HUMAN BIOLOGY

Chromosomes and human GenetiCs 401

4. The probability of a crossover occurring between two genes
   on the same chromosome.
   a. is unrelated to the distance between them
   b. increases the closer they are
   c. increases the farther apart they are
   d. is zero


5. A chromosome’s structure can be altered by.
   a. deletions c. translocations
   b. duplications d. all of the above


6. Nondisjunction can be caused by.
   a. crossing over in meiosis
   b. segregation in meiosis
   c. failure of chromosomes to separate during meiosis
   d. multiple independent assortments


7. A gamete affected by nondisjunction could have.
   a. a change from the normal chromosome number
   b. one extra or one missing chromosome
   c. the potential for a genetic disorder
   d. all of the above

seLf-Quiz Answers in Appendix VI

1. segregate during.
   a. Homologues; mitosis
   b. Genes on one chromosome; meiosis
   c. Homologues; meiosis
   d. Genes on one chromosome; mitosis


2. The alleles of a gene on homologous chromosomes
   end up in separate.
   a. body cells
   b. gametes
   c. nonhomologous chromosomes
   d. offspring
   e. both b and d are possible


3. Genes on the same chromosome tend to stay together
   during and end up in the same.
   a. mitosis; body cell d. meiosis; gamete
   b. mitosis; gamete e. both a and d
   c. meiosis; body cell

Table 20.1 examples of human Genetic Disorders and Genetic Abnormalities

Disorder or Abnormality Main Symptoms

Autosomal recessive inheritance

Albinism Absence of pigmentation

Cystic fibrosis Abnormal glandular secretions

leading to tissue, organ damage

Ellis–van Creveld syndrome Dwarfism, heart defects,

polydactyly

Fanconi anemia Physical abnormalities,

bone marrow failure

Galactosemia Brain, liver, eye damage

Hereditary methemoglobinemia Blue skin coloration

Phenylketonuria (PKU) Mental impairment

Sickle-cell anemia Adverse pleiotropic effects

on organs throughout body

Autosomal dominant inheritance

Achondroplasia One form of dwarfism

Camptodactyly Rigid, bent fingers

Familial hypercholesterolemia High cholesterol levels in blood;

eventually clogged arteries

Huntington’s disease Nervous system degenerates

progressively, irreversibly

Marfan syndrome Abnormal or no connective

tissue

Neurofibromatosis Tumors of nervous system, skin

Polydactyly Extra fingers, toes, or both

Progeria Drastic premature aging

Disorder or Abnormality Main Symptoms

X-linked recessive inheritance

Androgen insensitivity XY individual but having

syndrome female traits; sterility

Fragile X syndrome Mental impairment

Hemophilia Impaired blood clotting ability

Muscular dystrophies Progressive loss of

muscle function

Red–green color blindness Inability to distinguish

among some or all shades

of red and green

Changes in chromosome structure

Aniridia Eyes lacking an iris,

other abnormalities

Chronic myelogenous Overproduction of white

leukemia (CML) blood cells in bone marrow;

organ malfunctions

Cri-du-chat syndrome Mental impairment; abnormally

shaped larynx

Changes in chromosome number

Down syndrome Mental impairment;

heart defects

Klinefelter syndrome Sterility; mild mental

impairment

Turner syndrome (XO) Sterility; abnormal ovaries,

abnormal sexual traits

XXX syndrome Minimal abnormalities

XYY condition Mild mental impairment or

no effect

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