Chapter 11 McGraw Hill Notes

Basic Patterns of Human Inheritance

• An individual who is heterozygous for a recessive disorder is called a carrier.

• Which are recessive genetic disorders?

Cystic fibrosis

Albinism

Tay-Sachs disease

• Which statements about cystic fibrosis are true?

Chloride ions are not absorbed into the cells of a person with cystic fibrosis, causing thick mucus to block respiratory pathways in the lungs.

Cystic fibrosis is a recessive genetic disorder that affects the mucus-producing glands, digestive enzymes, and sweat glands.

Treatment for cystic fibrosis currently includes physical therapy, medication, special diets, and the use of replacement digestive enzymes.

• Which statements about albinism are true?

The absence of pigment in eyes can cause problems with vision.

A person with albinism has white hair, very pale skin, and pink pupils.

Albinism is a recessive genetic disorder resulting in the absence of the skin pigment melanin in hair and eyes.

• A person with a recessive genetic disorder will have a ________ genotype for that trait.

Homozygous

• An individual who is heterozygous for a recessive disorder is referred to as

A carrier

• Which statements about Tay-Sachs disease are true?

Tay-Sachs disease is a recessive genetic disorder caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides.

In a person affected by Tay-Sachs disease, the gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

• All of the following are recessive genetic disorders except:

Huntington’s Disase

• Which is a recessive genetic disorder that affects mucus-producing glands, digestive enzymes, and sweat glands?

Cystic fibrosis

• Albinism is a recessive genetic disorder resulting in the absence of the skin pigment melanin in hair and eyes.

• A person who does not have a genetic disorder that is caused by dominant alleles would have which of the following genotypes?

Homozygous recessive

• Which statements about galactosemia are true?

Galactosemia is a recessive genetic disorder characterized by the inability of the body to digest galactose.

Galactose must be broken down into glucose by an enzyme named GALT. Persons who lack or have defective GALT cannot digest galactose.

Persons with galactosemia should avoid milk products.

• Select statements about Huntington's disease that are true:

The symptoms include a gradual loss of brain function, uncontrollable movements, and emotional disturbances.

No preventive treatment or cure for this disease exists.

Huntington's disease is a dominant genetic disorder that affects the nervous system.

• Some disorders, such as the rare disorder Huntington’s disease, are caused by dominant alleles.

• A diagram that traces the inheritance of a particular trait through several generations is called a pedigree

• The dominant genetic disorder Huntington’s disease affects the nervous system. The symptoms of this disorder first appear in affected individuals between the ages of 30 and 50 years old.

• In a pedigree, a person who does not express a trait is represented by an unfilled square ad circle

• Select the statements about achondroplasia that are true.

Achondroplasia is the most common form of dwarfism.

A person with achondroplasia will have an adult height of about four feet and will have a normal life expectancy.

• True or false: Once an inheritance pattern is determined, the genotypes of the individuals can largely be resolved through pedigree analysis.

• Which is a recessive genetic disorder caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides?

Tay-Sachs disease

• When red-flowered snapdragons (CRCR) are crossed with white-flowered snapdragons (CWCW), the heterozygous offspring have pink flowers (CRCW). This scenario is an example of

Incomplete dominance

• In a pedigree, males are represented by squares, and females are represented by circles.

2 Complex Patterns of Inheritance

• In which pattern of inheritance is the heterozygous phenotype an intermediate phenotype between the two homozygous phenotypes?

Incomplete dominance

• In which pattern of inheritance is the heterozygous phenotype an intermediate phenotype between the two homozygous phenotypes?

Codominance

• The sickle-cell disease results from

Codominance

• Study the example of the snapdragon cross shown here. When red-flowered snapdragons (CRCR) are crossed with white-flowered snapdragons (CWCW), the heterozygous offspring have pink flowers (CRCW). This scenario is an example of

Incomplete dominance

• Select the statements that are true regarding the distribution of sickle-cell disease and malaria in Africa.

Some areas of Africa with sickle-cell disease overlap areas of widespread malaria.

The death rate due to malaria is lower where the sickle-cell trait is higher.

• Which forms of inheritance are determined by more than two alleles?

Multiple alleles

• Which explains why sickle-cell disease continues to increase in Africa?

People who are heterozygous for the sickle-cell trait have a higher resistance to malaria. Some of these people live to pass the trait to offspring.

• Which is an example of inheritance determined by multiple alleles?

ABO blood group in humans

• In which inheritance pattern are both alleles expressed in the heterozygous condition?

Codominance

• In rabbits, four alleles code for coat color: C, cch, ch, and c. Select the statements that are true about these four alleles.

Allele c is recessive and results in an albino phenotype when the genotype is homozygous recessive.

The hierarchy of dominance can be written as

C > cch > ch > c.

Allele C is dominant to the other alleles and results in a full color coat.

• Due to multiple alleles, the four alleles for rabbit-coat color produce ten possible genotypes and four phenotypes

• Paired chromosomes that determine an individual's gender are sex chromosomes

• A chromosome that is not a sex chromosome is called an autosome

• The ABO blood group has three forms of alleles: IA, IB, and i.

• A male has which sex chromosomes?

XY

• Traits controlled by genes located on the X chromosome are called sex-linked traits

• Males are affected by recessive X-linked traits more often than are females because

males only have one X chromosome

• An individual with two X chromosomes is a female

• Which statements about the allele for baldness are true?

The allele for baldness causes hair loss that follows a typical pattern called male-pattern baldness.

A male would be bald if he were heterozygous for the trait, while a female would be bald only if she were homozygous recessive.

The allele for baldness is recessive in females but dominant in males.

• Hemophilia is a recessive sex-linked disorder, characterized by delayed clotting of the blood.

• Which is a micrograph in which pairs of homologous chromosomes are arranged in decreasing size?

Karyotype

• How can some traits that are located on autosomes may appear to be sex-linked, even though they are not?

This occurs when an allele appears to be dominant in one gender but recessive in the other.

• Which statement about telomeres is false?

Telomeres are the sight of protein synthesis in a cell.

• All of the following are examples of sex-linked traits except:

Male-pattern baldness

• Which term describes cell division during which sister chromatids fail to separate properly?

Nondisjunction

3 Chromosomes and Human Heredity

• A karyotype can show when three copies of a chromosome exist in a person's genetic make up.

• Which statements are true about nondisjunction?

Nondisjunction can result in a set of three chromosomes called trisomy.

Nondisjunction can result in extra copies of a certain chromosome or only one copy of a particular chromosome in the offspring.

If nondisjunction occurs during meiosis I or meiosis II, the resulting gametes will not have the correct number of chromosomes.

• Select the statements about telomeres that are true.

Scientists have discovered that telomeres might be involved in both aging and cancer.

Telomeres serve a protective function for the structure of the chromosome.

• Down syndrome is the result of an extra chromosome 21. Therefore, Down syndrome often is called trisomy 21.

• A male with a genotype of XX has Klinefelter's syndrome.