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Lecture 12.1 Chromosomes and Inheritance
Genes are short segments of DNA that determine
our traits Sex chromosomes determine the sex
(gender) of an individual and the remaining
chromosomes are called AUTOSOMES. Female
have XX (sex) chromosomes and 44 autosomes
.Males have XY (sex) chromosomes and 44
autosomes.Dads determine the sex of a child,
since their sperms can either have an X or Y
chromosome.
Sex linked genes
Genes that exist on the sex chromosomes are
called X linked or Y linked. A sex linked trait is
coded for by an allele found on a sex chromosome.
Because males have only one X chromosome, a
male who carries a recessive allele on the X
chromosome will have the sex linked trait.
Linked Genes
These genes are inherited together since they are
close to each other on the same chromosome. The
further apart the genes are located, the more
likely a cross over will occur. Chromosome maps
show the position of the genes.
Mutations
A mutation is a change in the nucleotide base
sequence of a gene or DNA. They are constantly
being generated in a gene pool. Germ cell
mutations occur in the sex cells. They don’t affect
the organism, but are passed on to the offspring.
Somatic cell mutations occur in the body cells and
affect the organism but not the offspring (skin
cancer).Mutations can be lethal or beneficial.
Chromosome Mutations
These are changes in the structure of a
chromosome or loss or gain of an entire
chromosome.
Gene mutations are changes in the nucleotides in a
gene.
Lecture 12.2 Human Genetics
The inheritance of genetic traits can be studied
by using a PEDIGREE chart.
Squares stand for males and circles for females.
A filled symbol means the person has the disease
and empty means he does not.
A half filled symbol shows they are carriers of
the disease.
Patterns of inheritance.
An autosomal trait shows up equally in males and
females. A sex linked trait usually show up in
males, and many are caused by recessive genes
(color blindness and hemophilia)
Polygenic inheritance.
This is when many genes control a trait like skin
color.
Multiple alleles
Many genes have more then three alleles,the ABO
blood group in humans is an example.
X- linked traits
These are traits that are carried on the X
chromosome ,like color blindness.A pedigree will
show many males are affected and no affected
female.
Sex influenced traits
Males and females can show different phenotypes
even if they have the same genotype. Male
pattern baldness is an example. The high level of
testosterone in males is responsible for this.
Detecting genetic diseases.
Amniocentisis tests a fetus’s fluid for defective
disorders.
Gene therapy allows us to replace a defective gene
with a healthy one.