Transcript The Human Genome

The Human Genome
Chapter 14
Section 1
karyotype
(KAR-ee-uh-typ).
• photograph cells in mitosis, when
the chromosomes are fully
condensed and easy to see.
• The biologists then cut out the
chromosomes from the
photographs
• Then group them together in
pairs.
• Two of 46 chromosomes in
humans are known as sex
chromosomes, because they
determine an individual's sex.
• To distinguish them from the sex
chromosomes, the remaining 44
chromosomes are known as
autosomal chromosomes, or
autosomes
From Gene to Molecule
• In both cystic fibrosis and
sickle cell disease, a small
change in the DNA of a
single gene affects the
structure of a protein,
causing a serious genetic
disorder.
(test question)
In a population, approximately
half of the
zygotes are XX (female) and half
are XY (male).
X and Y chromosomes
• Females have two X chromosomes, but
males have only one. If just one X
chromosome is enough for cells in males,
how does the cell “adjust” to the extra X
chromosome in female cells?
• In female cells, one X chromosome is
randomly switched off. That turned-off
chromosome forms a dense region in
the nucleus known as a Barr body.
pedigree chart
pedigree chart example
Fun Fact about Cats
• a gene that controls the color of coat spots is
located on the X chromosome. One X
chromosome may have an allele for orange
spots and the other may have an allele for black
spots. In cells in some parts of the body, one X
chromosome is switched off. In other parts of the
body, the other X chromosome is switched off.
As a result, the cat's fur will have a mixture of
orange and black spots. Male cats, which have
just one X chromosome, can have spots of only
one color.
Calicos are female
Human Chromosomes
• A human diploid cell contains more than 6
billion base pairs of DNA. All of this DNA is
neatly packed into the 46 chromosomes
present in every diploid human cell.
• only about 2 percent of the DNA in your
chromosomes functions as genes—that is,
is transcribed into RNA
• Genes are scattered among long
segments of DNA that do not code for
RNA.
Sex-Linked Genes
• Males have just one X chromosome.
Thus, all X-linked alleles are expressed
in males, even if they are recessive.
• color blind
• Colorblindness
• Hemophilia
• Duchenne Muscular Dystrophy
assignment
• Page 348 1-2
• Page 354 1-3