Wi10-Lec 9

Wi10-Lec 9 - Lecture 9 Inheritance and the DNA code...

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1 Lecture 9 Inheritance and the DNA code Announcements • 2 Debates this Thursday 2/4/10 – Be there! Debates will be on the final!
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2 Pleiotropy: How can one gene influence multiple traits? The SRY Gene ± S ex-determining R egion on the Y -chromosome” ± Causes fetal gonads to develop as testes shortly after fertilization. ± Following the gonads’ secretion of testosterone, other developmental changes also occur.
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3 How Is Sex Determined? During Gamete formation sex chromosomes segregate The X-Y system The X-0 system Parents Sperm Ova Zygotes (offspring) Inheritance of Sex-Linked Genes • The sex chromosomes have genes for many characters unrelated to sex • A gene located on either sex chromosome is called a sex-linked gene • Sex-linked genes follow specific patterns of inheritance
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4 Sex Linked Genes • Females: 2X chromosomes – Can be either homozygous or heterozygous for genes on the X chromosome. • Males: Only 1X chromosome – considered hemizygous for genes on the X chromosome What does this mean?
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5 Sex Linked Disorders Much more common in males than in females • Color blindness • Duchenne muscular dystrophy • Hemophilia ? If a male has a sex-linked disorder, did he inherit it from his father? ?
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6 How Are Human Genetic Disorders Investigated? Human geneticists study the inheritance of disease- causing alleles by searching medical, historical, and family records to study past crosses. Fig. 9-20 A pedigree for a dominant trait A pedigree for a recessive trait How to read pedigrees I, II, III = generations = male = female = parents = offspring or = shows trait or = does not show trait or = known carrier (heterozygote) for recessive trait or = cannot determine the genotype from this pedigree (a) (b) I II III I II III IV ? ??? ? ?? ? ? Pedigrees
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7 Some human genetic disorders are caused by recessive alleles • A heterozygote will remain healthy, but people who inherit two copies of a recessive, defective allele will have the disorder Sickle Cell Anemia, a recessive genetic disorder People homozygous for the sickle-cell allele synthesize only defective hemoglobin; many of their red cells become sickled. Fig. 9-21
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8 Sickle Cell Anemia • Defective allele for hemoglobin synthesis causes sickle-cell anemia – Sickle cell hemoglobin cannot transport oxygen correctly – Sickled cells more fragile,die early, causing anemia – But…heterozygotes for the sickle-cell allele are resistant to malaria Dominantly Inherited Disorders • Only a single defective allele is necessary to cause the disorder.
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Wi10-Lec 9 - Lecture 9 Inheritance and the DNA code...

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