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Updated April 2006Created by C. Ippolito April 2006 Chapter 12 Patterns of Inheritance.

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Presentation on theme: "Updated April 2006Created by C. Ippolito April 2006 Chapter 12 Patterns of Inheritance."— Presentation transcript:

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2 Updated April 2006Created by C. Ippolito April 2006 Chapter 12 Patterns of Inheritance

3 Updated April 2006Created by C. Ippolito April 2006 Gene and Allele Gene - sequence of DNA DNA found in a specific site (locus) on a chromosome. –Determines –Determines a trait or characteristic characteristic in a human. Allele Allele - alternate forms forms of a gene that occupy the same loci on a chromosome. –The interaction of 2 alleles on a chromosome pair determine a person’s trait. 2

4 Updated April 2006Created by C. Ippolito April 2006 male parentSex of a child is determined by the male parent. –Sex cells of parents contain one member of each pair. eggsperm –The egg will always have an X sperm can have an X or Y. X chromosome Female - egg is fertilized by a sperm bearing an X chromosome. Y chromosome Male - egg is fertilized by a sperm bearing an Y chromosome. Sex Determination 3

5 Updated April 2006Created by C. Ippolito April 2006 Mendel’s Laws GregorGregor Mendel – Austrian monk – first to explain how characteristics are passed –Experimented with pea plants

6 Updated April 2006Created by C. Ippolito April 2006 Law of Segregation Each trait is determined by two two factors factors. –In sex cells factors factors separate separate. –Zygote gets one factor from each parent.

7 Updated April 2006Created by C. Ippolito April 2006 Law of Dominance Mendel determined that certain factors overpowered the appearance of others. –Dominant –Dominant – overpowers presencepresence of factor forces forces trait trait to appear appear regardless of the form of the other factor on its companion chromosome. –Recessive –Recessive - is overpowered Both chromosomes must possess possess this factor for trait to appear

8 Updated April 2006Created by C. Ippolito April 2006 Genotype the actual actual gene gene pairs pairs or alleles present to cause a trait. –There are two genotypes: Homozygous –Genotype with two two identical identical alleles alleles causing a trait. »TT »TT - homozygous dominant »tt »tt - homozygous recessive - the only only way a recessive recessive can show Heterozygous –Genotype with two two different different alleles alleles causing a trait. »Tt »Tt - only dominant appears

9 Updated April 2006Created by C. Ippolito April 2006 Phenotype the physical physical appearance caused by the alleles. –Both TT TT and Tt Tt have same appearance appearance - tallness

10 Updated April 2006Created by C. Ippolito April 2006 Law of Independent Assortment Factor inherited in one gene does not affect the factor that will be inherited in another gene –not true if genes are linked - found on same chromosome

11 Updated April 2006Created by C. Ippolito April 2006 Polygenic (Multifactorial ) Inheritance Single trait controlled by two or more sets of alleles. –Traits show continuous variation “bell curve” –The greater the number of alleles the more perfect the bell curve will be. Known polygenic traits: –Skin Color –Height Possible polygenic traits –Cleft Palate –Club Foot –Hypertension –Diabetes –Schizophrenia –Allergies 10

12 Updated April 2006Created by C. Ippolito April 2006 Multiple Alleles Trait controlled one gene pair with more than two distinct alleles. –Human Blood types I A - codominant -causes A blood I B - codominant -causes B blood i - recessive -cause O blood Incomplete Dominance –Alleles for A and B do not dominate so the heterozygote I A I B has what is known as Type AB blood 11

13 Updated April 2006Created by C. Ippolito April 2006 Blood Types Type A I A i - heterozygous for A I A I A - homozygous for A produces anti-B can be given A or O blood Type B I B i - heterozygous for B IBIB IBIB - homozygous for B produces anti-A can be given B or O blood Type AB I A I B - heterozygous for AB produces no antibody Universal Receiver can be given any blood Type O ii - homozygous for O produces anti-A and anti- B Universal Donor can be given only O blood  Protein marker (antigen) on membrane of the RBC. 12

14 Updated April 2006Created by C. Ippolito April 2006 Pleiotropy One gene affects many traits. Sickle Cell Anemia –Recessive - mainly affects African Americans abnormal hemoglobin Mutation substituted a valine for glutamic acid originated in areas where malaria was endemic –Hb N = normal Hb n = sickle –Hb N Hb N - normal but can get malaria –Hb N Hb n - normal but immune to malaria –Hb n Hb n - sickle cell anemia 13

15 Updated April 2006Created by C. Ippolito April 2006 Linked Traits –Inherited together because on same chromosome pair Exception Law of Independent Assortment Gene Linkage 14

16 Updated April 2006Created by C. Ippolito April 2006 During synapsis of meiosis chromosomes exchange pieces Breaks linkage Crossing Over 15

17 Updated April 2006Created by C. Ippolito April 2006 Sex-Linked Genes genes on the “X” with no equivalent part on the “Y” –appear more often in males - inherit only one allele hemophilia Duchenne Muscular Dystrophy colorblindness

18 Updated April 2006Created by C. Ippolito April 2006 chromosome pairs do not separate properly –Nondisjunctionfailure separateproperly –Nondisjunction is the failure of chromosome pairs to separate properly. Chromosome Abnormalities

19 Updated April 2006Created by C. Ippolito April 2006 The failure to separate results in: extra chromosome –sex cells extra chromosome –or missing chromosome –sex cells missing chromosome Nondisjunction

20 Updated April 2006Created by C. Ippolito April 2006 Down Syndrome TrisomyTrisomy 21 –1:800 < 40 ♀ 1:90 > 40 ♀ –short stature; enlarged tongue –rounded head; eyefold –mental –mental retardation

21 Updated April 2006Created by C. Ippolito April 2006 Down Syndrome Karyotype

22 Updated April 2006Created by C. Ippolito April 2006 Cri du Chat Syndrome MonosomyMonosomy 5 (piece deleted) –moon face as infant –malformed larynx –eyefold –misshapen, low ears –severe –severe mental retardation

23 Updated April 2006Created by C. Ippolito April 2006 Fragile X Syndrome 1:1000 ♂ 1:2500 ♀ children –normal but hyperactive hyperactive or autistic adults: –short stature; long face –prominent jaw; large ears –stubby hands –♂ ’s more likely to be mentally deficient

24 Updated April 2006Created by C. Ippolito April 2006 4545, XO XO 1:6000 ♀ –short with broad chest –webbed neck –ovaries, oviduct, uterus small –no –no puberty puberty; no menstruation –most normal mentally Turner Syndrome

25 Updated April 2006Created by C. Ippolito April 2006 Turner Syndrome Karyotype

26 Updated April 2006Created by C. Ippolito April 2006 4747, XXY XXY 1:1500 ♂ –genitalia, testes, prostate small –no 2o 2o sex characteristics –some breast development –large hands, feet; long limbs –slow but no deficiency (XXXY) Klinefelter Syndrome

27 Updated April 2006Created by C. Ippolito April 2006 Klinefelter Karyotype

28 Updated April 2006Created by C. Ippolito April 2006 4747, XYY XYY 1:1000 ♂ –taller than normal –persistent acne –speech & reading problems –more aggressive due to size criminal –“criminal” syndrome Jacob Syndrome

29 Updated April 2006Created by C. Ippolito April 2006 Human Genetic Disorders

30 Updated April 2006Created by C. Ippolito April 2006 Achondroplasia Autosomal dominant allele Gene controlling fibroblast function –short stature, legs and arms short compared to trunk (body), prominent forehead, a protruding jaw, bowed legs Diagnosis –X-ray and clinical interview –Molecular testing can identify mutated gene (FGFR3) Treatment –monitor growth, check for apnea, surgical correction if walking difficult Genetic Counseling

31 Updated April 2006Created by C. Ippolito April 2006 Huntington’s Chorea Autosomal dominant allele –1:20,000 births Chronic neurological disease –slow destruction of brain cells. –uncontrolled motions –appears in middle age (40’s) –death within 10 to 20 years of onset Woody Guthrie - hobo poet and folk singer - “This Land is Your Land” No Cure; No treatment Gene has been identified and presence can be determined by blood test 30

32 Updated April 2006Created by C. Ippolito April 2006 Albinism Autosomal recessive allele Missing pigments –in skin, hair, and eyes –low vision due to abnormal retina Treatment –sunscreen protection and opaque clothing –vision aids Type I –missing enzyme to form pigment Type II –some pigment formed “P” gene defective

33 Updated April 2006Created by C. Ippolito April 2006 Cystic Fibrosis Autosomal recessive allele –1:20 Caucasians are carriers –occurs in 1:2,500 births bronchial mucus becomes very thick and viscous –Mucus sits in alveoli and bronchi –Daily manual message known as “cupping and clapping” used to loosen mucus. –Regular visits to hospital needed to “suction” lungs usually die before their 18th birthday –current treatment may extend life into 28 No cure but gene has been identified Genetic screening possible 32

34 Updated April 2006Created by C. Ippolito April 2006 Phenylketonuria (PKU) Autosomal recessive –1:5,000 No enzyme – to break down phenylalanine. –phenylketone build up which can harm developing brain cells. –mental retardation. Diagnosis - blood test at birth. Treatment –special diet low in phenylalanine until age 7. Adults –excess phenylalanine causes headaches 33

35 Updated April 2006Created by C. Ippolito April 2006 Tay Sachs Disease Autosomal recessive –high occurrence in American Jews - 1:1,000 births –higher occurrence in Ashkenazy Jews - 1:40 births Lipid buildup around nerve cells. –Normal until 4 months of age. –5th month - lethargy –8th month reactions and movements not normal –child becomes blind, deaf, has seizures, paralysis, and dies before 5th year. No cure, no treatment, no definite test for presence of gene Genetic Counseling - Carriers should not marry 34

36 Updated April 2006Created by C. Ippolito April 2006 Human Traits Pedigree Chart –a diagram that shows the relationships within a family a circle represents a female a square represents a male horizontal line connecting a circle to a square represents a marriage a filled-in circle or square shows that the individual has the trait vertical line(s) and brackets below that line show their child(ren)


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