Transcript Biology Chapter 7

Section One: Chromosome and
Phenotype
 Phenotype
 Different alleles produce
different phenotypes
 Genetic disorders can be
predicted by examining alleles

Disorders can be caused by
recessive alleles
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Caused by recessive alleles on
autosomes
2 copies of the recessive allele must
be present to cause the disorder
Carrier: does not show symptoms
of the disease, but can cause the
disease causing allele to offspring
Disorders can be caused by
dominant alleles

Less common
Section One: Chromosomes and
Phenotype
 Sex-linked Traits
 Sex-linked genes: genes
located on the sex
chromosomes
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X chromosomes have more
influence over phenotype
Males only get one copy of X
and one copy of Y
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Which means if the copy a
male receives is recessive, it
will be expressed
X Chromosome
Inactivation: in females, one
of the two x chromosomes
is “inactivated”
Section Two: Complex Patterns of
Inheritance
 Incomplete and
Codominance
 Incomplete Dominance:
a heterozygous
phenotype is
somewhere between the
2 homozygous
phenotypes
 Codominance: both
traits are fully and
separately expressed
Section Two: Complex Patterns of
Inheritance
 Polygenic Traits and Epistasis
 Polygenic Trait: traits produced by two or more genes
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Example: Human skin color and eye color
 Epistasis: one gene interferes with the expression of
other genes
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Example: albinism
Section Two: Patterns of
Inheritance
 Environment and Genotype
 Temperature dependent sex determination
 Are the nutrients necessary for that trait present?
Section Three: Gene Linkage and
Mapping
 Linkage Maps
 Maps of relative locations, or loci, of genes on a
chromosome
 Shows how often crossing over occurs between two
genes occur
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The farther apart two genes are on the genome, the more likely
they are to cross over
Section Four: Human Genetics and
Pedigrees
 Human Genetics
 Females carry sexlinked genetic disorders
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They are called carriers
They have an extra X
chromosome to override
the X chromosome with
the disorder
When males receive the X
chromosome with the
disorder, they do not have
another X chromosome,
only a Y chromosome
Section Four: Human Genetics and
Pedigrees
 Pedigree: a chart that can
help trace the
phenotypes and
genotypes in a family to
determine whether
people carry recessive
alleles
 Can be used for
autosomal genes and
sex-linked genes
Section Four: Human Genetics and
Pedigrees
 Pedigrees
 Tracing Autosomal Genes
Section Four: Human Genetics and
Pedigrees
 Pedigrees
 Tracing Sex-linked Genes
Section Four: Human Genetics and
Pedigrees
 Mapping Human
Chromosomes
 Karyotype: a picture of
all the chromosomes in
a cell
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Can show changes in
chromosomes
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Deletions or extra copies