Chapter 14 Chromosomes and Human Inheritance Cengage Learning 2016 14.1 Shades of Skin Variations in skin color may have evolved as a balance between vitamin D production and UV protection
More than 100 gene products are involved in the synthesis of melanin, and the formation and deposition of melanosomes Mutations in some of these genes may have contributed to regional variations in human skin color Cengage Learning 2016 Variation in Human Skin Color
Variation in human skin color begins with differences in alleles inherited from parents. Above, twins Kian and Remee with their parents. Both of the childrens grandmothers are of European descent, and have pale skin. Both of their grandfathers are of African descent, and have dark skin. The twins inherited different alleles of some genes that affect skin color from their parents, who, given the appearance of their children, must be heterozygous for those alleles. Cengage Learning 2016 14.2 Human Chromosomes Humans live under variable conditions, select our own mates, and reproduce if and when desired
This makes studying human genetics more complicated than in simple laboratory organisms like fruits flies and pea plants Inheritance patterns in humans are typically studied by tracking observable traits in families over Cengage Learning 2016 generations
Pedigrees A standardized chart of genetic connections (pedigree) is used to determine the probability that future offspring will be affected by a genetic abnormality or disorder Pedigree analyses also reveals whether a trait is associated with a dominant or recessive allele, and whether the allele is on an autosome or a sex chromosome
Cengage Learning 2016 Pedigree Symbols Cengage Learning 2016 Cengage Learning 2016 Methemoglobinemia Methemoglobin is a type of hemoglobin. Methemoglobinemia is a blood condition where the
patient has abnormal quantities of methemoglobin. Hemoglobin is the molecule that is present in the red blood cells and helps in distributing the oxygen all over the body; whereas, methemoglobin does not have the ability to release oxygen. When a patient suffers from methemoglobinemia, the hemoglobin in the body is not able to release oxygen in an effective manner to the body tissues. Malfunction of the enzyme cytochrome b5 reductase. Cengage Learning 2016
Types of Genetic Variation Single genes on autosomes or sex chromosomes govern more than 6,000 genetic abnormalities Most human traits, including skin color, are polygenic (influenced by multiple genes), and some have epigenetic contributions or causes Cengage Learning 2016
Genetic Abnormalities and Disorders A genetic abnormality is an uncommon version of a trait that is not inherently life-threatening A genetic disorder causes medical problems that may be severe A genetic disorder is often characterized by a specific set of symptoms (a syndrome)
Cengage Learning 2016 Some Genetic Abnormalities and Disorders Cengage Learning 2016 Patterns of Inheritance Based on variations in single genes (Mendelian patterns) Autosomal dominant
Autosomal recessive X-linked recessive (sometimes called sexlinked) X-linked dominant Based on variations in whole chromosomes Changes in chromosome number Changes in chromosome structure Cengage Learning 2016
Recurring Genetic Disorders Cengage Learning 2016 14.3 Examples of Autosomal Inheritance Patterns Cengage Learning 2016 The Autosomal Dominant Pattern
Sam Berns Ted Talk (inspiring) Cengage Learning 2016 Autosomal Dominant Inheritance normal mother affected
father aa Aa meiosis and gamete formation A
A a Aa aa a Aa
aa affected child normal child A disorder-causing allele (dominant) A A dominant allele (red) on an auto-
B Achondroplasia affects Ivy Broadhead C Five-year-old Megan is already showing some affects all heterozygous people. (left), her brother, father, and grandfather. symptoms of HutchinsonGilford progeria.
(A) 2016 Cengage Learning; (B) Newcastle Photos and Ivy & Violet Broadhead and family;(C) Photo courtesy of The Progeria Research Foundation. Cengage Learning 2016 Cengage Learning 2016 The Autosomal Recessive Pattern Cengage Learning 2016 Autosomal Recessive Inheritance
carrier mother carrier father affected child Aa Aa carrier child normal child
meiosis and gamete Formation A a A
AA Aa a Aa aa a disorder-causing allele
(recessive) A Only people homozygous for a recessive allele on an autosome have the associated trait. In this example, both parents are carriers. Each of their children has a 25 percent chance of inheriting two alleles, and being affected by the trait. B Conner Hopf was diagnosed with TaySachs disease at age 7 12 months. He died before his second birthday.
(A) 2016 Cengage Learning; (B) Courtesy of Conners Way Foundation, www.connersway.com Cengage Learning 2016 12.4 Examples of X-Linked Inheritance Patterns Cengage Learning 2016 The Human X chromosome
dystrophin (muscular dystrophy) (anhidrotic ectodermal dysplasia) IL2RG (SCID-X1) XIST X chromosome inactivation control (hemophilia B) (hemophilia A) (red-decient color blind)
X Cengage Learning 2016 (green-decient color blind) The X-Linked Recessive Pattern Cengage Learning 2016 Some X-Linked Recessive Disorders
Cengage Learning 2016 X-linked Recessive Inheritance carrier mother normal father XX XY meiosis
and gamete formation X Y X XX
XY X XX XY You may have one form of red green color blindness if you see a 7 in this circle instead of a 29.
normal daughter or son carrier daughter affected son X recessive allele on X chromosome A In this example, the mother carries
a recessive allele on one of her two X chromosomes (red). Cengage Learning 2016 You may have another form of red green color blindness if you see a 3 instead of an 8 in this circle. B A view of color blindness. The photo on the left shows how a person with redgreen color blindness sees the photo on the right. The perception of blues and yellows is normal; red and green appear similar. The circle diagrams are part of a standardized test for color blindness. A set of 38 of these
diagrams is commonly used to diagnose deciencies in color perception. left, 2016 Cengage Learning; middle left-right, Photo by Gary L. Friedman, www.FriedmanArchives.com, right top-botttom, Life Nature Library, The Primates, 1965, Sarel Eimerl and Irven DeVore. Hemophilia A in Descendents of Queen Victoria of England Cengage Learning 2016 14.5 Heritable Changes in Chromosome Structure
Cengage Learning 2016 Duplication A section of a chromosome gets repeated Cengage Learning 2016 Deletion
A section of chromosome gets lost Cengage Learning 2016 Inversion A section of a chromosome gets flipped so it runs in the
opposite orientation Cengage Learning 2016 Translocation A piece of a broken chromosome gets reattached in the wrong place. This example shows a reciprocal translocation, in which two nonhomologous chromosomes exchange chunks Cengage Learning 2016
Chromosome Changes in Evolution Cengage Learning 2016 Evolution of X and Y Chromosomes from Homologous Autosomes Cengage Learning 2016 Differences Among Closely Related
Organisms Humans have 23 pairs of chromosomes; chimpanzees, gorillas, and orangutans have 24 Two chromosomes fused end-to-end during human evolution
telomere sequence human Cengage Learning 2016 chimpanzee 14.6 Heritable Changes in Chromosome Number
Cengage Learning 2016 Polyploidy and Aneuploidy Many flowering plant species, and some insects, fishes, and other animals, are polyploid they have three or more complete sets of chromosomes Trisomy and monosomy are examples of aneuploidy, in which an individuals cells have too many or too few copies
of a chromosome Cengage Learning 2016 Nondisjunction Cengage Learning 2016 Nondisjunction Cengage Learning 2016
Nondisjunction Metaphase I Anaphase I Telophase I Metaphase II Anaphase II
Telophase II Stepped Art Cengage Learning 2016 Autosomal Change and Down Syndrome Cengage Learning 2016
Trisomy 21: Genotype Cengage Learning 2016 Trisomy 21: Phenotype Cengage Learning 2016 Change in Sex Chromosome Number
Some disorders can be detected early enough to start countermeasures before symptoms develop Example: Most hospitals in the United States now screen newborns for mutations that cause phenylketonuria (PKU) In prenatal diagnosis, an embryo or fetus is tested before birth to screen for sex or genetic problems
Cengage Learning 2016 Prenatal Diagnosis Cengage Learning 2016 Imaging A Human Fetus A Conventional ultrasound. B 4D ultrasound.
Cengage Learning 2016 C Fetoscopy. (A) Mediscan/Corbis; (B) LookatSciences/Phototake, Inc.; (C) Neil Bromhall/Science Source Invasive Procedures amniotic sac
chorion Lennart Nilsson/Bonnierforlagen AB Cengage Learning 2016 Preimplantation Diagnosis Cengage Learning 2016 Embryo After 3 Mitotic Divisions
Cengage Learning 2016 Points to Ponder How do the sex chromosomes actually determine the sex of the individual? What are some of the characteristics governed by genes of the X and Y chromosomes? Are any human traits Y-linked?
LectureObjectives. Identify the gross features of the brainstem.. Briefly describe the . internal structure . of the brainstem (ascending and descending pathways, sensory and motor cranial nuclei, substantia nigra, red nucleus, olivary nucleus and reticular formation).
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