Download 14-1 - Fort Bend ISD

Beefalo is a cross between Bison (buffalo) and domestic or exotic
cattle of any breed. The purpose of the species cross was to blend
the outstanding qualities of the Bison with outstanding qualities of
the bovine breeds of the world.
The cross between the Bison and beef breeds combined the
superior hardiness, foraging ability, calving ease, and meat quality
of the Bison with the fertility, milking ability, and ease of handling
from the bovine.
Zorse
Liger
14-1
HUMAN HEREDITY
What is a chromosome?
How many chromosomes do
humans have?
**A Picture of chromosome arranged in rows
is a karyotype
Humans have 23 pairs (46) chromosomes
Two of the 46 chromosomes are called
sex chromosomes because they
determine an individual’s sex
Females have two copies of a large X
chromosome. Males have one X and one
small Y chromosome
The remaining 44 chromosomes are
known as autosomal chromosomes or
autosomes.
All human egg cells carry a single X
chromosome (23, X). However, half of all
sperm cells cells carry an X chromosome
(23,X) and half carry a Y chromosome
(23,Y). This ensures that just about half
the zygotes will be 46XX and half will be
46XY
Is this a male or female’s
karyotype?
*** Human genes are inherited according to
Mendel’s principles. However, in order to
apply Mendelian genetics to humans,
biologists must identify an inherited trait
controlled by a single gene. First they
must establish that the trait is actually
inherited and not the result of
environmental influences. Then, they have
to study how the trait is passed from one
generation to the next.
A pedigree chart shows relationships
within a family.
If a trait is dominant, then all family
members who lack the trait must have
homozygous recessive (aa, bb, ff, etc.)
alleles.
White forelock trait = Dominant trait
Female
Male
Horizontal line
connecting a male
and a female
represents a
marriage
WW or Ww?
A shaded circle or
square indicates that a
person expresses the
trait
Vertical lines and a
bracket connect
parents to their
children
ww
A circle or square that is not
shaded indicates that a person
does not express the trait.
Some traits, such as the shape of eyes or
ears are actually polygenetic, controlled by
many genes.
Of course, many personal traits are also
governed by environmental factors.
**The human genome – our complete set of
genetic information- includes tens of
thousands of genes.
**Some of the very first human genes to be
identified were those that control blood
type.
The best known genes that determine
human blood types are the ABO blood
groups and Rh blood groups.
The Rh blood group is determined by a
single gene with two alleles- positive &
negative. The positive (Rh+) allele is
dominant, so persons who are Rh+/Rh+
or Rh+/Rh- are said to be Rh positive!
Individuals with Rh-/Rh- alleles are Rh
negative!
There are 3 alleles for the ABO blood
group gene: IA IB and i
Alleles IA and IB are codominant. The
alleles produce molecules known as
antigens on the surface of red blood cells
Individuals with alleles IA and IB produce
both A and B antigens, making them blood
type AB
The i allele is recessive.
Persons with IAIA or IAi produce only the A
antigen, so they are blood type A.
Those with IBIB or IBi produce only the B
antigen, so they are blood type B
Those persons who are homozygous for
the i allele (ii) produce no antigen, and
have blood type O
Human Disorders
**Some genetic disorders are caused
by autosomal recessive alleles
carried on chromosomes.
Examples: albinism, cystic fibrosis,
galactosemia, phenylketonuria, TaySachs disease.
***Other genetic disorders are caused by the
dominant alleles, that are expressed even
if a recessive allele is present.
Examples: achondroplasia, Huntington’s
disease, hypercholesterolemia
*** Codominant alleles (2 dominant alleles)
cause other disorders.
Example Sickle Cell Anemia
*** 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.
**Cystic Fibrosis (CF) is caused by a a recessive
allele on Chromosome 7.
There is a deletion of 3 bases (for the missing
amino acid, phyenylalanine) in the middle of a
sequence for a protein called CFTR. Normal
CFTR is chloride ion (Cl-) channel through cell
membranes. WITHOUT the protein CFTR, Clions CANNOT pass across biological
membranes.
**Sickle Cell Disease is a common genetic
disorder in African-Americans. It is
characterized by the bent & twisted shape
of red blood cells.
These misshapen cells are rigid and get
stuck in capillaries so that oxygen cannot
get to cells and tissues.
*Just ONE DNA base is changed to cause
this disease. Valine is substituted for
glutamic acid. This results in abnormal
hemoglobin that sticks together, producing
the sickle-shaped cells.
Sickle Cell Disease These red
blood cells contain the
abnormal hemoglobin
characteristic of sickle cell
disease.
Problem Solving: What are the
genotypes of the following? A,B ,C
B
C
A
14.2
Human Chromosomes
** Chromosomes 21 and 22 were the first
human chromosomes whose sequences were
determined.
**Chromosome 22 contains as many as 545
different genes, some of which are important
for health.
One allele may cause a form of leukemia
Another may cause neurofibromatosis
Long stretches of DNA may be repetitive and not code
for proteins -unstable- rearrangements can occur.
**Chromosome 21 has about 225 genes.
One is associated with amyotrophic lateral sclerosis
Also has long regions with no genes
***Genes located close together on the same
chromosomes are linked, meaning they
tend to be inherited together.
***Sex-linked genes are those with a special
pattern of inheritance located on the X or Y
chromosomes.
More than 100 genes have been found on
the X chromosome. (Only a few have been
found on the Y)
Colorblindness – three human genes
associated with color-blindness are located
on the X chromosome.
Sex cell inheritance patterns for male and female children
Males have just ONE X chromosome. All
sex-linked alleles are expressed in males,
EVEN if they are recessive. So, if a male
receives a recessive allele on the X
chromosomes, the trait WILL be
expressed!!!!
For a female to show the sex-linked
recessive trait (such as color-blindness), she
MUST receive 2 copies of the recessive
allele, one on each of her X chromosomes.
Hemophilia is another example of a sexlinked disorder. (2 genes for blood clotting on
X chromosome)
Female
The "a" recessive allele will not
be expressed in her phenotype
Male
The "a" recessive allele will be
expressed in his phenotype
Duchenne Muscular Dystrophy – sex –
linked gene is defective in that it
doesn’t code properly for a muscle
protein.
INTERESTING FACTS
**Females have 2 X chromosomes! Males
have just one!
**ONE X CHROMOSOME is enough for
males. It is also enough for females,
Sooooo in female cells, one X
chromosome is randomly “switched off.”
The turned off chromosome forms a dense
region in the nucleus called a Barr Body!!!
**WEIRD CAT INFO!!
** In cats, a gene that controls coat spot
colors is located on the X chromosomes.
One X may have alleles for orange spots.
The other X may have alleles for black
spots. The cat’s cells may randomly
“switch-off” one chromosome or another in
different parts of cat’s body. As a result,
female cats may have a mixture of orange
and black spots. Male cats have spots of
only one color.
If a cat’s fur has three colors (orange, white,
black….calico), then the cat is most likely
female!!!!
Calico Cat This cat's fur color is controlled by a gene on the X chromosome.
CHROMOSOME DISORDERS!!
**There is a common error in meiosis called
nondisjunction this means that chromosomes do
not separate properly. Abnormal number of
chromosomes may end up in gametes.
Sometimes individuals may have 3 copies of a
chromosome (trisomy)
Down Syndrome – 3 copies of chromosome 21
Edward’s syndrome – 3 copies of 18 (trisomy
18)
Klinefelter Syndrome – XXXY XXXXY
Turner Syndrome – Females with only one X
14.3 Human Molecular
Genetics
**Certain disease-causing alleles have
slightly different DNA sequences from their
normal counterparts. There are tests that
can spot these differences.
Labeled DNA probes are specific DNA
base sequences that detect the
complementary base sequences found in
the disease-causing alleles.
There are tests that search for changes in
restriction enzymes cutting sites.
Tests detect differences between lengths
of normal and abnormal DNA
DNA FINGERPRINTING!!
**No individual is exactly like another, except
identical twins.
**DNA fingerprinting analyzes sections of
DNA that have little or no known function
but vary widely from one individual to
another.
How it works:
Small samples of DNA are cut with a restriction
enzyme.
2. Separated by size with gel electrophoresis
3. Fragments containing high variable regions are
detected with a DNA probe, revealing a series
of DNA bands of various sizes
4. If enough combinations of restriction enzymes
are used, a pattern of bands is produced that
is different from the pattern of anyone else in
the world.
1.
Human Genome Project! Ongoing
effort to analyze the human DNA
sequence
Completed in 2003!!
How was it done?
Sequences were determined in widely spaced
regions – markers
“shot gun sequencing” – cut DNA into random
fragments, find and link overlapping areas
There are relatively FEW genes in a human DNA
molecule
Genes are found by locating promotors (DNA sites
known for being bonding sites for RNA
polymerase) Promoters indicate the start of a gene
Locate introns and exons
GENE THERAPY!!
Absent or faulty gene is replaced by a normal ,
working gene. (This way, the body can make the
correct protein or enzyme it needs, which
eliminates the cause of the disorder.)
Viruses are often used in gene therapy, because
they have the ability to enter a cell’s DNA
Virus particles are modified so they do not cause
diseases. Then a DNA fragment containing a
replacement gene is spliced to viral DNA. The
patient is then infected with the modified gene
particles, which should carry the gene into cell to
correct genetic defects.