Transcript Chapter 15: Chromosomal Basis of Inheritance

Chapter 15:
Chromosomal Basis
of Inheritance
(Link between Meiosis or cellular processes
and Genetics)
Objectives
1.
Mendelian Genetics is based on
the physical behavior of
chromosomes
2.
Sex linked genes have unique
inheritance patterns
3.
Linked genes are often inherited
together due to physical proximity
on the chromosome
4.
Alterations of chromosome
number or structure results in
genetic disorders
5.
There are some exceptions to the
inheritance patterns
Chromosome Theory
Chromosomes are what
segregates and undergo
independent assortment.
Chromosomal Behavior determines
sex of organism
-There is a sex
determining region
on the Y
chromosome.
-Gonads are
generic until about
2 months
-SRY gene is
responsible for the
formation of the
testes
Sex Linked Genes
-Sex linked recessive genes
for color blindness
-homozygous recessive
females have the trait
-males that get the recessive
allele from mom will have the
disease
X Chromosome Inactivation
-One of the X chromosomes in females
becomes in active.
-Barr Bodies are the inactive version of the X
chromosome
-Inactivation doesn’t happen right away
-Females that are heterozygous for a certain
X chromosome trait can express both traits
during development.
-Inactive versions produce the same in active
versions during mitosis.
Linked Genes
and
Recombinant
Chromosomes
-Parental types vs Recombinants
p. 294
-Recombinations can happen when chromosomes
segregate indpendently or after crossing over has
occurred
-Crossing over is responsible for recombinant genes if
they are located on the same chromosome
Location of genes on a chromosome
Chromosomal Dissorders
-Nondisjunction – homologous chromosomes don’t move apart
-Aneuploidy – when a zygote has an abnormal chromosome amount
-Sex Chromosomes dissorders (Most are normal)
-monosomic one less
-trisomic one extra
-Downs Syndrome (trisomy 21) – the older the
woman is the greater the odds of having a baby with
Downs
(polyploidy)
Klinefelters syndrome XXY – male is
sterile
Turnner syndrome XO only known
viable monosomy in humans –
Females are sterile
*Barr Bodies are reason success of individuals
Alterations of Chromosome Structures
*Many cases cause severe problems – most don’t make it to
birth