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Human Heredity Chapter 14 Human Chromosomes • Chromosomes are only visible during cell division (mitosis/meiosis). • To analyze chromosomes, biologist photograph cells during mitosis and align the chromosomes in homologous pairs. • This picture is known as a karyotype Types of Chromosomes On a human karyotype: • Chromosome pairs 1-22 are known as autosomes. – They code for traits that are not related to sex. – Both males and females have the same type • Chromosome pair 23 contains the sex chromosomes. – Males have XY and females have XX. Boy or Girl? Boy or Girl? Did you know??? • Sex is determined by the father of a child. • You have a 50% chance of having a boy or a girl ? Who decides? Mom can give X Dad can give X or y X X X XX XX y Xy Xy Dad determines sex of the baby. SO ____ If dad gives X with mom’s X = girl If dad give y with mom’s X = boy Human GENETIC DISORDERS CHROMOSOMAL MUTATIONS ____________________________: structure Change in the ______________ or number ____________ of chromosomes Homologous chromosomes fail to separate ________________ during MEIOSIS NONDISJUNCTION = _________________________ One cell gets 2 copies of the chromosome the other cell gets none. Down syndrome = TRISOMY 21 Down syndrome (Trisomy 21) • Most common chromosomal abnormality • Mild to severe mental retardation • Risk of having a child with Down syndrome increases with age of mom Sex Linked GENETIC DISORDERS SEX CHROMOSOMES CAN CARRY OTHER GENES TOO SEX LINKED TRAITS = ___________________ These traits show up in different _______________ percentages in males and females because they move with the sex chromosomes Y-LINKED GENES: carried on Y chromosome Genes ______________ EXAMPLE: Hairy pinna Y linked ONLY show up in males _________genes _____ X-LINKED GENES: ____________ are carried on the X chromosome X-linked recessive disorders MORE frequently show up _____________ MALES than females in ______ because males only have ONE X chromosome. ______ HEMOPHILIA CAUSE: Blood clotting proteins carried Mutation in genes for __________________ on X chromosome ______ Blood clotting proteins are missing so person with this disorder can’t stop bleeding when injured; can bleed to death ________________ from minor cuts or suffer internal bleeding from bruises or bumps. Muscular Dystrophy CAUSE: deletion in gene that codes for a muscle protein _______________ On X Chromosome Results in weakening ____________________ and loss of skeletal muscle ___________________ 1 out of 3000 males in US http://www.cadenhead.org/workbench/gems/jerry-lewis-telethon.jpg http://www.tokyo-med.ac.jp/genet/chm/dei.gif COLORBLINDNESS CAUSE: Color vision Mutation in one of three genes for _______________ carried on X chromosome Persons with this disorder have trouble distinguishing colors. Seen in 1 in 10 males 1 in 100 females http://gizmodo.com/gadgets/peripherals/samsung-develops-lcd-for-colorblind-036306.php When Harry Met Sally… • Harry and Sally are two normal vision adults who have a color blind son. – B – normal vision b – color blind – What are the genotypes of Harry and Sally? • XBY, XBXb • Show the cross between Harry and Sally. http://www1.istockphoto.com/file_thumbview_approve/23 41727/2/istockphoto_2341727_cute_cartoon_couple_drinki ng_vector.jpg When Harry Met Sally… Give all of the possible genotypes and phenotypes of their offspring. • _________ – normal vision daughter • ________ – normal vision daughter (carrier) • ________ – normal vision son • ________– color blind son • Sally’s dad has normal vision. Is Sally’s Mom colorblind? • She could be colorblind, or she could be a carrier for the colorblindness trait. http://www1.istockphoto.com/file_thumbview_approve/23 41727/2/istockphoto_2341727_cute_cartoon_couple_drinki ng_vector.jpg PEDIGREE CHARTS • Show the relationships within a family to study one particular observable trait/phenotype. • Refer to page 342 in text. • Circle=female • Square=male • Horizontal line=marriage • Vertical line and bracket=children • Shaded=person expresses trait • Unshaded=person does not express trait. Pedigree Chart for Color Blindness