Essential Questions - Bixby · Codominance Sickle-cell disease • Changes in hemoglobin cause red...

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

Review

• genes

New

• carrier

• pedigree


Vocabulary


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.


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.



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.



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.


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


Pedigrees

• A pedigree is a diagram that traces the inheritance of a particular trait

through several generations.


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.


Recessive disorder

Dominant disorder

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.



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

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?

Complex Patterns of InheritanceCopyright © McGraw-Hill Education

Review

• gamete

New

• incomplete dominance

• codominance

• multiple alleles

• epistasis

• sex chromosome

• autosome

• sex-linked trait

• polygenic trait


Vocabulary

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.


Codominance

• In codominance, both the dominant and recessive alleles are expressed in

heterozygous individuals.


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.


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.


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.


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.


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.


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.


Dosage Compensation

Barr bodies

• The inactivated X chromosome can be observed in cells.

• Darkly stained, inactivated X chromosomes are called Barr bodies.


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.


Sex-Linked Traits

Red-green color blindness

• Recessive, X-linked trait

• Mothers are carriers.


Sex-Linked Traits

Hemophilia

• Recessive, X-linked trait that causes delayed clotting of blood


Polygenic Traits

• Polygenic traits arise from the interaction of multiple pairs of genes.

• Include such traits as skin color, height, and eye color


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.


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.



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

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

Review

• mitosis

New

• karyotype

• telomere

• nondisjunction


Vocabulary

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.


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.


Nondisjunction• Cell division where sister chromatids fail to

separate properly is called nondisjunction.


Nondisjunction

Down syndrome

• Result of an extra chromosome 21

• Characteristics include distinctive facial

features, short stature, heart defects, and

mental disability.


Fetal testing• Fetal tests can provide information on potential genetic disorders and

chromosomal status of developing babies.



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

Essential Questions - Bixby · Codominance Sickle-cell disease • Changes in hemoglobin cause red...

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