Download Chromosome Theory of Inheritance -States that genes or alleles

Chromosome Theory of Inheritance
-States that genes or alleles (form of a gene) are
located at specific loci (locations) on
chromosomes
-Chromosomes segregate and show independent
assortment during meiosis
Linked Genes
-Traits that are located near each other on the
same chromosome and tend to be inherited
together
If Genes Are Linked
-Independent assortment of trait fails
-Linkage may be “strong” or “weak”
Crossing-Over
-Breaks up linkages and creates new ones
-Recombinant offspring formed that doesn’t
match the parental types
Linkage Strength
-Degree of strength related to how close the
traits are on the chromosomes
-Weak linkage: farther apart
-Strong linkage: Closer together
Genetic Linkage Maps
-Constructed from crossing-over frequencies
-1 map unit= 1% recombination frequency
-Map units are used to express relative distances
along the chromosomes
-The less often a gene crosses over with another
one, the closer it must be to it, so if the
frequency is low, the distance between the two
must be small
Alteration of Chromosome Number or Structure
Because of Mistakes During Meiosis Cause Some
Genetic Disorders:
-Nondisjunction occurs when members of a pair
of homologous chromosomes do not separate
properly during meiosis I, or sister chromatids
don’t separate properly during meiosis II
Result
-One gamete receives two copies of the
chromosome while the other gamete receives
none
-If the faulty gametes engaging in fertilization,
the offspring will have an incorrect chromosome
number, this condition is called aneuploidy
-Nondisjunction: If chromosomes don’t separate
properly during meiosis I or II, gametes will end
up with too many or too few chromosomes,
leading to chromosomal abnormalities in the
zygotes they produce
When Meiosis Goes Wrong
Single Chromosome Alterations
-Fertilized eggs that have received thee copies of
the chromosome in question are said to be
trisomic
-Those that only receive one copy of a
chromosome are monosomic
Human Disorders Caused by Chromosome
Alterations
-Down Syndrome: Aneuploid condition also
known as trisomy 21, three copies of
chromosome 21
-Turner Syndrome: Monosomic condition where
females have one sex chromosome x. Are
females but sterile. Is the only monosomic
condition in humans
-Klinefelter Syndrome: Aneuploid condition in
which a male posses the sex chromosomes XXYare male but sterile
Polyploidy-Multiple Chromosome Alterations
-Is the condition of having more than two
complete sets of chromosomes, forming a 3n or
4n individual. Rare in animals this condition is
fairy frequent in plants
-This often results in sterility, but increased vigor
of those polyploidy plant individuals
Portions of a chromosome may also be lost or
rearranged during meiosis, resulting in
chromosomal structural mutations that can have
large effects on the zygote (4 types)
-Deletion: occurs when a chromosomal fragment
is lost, resulting in missing genes
-Duplication: occurs when the chromosome
fragment that broke off during deletion becomes
attached to its sister chromatid and the zygote
gets a double dose of the gene added on the
chromosome
-Inversion: occurs when a chromosome fragment
breaks off and reattached to its original positionbut backward
-Translocation: occurs when the deleted
chromosome fragment joins a non-homologous
chromosome