9 - GENETICS Incomplete, Codominance and Polygenic Inheritance ...
Essential Questions - Bixby · Codominance Sickle-cell disease • Changes in hemoglobin cause red...
Transcript of Essential Questions - Bixby · Codominance Sickle-cell disease • Changes in hemoglobin cause red...
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Essential Questions
• How can genetic patterns be analyzed to determine dominant or recessive
inheritance patterns?
• What are examples of dominant and recessive disorders?
• How can human pedigrees be constructed from genetic information?
Basic Patterns of Human InheritanceCopyright © McGraw-Hill Education
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Review
• genes
New
• carrier
• pedigree
Basic Patterns of Human InheritanceCopyright © McGraw-Hill Education
Vocabulary
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Basic Patterns of Human InheritanceCopyright © McGraw-Hill Education
Recessive Genetic Disorders
• A recessive trait is expressed when the individual is homozygous recessive
for the trait.
• Those with at least one dominant allele will not express the recessive
disorder.
• An individuals who is heterozygous for a recessive disorder is called a
carrier.
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Recessive Genetic Disorders
Cystic fibrosis
• A disorder that affects the mucous-producing glands, digestive enzymes, and
sweat glands.
• Chloride ions are not properly transported out of cells of a person with cystic
fibrosis.
• Cystic fibrosis causes mucus excretion that clogs ducts in the pancreas,
interrupts digestion, and blocks respiratory pathways in the lungs.
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Recessive Genetic Disorders
Albinism
• Albinism is caused by altered genes, resulting in the absence of the skin
pigment melanin in hair and eyes.
• Individuals with albinism have very pale skin, white hair, and pink irises.
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Recessive Genetic Disorders
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.
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Dominant Genetic Disorders
Huntington’s disease
• Affects the nervous system, causing gradual loss of brain function
• Occurs in 1 out of every 10,000 people in the US
Achondroplasia
• Causes small body size and limbs that are comparatively short
• Caused by an abnormal gene that affects bone growth
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Pedigrees
• A pedigree is a diagram that traces the inheritance of a particular trait
through several generations.
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Analyzing Pedigrees
• Pedigrees can be used to
examine both recessive and
dominant genetic disorders.
• Information about an individual’s
genotype can be inferred from
the phenotype of his/her parents
and offspring.
Basic Patterns of Human InheritanceCopyright © McGraw-Hill Education
Recessive disorder
Dominant disorder
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Analyzing 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.
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Basic Patterns of Human InheritanceCopyright © McGraw-Hill Education
Review
Essential Questions
• How can genetic patterns be analyzed to determine dominant or recessive
inheritance patterns?
• What are examples of dominant and recessive disorders?
• How can human pedigrees be constructed from genetic information?
Vocabulary
• carrier
• pedigree
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Essential Questions
• What are the differences between various complex inheritance patterns?
• How can sex-linked inheritance patterns be analyzed?
• How can the environment influence the phenotype of an organism?
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Review
• gamete
New
• incomplete dominance
• codominance
• multiple alleles
• epistasis
• sex chromosome
• autosome
• sex-linked trait
• polygenic trait
Complex Patterns of InheritanceCopyright © McGraw-Hill Education
Vocabulary
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Incomplete Dominance
• In some organisms, heterozygous individuals will display the dominant
phenotype.
• With incomplete dominance, the heterozygous phenotype is an intermediate
phenotype between the two homozygous phenotypes.
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Codominance
• In codominance, both the dominant and recessive alleles are expressed in
heterozygous individuals.
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Codominance
Sickle-cell disease
• Changes in hemoglobin cause red blood cells to become sickle shaped.
• People who are heterozygous for the trait have both normal and sickle-shaped cells.
Sickle-cell disease and malaria
• Those who are heterozygous for the sickle cell trait also have a higher resistance to malaria.
• The death rate due to malaria is lower where sickle-cell trait is higher, meaning more people live to pass it on to their offspring.
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Multiple Alleles
Blood groups in humans
• Some forms of inheritance are
determined by more than two
alleles, referred to as multiple
alleles.
• The ABO blood group has
three forms of alleles,
sometimes called AB markers.
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Multiple Alleles
Coat color of rabbits
• Multiple alleles can demonstrate a hierarchy of dominance.
• In rabbits, four alleles code for coat color: C, cch, ch, and c.
• The hierarchy of dominance is C > cch > ch >c.
• The presence of multiple alleles increases the possible number of
genotypes and phenotypes.
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Epistasis
• Epistasis is an interaction where of one allele hiding the effects of
another allele.
• Seen in the coat color of Labrador retrievers
• Dominant allele E determines whether the coat will have dark
pigment.
• Allele B determines how dark the coat will be.
• When a dog has recessive ee alleles, the coat will be yellow,
because the e allele masks the effects of the B allele.
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Sex Determination
• One pair of chromosomes, sex
chromosomes, determine an
individual’s gender.
• XX: female
• XY: male
• The other 22 pairs of
chromosomes are called
autosomes.
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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.
• In female, one X chromosome is inactivated in each cell.
• Called dosage compensation or x-inactivation
• Which X stops working in each cell is random.
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Dosage Compensation
Barr bodies
• The inactivated X chromosome can be observed in cells.
• Darkly stained, inactivated X chromosomes are called Barr bodies.
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Sex-Linked Traits
• Traits controlled by genes located on the X chromosome are sex-linked
traits.
• Because males have only one copy of the X chromosome, they are
more affected by recessive X-linked traits.
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Sex-Linked Traits
Red-green color blindness
• Recessive, X-linked trait
• Mothers are carriers.
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Sex-Linked Traits
Hemophilia
• Recessive, X-linked trait that causes delayed clotting of blood
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Polygenic Traits
• Polygenic traits arise from the interaction of multiple pairs of genes.
• Include such traits as skin color, height, and eye color
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Environmental Influences
Sunlight and water
• Without enough sunlight, most plants will not produce flowers.
• Insufficient water causes plants to drop their leaves.
Temperature
• Most organisms experience phenotypic changes with extreme heat.
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Twin Studies
• Help 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.
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Complex Patterns of InheritanceCopyright © McGraw-Hill Education
Review
Essential Questions
• What are the differences between various complex inheritance patterns?
• How can sex-linked inheritance patterns be analyzed?
• How can the environment influence the phenotype of an organism?
Vocabulary
• incomplete dominance
• codominance
• multiple alleles
• epistasis
• sex chromosome
• autosome
• sex-linked trait
• polygenic trait
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Essential Questions
• How are karyotypes used to study genetic disorders?
• What is the role of telomeres?
• How is nondisjunction related to Down syndrome and other abnormal
chromosome numbers?
• What are the benefits and risks of diagnostic fetal testing?
Chromosomes and Human HeredityCopyright © McGraw-Hill Education
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Review
• mitosis
New
• karyotype
• telomere
• nondisjunction
Chromosomes and Human HeredityCopyright © McGraw-Hill Education
Vocabulary
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Karyotype Studies• Scientists study not only genes but entire chromosomes.
• Images of chromosomes stained during metaphase allow scientists to study
sister chromatids and homologous chromosomes.
• Karyotype – micrograph in which the pairs of homologous chromosomes are
arranged in decreasing size.
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Telomeres• Telomeres are protective caps on the end of chromosomes.
• Telomeres consist of DNA and proteins.
• They serve as a protective function for the structure of the chromosome.
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Nondisjunction• Cell division where sister chromatids fail to
separate properly is called nondisjunction.
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Nondisjunction
Down syndrome
• Result of an extra chromosome 21
• Characteristics include distinctive facial
features, short stature, heart defects, and
mental disability.
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Fetal testing• Fetal tests can provide information on potential genetic disorders and
chromosomal status of developing babies.
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Chromosomes and Human HeredityCopyright © McGraw-Hill Education
Review
Essential Questions
• How are karyotypes used to study genetic disorders?
• What is the role of telomeres?
• How is nondisjunction related to Down syndrome and other abnormal
chromosome numbers?
• What are the benefits and risks of diagnostic fetal testing?
Vocabulary
• karyotype
• telomere
• nondisjunction