Transcript Chapter 14 notes

• 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
Human Heredity 14-1
 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
Human Heredity 14-1
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 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 Heredity 14-1
• 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.
Human Heredity 14-1
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.
Human Heredity 14-1
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.
Blood Type
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!
Blood Type
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.
Blood Type
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.
Human Disorders
• Other genetic disorders are caused by the
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dominant alleles, that are expressed even
if a recessive allele is present.
Examples: achondroplasia, Huntington’s
disease, hypercholesterolemia
Co-dominant alleles (2 dominant alleles)
cause other disorders.
Example Sickle Cell Anemia
Go over all the disorders in your textbook.
Human Chromosomes 14-2
**Chromosomes 21 and 22 were the first human
chromosomes whose sequences were
determined.
**Chromosome 22 contains as many as 545
different genes
**Chromosome 21 has about 225 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
Sex Linked
Males have just ONE X chromosome. All sexlinked 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 sex-linked
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
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
Molecular Genetics 14-3
**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: How
was it done?
video