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chromosomes and genes 1. what are the degrees of dominance?

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Chromosomes and Genes
Mader: Biology 8th Ed.
CHROMOSOMES AND GENES
•
1. WHAT ARE THE DEGREES OF
DOMINANCE?
•
2. IN WHAT WAYS DO GENES BEHAVE?
•
3.WHAT IS THE CHROMOSOMAL
THEORY AND WHAT HAPPENS WHEN
THE NUMBER CHANGES?
Mader: Biology 8th Ed.
CHROMOSOMES AND GENES
•
1. WHAT ARE THE DEGREES OF
DOMINANCE?
•
SIMPLE OR COMPLETE DOMINANCE
Mader: Biology 8th Ed.
SIMPLE OR COMPLETE DOMINANCE
•
EXAMPLE:
•
Rh FACTOR IN BLOOD TYPING OF
HUMANS
•
Rh+ INDIVIDUALS ARE DOMINANT TO
Rh- INDIVIDUALS .
Mader: Biology 8th Ed.
Rh FACTOR IS SIMPLE DOMINANT TRAIT
•
GENOTYPE
•
PHENOTYPE
•
Rh+Rh+
•
HAS Rh+ BLOOD TYPE
•
Rh+Rh-
•
HAS Rh+ BLOOD TYPE
•
HAS Rh- BLOOD TYPE
•
Rh-RH-
•
Mader: Biology 8th Ed.
CHROMOSOMES AND GENES
•
1. WHAT ARE THE DEGREES OF
DOMINANCE?
•
INCOMPLETE DOMINANCE
Mader: Biology 8th Ed.
Incomplete Dominance
•
Exhibited when the heterozygote has an
intermediate phenotype between that of
either homozygote.
Mader: Biology 8th Ed.
Incomplete Dominance
Mader: Biology 8th Ed.
CHROMOSOMES AND GENES
•
1. WHAT ARE THE DEGREES OF
DOMINANCE?
•
CODOMINANCE
Mader: Biology 8th Ed.
CODOMINANCE
•
•
•
SICKLE CELL ANEMIA
THE SICKLING GENE “s” CAUSES
PRODUCTION OF AN ABNORMAL
HEMOGLOBIN THAT CRYSTALIZES AT
LOW OXYGEN CONCENTRATIONS
THE NORMAL GENE “S” CAUSES
PRODUCTION OF NORMAL
HEMOGLOBIN
Mader: Biology 8th Ed.
SICKLE CELL ANEMIA
•
GENOTYPE
•
SS
•
PHENOTYPE
•
NORMAL HEMOGLOBIN
•
•
•
Ss
ss
•
EXTREMELY LOW OXYGEN
CONDITIONS RESULT IN
SICKLING IN THE EXTREMITIES
SICKLING EPISODES
CAN BE FREQUENT
AND INCLUDE MAJOR
ORGANS
Mader: Biology 8th Ed.
SICKLE CELL ANEMIA
Mader: Biology 8th Ed.
CHROMOSOMES AND GENES
•
2. IN WHAT WAYS DO GENES BEHAVE?
Mader: Biology 8th Ed.
2. IN WHAT WAYS DO GENES BEHAVE?
•
•
PLEIOTROPISM – ONE GENE HAS MANY
EFFECTS
EXAMPLE MARFAN SYNDROME (A
COLLECTIONS OF SYMPTOMS ASSOCIATED
WITH A CONDITIONS IS CALLED A
SYNDROME)
Mader: Biology 8th Ed.
PLEIOTROPISM
•
MARFAN SYNDROME
SYMPTOMS: TALL AND THIN WITH LONG
LEGS, ARMS AND FINGERS
NEARSIGHTEDNESS
WALL OF AORTA IS WEAK, ENLARGES
AND OFTEN SPLITS RESULTING IN
DEATH
Mader: Biology 8th Ed.
PLEIOTROPISM
•
MARFAN SYNDROME
ALL THESE SYMPTOMS ARE TRACED TO ONE
DEFECTIVE DOMINANT GENE THAT CAUSES
AN INABILITY TO PRODUCE NORMAL
FIBRILLIN. FIBRILLIN IS A PROTEIN THAT
STRENTHENS ELASTIC FIBERS
MANY BELIEVE THAT ABRAHAM LINCOLN HAD
MARFAN SYNDROME
Mader: Biology 8th Ed.
2. IN WHAT WAYS DO GENES BEHAVE?
•
EPISTASIS IN MULTIGENIC TRAITS
•
ONE ABNORMAL GENE INTERFERES
WITH THE ACTION OF ANOTHER
NORMAL GENE.
Mader: Biology 8th Ed.
EPISTATSIS
•
PARENTS ARE TWO WHITE FLOWERING
PLANTS THAT PRODUCE ONLY PURPLE
OFFSPRING. WHEN AN F2 IS PRODUCED
FROM THE PURPLE OFFSPRING OF THE
F1 THEY PRODUCE A PHENOTYPIC
RATIO OF 9 PURPLE TO 7 WHITE. THIS
CAN’T BE EXPLAINED BY ANY MODE OF
INHERITANCE DISCUSSED SO FAR.
Mader: Biology 8th Ed.
EPISTATSIS IN WHITE-PURPLE FLOWERS
•
P1 AAbb(WHITE FLOWER) X aaBB(WHITE FLOWER)
•
F1
•
F2
AaBb (PURPLE FLOWER)
AABB, AABb,AaBB,AaBb,AABb,
(PURPLE FLOWERS)
AAbb, Aabb,aaBB,aaBb,aabb
(WHITE FLOWERS)
Mader: Biology 8th Ed.
AA OR Aa
BB
ACTIVE ENZYME A
ACTIVE ENZYME B
PRECURSOR
OR Bb
INTERMEDIATE
PRODUCT
IF EITHER GENE A OR B IS
HOMOZYGOUS RECESSIVE IT
BLOCKS PRODUCTION OF THE
FINAL PURPLE PRODUCT
Mader: Biology 8th Ed.
PURPLE
PRODUCT
Multiple Allelic Traits
•
When a trait is controlled by multiple alleles,
the gene exists in several allelic forms.
– ABO blood types
Phenotype
Genotype
A
IAIA,IAi
B
IBIB,IBi
AB
IAIB
O
ii
Mader: Biology 8th Ed.
Inheritance of Blood Type
Mader: Biology 8th Ed.
Polygenic Inheritance
•
Occurs when a trait is governed by two or
more sets of alleles.
– Each dominant allele has a quantitative
effect on the phenotype, and these effects
are additive.
пЃ¶ Result in continuous variation of
phenotypes.
Mader: Biology 8th Ed.
Height in Human Beings
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
Environment and Phenotype
•
GENE EXPRESSION MAY BE ALTERED
BY THE ENVIRONMENT
Mader: Biology 8th Ed.
•
Himalayan Rabbits - Enzyme coding for
black fur is active only at low temperatures.
– Black fur only occurs on extremities.
Where body temperature is low.
Mader: Biology 8th Ed.
DARK FUR DEVELOPS UNDER THE
ICE PACK DUE TO LOW
TEMPERATURE INTERACTION WITH
THE GENE
Mader: Biology 8th Ed.
3.WHAT IS THE CHROMOSOMAL THEORY
AND WHAT HAPPENS WHEN THE
NUMBER CHANGES?
Mader: Biology 8th Ed.
CHROMOSOMAL THEORY OF
INHERITANCE
•
GENES “RIDE” ON THE CHROMOSOMES
THEREFORE WHAT HAPPENS TO THE
CHROMOSOME AFFECTS THE GENES
LOCATED ON IT
Mader: Biology 8th Ed.
Chromosomal Inheritance
•
•
All but one pair of chromosomes in males
and females are the same.
– Autosomes - Nonsex chromosomes
The different pair, sex chromosomes,
determines the sex of an individual.
– X-linked (sex-linked) is the term used for
genes carried on the X chromosome.
Mader: Biology 8th Ed.
X-Linked Alleles
•
X-linked alleles have a different pattern of
inheritance than alleles on autosomes
because the Y chromosome is blank for
these alleles.
– Inheritance of a Y chromosome cannot
offset the inheritance of an X-linked
recessive allele.
Mader: Biology 8th Ed.
Drosophila
Mader: Biology 8th Ed.
Human X-Linked Disorders
•
Color Blindness
– In humans, color vision receptors in the
retina are three different classes of cone
cells.
пЃ¶ Only one type of pigment is present in
each class of cone cell.
пѓ� The allele for blue-sensitive is
autosomal, but the red- and greensensitive proteins are on the X
chromosome.
Mader: Biology 8th Ed.
Human X-Linked Disorders
•
•
Muscular Dystrophy
– Absence of protein dystrophin allows
calcium to leak into muscle cells.
Hemophilia
– Hemophilia A due to lack of clotting factor
IX and hemophilia B due to lack of clotting
factor VIII.
Mader: Biology 8th Ed.
Hemophilia Pedigree
Mader: Biology 8th Ed.
Gene Linkage
•
The existence of several GENES on the
same chromosome.
– GENES on the same chromosome form a
linkage group because they tend to be
inherited together.
пЃ¶ Can be used to build a linkage map.
Mader: Biology 8th Ed.
Constructing a Chromosome Map
•
A linkage map can also be called a
chromosome map because it tells the order
of gene loci on chromosomes.
– If crossing-over occurs between two
linked alleles of interest, a dihybrid
produces four types of gametes instead of
two.
Mader: Biology 8th Ed.
Crossing-Over
Mader: Biology 8th Ed.
Linkage Data
•
The percentage of recombinant phenotypes
can be used to map chromosomes because
there is a direct relationship between the
frequency of crossing-over and the distance
between alleles.
– Assumed 1% crossing-over equals 1 map
unit.
Mader: Biology 8th Ed.
Changes in Chromosome Number
•
Polyploidy
– Occurs when eukaryotes have more than
2n number of chromosomes.
пЃ¶ Named according to number of sets of
chromosomes.
пѓ� Major evolutionary force in plants.
 Some estimate 47% of flowering
plants are polyploids.
Mader: Biology 8th Ed.
Changes in Chromosome Number
•
Monosomy and Trisomy
– Monosomy (2n - 1) occurs when an
individual has only one of a particular type
of chromosome.
– Trisomy (2n + 1) occurs when an
individual has three of a particular type of
chromosome.
Mader: Biology 8th Ed.
Down Syndrome
•
Down syndrome (Trisomy 21) is caused by
three copies of chromosome 21.
Mader: Biology 8th Ed.
Changes in Sex Chromosome Number
•
An abnormal sex chromosome number is
the result of inheriting too many or too few X
or Y chromosomes.
– Nondisjunction during oogenesis or
spermatogenesis.
Mader: Biology 8th Ed.
Sex Chromosome Syndromes
•
Turner
(XO)
Klinefelter
(XXY)
Mader: Biology 8th Ed.
Sex Chromosome Syndromes
•
•
Poly-X Females
– More than two X chromosomes and extra
Barr bodies in the nucleus.
пЃ¶ Range from tall and thin to tall and
severely retarded depending on number
of X chromosomes.
Jacobs Syndrome
– XXY due to nondisjunction during
spermatogenesis.
пЃ¶ Taller than average
Mader: Biology 8th Ed.
Changes in Chromosome Structure
•
•
Deletion
– End of a chromosome breaks off, or two
simultaneous breaks lead to loss of an
internal segment.
Translocation
– Movement of a chromosome segment
from one chromosome to another, nonhomologous chromosome.
Mader: Biology 8th Ed.
Changes in Chromosome Structure
Mader: Biology 8th Ed.
Changes in Chromosome Structure
•
Duplication
– Presence of chromosomal segment more
than once in the same chromosome.
пЃ¶ Known to occur as a result of an
inversion in which segment is turned
180o.
Mader: Biology 8th Ed.
Changes in Chromosome Structure
Mader: Biology 8th Ed.
Human Syndromes
•
Deletion Syndromes
– Williams syndrome - Loss of segment of
chromosome 7.
– Cri du chat syndrome (cat’s cry) - Loss of
segment of chromosome 5.
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.
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