CHAPTER 13: HUMAN GENETICS

I. chromosomes: 46 in humans

            A. karyotype: pictorial display of pairs of chromosomes

                        1. sex chromosomes: X and Y

                        2. autosomes: all pairs of chromosomes except X and Y

            B. nondisjunction: homologous chromosomes don't separate during meiosis

                        1. monosomy (2n - 1), are missing a chromosome

                        2. trisomy (2n +1), have too many chromsomes

                                    a. trisomy 21: Down syndrome, may be due to women over age 40,

                                        may be hereditary, with a translocation on chromosome 14, Gart

                                        gene for increased level of purines in blood, mental retardation,

                                        round face, narrow, slanting eyelids, enlarged tongue

            C. sex chromosome abnormalities

                        1. XYY males: Jacob's syndrome: tall, persistent acne, barely normal

                            intelligence

                        2. XO: Turner syndrome females: short, don't go through puberty,

                            infertile, may have congenital heart defects

                        3. XXY: Klinefelter syndrome: sterile males, may be some breast

                           development or subnormal intelligence

                        4. XXX: Triplo-X: may have menstrual irregularities, early onset of

                            menopause

                        5. Fragile X syndrome: hyperactive, autistic, speech delayed, may have

                            learning disabilities

                        6. Barr bodies: dark-staining spot on cells of female cells; one X will be

                            functional, any others will not be in any cell

            D. prenatal testing

                        1. amniocentesis: fluid from amniotic sac surrounding fetus

                        2. chorionic villi sampling: sample from lining of uterus and chorion

II. Autosomal traits

            A. autosomal dominant

                        1. ch. 17: neurofibromatosis: benign tumors of skin or deeper tissues

                        2. ch. 4: Huntington disease: progressive nervous system degeneration,

                            doesn't appear until middle age, triplet repeats or genomic imprinting

            B. autosomal recessive disorders

                        1. Tay-Sachs disease: lack lysosome activity, leads to destruction of

                            nervous system

                        2. ch. 7: cystic fibrosis: function of mucous and sweat glands, only live

                            until mid 20's

                        3. ch. 12:. PKU: lack enzyme to break down phenylalanine, retardation

                            prevented by diet until age 7

            C. pedigree chart: shows pattern of inheritance for a condition

                        1. square for males, circle for females

                        2. shaded indicates presence of condition

                        3. carriers: don't express a condition, but carry a gene

            D. Polygenic traits: 2 or more loci, additive effect, also subject to environmental

                 change

                        1. skin color

                        2. cleft lip - cleft palate

                        3. clubfoot

                        4. congenital hip dislocations

                        5. hypertension

                        6. diabetes

                        7. schizophrenia

                        8. allergies

                        9. cancers

E. multiple alleles: more than 2 alleles

            1. blood type: A, B, O, AB

            2. Rh: another gene, + or -

            F. Degrees of dominance:

                        1. codominance: alleles equally expressed, blood type

                        2. incomplete dominance: sickle-cell trait,

                                    a. Hb^AHb^A normal hemoglobin

                                    b. Hb^SHb_S dies from sickle cell anemia

                                    c. Hb^AHb^S sickle-cell trait, immunity to malaria

III. sex-linked genes

            A. Y chromosome: SRY gene determines male characteristics

            B. X-linked: inherited from the mother on the X chromosome, seen more often in

                 males

                        1. color blindness: green, or red on X, blue is autosomal

                                    a. X^B: normal vision

                                    b. X^b: color blindness

                                    c. carrier female, X^BX^b

                                    d. male: normal: X^BY or color blind: X^bY

                        2. Duchenne's muscular dystrophy: wasting away of the muscles, toe

                            walking

                        3. hemophilia: missing a clotting factor

            B. sex-influenced traits: expressed differently in the two sexes

                        1. pattern baldness: autosomal, dominant in males (testosterone)