where malaria is endemic.
An autosome is any chromosome other than an X or
Y.
Endemic means common to a certain area.
6
What Works in Peas (genetically speaking) Works
in People
¼ of offspring of two carriers of a recessive
allele are expected to show the recessive trait
½ of offspring are expected to be carriers.
7
Many Human Traits are Autosomal Dominant Traits
For disease traits, autosomal dominant
inheritance is far less common than autosomal
recessive inheritance.
8
Pedigree Analysis is a Key Tool in Human Genetics
Analyzing a pedigree is like puzzle-building
you try things (assigning potential genotypes)
until the pieces fit and youre as certain as you
can be about genotypes and how disorders are
transmitted (autosomal vs. X-linked dominant vs.
recessive).
9
Pedigree Charts

• Males
• Females
• Unaffected individuals Empty
• Carrier (not ill) Half filled
• Affected Individuals Filled in
• Dead individuals

10
Pedigrees Basic rules

• Each generation is assigned a Roman numeral (I,
  II, II, IV.), beginning with the earliest
  generation
• Individuals within generations are assigned
  Arabic numerals (1,2,3) beginning with the left
  and moving to the right.

I
1
2
II
1
2
3
4
5
11
People who have children together are
connected by a horizontal line
Their children are connected to them with a
vertical line. Siblings are connected as shown.
12
A a
A a
Aa
Aa

1. Determine the genotypes of the offspring shown in
   the pedigree above.
2. Is the trait represented above an autosomal
   Dominant or Autosomal recessive trait?

13
Patterns of dominant traits

• trait tends to appear each generation
• normal and affected individual expected to
  produce normal and affected children (approximate
  11 ratio)
• Affected individuals generally heterozygous if
  it is a rare trait
• Aa x aa ---gt 1/2 Aa 1/2 aa

14
Patterns of dominant traits

• at least one parent must be affected in order
  for children to be affected
• Aa x aa
• normal parents will always produce normal
  offspring
• aa x aa ---gt aa

15
Autosomal dominant traits

• There are few autosomal dominant human diseases
  (why?), but some rare traits have this
  inheritance pattern
• Only need to get the trait from one parent to be
  affected.

ex. achondroplasia (a sketelal disorder causing
dwarfism)
16
A Pedigree of a Dominant Human Trait
Note that the trait appears in every generation
and ½ the offspring of an affected heterozygote
are expected to show the trait.
17
Patterns of recessive traits

• may appear to skip generations
• most children of normal and affected parents are
  normal
• AA x aa ---gt Aa
• all children of two affected parents will be
  affected
• aa x aa ---gt aa

18
Patterns of recessive traits

• normal parents may produce affected offspring
• Aa x Aa ---gt 3/4 normal 1/4 affected
• affected children often result when parents are
  blood relatives

19
A Pedigree of a Recessive Human Trait
Note that the trait can appear in offspring of
parents without the trait.
Heterozygotes who do not show the trait are
termed carriers.
20
Amyotrophic lateral sclerosis (ALS) Lou Gehrigs
disease Dominant one gene is enough to give
the
disease. 1/50,000 (?)
?
It is a disease of the nerve cells in the brain
and spinal cord that affects voluntary muscle
movement.
21
Xeroderma pigmentosum (XP) inability to repair UV
damage to DNA skin tumors, death
People with XP can NOT be exposed to to any
sunlight.
Autosomal Dominant or recessive?
22
X-linked Inheritance When Men and Woman Play by
Different Rules
Behind the 8-ball? Colorblindness is an X-linked
recessive trait.
23
X-linked Inheritance
There are many X-linked recessive traits.
24
Bellringer 3/11/14
The disease represented is an autosomal recessive
disease called Tay-Sachs Disease. T- normal t-
Tay-Sachs Disease

• In the pedigree above, how many generations are
  there?
• What is the genotype of the two shaded shapes.
• Explain how the affected children were able to
  inherit the disease, yet their parents did not.