Chapter 8 Section 4 Complex Patterns of Heredity

Chapter 8 Section 4 Complex Patterns of Heredity Objectives • Identify five complex patterns of heredity. • Describe how mutations can cause genetic disorders. • List several genetic disorders and describe their modes of inheritance • Evaluate the benefits of genetic counseling. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

New Vocabulary • • Polygenic inheritance Incomplete dominance Codominance Multiple alleles Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Complex Patterns of Inheritance • Patterns of Inheritance that are explained by Mendel’s rules and laws are often referred to as simple ________. . . 2 contrasting forms of a trait – They involve _____ • However, many inheritance patterns are more ______ than those studied by Mendel complex Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Your text discusses five types of complex inheritance… – _________ inheritance polygenic incomplete – _______ dominance codominance – ________ – _______ alleles multiple Sex-linked – ________ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Polygenic Inheritance • When _______ several genes influence a trait, the trait is said to be a _________ trait. polygenic • The genes for a polygenic trait may be scattered same along the ____ chromosome or located on different ________ chromosomes. • Familiar examples of polygenic traits in humans height weight eye include _____, ______, and _______ skin hair color, _______ color, and ____ color Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• When several genes control a trait, a great range of ________ is seen in the phenotypes variation – For example, there is wide range of human height weight ______ and _______ color – For human hair, eye, and skin _____, there light is also a wide range in phenotypes from _______ dark to ______ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

curve • When graphed, polygenic traits usually show a ______ minimum value to the ranging from the _______ maximum value ________ maximum value minimum value Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• As shown in this graph for stem height, what height is the most common? 10 cm • Least common? 4 cm or 16 cm maximum value minimum value Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Incomplete Dominance • This inheritance pattern causes the phenotype of a heterozygous ________ individual to be intermediate _________ between the two homozygotes. • For example, when a snapdragon with red flowers is crossed with a snapdragon with white flowers, a pink flowers is produced. snapdragon with ______ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Use the following genotypes to complete and analyze the following cross… RR = Red R’R’= White RR’ = Pink Genotype Ratio? 1 RR : 2 RR’ : 1 R’R’ R RR RR’ R’ R’R’ RR’ Phenotype Ratio? 1 Red : 2 Pink : 1 White Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

texture • In humans, hair ______ is governed by incomplete dominance – What would be the intermediate result produced by a cross of one parent with straight hair and another with curly hair? Wavy hair Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Codominance • Codominant alleles cause the phenotypes of ____ both homozygotes to be expressed _______ equally feather color of • Codominance controls the _____ chickens Black feathers – BB = _________ White feathers – WW = _________ Black and white (checkered) – BW = _________ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Multiple Alleles • Genes with _______ three or more alleles are said to have multiple alleles. • For example, in the human population, blood types IA IB are determined by three alleles…. _____, and i ______ carbohydrates • The superscripts A and B refer to ________ on the surface of red blood cells – These carbohydrates are also called ______ surfaceor _______antigens molecules Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Even for traits controlled by genes with multiple alleles, an individual can have only _____ two of the possible alleles for that gene. i • IA and IB are dominant to _____ • IA and IB are __________ to each other codominant Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Blood Type A – surface molecules are _______ square – Caused by two allele combinations… IAIA • ____ IAi • ____ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Blood Type B – surface molecules are _______ rounded – Caused by two allele combinations… • ____ IBIB IBi • ____ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Blood Type AB – Red blood cells have both _____ A and B surface molecules because they are _________ codominant – Caused by one allele combination… IAIB • ____ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Blood Type O – Red blood cells have ____ no surface molecules – Caused by one allele combination… • ____ ii Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• It is important to determine blood types before a patient receives transfusion because incompatible surface a blood ________ immune system and can molecules trigger the body’s _______ death cause ______ – Since blood type O has ______ no surface molecules, it can be _______ added to any ABO blood type • It is called a universal _______ donor both surface molecules, it can – Since blood type AB has ______________ any ABO blood type receive acceptor • It is called a universal _______ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• The Rh factor is another surface molecule on red blood cells. . . have – If you are Rh positive, you ______ this extra surface molecule not have this – If you are Rh negative, you do _____ extra surface molecule negative – Negative individuals may only receive _____ versions of A, B, AB, and O blood types Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• A child is produced with type O blood. Is it possible for the mother to have type AB blood and the father to have type O blood? • Let’s find out with a Punnett square! IA IB i IAi IBi • Blood tests can determine who are _______ possible DNA tests are needed to determine parents, but _____ actual parenthood. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Characters Influenced by the Environment • An individual’s phenotype often depends on environment conditions in the _________. genes • Because identical twins have identical _____, they are often used to study environmental influences. – Since they are genetically identical, any differences between them are attributed to _________ influences. environmental Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Example 1 – Temperature affects the color fur of an arctic fox • ______ white or ______ brown • Example 2 Nutrition – ________ affects human height and weight • Malnutritioned individuals will not reach the height or weight determined by their genes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Your text also discusses several genetic disorders… – Most genetic disorders are the result of a faulty proteins ________ and are caused by the two recessive alleles inheritance of _____ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Cystic Fibrosis (CF) • _______ recessive genetic disorder • Caused by a defective gene that normally produces a chloride protein responsible for moving ______ ions into and out of cells – This causes the formation and accumulation of a thick _____ in the _______, mucus lungs _____, liver intestines, and _______ pancreas Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity fatal • Cystic fibrosis is the most common ______ hereditary disorder among Caucasians. • One in ____ 25 Caucasian individuals has at least ____ copy of the defective gene one – These individuals don’t have cystic fibrosis but carriers they are considered ________ 2500 • About one in _____ Caucasians born in the United States inherits cystic fibrosis Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Tay - Sachs Disease • Caused by recessive alleles that produce a defective ______ enzyme. brain Jewish • Common in ______ populations nervous ______ system • In early childhood, the ______ system begins to break down, eventually leading to death ______ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Sickle Cell Anemia • Sickle cell anemia is also caused by inheriting two ______ recessive alleles. – These alleles produce a defective form of the protein hemoglobin __________, which causes many red blood cells to sickle bend into a _______ shape, affecting their ability to carry oxygen ________ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

damage • Tissue ________ may result if certain cells are not receiving enough oxygen block • The sickle cells may also _______ small vessels and _______ easily rupture Heterozygous • ___________ individuals actually have _____ normal red blood cells and sickle cells both – Due to this occurrence, many texts actually list this codominant disease as being controlled by ______ inheritance instead of simple recessive Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Heterozygous individuals are protected from the affects of a parasite that invades red blood cells and malaria causes __________ – The sickle shape causes resistance to the ________ parasite • Sickle cell alleles are most common in ______ Americans African 12 – One in ______ African Americans are heterozygous for the disease 500 African Americans has sickle cell – One in ______ anemia Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Hemophilia • Another recessive genetic disorder is hemophilia, a clot condition that impairs the blood’s ability to ____. sex-linked trait because the • Hemophilia is a _______ genes that control blood clotting are found on the _____ X chromosome. – How many recessive alleles must a female inherit to have hemophilia? 2 – And males? 1 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Huntington’s Disease (HD) • Huntington’s disease is a genetic disorder caused by a ______ dominant allele located on an ______. autosome – How many alleles does an individual need to inherit to have HD? 1 • The first symptoms of HD— mild forgetfulness, irritability, and slurred speech —appear in victims in their _____ or 30 s _____ 40 s – Many people have had children by this age, so HD is often ______ on in families. passed • In time, HD causes loss of ______ muscle control, uncontrollable physical spasms, severe mental illness, and eventually ______. death Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Review Question! – How are these inherited diseases different from the causes of an inherited disease like Down syndrome? Down syndrome is due to a nondisjunction Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Treating Genetic Disorders • Most genetic disorders cannot be cured, although progress is being made. • A person with a family history of genetic disorders testing may wish to undergo genetic ________ and counseling parent _______ before becoming a ______. • In some cases, a genetic disorder can be treated ______ if it is diagnosed early enough. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

• Example 1 – Phenylketonuria or _______ PKU is treatable genetic disorder caused by a faulty enzyme that is incapable of breaking down the amino acid __________. phenylalanine – Phenylalanine is found in food products like ____ and ________ sweeteners milk artificial – If newborns with PKU eat these food products, they will develop irreversible symptoms of ________________ mental retardation Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

test – After birth, infants are given a PKU ______. – If positive for PKU, what do you think would be an easy and appropriate form of treatment for the infant? Eliminating phenylalanine from their diet HD • Example 2 …there also tests to detect ______. . . if positive, couples may choose to _____ refrain from having children Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Chapter 8 Section 4 Complex Patterns of Heredity Gene Therapy • Gene technology may soon allow scientists to correct replacing certain recessive genetic disorders by ______ healthy defective genes with copies of ______ ones, an approach called gene therapy. • The essential first step in gene therapy is to isolate _______ a copy of the gene. – Example: the cystic fibrosis gene was isolated in 1989 ____ Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

recombinant – Scientists then make use of ________ DNA technology to insert the healthy gene into defective tissues Restriction • _________ enzymes are used to cut out needed portions of DNA and to insert them into a virus vector like a ______ virus • The virus then inserts correct the _______ DNA into defective cells Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

cold • Scientists have used the ____ virus to successfully correct defective lung tissues in a petri humans _____ dish, but not yet in actual _____ since we develop an immunity to the virus after ______ infection • For this technology to work, scientists will have to use a virus that the human body doesn’t _______, recognize harmful effects yet doesn’t produce ______ Adeno - _____ associated – A virus called AAV, ______ virus, seems promising Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Objective 1 • Identify five complex patterns of heredity. polygenic incomplete codominance Multiple alleles Sex-linked Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Objective 2 • Describe how mutations can cause genetic disorders. Mutations in your DNA produce faulty proteins that result in genetic disorders Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Objective 3 • List several genetic disorders and describe their modes of inheritance Cystic fibrosis Simple recessive Tay-sachs Simple recessive Sickle cell Hemophilia codominant X-linked & recessive Huntington’s Disease Simple dominant Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.

Objective 4 • Evaluate the benefits of genetic counseling. Determine the chances of an offspring inheriting the disease Discuss treatment options Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.