Download Chapter 13: Patterns of Inheritance

Chapter 13: Patterns of Inheritance
I. The Faces of Variation
A. Variation in Appearance
B. Sources of Variation
1. Differences in diet during development
2. Variation in environment, color of
3. Similarities within
II.Early Ideas About Heredity: The Road to Mendel
A. Early Genetic Concepts
1. Heredity occurs within
a. Cannot create bizarre creatures by cross breeding
b. Common animals are not combinations of breeding
2.
are transmitted directly
a. Once thought body parts transmitted in sex cells
b. Male and female traits
in offspring
3. Resultant paradox
a. If no variation enters from outside species
b. If variation blended with each generation
c. In time, would result in
species variation
B. Koelreuter Experiments
1. Hybridized tobacco plants
a. Offspring appeared different from either parent
b. Crosses of hybrids resulted in further
c. Offspring resembled
1. Parental traits
2. Traits
for a generation, reappeared in
next
3. Alternative forms segregating among offspring
C. T. A. Knight Experiments
1. Crossed true-breeding peas, purple and white flowers
2. All offspring of first cross had
3. Offspring of next cross had
flowers
4.
flowers predominated over white flowers
D. Early, Pre-Mendel Genetic Concepts
1. Some forms of inherited traits masked in one generation
2. Forms of a trait
among offspring
a. Some forms represented more
than others
III. Mendel and the Garden Pea
A. Carried Out First Quantitative Studies
B. Used Garden Pea Familiar to Earlier Investigators
1. Expected segregation among offspring, via early studies
C. Many true-breeding traits, studied only seven
D. Small plants, easy to grow, short generation time
1.
parts within flower
2.
3.
male and female from same flower
female with other flower's pollen (male)
IV. Mendel's Experimental Design
A. Allowed Several Generations of Self-Fertilization
1. Progeny produced only a single form of a trait
2. Assured that forms of traits were transmitted regularly
B. Conducted Crosses Between Alternate Forms of a Trait
1. Removed male parts from a flower with white flowers
2. Fertilized with pollen from plant with purple flowers
3. Performed reciprocal crosses white flower pollen on purple flower
C. Allowed Self-Fertilization of Hybrids
D. Allowed segregation of alternate forms of traits
1. Counted number of offspring of each type per generation
2. Quantification of results most important to studies
V. What Mendel Found
A.First Filial ( ) Progeny Resembled One of Parents
1. Trait expressed in F1 called
2. Trait masked in F1 called
3. All seven traits had dominant and recessive forms
B. Planted F1 Seeds To Produce F2 (
) Generation
1. Determined proportion of dominant to recessive
2.
of plants exhibited dominant form
3.
of plants exhibited masked, recessive form
4. Dominant:recessive ratio was close to
for all seven
traits
C. Subsequent Generations
1.
individuals bred true
2. One third of dominant individuals bred true
3. Two thirds of dominant individuals produced 3:1 progeny
4. 3:1 ratio really
ratio, separating dominant
genotypes
VI .How Mendel Interpreted His Results
A. Understood Four Things About Nature of Heredity
1. Alternatives of traits are inherited intact
2. One form did not appear in F1, but reappeared in F2
3. Pairs of alternative forms
among progeny
4. Characteristic Mendelian Ratio of segregation is
B. Mendel's Model
1. Parents transmit factors that provide information about traits
2. Each individual contains
factors for each trait
a. May code for same form or alternative forms
3.
set of chromosomes in individuals
4. Haploid chromosomes randomly distributed in
5. Not all copies of a factor are identical
a. Alternate forms of factor called
b. Individual is
when both alleles are the same
c. Individual is
when alleles are different
6. Position of gene on DNA is called its
7. Alleles from each parent do not influence one another
a. They remain discrete and "uncontaminated "
b.They do not blend with one another
c. They further segregate
when forming progeny
8. Presence of a factor does not insure its expression
a.
dominant expressed, recessive
unexpressed
b. Genotype is the
(blueprint)
c. Phenotype is the
(outcome)
C. The F1 Generation
1. Use letter of
to name allele
2.
trait is upper case letter (W) purple
3.
is lower case letter (w) white
a. Designation of alleles in individuals
1. True-breeding white flower = ww
2. True-breeding purple flower = WW
3. Heterozygous purple flower = Ww
b. Mendel's first cross = ww x WW
1. Each parent can produce gametes of only its kind
a. Purple gametes contain only
allele
b. White gametes contain only
allele
2. Resulting progeny all Ww, W dominant, all
D. The F2 Generation
1. All are heterozygous, purple, cross = Ww x Ww
2. Alleles segregate
in gametes, either
3. Construct Punnett square to determine progeny of cross
4. Square predicts
phenotypic ratio
E. Further Generations
1. Three kinds of F2 individuals
a. Pure-breeding white flowers
b. Heterozygous purple flowers
c. Pure-breeding purple flowers
d. genotypic ratio
F. The Testcross
1. Used to Determine Genotype of
a. Observing phenotype insufficient, WW and Ww appear same
2. Cross unknown to organism
a. Homozygous dominant (WW) produces dominant phenotype
b. Heterozygous (Ww) produces
genotypes of offspring
c. Homozygous recessive as known
d. All Ww offspring indicates
e. Half Ww, half ww offspring indicates
3. Experimental cross with homozygous recessive called a
VII. Mendel's First Law of Heredity:
A. Explained segregation without cellular knowledge
B. Behavior of alternative alleles
1. Alternative forms encoded by
alleles
2. Alternative alleles separate in
3. Each gamete has
possibility to get either allele
VIII. Independent Assortment
A. Mendel Questioned Effect of Traits Upon One Another
1. Establish pure-breeding lines differing in two traits
2. Cross contrasting pairs of traits
3. Results in F1 generation of identical
a. Dihybrids are individuals
4. Allow dihybrids to self-fertilize
a. 1/4 chance for a single trait to occur
b. 1/4 x 1/4 = 1/16 for any pair to occur
c. Predicts 9:3:3:1 ratio
B. Mendel's Second Law of Heredity:
1. Genes located on different chromosomes assort
2. Mendel picked traits on different chromosomes
IX. From Genotype to Phenotype: How Genes Interact
A. Complex Genetic Patterns
1. Multiple alleles:
2.
: many genes act sequentially or jointly
3.
: one gene modifies expression of other gene
4.
: multiple genes act jointly
5.
: gene has more than one effect on phenotype
6.
: alternative alleles not dominant or recessive
B. Environmental effects:
1. Modified Mendelian Ratios
2. Difficult to determine phenotypic classes
3. Example corn seed coat pigment
C. Epistasis
1. causes a
ratio
2.
produced early in the pathway blocks the
flow of material later
3. Labs
a. “E” gene for
pigment
b. “B” gene for
of the pigment
XI. Human Genetic Disorders
A. Variant Alleles May Be Produced by
1. Detrimental alleles are generally
in populations
2. Can become more populous in
communities
3. Are frequently
diseases
4. Are maintained in populations in
carriers
B.
: detrimental gene at high frequency in population
1. Cystic Fibrosis
a. Most
genetic disorder in Caucasians
b. 1 in 20 carry single copy of defective gene
c. 1 in 1800 are homozygous recessive, exhibit disease
d. Affected individuals secrete
e. Defect in transport of
ions across membranes
2. Sickle-Cell Anemia
a. Improper transport of
due to defective
b. Results from alteration in
amino acid
c. Red blood cells become stiff and
d. Blood cells clog blood vessels, are unable to enter
e. Disorder of homozygotes but heterozygotes
f. Most common disorder among those of
descent
3. Tay-Sachs Disease
a. Causes fatal
deterioration in children
b. Allele codes for nonfunctional form of
c. Cannot degrade
in brain cell lysosomes
1.
swell and burst, killing brain cells
d. Highest occurrence in
populations
1. 1 in 28 in specific population carry defective gene
2. 1 in 3600 of same population exhibit disease
3. 1 in 300,000 of overall population exhibit disease
4. Phenylketonuria
a. Abbreviated
b. Affected individuals unable to break down
c. Converted to other chemicals that accumulate in
d. Interfere with development of
in infants
e. Can be treated by controlling
f. In US, 1 in 15,000 are homozygous recessive
5. Hemophilia
a. Loss of activity in
b. Disorder due to
condition
c. Most clotting proteins located on
d. Two (VII and IX) located on
chromosome
1. More prominent in
since they possess only one
2. If X defective,
3. Y lacks comparable allele
4. Most common form has defective IX fig 13.32
a. Called
, prominent in family
b. Carried into royal families of Europe fig 13.34
6. Huntington's Disease
a. Hereditary condition caused by
b. Causes progressive deterioration of
c. Maintained in population, 1 in 10,000 affected
1. Symptoms develop after
2. Allele transmitted prior to its
activity
XI. Multiple Alleles
A. Most Genes Possess More Than
Possible Alleles
B. ABO Blood Groups
1.
alleles affect cell surface antigens
2. Gene designated I
a. Allele B codes for
b. Allele A codes for
c. Allele O codes for
3. A and B are
and can be expressed together
4. A and B are both dominant over
5. Four phenotypes produced from three alleles
a. Type A: genotype
b. Type B: genotype
c. Type AB: genotype
d. Type O: genotype
6. Blood may
due to presence of antigens
a. Type A recognizes type B blood with B antigens
b. Type A recognizes type AB blood with A and B antigens
c. Type A does not recognize type O blood, no antigens
d. Type AB does not recognize either A or B as foreign
XII. The Rh Blood Group
A. Associated with presence of Rh cell surface markers
1. Rh+ possess marker, most adult humans
2. Rh- lacks marker, fewer in number
B. Rh- is homozygous recessive condition
1. Blood may agglutinate due to presence of antigens
C. Rh- mother, Rh+ child (Rh+ father)
1. Rh+ blood crosses placenta into mother's blood
2. Induces production of anti-Rh
in mother's
3. In later pregnancy,
can cross back
4. Cause next baby's blood to clump:
XIII. Gene Therapy
A. Gene Transfer Therapy
1. modified
cells to produce a defective enzyme
B. Cystic Fibrosis
1. piggybacked (vector)a healthy cf gene onto an
a. temporarily successful, then attacked by the
system
C. Gene Therapy Problems
1. adenovirus causes a strong
response
2. adenovirus infection can
3. random insertion of DNA in the human chromosome – may cause a)
which leads to cancer
b
D. AVV (adeno associated virus)
1.only two genes, much less likely to
response
2. used for anemia in monkeys –
3. used for
degeneration in dogs
4. 2000 used in a clinical trial of
, does not cause a strong
production
XIV. Chromosomes: The Vehicles of Mendelian Inheritance
A. Many Organelles Segregate in Meiosis
B. Sutton's Explanation
1. Hereditary material resides in
2. Chromosomes segregate in
copies of each chromosome in
3. Homologous chromosomes assort in
C. Sex Linkage
1. Proof of Chromosomal Theory of Inheritance
a. Discovery of mutant, white-eyed male fruit fly
b. Crossed with wild type red-eyed female
c. All progeny had red eyes, concluded red eye color dominant
2. Cross of F1 generation
a. 3:1 ratio red to white eyes
b. All recessive white eye flies were male
3. Testcross F1 to white-eyed male
a. 1:1:1:1 ratio
b. Eye color and sex equally represented
c. Explanation: eye color gene related to sex chromosome
4. Eye Color Gene Located on Sex Chromosome in Fruit Flies
a. Two kinds of sex chromosomes,
b. XX =
, XY =
c. Eye color gene located on the chromosome
d. Sex linked trait
D. Crossing Over
1. More Independently Assorting Factors Than Chromosomes
2. Janssen's X configuration of chromosomes during meiosis
a. Mechanism for exchange of
b. Physical change in chromosomes
c. Observed corresponding change in
3. Crossing over can occur at
along chromosome
4. Independent assortment more likely if genes are
E. Genetic Maps
1. Distance between genes =
2. Map unit, centimorgan = 1% recombination
3. Monitor recombination among three or more genes
a. Wild type is most
b. Syntenic alleles located on
c. Linked genes
assort independently
d. Three-point cross occurs with
linked genes
e. Human genetic maps used to determine genetic disorders
XV. Human Chromosomes
A. Morphology of Human Chromosomes
1. 46 chromosomes in
pairs
2. Divided into seven groups
B. Sex Chromosomes
1.
pairs of autosomes,
sex chromosomes
2.
is normal male
a.
has few active genes, counterparts to X alleles
b. Genes for maleness present on
c. Male possesses at least one
3.
is normal female
a. Female possesses no chromosome
b. One X inactivated in form of
c. Other X active and expressed, activity of X is
in each cell
4. Y found to have
chromosomes
a. most active in
b. some make
c. has 8 palidrome sequences that are used for
C. Human Abnormalities Due to Alterations in Chromosome Number
1. Primary Nondisjunction
a. Can result in severe abnormalities
1) Downs Syndrome
a).Monosomics possess one less copy of an
b) Trisomics possess one extra copy of an
c) Most do not survive
d) Down syndrome results from
1. Affects physical and mental development
2. Arises from
during meiosis
3. More likely to occur in pregnancy of
b. Nondisjunction Involving the Sex Chromosomes
1) The X chromosome
a) Produces XX gamete and O gamete
b) XX plus normal X results in XXX individual
1. Two Barr bodies, one active X
2. Sterile, but otherwise normal female
c). XX plus normal Y results in XXY individual
1.
syndrome
2. Sterile male with
characteristics
d). O plus normal Y results in inviable YO individual
e). O plus normal X results in XO individual
1.
syndrome
2. Sterile female with characteristic appearance
2). The Y Chromosome
a). Produces YY gametes
b). YY plus normal X results in XYY individual
c). Fertile males with normal appearance
d). Greater numbers of individuals in penal institutions
XVI.Genetic Counseling
A. In Absence of Cures Seek to Not Produce Children With Disorders
1. Identify parents at risk
2. Assess genetic state of early embryos
a. High risk of Down syndrome in older women
B. Prenatal Diagnosis of Disorders
1. Amniocentesis
a. Observe fetus and position via
b. Fetal cells grown in
c. Cells examined for
2. Chorionic villi sampling
a. Can be performed
than amniocentesis at
b. Tests for genetic disorders
c. Enzyme activity tests
1. Association with genetic
2. Cut DNA with
enzymes
a. Observe restriction fragment-length
b. Identify heterozygotes