Transcript Chapter 12 College Prep Biology

Chapter 12
College Prep
Biology
Patterns of Heredity
&
Human Genetics
1
Chapter 12
Differing hormone levels among sexes can cause
a single genotype to express more than one
phenotype
 Co-Dominant Alleles are when phenotypes of
both homozygotes are produced in the
heterozygous ex. Roan color in cattle
 Multiple Alleles occur when there are more
than two alleles for a single trait.

2
A trait for example that is controlled by four
alleles is said to have multiple alleles
 Eye color in humans/ Blood type are both
examples of Multiple Allelic inheritance
 Incomplete Dominance -a blending of traits;
a type of inheritance shown when a red flower is
crossed with a white flower and only pink
flowers are produced
 Most human genetic disorders are caused by the
expression of Recessive Alleles

3





Humans have 22 pairs of Autosome type
chromosomes
23rd pair that differs in males and females are called
sex chromosomes
Sex Linked traits are those traits carried on the X
and Y chromosomes. For the most part it is said that
they are carried on the X-chromosome.
Examples- red/green color blindness and Hemophilia
But a few are actually carried on the y chromosome
called the maleness chromosome
4



B/c most sex-linked traits are carried on the X-chromosome it
is normally NOT possible for a color blind father to pass the
sex-linked gene on to his son (as he gives the y chromosome
to his son and not the X)
Red green color blindness in humans is a sex-linked trait that
shows POLYGENTIC inheritance. It is caused by a recessive
allele carried on the X-chromosome
Polygenic inheritance: shows the inheritance pattern of a
trait that is controlled by two or more genes. Ex. Skin. Color
and height
5




PKU – human genetic defect that results in the failure to
metabolize the amino acid phenylalanine. It can result in
mental retardation
Dietary adjustments – used to treat PKU
Cystic Fibrosis – Defective protein in the plasma
membrane, resulting in the formation of thick mucus in
the lungs and digestive tracts.
Tay-Sachs: Recessive disorder opf the central nervous
system. Results from the absence of an enzyme that
normally breaks down a lipid.
6
Which one does not belong?
Heterozygous, Hybrid, Carrier, Homozygous.
Homozygous b/c the other terms involve
contrasting alleles for a trait. A homozygous
individual possesses two identical alleles for a
trait.
 Red blood cells, phenylalanine, oxygen
deprivation, hemoglobin. Phenylalanine b/c the
other terms all relate to sickle cell anemia.
Phenylalanine is the amino acid that cannot be
metabolized by individuals with PKU

7
Which one does not belong?
Huntingdon’s disease, cystic fibrosis, PKU, taySachs disease. Huntington's disease b/c it is
caused by an autosomal dominant allele,
whereas the others are the result of autosomal
recessive alleles.
 Huntington’s – lethal disorder-results in a
breakdown of certain areas of the brain.

8
Which one does not belong?
Genotype, phenotype, heterozygous, homozygous
Phenotype b/c the other three terms describe
the gene combination of an organism and not
the expression of those genes
9
A pedigree is a graphic representation of
genetic inheritance
 Insert – handout on pedigree chart

10