Transcript PEDIGREE CHARTS - Rankin County School District

Chapter 11
Human Genetic
Analysis
Complex inheritance of traits does not
follow inheritance patterns described
by Mendel.
 Several
genes can influence a trait- polygenic
trait.
 Determining the effect of these genes is
difficult.
Example: A horse with red hair mates with a horse with
white hair, and their offspring has both red and white hair.
How can this be?
Codominance


When two dominant alleles are expressed at the
same time, both forms of the trait are displayed.
Different from incomplete dominance because both
traits are displayed.
Example:
red flower x white flower =
red and white flowered offspring
equal number of red and white flowers
Example:
Black horse x white horse = roan coat
equal number of black and white hairs
Intermediate Traits

Incomplete dominance - an individual displays a trait
that is intermediate between the two parents.
red flower x white flower = pink flower
Neither the red nor the white allele is completely dominant
Example:

Multiple Alleles
Genes with three or more alleles are said to have multiple
alleles.
 When traits are controlled by genes with multiple alleles, an
individual can have only two of the possible alleles for that
gene.
Example: Blood types in humans


Three different alleles –IA, IB, and i result in four different blood
phenotypes – A, AB, B, and O.
X-Linked Traits
The
trait is carried by females on the X
chromosome through a recessive allele.
Males will have the disorder because they only
have one X chromosome.
Traits influenced by the
Environment
An individual’s phenotype often depends on conditions
in the environment.
Example: fur color in Siamese cats


Dark fur around cooler parts of the body- ears, nose,
paws, and tails.
Example:

skin tone in humans
Exposure to the sun alters the color of the skin.
Mutations
 Changes
in genetic material.
 The
harmful effects produced by inherited
mutations are called genetic disorders.
 Many
mutations are carried by recessive
alleles in heterozygous individuals.
“carriers”
Genetic Counseling
o
Genetic counseling is a form of medical
guidance that informs people about
genetic problems that could affect them
or their offspring.
1. Genetic Abnormality
 Rare, uncommon version of a trait.
2. Genetic Disorder
 An inherited condition that sooner or
later will cause mild to severe medical
problems.
3.
Syndrome
A
recognized set of symptoms that
characterize a given disorder.
4. Disease
 Illness caused by infectious, dietary, or
environmental factors, NOT by inheritance
of mutant genes.
Disorder
Mutation
Chromosome
Color blindness
P
X
Cystic fibrosis
P
7q
Down syndrome
C
21
Hemophilia
P
X
Klinefelter syndrome
C
X
Sickle-cell disease
P
11p
Tay–Sachs disease
P
15
P – Point mutation, or any insertion/deletion
entirely inside one gene
D – Deletion of a gene or genes
C – Whole chromosome extra, missing, or both
T –Trinucleotide repeat
disorders: gene is extended in length
Karyotypes
Karyotypes
 micrograph
in which the pairs of
homologous chromosomes are arranged
in decreasing size
 22 autosomes are matched together with
one pair of nonmatching sex
chromosomes
 Used to study chromosomes in hopes of
identifying genetic abnormalities or
disorders.
PEDIGREE CHARTS
© 2007 Paul Billiet ODWS
What is a pedigree chart?
a
chart of the genetic history of a family
over several generations.
 used
to study the transmission of
hereditary conditions
© 2007 Paul Billiet ODWS
Constructing a Pedigree
 Female
 Male
Connecting Pedigree Symbols

Married Couple

Children
Symbols used in pedigree charts
 Affected
 X-linked
 Carrier
 Deceased
© 2007 Paul Billiet ODWS
.
.
Symbols used in pedigree charts




Normal male
Affected male
Normal female
Affected female
© 2007 Paul Billiet ODWS
Organizing the pedigree chart

A pedigree chart of a family showing 20 individuals
© 2007 Paul Billiet ODWS
Organising the pedigree chart

Generations are identified by Roman numerals.
I
II
III
IV
© 2007 Paul Billiet ODWS
Organising the pedigree chart


Individuals in each generation are identified by Arabic numerals
numbered from the left
Therefore the affected individuals are II3, IV2 and IV3
I
II
III
IV
© 2007 Paul Billiet ODWS
Interpreting a Pedigree Chart
1.
Determine if the pedigree chart shows an autosomal
or X-linked 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.

Example of Pedigree Charts
 Is
it Autosomal or X-linked?
Answer
 Autosomal
2.


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.
Example of Pedigree Charts
 Dominant
or Recessive?
Answer
 Dominant
Example of Pedigree Charts

Dominant or Recessive?
Answer

Recessive