PATTERNS OF PATTERNS OF INHERITANCE AND INHERITANCE AND HUMAN GENETICSHUMAN GENETICS

BY BY

DAWN M. THOMPSONDAWN M. THOMPSON

SIMPLE RECESSIVE SIMPLE RECESSIVE INHERITANCEINHERITANCE

► CYSTIC FIBROSIS:CFCYSTIC FIBROSIS:CF

1.1. Common in white Americans 1:2000Common in white Americans 1:2000

2.2. Caused by defective protein in plasma Caused by defective protein in plasma membrane.membrane.

3.3. Mucus accumulates in lungs and digestive tract.Mucus accumulates in lungs and digestive tract.

4.4. Controlled by physical therapy, diet, drug Controlled by physical therapy, diet, drug therapytherapy

5.5. Life expectancy improving annuallyLife expectancy improving annually

6.6. Person must have 2 recessive alleles to suffer Person must have 2 recessive alleles to suffer from CF. 1 allele carrier but shows from CF. 1 allele carrier but shows nono symptomssymptoms

PKUPKU►PhenylketouriaPhenylketouria►Caused by the absence of an enzyme Caused by the absence of an enzyme

that converts the amino acid that converts the amino acid phenylalanine to tyrosine.phenylalanine to tyrosine.

►Accumulation of phenylalanine leads to Accumulation of phenylalanine leads to mental retardation and CNS damagemental retardation and CNS damage

►Newborns are given a blood test to Newborns are given a blood test to check for the absence of the enzymecheck for the absence of the enzyme

►Milk products are high in phenylalanineMilk products are high in phenylalanine►Disorder is treatable by controlling diet Disorder is treatable by controlling diet

from birthfrom birth

OTHER RECESSIVE TRAITSOTHER RECESSIVE TRAITS

► TAY-SACHSTAY-SACHS► ATTACHED EAR LOBESATTACHED EAR LOBES

DO PROBLEM SOLVING LAB 12.1 p317DO PROBLEM SOLVING LAB 12.1 p317

SIMPLE DOMINANT TRAITSSIMPLE DOMINANT TRAITS

► HUNTINGTON’S DISEASE:HUNTINGTON’S DISEASE:1.1. Lethal disorder, no treatmentLethal disorder, no treatment2.2. Certain areas of the brain breakdownCertain areas of the brain breakdown3.3. Symptoms; neurological and muscular Symptoms; neurological and muscular

show at the age of 30+ show at the age of 30+ 4.4. Genetic testing is available before Genetic testing is available before

symptoms showsymptoms show5.5. Ethical issues Ethical issues 6.6. Every child of an affected person has a Every child of an affected person has a

50/50 chance of inheriting the disease50/50 chance of inheriting the disease7.7. Only 1 defective allelle required for person Only 1 defective allelle required for person

to show diseaseto show disease

OTHER DOMINANT TRAITSOTHER DOMINANT TRAITS

1.1. Unattached ear lobesUnattached ear lobes2.2. Tongue rollingTongue rolling3.3. Hapsburg lipHapsburg lip4.4. Hitchhiker’s thumbHitchhiker’s thumb5.5. Hairy fingersHairy fingers6.6. Almond shaped eyesAlmond shaped eyes7.7. Thick lipsThick lips8.8. Widow’s peakWidow’s peak

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE►Heterozygous phenotype is intermediate Heterozygous phenotype is intermediate

between those of the two homozygotesbetween those of the two homozygotes► Red flower x white flowerRed flower x white flower► Intermediate phenotype is pinkIntermediate phenotype is pink

R’ R’

R

R

R’R R’R

R’R R’R

F1

RR R’R

R’R

R’R’

R R’

R

R’

F2

CODOMINANCECODOMINANCE

► CODOMINANT ALLELES CAUSE THE PHENOTYPE OF CODOMINANT ALLELES CAUSE THE PHENOTYPE OF BOTH HOMOZYGOTES TO BE PRODUCED IN THE BOTH HOMOZYGOTES TO BE PRODUCED IN THE HETEROZYGOTE INDIVIDUALS. BOTH ALLELES ARE HETEROZYGOTE INDIVIDUALS. BOTH ALLELES ARE EXPRESSED EQUALLYEXPRESSED EQUALLY

B W

B

W

BB BW

BW WW

B = black feathers in chickens

W = white feathers in chickens

BB = black chicken

BW = checkered chicken

WW = white chicken

CODOMINANT TRAITSCODOMINANT TRAITS

► SICKLE-CELL ANEMIASICKLE-CELL ANEMIA

1.1. Common among African Americans 1:12Common among African Americans 1:12

2.2. Homozygous people for trait differ by 1 Homozygous people for trait differ by 1 amino acid coding for hemoglobin compared amino acid coding for hemoglobin compared to normal peopleto normal people

3.3. Abnormal hemoglobin is sickle celledAbnormal hemoglobin is sickle celled

4.4. Sickle shaped cells block blood vessels Sickle shaped cells block blood vessels reducing the amount of oxygen reaching the reducing the amount of oxygen reaching the tissuestissues

5.5. Shortened life spanShortened life span

HETEROZYGOUS ADVANTAGEHETEROZYGOUS ADVANTAGE

►People who are heterozygote for the People who are heterozygote for the trait produce both normal and trait produce both normal and abnormal hemoglobinabnormal hemoglobin

►Show no symptoms of sickle- cell Show no symptoms of sickle- cell anemiaanemia

►Less likely to suffer from malaria Less likely to suffer from malaria ►This explains why African’s suffer more This explains why African’s suffer more

from sickle-cell anemiafrom sickle-cell anemia

MULTIPLE PHENOTYPES FROM MULTIPLE PHENOTYPES FROM MULTIPLE ALLELESMULTIPLE ALLELES

►Traits controlled by more than two Traits controlled by more than two alleles have multiple allelesalleles have multiple alleles

BLOOD GROUPSBLOOD GROUPS

►ABO blood groupABO blood group►Single gene I has 3 different allelesSingle gene I has 3 different alleles►Blood type A Blood type A genotype Igenotype IAA I IAA I IAA i i►Blood type BBlood type B genotype I genotype IBB I IBB I IBB i i►Blood type ABBlood type AB genotype Igenotype IAA I IB (codominant)B (codominant)

►Blood type OBlood type O genotype ii genotype ii (recessive)(recessive)

► Important in blood transfusions and Important in blood transfusions and paternity suits paternity suits

►Refer to ABO blood group information Refer to ABO blood group information page 325 page 325

SEX DETERMINATIONSEX DETERMINATION

► Autosomes 22 pairs of homologous Autosomes 22 pairs of homologous chromosomeschromosomes

► 23 rd pair of chromosomes are sex 23 rd pair of chromosomes are sex chromosomes X and Ychromosomes X and Y

► Female XX chromosomesFemale XX chromosomes► Male XY chromosomesMale XY chromosomes► Gametes carry either an X or Y chromosomeGametes carry either an X or Y chromosome► Fertilization results in offspring having either Fertilization results in offspring having either

XX or XY chromosomesXX or XY chromosomes► There is a 50:50 chance of producing a male There is a 50:50 chance of producing a male

or female each time an offspring is produced.or female each time an offspring is produced.

SEX-LINKED INHERTANCESEX-LINKED INHERTANCE

►Experiments conducted by MorganExperiments conducted by Morgan►Worked with Drosophila (fruit flies)Worked with Drosophila (fruit flies)►Easy to keep: feed on banana, live in a Easy to keep: feed on banana, live in a

vial, reproduce in a few days, produce vial, reproduce in a few days, produce large numbers of offspring.large numbers of offspring.

►Observed males had white eyes more Observed males had white eyes more often than femalesoften than females

►Suggested gene for eye color was Suggested gene for eye color was carried on the X chromosome and Y carried on the X chromosome and Y chromosome has no corresponding chromosome has no corresponding gene for eye colorgene for eye color

INHERITANCE OF EYE COLOR IN INHERITANCE OF EYE COLOR IN DROSOPHILADROSOPHILA

COLOR BLINDNESSCOLOR BLINDNESS

►X-linked disorderX-linked disorder► Inability to differentiate between two Inability to differentiate between two

colors such as red and greencolors such as red and green►Males are more susceptible because Males are more susceptible because

they have to inherit 1 defective X they have to inherit 1 defective X chromosome to suffer from the disorder chromosome to suffer from the disorder females needed to inherit 2 defective females needed to inherit 2 defective chromosomes.chromosomes.

►Most serious problem is the inability to Most serious problem is the inability to detect traffic light colorsdetect traffic light colors

HEMOPHILIAHEMOPHILIA

► X-linked disorderX-linked disorder► Caused by a lack of factor VIII a blood Caused by a lack of factor VIII a blood

clotting enzymeclotting enzyme► Inability to clot the bloodInability to clot the blood► 1:10,000 males 1:100million females 1:10,000 males 1:100million females ►Males are more susceptible because they Males are more susceptible because they

have to inherit 1 defective X chromosome to have to inherit 1 defective X chromosome to suffer from the disorder females needed to suffer from the disorder females needed to inherit 2 defective chromosomes.inherit 2 defective chromosomes.

► Treated by blood transfusions and injections Treated by blood transfusions and injections of factor VIII.of factor VIII.

► Treatments are expensive and some people Treatments are expensive and some people have contracted AIDS.have contracted AIDS.

POLYGENTIC INHERITANCEPOLYGENTIC INHERITANCE

►A trait is controlled by two or more A trait is controlled by two or more genes.genes.

► Inheritance of eye color, height, stem Inheritance of eye color, height, stem length, skin color.length, skin color.

►Bell shaped curve.Bell shaped curve.

ENVIRONMENTAL ENVIRONMENTAL INFLUENCESINFLUENCES

► Factors that determine how genes or Factors that determine how genes or expressed in an organism.expressed in an organism.

► External environmental: temperature, light, External environmental: temperature, light, chemicals, and infectious agents influence chemicals, and infectious agents influence gene expression. Temperature determines gene expression. Temperature determines coat color of artic foxescoat color of artic foxes

► Internal environmental: males and females Internal environmental: males and females differ because of differences in hormones differ because of differences in hormones and structures. Horn size in males greater and structures. Horn size in males greater than females.than females.

►Male pattern baldness and feather color in Male pattern baldness and feather color in peacocks is influenced by different peacocks is influenced by different hormones in different sexeshormones in different sexes

ENVIRONMENTAL ENVIRONMENTAL INFLUENCESINFLUENCES

CHANGES IN CHROMOSOME CHANGES IN CHROMOSOME NUMBERSNUMBERS

►Nondisjunction: paired chromosomes fail to Nondisjunction: paired chromosomes fail to separate properly during meiosisseparate properly during meiosis

► TRISOMY: 47 chromosomesTRISOMY: 47 chromosomes►Down’s syndrome: chromosome 21 3 copies Down’s syndrome: chromosome 21 3 copies

inside of 2. Mental retardation etc, higher inside of 2. Mental retardation etc, higher incidence in women over 40.incidence in women over 40.

► Klinfelter’s syndrome: males, extra X or Y Klinfelter’s syndrome: males, extra X or Y chromosome.chromosome.

►MONOSOMY: 45 chromosomesMONOSOMY: 45 chromosomes► Turner’s syndrome: females, missing X Turner’s syndrome: females, missing X

chromosome, mental retardation, sterile.chromosome, mental retardation, sterile.

KARYOTYPEKARYOTYPE

►Chart of chromosome pairs used to Chart of chromosome pairs used to evaluate unusual chromosome evaluate unusual chromosome numbers in cells.numbers in cells.

►Amniocentesis is the procedure by Amniocentesis is the procedure by which the cell are collected for which the cell are collected for analysis and production of the analysis and production of the karyotype.karyotype.