Download Notes GENES ON CHROMOSOMES

GENES ON CHROMOSOMES Chapter 11 & Chapter
13
I.
II.
Introduction
A.
Chromosome Theory of Heredity
1. Def. – genes are located on
chromosomes
a.
Locus – point on a chromosome
where a given gene is located.
2.
Reason: early geneticists saw a
relationship between Mendel’s
discoveries and the way
chromosomes move during meiosis.
Tests of the Chromosome Theory of Heredity
A.
Sex Determination
1.
Discovered through Morgan’s work with
Drosophila
a.
Good subject for genetic studies:
1. small
2. easily handled
3. produce a large number of
offspring in a short period of
time.
b.
Chromosomes of fruit fly - diagram
c.
Gametes of fruit fly:
1.
Egg - 3 autosomes and X
2.
Sperm – 3 autosomes and X
or Y
Result of fertilization: 50:50
chance of producing male or
female
2.
Relation to Chromosome Theory of
Heredity:
a.
Presence of “Y” determines traits in
fruit flies:
! Examples: sex in fruit fly
Pigmentation of
abdomen
3.
Sex determination in animals is not
always”Y” for males: p.341
! Examples: some birds have :
female = xy and male =xx
X-Linkage:
1.
Def. Traits carried on the sex
chromosomes
2.
Discovery: Morgan’s work with fruit
flies
3.
Relationship to C.T. of H. – again links
trait with chromsomes:
4.
Other examples in humans: p. 350
! Red-green colorblindness
! Hemophilia
! Carriers: females who are
heterozygous for the trait because
there is a 50:50 chance that they
will possess the trait to their male
offspring.
5.
X-inactivation and Barr Bodies: p. 351
d.
B.
a.
General Description: female
mammals show the presence of a
“Barr Body” when stained during
interphase.
1.)
Barr Body
a.)
Def. – a dense stainable
structure which is one of
the X chromosomes
b.)
Why is it inactive? Is
coiled
2.)
Explanation: During early
embryonic development in
the female, some of the X’s
are inactivated. Therefore
there are two populations of
traits in one organism and
two different gene
expressions.
3.)
Example: Calico cat
P. 363 # 1,5,6,7,15
" P. 365 #2,3
Chromosome Abnormalities:
A.
Usually two types:
1. involve chromosome #
2. involve chromosome structure
"
III.
B.
Types:
1.
Nondisjunction(C.N.) p. 352
Definition: failure of homologous
chromosomes to separate during
meiosis.
! Examples: Down’s Dyndrome
Klinefelter and Turner
Polyploidy(C.N.)
a.
Def.: complete nondisjuntion of
entire gamete
! Not a problem in plants; can
actually introduce new
combinations but is lethal in
animals.
Structural Alterations page 308
! When- during crossing over
a. Types:
1.)
Deletion
a.)
Def.: segment of
chromosome is lost
b.)
Examples: some forms
of leukemia
2.)
Inversion
a.)
Def.: segment is turned
around
b.)
Examples
3.)
Translocation
a.)
Def.: segment of a
chromosome breaks off
and attaches to a nonhomologue
b.)
Examples
!
2.
3.
c.)
IV.
V.
VI.
Cause: chemicals, xrays, radiation
Linkage page 279
A.
Def.- more than one gene on a
chromosome
B.
Behavior- do not follow the Law of
Independent Assortment, segregate
together.
C.
Linkage and variety: reduces variety
! Producing variety: crossing over
Chromosomal Maps
A.
How derived: determined by frequency of
crossing-over
! Meaning: genes that are linked crossover more frequently
B.
What is allows: drawing genetic maps
! Def.: shows the location of genes on
chromosomes
! P. 283 # 10
! P. 285 # 5,7,8
Other Genetic Characteristics:
! Multiple Alleles: more than one allele
determines a trait. Page 273
! Example: Blood types page 344
Three alleles: IA, IB, IO
" IA & IB are codominant
(definition: both alleles are
expressed)
" IO is recessive
" P. 363 # 4
"
P. 365 # 4,6