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AP BIOLOGY – GENETICS
I Gregor Mendel
A. Gregor Mendel
1. Mendel was an __________________monk.
2. Mendel formulated two fundamental laws of heredity in the early __________________s.
3. He had previously studied science and mathematics at the __________________.
4. At time of his research, he was a __________________at a local technical high school.
B. Blending Concept of Inheritance
1. This theory stated that offspring would possess traits intermediate between those of different __________________.
2. Red and white flowers produce pink; a later return to red or white progeny was considered instability
in __________________
3. __________________wanted to develop a theory of evolution based on hereditary principles; blending
theory was of no help.
a. The blending theory did not account for variation and could not explain __________________.
b. The particulate theory of inheritance proposed by Mendel can account for presence of differences
among member of a population __________________
c. Mendel's work was unrecognized until _____; Darwin was never able to use it to support his theory of evolution.
C. Mendel's Experimental Procedure
1. Mendel did a __________________ (he had a mathematical background).
2. He prepared his experiments carefully and conducted preliminary studies.
a. He chose the _____________, Pisum sativum, because peas were easy to cultivate, had a short generation time,
and could be cross-pollinated.
b. From many varieties, Mendel chose __________________varieties for his experiments.
c. True-breeding varieties had all offspring __________________the parents and like each other.
d. Mendel studied simple traits (e.g., seed shape and color, flower color, etc.).
3. Mendel traced inheritance of individual traits and kept careful records of numbers.
4. He used his understanding of mathematical principles of probability to interpret results.
II. The Monohybrid Cross
A. Cross-pollination Monohybrid Crosses
1. A ________is the product of parent organisms that are true-breeding for different forms of one trait.
2. A monohybrid cross is between two parent organisms ___________for two distinct forms of a trait.
3. Mendel tracked each trait through two generations.
a. P generation is the __________________in a breeding experiment.
b. F1 (for filial) generation is the __________________in a breeding experiment.
c. F2 generation is the __________________in a breeding experiment.
d. He also performed ______________of pollen on stigmas (e.g. tall-with-short and short-with tall).
B. Mendel's Results
1. His results were contrary to those predicted by a blending theory of inheritance.
2. He found that the F1 plants resembled only __________________.
3. Characteristic of other parent reappeared in about 1/4 of F2 plants; 3/4 of offspring resembled the F1
plants.
4. Mendel saw that these 3:1 results were possible if
a. __________________contained two factors for each trait, one dominant and one recessive;
b. factors separated when gametes were formed; a gamete carried on copy of __________________;
c. Random fusion of all possible gametes occurred upon fertilization.
5. Results of his experiments led Mendel to develop his first law of inheritance:
a. __________________: Each organism contains two factors for each trait; factors segregate in
formation of gametes; each gamete contains one factor for each trait.
b. Mendel's law of segregation is consistent with a particulate theory of inheritance because many
individual factors are passed on from generation to generation.
c. __________________explains variations and why offspring differ from their parents.
C. As Viewed By Modern Genetics
1. Each trait in a pea plant is controlled by __________________alternate forms of a gene that occur at
the same gene locus on homologous chromosomes.
a. A dominant allele __________________expression of a recessive allele; it is represented by an
uppercase letter (T).
b. A recessive allele is an allele that exerts its effect only in the homozygous state; its expression is
masked by a dominant allele; it is represented by a lowercase letter (t).
2. __________________is specific location of a particular gene on homologous chromosomes.
3. In Mendel's cross, the parents were ___________; each parent had two identical alleles for a trait – they
were homozygous, indicating they possess two identical alleles for a trait.
a. __________________genotypes possess two dominant alleles for a trait (TT).
b. __________________genotypes possess two recessive alleles for a trait (tt).
4. After cross-pollination, all individuals of the F1 generation had one of each type of allele.
a. Heterozygous genotypes possess one of each allele for a particular trait (Tt).
b. The allele not expressed in a heterozygote is a __________________
D. Genotype Versus Phenotype
1. Two organisms with different allele combinations can have same _______________(e.g., TT and Tt pea
plants are both tall; therefore, it is necessary to distinguish between alleles and appearance of organism).
2. __________________ refers to the alleles an individual receives at fertilization.
3. __________________refers to the physical appearance of the individual.
E. Monohybrid Genetics Problems
1. First determine with characteristic is________________; then code the alleles involved.
2. Determine ________________for both parents; an individual has two alleles for each trait; each gamete
has only on allele for each trait.
3. Each gamete has a ________________chance of having either allele.
F. Laws of Probability
1. ________________ is the likely outcome a given event will occur from random chance.
a. With each coin flip there is a 50% chance of heads and 50% chance of tails.
b. Chance of inheriting one of two alleles from a parent is also ________________
2. Multiplicative law of probability states that the chance of two or more independent events occurring together
is the ________________ of the probability of the events occurring separately.
a. Chance of inheriting a specific allele from one parent and a specific allele from another is ________________
b. Possible combinations for the alleles Ee of heterozygous parents are the following:
EE = 1/2 x 1/2 = ¼; eE = 1/2 x 1/2 = 1/4 Ee= 1/2 x 1/2 = 1/4 ee = 1/2 x 1/2 = 1/4
3. Additive law of probability calculates probability of an event that occurs in two or more independent ways;
it is sum of individual probabilities of each way an event can occur; in the above example where unattached
earlobes are dominant (________________the chance for unattached earlobes is 1/4 + 1/4 + 1/4 = 3/4.
G. The Punnett Square
1. Provides a simple method to calculate pro________________ of a genetic cross.
2. In a Punnett square, all possible types of sperm alleles are lined up ________________all possible egg alleles are lined up
________________every possible combination is placed in squares.
3. The larger the sample size examined, the more likely the outcome will reflect predicted ratios; a large number
of offspring must be counted to observe the expected results; only in that way can all possible genetic types
of sperm fertilize all possible ________________.
4. We cannot t________________ humans in order to count many offspring; in humans, the ________________is used to
estimate the probability of any child having a particular characteristic.
5. Punnett square uses ________________; it does not dictate what the next child will inherit.
6. "________________": if two heterozygous parents have first child with attached earlobes
(likely in 1/4th of children), second child born still has 1/4 chance of having attached earlobes.
H. One-Trait Testcross
1. Mendel performed testcrosses by crossing his F1 plants with ________________
2. Results indicated the recessive factor with present in the F1 plants; ________________.
3. A testcross is between an individual with ________________and individual with ________________to
see if the individual with dominant phenotype is homozygous or heterozygous.
III. The Dihybrid Cross
A. Dihybrid Crosses
1. A dihybrid cross is an experimental cross between ________________parent organisms that are true-breeding for different
forms of two traits; produces offspring heterozygous for both traits.
2. Mendel observed that the F1 individuals were ________________.
B. Plants to Self-Pollinate
1. Mendel observed four phenotypes among ________________; he deduced second law of heredity.
2. Mendel's law of ________________states members of one pair of factors assort independently of
members of another pair; all combinations of factors occur in gametes.
C. Dihybrid Genetics Problems
1. Laws of probability indicate a 9:3:3:1 phenotypic ratio of F2 offspring resulting in the following:
a. 9/16 of the offspring are dominant for both traits;
b. 3/16 of the offspring are dominant for one trait and recessive for the other trait;
c. 3/16 of the offspring are dominant and recessive opposite of the previous proportions; and
d. 1/16 of the offspring are recessive for both traits.
2. The Punnett Square for Dihybrid Crosses
a. A larger Punnett square is used to calculate probable results of a dihybrid cross.
b. A phenotypic ratio of 9:3:3:1 is expected when ________________ for two traits are crossed and simple
dominance is present for both genes.
c. ________________explains these results of independent assortment.
D. Two-Trait Test Cross
1. A ________________ test cross tests if individuals showing two dominant characteristics are homozygous for both
or for one trait only, or is heterozygous for both.
2. If an organism heterozygous for two traits is crossed with another recessive for both traits, expected
phenotypic ratio is ________________
3. In dihybrid genetics problems, the individual has ________________, two for each trait.
IV. Mendelism and the Genotype
A. Incomplete Dominance and Codominance
1. Incomplete dominance: offspring show traits i________________ between two parental phenotypes.
a. Red and white-flowered four o'clocks produce ________________offspring.
b. Incomplete dominance has a biochemical basis; level of gene-directed protein production may
be between that of the two ________________
c. One allele of a heterozygous pair only partially dominates ________________of its partner.
d. This does not support a blending theory; parental phenotypes reappear in F2 generation.
2. ________________is a pattern of inheritance in which both alleles of a gene are expressed.
a. A person with AB blood has both ________________on their red blood cells.
b. With codominance, both alleles produce and ________________.
B. Genes That Interact
1. More than one pair of genes may interact to produce the phenotype.
2. __________absence of expected phenotype as a result of masking expression of one gene pair by the
expression of another gene pair.
a. The homozygous recessive condition masks the effect of a dominant allele at another locus.
b. Crossing sweet pea plants produces purple; F2 generation has a 9:7 rather than 9:3:3:1 dihybrid
ratio; explained by homozygous recessive blocking production of a metabolic enzyme.
c. Albino animals inherit allelic pair (aa) preventing production of melanin, expression of eye, hair, color.
C. Pleiotropy
1. ________________: a single gene exerts an effect on many aspects of an individual's phenotype.
a. ________________: a mutant gene is unable to code for production of a normal protein, ________________
b. Results in the inability to produce normal connective tissue.
c. Individuals with Marfan syndrome tend to be tall and thin with _____________________________; are
nearsighted; and the wall of their aorta is weak.
d. From his lanky frame and other symptoms, ________________may have had Marfan syndrome.
D. Multiple Alleles
1. There may be more than ________________for one locus, but each individual inherits only tow alleles.
2. A multiple allele system is peppered moths has three possible alleles for wing color in order of
dominance: M > M' > m; therefore, there are three possible phenotypes.
3. The ABO system of human blood type involves three alleles (A, B, and O).
4. As a result, there are four possible phenotypes or blood types: A, B, AB, and O.
E. Polygenic Inheritance
1. Polygenic inheritance occurs when a trait is controlled by ________________at different loci.
2. Allelic pairs at different loci on a chromosome or on different chromosomes all control one trait.
3. Gene alleles can be contributing or non-contributing.
4. Contributing alleles have an addictive effect, resulting ________________variations.
5. Examples include seed color in wheat and skin color and height in humans.
6. Polygenic traits are subject to ________________that cause intermediate phenotypes; so they
produce continuous variations whose frequency distribution forms a normal (bell-shaped) curve.
F. Environment and the Phenotype
1. Both genotype and environment affect ________________; relative importance of both influences vary.
2. ________________ (above and below water level) influences the phenotype of water buttercup,
Ranunculus peltatus.
3. ________________ can affect the phenotypes of some plants (e.g., primroses) and animals
(e.g., Siamese cats, Himalaya rabbits).
V Mendelism and Chromosomes
A. Chromosomal Theory of Inheritance
1. Genes are located on chromosomes; behavior of chromosomes during mitosis was described in
1875 and for meiosis, in 1890's.
2. Chromosome theory independently proposed in 1902 by ________________and ________________
3. Accounts for the similarity of chromosomal behavior during ________________________________
4. Theory is supported by the following observations:
a. Both chromosomes and factors (now called alleles) are paired in ________________.
b. Chromosomes and alleles of each pair separate during ________________ so gametes have one-half.
c. Chromosomes and alleles of separate independently; gametes contain all ________________
d. ________________ restores diploid chromosome number and paired condition for alleles in zygote.
B. Sex Chromosomes
1. In most animal species, chromosomes can be categorized as two types:
a. ________________ are non-sex chromosomes that are the same number and kind between sexes.
b. ________________determine if the individual is male or female.
2. Sex chromosomes in the human female are ________________; those of the male are ________________.
3. Males produce X-containing and Y-containing gametes; therefore males determine the sex of offspring.
4. Besides genes that determine sex, sex chromosomes carry many genes for traits unrelated to sex.
5. ________________is any gene located on X chromosome; used to describe genes on X chromosome that
are missing on the Y chromosome.
C. X-Linked Alleles
1. Work with fruit flies by ___________(Columbia University) confirmed genes were on chromosomes.
a. Fruit flies are cheaply raised in common laboratory glassware.
b. Females only mate once and ________________________________
c. Fruit fly generation time is ________________, allowing rapid experiments.
2. Experiments involved fruit flies with XY system similar to ________________
a. Newly discovered mutant male fruit fly had white eyes.
b. Cross of white-eyed male with dominant red-eyed female yield expected 3:1 red-to-white ratio;
however, all white-eyed flies were males!
c. An allele for eye color on the X but not Y chromosome supports the results of the cross.
d. Behavior of allele corresponds to chromosome, confirming chromosomal theory of inheritance.
3. X-Linked Problems
a. X-linked alleles are designated as superscripts to X chromosome.
b. Heterozygous females are ________________they do not show the trait but can pass it on.
c. Males are never carriers but express the ________________on the X chromosome.
d. One form of ________________is X-linked recessive.
D. Linkage Groups
1. Fruit flies have ________________of chromosomes to hold thousands of genes; Sutton concluded each
chromosome must hold many genes.
2. All alleles on a chromosome form a _____________that stays together except when crossing over.
3. ________________causes recombinant gametes and at fertilization, recombinant phenotypes.
4. Linked alleles do not obey ________________because they tend to go into the gametes together.
5. Crosses involving linked genes do not give same results as unlinked genes.
6. ________________ forms only two types of gametes and produces offspring with only two phenotypes.
E. Chromosome Mapping
1. Percentage of recombinant phenotypes measures ________________ between genes to map the chromosomes.
2. Linked genes indicate the distance between genes on the chromosomes.
3. If 1% of crossing-over equals one map unit, then 6% recombinants reveal 6 map units between genes.
4. If crosses are performed for three alleles on a chromosome, only one map order explains map units.
5. Humans have few offspring and a long generation time, and it is not ethical to ________________;
therefore ________________ methods are used to map human chromosomes.
VI. Chromosomal Mutations
A. Mutations
1. ________________or genes that pass to offspring if they occur in gametes.
2. Mutations increase the amount of ________________ among offspring.
3. Chromosomal mutations include changes in chromosome number and structure.
B. Changes in Chromosome Number
1. ________________ occurs when and individual has only one of a particular type of chromosome.
2. ________________occurs when and individual has three of a particular type of chromosome.
3. _____________is the failure of chromosomes to separate; it is more common during meiosis I than
meiosis II; it can occur in mitosis.
4. Monosomy and trisomy occur in plants and animals; in autosomes of animals, it is ________________.
5. Nonlethal human monosomies and trisomies include the following:
a. ________________: monosomy where the individual has single X chromosome.
b. ________________is most common trisomy among humans; it involves chromosome 21.
6. Polyploidy: offspring end up with more than two complete sets of chromosomes.
a. Terms indicate how many sets of chromosomes are present (triploids [3n], tetraploids [4n], etc.).
b. Polyploidy does not ________________in animals; judging from trisomies, it would be lethal.
c. Polyploidy is a major evolutionary mechanism in plants; probably involved in 47% of flowering
plants including major crops.
d________________in plants can result in doubled number of chromosomes; an even number of chromosomes
can undergo synapsis during meiosis; successful polyploidy results in a new species.
C. Changes in Chromosomal Structure
1. Environmental factors ________________, can cause chromosomes to break;
if the broken ends do not rejoin in the same pattern, this causes a change in chromosomal structure.
2. ________________a segment that has become separated from the chromosome is reinserted at the same place
but in reverse; the position and sequence of genes are altered.
3. ________________: a chromosomal segment is removed from one chromosome and inserted into another,
nonhomologous chromosome. Translocation heterozygotes usually have reduced fertility due to
production of abnormal gametes.
4. A ________________ is a type of mutation in which an end of a chromosome breaks off or when two simultaneous
breaks lead to the loss of a segment.
a. Even if only one member of pair of chromosomes is affected, a deletion can cause ________________
b. ________________chat syndrome is deletion in which an individual has a small head, is mentally retarded, has
facial abnormalities, and abnormal glottis and larynx resulting in a cry resembling that of a cat.
5. ________________is a doubling of a chromosomal segment.
a. A broken segment from one chromosome can simply attach to its homologue.
b. Unequal crossing-over may occur.
6. Multiple copies of genes can mutate differently and provide additional genetic variation for a species.
VII Changes in Chromosome Number
A. Karyotypes
1. Human somatic (body) cells have ________________of autosomes, ________________of sex chromosomes; total of 46.
2. ________________ shows chromosomes paired according to size, shape, and appearance in metaphase.
a. To view chromosomes, cells are treated and ________________ just prior to dividing.
b. Chromosomes are then________________ by homologous pairs, often by computer imaging.
c. Members of a pair have the ________________
d. Chromosomes in a ________________ are aligned from largest to smallest.
e. A karyotype can be used to diagnose ________________.
3. Sex chromosomes of a normal male are X and Y; a normal female has two X chromosomes.
4. All chromosomes besides X and Y are autosomes.
5. To view chromosomes of an unborn child, cells must be sampled from an embryo.
a. ________________sampling removes a small tissue sample from the embryo side of the placenta.
b. ________________s uses a long needle to extract fetal cells floating in the amniotic fluid.
B. Nondisjunction
1. Nondisjunction during meiosis causes an abnormal chromosome number in ________________
2. Nondisjunction is a failure of one or more ________________________________.
3. Nondisjunction can occur when homologous chromosomes fail to separate during meiosis I or
when daughter chromosomes fail to separate during meiosis II.
4. Results in gametes with either ________________________________chromosomes.
5. If abnormal gametes fertilize normal gametes, a monosomy (2n - 1) or trisomy (2n + 1) results.
6. A ________________ is the set of symptoms that occur with a medical condition.
C. Down Syndrome
1. Down syndrome is most common autosomal trisomy, involves ________________
2. Most often, Down syndrome results in three copies of chromosome 21 due to nondisjunction during gametogenesis.
a. In 23% of cases, the ________________ had the extra chromosome 21.
b. In 5% of cases, there ________________with chromosome 21 attached to chromosome 14; this translocation
could have occurred generations earlier and is not age-related.
3. Chances of a woman having Down syndrome child increase ________________
4. Chorionic villi sampling testing or amniocentesis and karyotyping detects a Down syndrome child.
5. Down syndrome child has tendency for ________________________________________________.
6. ________________, located on bottom third of chromosome 21, leads to high level of purines and is associated
with mental retardation; future research may lead to suppression of this gene.
D. Abnormal Sex Chromosomal Inheritance
1. ________________females have only one sex chromosome, and X.
a. Turner females are short, have broad ________________.
b. Ovaries of Turner females never become functional; therefore, do not undergo puberty.
2. ________________males have one Y chromosome and two or more X chromosomes.
a. Affected individuals are sterile males; testes and prostate are underdeveloped.
b. Individuals have ________________and long arms and legs.
3. ________________have three or more X chromosomes.
a. There is no ________________; most lack any physical abnormalities.
b. There is an increased risk of having triplo-X daughters of XXY sons.
c. May experience menstrual irregularities, including early onset of ________________
4. ________________with ________________have two Y chromosomes instead of one.
a. Results from nondisjunction during meiosis II.
b. Usually ________________ than average; suffer from persistent acne; tend to have lower intelligence.
c. Earlier claims that XYY individuals were likely to be ________________
E. Fragile X Syndrome
1________________________________; most often found in males.
2. As children________________; delayed speech; account for part of higher proportion of males
in institutions for mentally retarded.
3. As adults: ________________, unusually protruding ears.
4. Occurs in females, but symptoms are less severe.
5. Passes from ________________ male carrier to grandson.
6. Traced to excessive repeats of base triple CGG (________________________________); up to 230 copies compared
to normal 6-to-50 copies.
VIII Changes in Chromosome Structure
A. Predicting Offspring
1. Genetic disorders are medical conditions caused by _________________ from parents.
2. Males are designated by _________________; shaded circles and squares are affected individuals;
line between square and circle represents a union; vertical line leads to offspring.
3. A carrier is a _________________who has no apparent abnormality but can pass on an allele for a
recessively inherited genetic disorder.
4. Autosomal dominant and autosomal recessive alleles have different patterns of inheritance.
a. Characteristics of autosomal dominant disorders
1) Affected children usually have an _________________.
2_________________are affected. Two affected parents can produce unaffected child; two unaffected parents
will not have affected children.
b. Characteristics of _________________disorders
1) Most affected children have normal parents since heterozygotes have a normal phenotype.
2) Two affected parents _________________produce and affected child.
3) Close relatives who reproduce together are more likely to have affected children.
5. Chance has no memory; each child born to heterozygous parents has a 25% chance of having a disorder
regardless of prior siblings' conditions.
B. Autosomal Dominant Disorders
1. Neurofibromatosis
a. This is an autosomal dominant disorder that affects one in 3,000 people (or _________________.).
b. Affected individuals have tan skin spots at birth, which develop into _________________
c. Neurofibromas are _________________comprised of nerve cells or other cell types.
d. Most case symptoms are mild, patients live a normal life; sometimes symptoms are severe:
1) skeletal deformities, including a large head;
2) eye and ear tumors that can lead to blindness and hearing loss; and
3) learning disabilities and hyperactivity.
4) Such variation is called variable expressivity.
e. Gene that codes for neurofibromatosis is huge; includes three smaller nested genes.
1) It was discovered in 1990 on _________________
2) It is a tumor-suppressor gene active in _________________
3) When it _________________a benign tumor results.
2. Huntington Disease
a. This is also an autosomal dominant disorder that affects one in 20,000 people.
b. It leads to progressive degeneration of _________________which in turn causes severe muscle spasm,
personality disorders, and death in _________________from onset.
c. Most appear normal until they are of _________________and already have had children who might carry
the gene; occasionally, first signs of the disease are seen in teenagers or even younger.
d. The gene for Huntington disease is located on _________________.
e. Gene contains many repeats of base triple CAG (cytosine, adenine, guanine); normal persons have
11-34 copies; affected persons have 42-120 or more copies.
f. Severity and time of onset of associated disorders depend on number of _________________.
g. Apparently, persons most at risk are those inheriting the gene from their fathers.
1) Genomic imprinting is hypothesis that risk varies by source of gene (sex of parent).
2) Genes may be imprinted differently during formation of _________________
C. Autosomal Recessive Disorders
1. Cystic Fibrosis
a. This is most common lethal genetic disease in Caucasians in U.S.
b. About 1 in 20 Caucasians _________________, and about 1 in 2,500 births has this disorder.
c. Involves production of viscous form of mucus in the lungs and pancreatic ducts.
1) Resultant accumulation of _________________s in the respiratory tract interferes with gas exchange.
2) _________________must be mixed with food to supplant the pancreatic juices.
d. New treatments have raised average life expectancy to _________________.
e. Chloride ions (Cl-) fail to _________________
f. Since water normally follows Cl-, _________________causes thick mucus.
g. Cause is mutated gene on _________________; attempt to insert gene into nasal epithelium has had
limited success and restores about 25% of Cl- ion transport ability.
h. Genetic testing for adult carriers and fetuses is possible.
2. Tay-Sachs Disease
a. Usually occurs among _________________in the U.S. of central and eastern European descent.
b. Symptoms are not initially apparent; infant's development begins to slow at 48 months, neurological
and ___________________________________________________, develops
seizures, eventually becomes paralyzed, dies by age of three or four.
c. Results from lack of enzyme _________________ (Hex A) and subsequent storage of its substrate,
glycosphingolipid, in lysosomes.
d. Primary sites of storage are cells of the brain; accounts for _________________.
e. No treatment or cure; prenatal diagnosis is by amniocentesis and chorionic villi sampling.
3. Phenylketonuria (PKU)
a. PKU occurs 1 in every 5,000 births; it is most common inherited disease of nervous system.
b. Lack of enzyme needed to metabolize amino acid phenylalanine results in accumulation of the amino
acid in nerve cells of the brain; this __________________________________.
c. PKU is caused by a mutated gene on _________________
d. Now newborns are routinely tested in hospital for high levels of phenylalanine in the blood.
e. If infant has PKU, child is placed on __________________________________until brain is fully developed near age 7.
E. Beyond Simple Mendelian Inheritance
1. Polygenic Inheritance
a. Polygenic inheritance occurs when one trait _________________by two or more sets of alleles.
b. Dominant alleles have a quantitative effect on the phenotype: each adds to the effect.
c. Result is a continuous variation in phenotypes: a bell-shaped curve.
d. A hybrid cross for skin color provides a range of intermediates.
e. Includes ____________________________________________________________________.
f. Behavioral traits including ___________________________________________________may be associated
with particular genes but are not likely completely predetermined.
2. Multiple Alleles
a. Occur where a gene has three or more alternative expressions (alleles).
b. The ABO system of human blood type is a multiple allele system.
1) Two dominant alleles (A and B) code for presence of A and B antigens on red blood cells.
2) Also includes recessive allele (o) coding for no A or B antigens on red blood cells.
3) As a result, there are four possible phenotypes (blood types): _________________
c. The Rh factor is inherited independently from the ABO system; the Rh+ allele is dominant.
3. Sickle-cell disease is a blood disorder controlled by _________________alleles.
a. Codominance occurs when alleles are equally expressed in a heterozygote.
b. HbA HbA individuals are normal; HbS HbS have sickle-cell trait.
c. With sickle-cell disease, red blood cells are _________________ (sickle-shaped) rather than _________________
due to abnormal hemoglobin that the cells contain.
d. Due to irregular shape, sickle-shaped red blood cells _________________and break down; results in poor
circulation_________________, low resistance to infection, hemorrhaging, damage to organs, jaundice, and pain
of abdomen and joints.
e. Persons heterozygous for sickle-cell (HbAHbS) are usually asymptomatic unless stressed.
f. In __________________________________, infants heterozygous (HbAHbS) for sickle-cell allele have better chance
of surviving; malaria parasite dies as potassium leaks from sickled cells.
g. Bone marrow transplants pose high risks; other research focuses on fetal hemoglobin, etc.
A. Sex Chromosomes
1. Traits controlled by alleles on sex chromosomes are sex-linked.
2. Since Y chromosome is smaller, most sex-linked genes are on the X chromosome.
B. X-Linked Recessive Disorders
1. Males receive X-linked traits _________________, source of male's only X chromosome.
2. If female shows a recessive sex-linked trait, her father must have it and her mother is _________________
C. Some Disorders Are X-Linked
1. Color Blindness
a. Can X-linked recessive disorder involving mutations of genes coding for green or red sensitive cone
cells, resulting in inability to perceive green or red, respectively.
b. The possible genotypes for color blindness are as follows:
1) _________________= a female who has normal color vision;
2) _________________ = a carrier female who has normal color vision;
3) _________________= a female who is color blind;
4) _________________ = a male who has normal color vision; and
5) _________________ = a male who is color blind.
2. Duchenne Muscular Dystrophy
a. Duchenne muscular dystrophy is most common form; characterized by wasting away of muscles,
eventually leading to death; it affects one out of every 3,600 male births.
b. X-linked recessive disease involves a mutant gene that fails to produce protein _________________
c. Symptoms (e.g., waddling gait, toe walking, frequent falls, difficulty in rising) soon appear.
d. _________________until individual is confined to wheelchair; death usually occurs by age 20.
e. Affected males are rarely fathers; the gene passes from carrier mother to carrier daughter.
f. Lack of _________________caused calcium ions to leak into muscle cells; this promotes action of an enzyme
that dissolves muscle fibers.
g. As body attempts to repair tissue, fibrous tissue forms and cuts off blood supply.
h. Test detects carriers of Duchenne muscular dystrophy; treatments are under research.
3. Hemophilia
a. About one in 10,000 males is a hemophiliac with impaired ability of blood to clot.
b. Hemophilia has tow types: _________________is due to absence of clotting factor IX; _________________is
due to absence of clotting factor VIII.
c. Hemophiliacs _________________ after an injury and also suffer internal bleeding around joints.
d. Hemorrhages stop with transfusions of blood (or plasma) or concentrates of clotting protein.
e. Hemophiliacs were at high risk _________________if receiving blood or using blood concentrate to replace clotting factors.
f. Factor VIII is now available as a _________________.
g. Of Queen Victoria's 26 offspring, __________________________________
D. Some Traits are Sex-influenced
1. Some genes not located on the X or Y chromosome are expressed _________________the two sexes.
2. Male pattern baldness is caused by an autosomal allele that is dominant in males and due to presence of ____________________.