Download Human Inheritance Patterns - Fall River Public Schools

HUMAN INHERITANCE
PATTERNS
Objectives
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Explain the role of sex chromosomes in sex
determination
Describe how sex linkage affects the
inheritance of traits
Be able to interpret a pedigree chart
Explain the inheritance of ABO blood groups
Sex Determination

In mammals and most
insects, sex chromosomes
(X and Y) determine the
organism’s gender
 All
other chromosomes are
called autosomes
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
Males have one X and one
Y chromosome (XY)
Females have two X
chromosomes (XX)
Sex Determination
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
During gamete formation,
the pair of chromosomes
separate
Each gamete will have just
one sex chromosome
 Each
sperm will have either
an X or a Y chromosome
 Every egg will have an X
Looking at the Punnett
chromosome because
Square, there is a 50/50
females have only XX
chance that the offspring
chromosomes
will be a boy or a girl
Sex Determination

Remember…
 Females
are XX
 Males are XY
 NO organisms are YY…
 Except…
Sex Linkage

Sex linkage is the
presence of a gene on a
sex chromosome
 Genes
found on the X
chromosomes are X-linked
genes
 Genes found on the Y
chromosomes are Y-linked
genes
 Ex: eye color on Drosophila
flies
Pedigree Analysis
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Biologists discover how traits
are inherited by studying
phenotypes among members
of the same species from one
generation to the next
Biologists usually study
disease-causing genes
because they are easily traced
and are a great concern to the
human population
A pedigree is a family record
that shows how a trait is
inherited over several
generations
Pedigree Analysis
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Squares represent males
Circles represent females
A square or circle that is
colored in indicates that the
person displays the trait you
are monitoring
A square or circle that is halfcolored in indicates that the
person is a carrier
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Generally means the person is
heterozygous for the trait, and
the trait is recessive
Not all pedigrees show the
carriers!!
Pedigree Analysis
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This pedigree shows
a trait that is
autosomal recessive
It is autosomal
because both sexes
can have it
A person can:
Have the trait
 Not have the trait
 Be a carrier of the trait

Traits Controlled by a Single Allele
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Single-allele traits are
controlled by a single
allele of a gene
Huntington’s disease
(HD) is caused by a
dominant allele located
on an autosome
Cystic fibrosis (CF)
and sickle cell anemia
are controlled by
homozygous recessive
alleles on autosomes
Traits Controlled by Multiple Alleles
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Multiple-allele traits
are controlled by
three or more alleles
of the same gene that
code for a single trait
The ABO blood
groups in humans are
controlled by three
alleles
 IA, IB,
i
Genotype
Blood type
IAIA
A
IAi
A
IBIB
B
IBi
B
IAIB
AB
ii
O
Polygenic Traits

A trait that is controlled
by several genes is
called a polygenic trait
 Most
human
characteristics are
controlled by several
genes
 Ex: skin color
X-Linked Traits
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Colorblindness is a
recessive X-linked
disorder
Hemophilia (recessive)
occurs almost
exclusively in males
Duchenne muscular
dystrophy (recessive)
Not all X-linked traits
cause disorders

Most code for proteins
that perform normal
bodily functions
Sex-Influenced Traits
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Traits whose expression are
influenced by the presence
of male or female sex
hormones are called sexinfluenced traits
Males and females will
share the same genotype
but have different
phenotypes
Ex: baldness is influenced
by the presence of male
hormones (testosterone)
Review Questions

Explain the role of sex chromosomes in sex
determination.
Males have one X and one Y chromosome (XY)
 Females have two X chromosomes (XX)
 Males can produce a gamete with an X or a Y
 Females can only produce gametes with an X


Describe what sex linkage is and the two
types of sex-linked genes.
Sex linkage is the presence of a gene on a sex
chromosome
 The two types of sex-linked genes are X-linked genes
and Y-linked genes

Review Questions

Explain the inheritance of ABO blood
groups
 The
ABO blood groups in humans are controlled
by three alleles: IA, IB, i