Transcript Types Of Inheritance And Pedigrees

Types of Inheritance
Patterns
Gene Linkage
 Genes on the same chromosome are
considered linked and are called a linkage
group.
Human Sex-linked Inheritance
Sex-linked traits are distinguishable by their mode of
transmission through successive generations of a
family.
In humans it is preferable to speak in terms of Xlinked or Y-linked inheritance.
Red-green color blindness was the first human trait
proven to be due to a gene on a specific
chromosome. Hemophilia is another common
sex-linked trait.
Sex-Linked Traits
If a gene is found only on the X
chromosome and not the Y chromosome,
it is said to be a sex-linked trait.
Because the gene controlling the trait is
located on the sex chromosome, sex
linkage is linked to the gender of the
individual.
Usually such genes are found on the X
chromosome. The Y chromosome is thus
missing such genes.
The result is that females will have two copies of the sexlinked gene while males will only have one copy of this
gene.
If the gene is recessive, then males only need one such
recessive gene to have a sex-linked trait rather than the
customary two recessive genes for traits that are not sexlinked.
This is why males exhibit some traits more frequently than
females.
Examples of Sex-linked Traits:
Red-green colorblindness
Male Pattern Baldness
Hemophilia
Duchenne Muscular Dystrophy
Chromosome Mapping
 A chromosome map is a linear diagram of the
position of the alleles on a chromosome.
 The closer together the genes are linked on the
chromosome the less chance they will separate
during crossing over.
 The map distance is the distance between
genes on a single chromosome.
 The greater the distance between linked genes,
the more likely they are to cross over during
meiosis.
Sample Sex-linked Trait
Problems
 In humans, red-green colorblindness is a
recessive sex-linked trait. It is found on the X
chromosome, not the Y. Because, males only
have one X chromosome, they have a much
greater chance of having red-green
colorblindness. Females would have to be
homozygous recessive in order to have red-green
colorblindness
Multiple Alleles and Blood
Types
Pedigree
* is a tool that
can determine
the pattern of
inheritance of a
particular trait.
Multiple Alleles
 Within a
population, more
than two alleles
can exist
(although any
given individual
only has two
alleles).
 The human ABO blood groups are an example
of multiple alleles, and the relationship between
phenotype and genotype.
 There are four possible phenotypic blood types
for this particular gene: A, B, AB, and O. The
letters refer to two specific antigens on the
surface of red blood cells.
 Individuals can have the A antigen (blood type
A), the B antigen (blood type B), both the A and
B antigen (blood type AB), or neither antigen
(blood type O).
 Human blood type is determined by
codominant alleles. There are three
different alleles, known as IA, IB, and i.
The IA and IB alleles are codominant,
and the i allele is recessive.
 The possible human phenotypes for
blood group are type A, type B, type AB,
and type O. Type A and B individuals
can be either homozygous (IAIA or IBIB,
respectively), or heterozygous (IAi or IBi,
respectively).
Cross Type AB and a Type O
blood
 What are the
possible blood
types of the
offspring of a
cross between
individuals that
are type AB and
type O? (Hint:
blood type O is
recessive)
Type A and type B cross
 Four different
genetic crosses are
possible. All four
crosses must be
considered to
determine all
potential offspring.
However, one
cross (IAi mother x
IBi father) is most
informative.
Types of Inheritance patterns
Autosomal Dominant Inheritance
• using chromosomes
other than sex
chromosomes
• the traits would be
either dominant or
recessive
• whenever a recessive
phenotype occurs in a
child of parents who
exhibit the dominant trait,
the parents must be
heterozygous for that
trait
Autosomal Recessive Inheritance
 deals with
autosomes with
the recessive
genes being
inherited