Download Chapter 11: Complex Inheritance and Human Heredity • Main idea

Chapter 11: Complex Inheritance and Human Heredity
• Main idea: The inheritance of a trait over several generations can be shown in a pedigree
• Objectives
– Analyze generic patterns to determine dominant or recessive inheritance patterns
– Summarize examples of dominant and recessive disorders
– Construct human pedigrees from generic information
• Review Vocabulary
– Genes: segments of DNA that control the production of proteins
• New Vocabulary
– Carrier
– Pedigree
• Recessive Genetic Disorders
• Mendel’s work was ignored for more than 30 years
• During the early 1900’s scientists began to take an interest in heredity and Mendel’s work was
rediscovered
• Dr. Archibald Garrod, an English physician, became interested in a disorder linked to an enzyme
deficiency called alkaptonuria, which results in black urine and runs in families.
• A recessive trait is expressed when the individual is homozygous recessive for the trait.
• Therefore, those with at least one dominant allele will not express the recessive trait.
• An individual who is heterozygous for a recessive disorder is called a carrier
Cystic Fibrosis
• Affects the mucus-producing glands, digestive enzymes, and sweat glands
• Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the
sweat.
• Without sufficient chloride ions in the cells, a thick mucous is secreted.
Albinism
• Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
• White hair, Very pale skin & Pink pupils
Tay-Sachs Disease
• Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides.
Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration
Galactosemia
• Recessive genetic disorder characterized by the inability of the body to digest galactose.
Severity of condition varies
Dominant Genetic Disorders
• Caused by dominant alleles
• Those who do not have the disorder are homozygous recessive.
• Huntington’s disease affects the nervous system.
• Achondroplasia is a genetic condition that causes small body size and limbs that are comparatively
short
Pedigrees
• A diagram that traces the inheritance of a particular trait through several generations.
Pedigrees
• Inferring Genotypes
– Knowing physical traits can determine what genes an individual is most likely to have.
• Predicting Disorders
– Record keeping helps scientists use pedigree analysis to study inheritance patterns,
determine phenotypes, and ascertain genotypes.
11.2 Complex Patterns of Inheritance
• Main idea-Complex inheritance of traits does not follow inheritance patterns described by Mendel
• Objectives
– Distinguish between various complex inheritance patterns
– Analyze sex-linked and sex-limited inheritance patterns
– Explain how the environment can influence the phenotype of an organism
• Review Vocabulary
– Gamete: a mature sex cell (sperm or egg) with a haploid number of chromosomes
• New Vocabulary
– Incomplete dominance
- Codominance
– Multiple alleles
- Epistasis
– Sex chromosome
- Autosome
– Sex-linked trait
- Polygenic trait
Incomplete Dominance
• The heterozygous phenotype is an intermediate phenotype between the two homozygous
phenotypes.
Codominance
• Both alleles are expressed in the heterozygous condition
• Example
– Sickle-cell Disease
• Changes in hemoglobin cause red blood cells to change to a sickle shape
• People who are heterozygous for the trait have both normal and sickle-shaped cells
Multiple Alleles
• Blood groups in humans
• ABO blood groups have three forms of alleles
Multiple Alleles
• Coat Color of Rabbits
– Multiple alleles can demonstrate a hierarchy of dominance
– In rabbits, four alleles code for color: C, cch, cc, and c.
Epistasis
• Variety is the result of one allele hiding the effects of another allele.
eebb
eeB_
E_bb
E_B_
No dark pigment present
Dark pigment present
Sex Determination
• Sex chromosomes determine an individual’s gender
Dosage Compensation
• The X chromosome carries a variety of genes that are necessary for the development of both females
and males
• The Y chromosome mainly has genes that relate to the development of male characteristics
• Chromosome inactivation
Sex-linked Traits
• Genes located on the X chromosome
• Since males have only one chromosome, they are affected by recessive X-linked traits more often
than are females
• Red-green color blindness
• Hemophilia
Polygenic Traits
• Polygenic traits arise from the interaction of multiple pairs of genes
• Skin color, height, eye color, and fingerprint pattern
Environmental Influences
• Environmental factors affect phenotype
– Diet and exercise
– Sunlight and water
– Temperature
Twin Studies
• Helps scientists separate genetic contributions from environmental contributions.
• Traits that appear frequently in identical twins are at least partially controlled by heredity.
• Traits expressed differently in identical twins are strongly influenced by environment
11.3 Chromosomes and Human Heredity
• Main idea – Chromosomes can be studied using karyotypes.
• Objectives
– Distinguish normal karyotypes from those with abnormal numbers of chromosomes.
– Define and describe the role of telomeres.
– Relate the effect of nondisjunction to Down syndrome and other abnormal chromosome
numbers.
– Assess the benefits and risks of diagnostic fetal testing
• Review Vocabulary
– Mitosis- a process in the nucleus of a dividing cell, including prophase, metaphase, anaphase,
and telophase
• New Vocabulary
– Karyotype
– Telomere
– Nondisjunction
Karyotype Studies
• Karyotype-micrograph in which the pairs of homologous chromosomes are arranged in decreasing
size
• Images of chromosomes stained during metaphase
• Chromosomes are arranged in decreasing size to produce a micrograph
• 22 autosomes are matched together with one pair of nonmatching sex chromosomes
Telomeres
• Protective caps consist of DNA associated with proteins
• Serves a protective function for the sttructure of the chromosome
• Might be involved in both aging and cancer
Nondisjunction
• Cell division during which sister chromatids fail to separate properly
• Results in extra copy of chromosome or only one copy of a chromosome
• Having a set of three chromosomes of one kind is trisomy
• Having only one copy of a chromosome is monosomy
• Down Syndrome – Trisomy 21
• Distinctive facial features, short stature, heart defects, and mental disability
Nondisjunction
• Sex Chromosomes
• XX – Normal female
• XO – Female with Turner’s Syndrome
• XXX – Nearly normal female
• XY – Normal male
• XXY – Male with Klinefelter’s Syndrome
• XYY – Normal or nearly normal male
• OY – Results in death
Fetal Testing
• Used to diagnosis genetic disorders before birth
• Amniocentesis
– Benefits-diagnosis of chromosome abnormalities and other defects
– Risks-discomfort for expectant mother, slight risk of infection, and risk of miscarriage
• Chorionic villus sampling
– Benefits-diagnosis of chromosome abnormalities and certain genetic defects
– Risks-miscarriage, infection, and newborn limb defects
• Fetal blood sampling
– Benefits-diagnosis of genetic or chromosomal abnormality, checks for fetal problems and
oxygen levels, and medications can be given to the fetus before birth
– Risks-bleeding from sample site, infection, amniotic fluid might leak, and fetal death
Practice Questions:
• Identify the disease characterized by the absence of melanin
A. Albinism
B. cystic fibrosis
C. galactosemia
D. Tay-Sachs
• An individual with Tay-Sachs disease would be identified by which symptom?
A. excessive mucus production
B. an enlarged liver
C. a cherry-red spot on the back of the eye
D.vision problems
•
A.
B.
C.
D.
Under what circumstances will a recessive trait be expressed?
A recessive allele is passed on by both parents.
One parent passes on the recessive allele.
The individual is heterozygous for the trait.
There is a mutation in the dominant gene.

Which of Dr. Garrod’s observations about alkaptonuria was most critical to his determination that it
is a genetic disorder?
It appears at birth and runs in families.
It is linked to an enzyme deficiency.
It continues throughout a patient’s life, affecting bones and joints.
It is caused by acid excretion and results in black urine.
A.
B.
C.
D.
•
A.
B.
C.
D.
•
Albinism is a recessive condition. If an albino squirrel is born to parents that both have normal fur
color, what can you conclude about the genotype of the parents?
at least one parent is a carrier
both parents are carriers
both parents are homozygous recessive
at least one parent is homozygous dominant
A.
B.
C.
D.
When a homozygous male animal with black fur is crossed with a homozygous female with white fur,
they have offspring with gray fur. What type of inheritance does this represent?
dosage compensation
incomplete dominance
multiple alleles
sex-linked
•
A.
B.
C.
D.
Of the 23 pairs of chromosomes in human cells, one pair is the _______.
autosomes
Barr bodies
monosomes
sex chromosomes
•
A.
B.
C.
D.
Which is an example of a polygenic trait?
blood type
color blindness
hemophilia
skin color
•
A.
B.
C.
D.
What does a karyotype show?
The blood type of an individual.
The locations of genes on a chromosome.
The cell’s chromosomes arranged in order.
The phenotype of individuals in a pedigree.
•
A.
B.
C.
D.
What condition occurs when a person’s cells have an extra copy of chromosome 21?
Down syndrome
Klinefelter’s syndrome
Tay-Sachs syndrome
Turner’s syndrome
•
A carrier of hemophilia and her husband, who is unaffected by the condition, are expecting a son.
What is the probability that their son will have hemophilia?
25%
50%
75%
100%
A.
B.
C.
D.
•
A.
B.
C.
D.
Why are males affected by recessive sex-linked traits more often than are females?
Males have only one X chromosome.
Males have two X chromosomes.
Males have only one Y chromosome.
The traits are located on the Y chromosomes.
•
A.
B.
C.
D.
Shorthorn cattle have an allele for both red and white hair. When a red-haired cow is crossed with a
white-haired bull, their calf has both red and white hairs scattered over its body. What type of
inheritance does this represent?
codominance
dosage compensation
epistasis
sex-linked
•
A.
B.
C.
D.
Down Syndrome results from what change in chromosomes?
one less chromosome on pair 12
one extra chromosome on pair 21
one less chromosome on pair 21
one extra chromosome on pair 12
•
A.
B.
C.
D.
What condition occurs when a person’s cells have an extra copy of chromosome 21?
Down syndrome
Klinefelter’s syndrome
Tay-Sachs syndrome
Turner’s syndrome