Chapter 11 Complex Inheritance and Human Heredity

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Chapter 11 Complex Chapter 11 Complex Inheritance and Human Inheritance and Human

HeredityHeredity

11.1 Basic Patterns of Human 11.1 Basic Patterns of Human InheritanceInheritance

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Recessive Genetic DisordersRecessive Genetic Disorders Mendel’s work went unnoticed by the Mendel’s work went unnoticed by the

scientific community for about 30 years then scientific community for about 30 years then it was rediscovered in the early 1900s.it was rediscovered in the early 1900s.

At that time many scientists were interested At that time many scientists were interested in the cause of diseases and noticed that in the cause of diseases and noticed that some diseases “ran in families”.some diseases “ran in families”.

Alkaptonuria was the first identified Alkaptonuria was the first identified (recessive) genetic disorder. Alkaptonuria, (recessive) genetic disorder. Alkaptonuria, from an enzyme deficiency, causes black from an enzyme deficiency, causes black acidic urine and later in life affects bones acidic urine and later in life affects bones and joints.and joints.

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Recessive Genetic DisordersRecessive Genetic Disorders A recessive trait is

expressed when the individual is homozygous recessive for the trait.

Both parents would need to have at least one recessive allele.

Usually the parents are heterozygous (carriers) for the disorder.

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Cystic Fibrosis

Affects the mucus-producing glands, digestive enzymes, and sweat glands

Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.

Without sufficient chloride ions in the cells, a thick mucus is secreted

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Cystic Fibrosis

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Cystic Fibrosis

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Albinism Caused by altered genes, resulting in

the absence of the skin pigment melanin in hair and eyes

White hair. Very pale skin Pink pupils

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Albinism

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Tay-Sachs Disease

Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides

Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

Death by age 2Death by age 2

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Dominant Genetic DisordersDominant Genetic Disorders

99.9% of population is homozygous recessive for achondroplasia

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Huntington’s DiseaseHuntington’s Disease Affects the nervous Affects the nervous

systemsystem Latent disorder Latent disorder

affects age 30 to 50affects age 30 to 50 Gradual loss of Gradual loss of

brain function brain function (“holes” in brain)(“holes” in brain)

Genetic test Genetic test availableavailable

Result of allele Result of allele mutation at tip of mutation at tip of chromosome #4chromosome #4

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AchondroplasiaAchondroplasia

Most common form Most common form of dwarfismof dwarfism

75% of individuals 75% of individuals born to parents of born to parents of average size, result average size, result of new mutationof new mutation

Lethal spontaneous Lethal spontaneous abortion in abortion in homozygous homozygous dominant genotypedominant genotype

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Pedigree AnalysisPedigree Analysis

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Pedigree AnalysisPedigree Analysis Are femalesAre females

Are malesAre males Shaded in circles and Shaded in circles and

squares are affected squares are affected individualsindividuals

Roman Numerals (Roman Numerals (I – I – IVIV) are generations) are generations

Lines across Lines across represent represent

matingmating Lines down Lines down

represent offspringrepresent offspring

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Pedigree AnalysisPedigree Analysis Count the number of Count the number of

affected males and affected males and affected females. If most affected females. If most males and few or no males and few or no females most likely sex females most likely sex linked trait.linked trait.

Look at the affected Look at the affected individuals. If every individuals. If every individual with the trait individual with the trait has a parent with the has a parent with the trait then this trait is trait then this trait is dominant. If non-dominant. If non-affected parents produce affected parents produce an offspring with the trait an offspring with the trait then it is recessive.then it is recessive.

Determine the phenotype Determine the phenotype and genotype of every and genotype of every individualindividual

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Pedigree AnalysisPedigree Analysis Count the number of Count the number of

affected males and affected males and affected females. If most affected females. If most males and few or no males and few or no females most likely sex females most likely sex linked trait.linked trait.

Look at the affected Look at the affected individuals. If every individuals. If every individual with the trait individual with the trait has a parent with the has a parent with the trait then this trait is trait then this trait is dominant. If non-dominant. If non-affected parents produce affected parents produce an offspring with the trait an offspring with the trait then it is recessive.then it is recessive.

Determine the phenotype Determine the phenotype and genotype of every and genotype of every individualindividual

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Pedigree AnalysisPedigree Analysis Affected males: 1 Affected males: 1 Affected females: 2 (not Affected females: 2 (not

sex linked)sex linked) No affected individual No affected individual

has parent with the trait, has parent with the trait, means recessivemeans recessive

All affected individuals All affected individuals would be homozygous would be homozygous recessive, aarecessive, aa

All parents of affected All parents of affected individuals would be individuals would be heterozygous, Aaheterozygous, Aa

Siblings of affected Siblings of affected individuals would be individuals would be heterozygous (Aa) or heterozygous (Aa) or homozygous dominant homozygous dominant (AA)(AA)

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Pedigree AnalysisPedigree Analysis

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HeredityHeredity

11.2 Complex Patterns of 11.2 Complex Patterns of InheritanceInheritance

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Incomplete DominanceIncomplete Dominance

Many scientists repeated Mendel’s Many scientists repeated Mendel’s work expecting to get similar results work expecting to get similar results with different species. Carl Correns with different species. Carl Correns crossed white snapdragons with red crossed white snapdragons with red snapdragonssnapdragons

According to Mendelian genetics, According to Mendelian genetics, results would have yielded 100% results would have yielded 100% dominant phenotype (red or white)dominant phenotype (red or white)

Correns found 100% pinkCorrens found 100% pink

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Incomplete DominanceIncomplete Dominance

Incomplete Dominance is the appearance of Incomplete Dominance is the appearance of an intermediate phenotype an intermediate phenotype

Both alleles are expressed producing both Both alleles are expressed producing both the red and white proteins which gives the the red and white proteins which gives the appearance of pinkappearance of pink

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CodominanceCodominance

Both phenotypes of Both phenotypes of the two the two homozygotes are homozygotes are expressedexpressed

See red and white See red and white (not pink)(not pink)

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Both phenotypes of Both phenotypes of the two the two homozygotes are homozygotes are expressedexpressed

See red hairs and See red hairs and white hairs (not white hairs (not pink)pink)

Roan Cattle

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CodominanceCodominance Sickle cell disease Sickle cell disease

most common most common genetic disorder in genetic disorder in African Americans (1 African Americans (1 in 400).in 400).

In heterozygous In heterozygous condition both normal condition both normal (round) and sickle red (round) and sickle red blood cells are blood cells are producedproduced

Few disease Few disease symptoms in symptoms in heterozygous heterozygous individualindividual

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Sickle cells do not Sickle cells do not effectively carry effectively carry oxygen, cause oxygen, cause blockage in blood blockage in blood vessels, pain and vessels, pain and fatigue.fatigue.

Heterozygous Heterozygous condition protects condition protects against malaria against malaria (see p.303)(see p.303)

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Multiple AllelesMultiple Alleles More than two allelesMore than two alleles Human blood groups Human blood groups

have three alleles: ABOhave three alleles: ABO Blood Types: GenotypesBlood Types: Genotypes

A: IA: IA A IIA A oror IIAAiiB: IB: IB B IIB B oror IIBBiiAB: IAB: IA A IIB B

O: iiO: ii

Both IBoth IAA and I and IBB are dominant are dominant to i and are codominant to i and are codominant to each otherto each other

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Multiple AllelesMultiple Alleles

Multiple alleles can demonstrate a hierarchy of dominance.

In rabbits, four alleles code for coat color: C, cch, ch, and c.§ C is dominant to cch, ch, and c.§ cch is dominant to ch and c.§ ch is dominant to c.§ c is recessive to all

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Light gray

Dark gray Himalayan

Albino

Chinchilla

Multiple AllelesMultiple Alleles

?

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Variety is the result of one allele hiding the effects of another allele.

No dark pigment present in fur Dark pigment present in fur

eebb

eeB_ E_bb E_B_

EpistasisEpistasis

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Sex chromosomes determine an individual’s gender.

Human males are XY; females XX

Autosomes are the nonsex chromosomes

Humans have 22 pairs of autosomes

Sex DeterminationSex Determination

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Dosage CompensationDosage Compensation

The X chromosome is more than three The X chromosome is more than three times larger than the Y chromosome; times larger than the Y chromosome; has more than three times more has more than three times more informationinformation

Females (XX) have two copies of this Females (XX) have two copies of this information while males (XY) have only information while males (XY) have only one copy of the X chromosomeone copy of the X chromosome

In females one of the X chromosomes In females one of the X chromosomes stops working; which X is a random stops working; which X is a random event and becomes a Barr Bodyevent and becomes a Barr Body

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Dosage CompensationDosage Compensation Barr bodies form Barr bodies form

from the inactivated from the inactivated “extra” X “extra” X chromosome in chromosome in femalesfemales

Colors of the calico Colors of the calico cat are caused by cat are caused by the random the random inactivation of a inactivation of a particular X particular X chromosome (orange chromosome (orange on one X and black on one X and black on the other X on the other X chromosome) chromosome)

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Sex-Linked TraitsSex-Linked Traits

The X and Y chromosomes are not The X and Y chromosomes are not homologous (do not pair: carry homologous (do not pair: carry different information) different information)

Males only have one X chromosome; Males only have one X chromosome; only one allele for each trait; only only one allele for each trait; only need one recessive to show the traitneed one recessive to show the trait

Males show the sex linked traits Males show the sex linked traits much more often than femalesmuch more often than females

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Red Green Color Red Green Color BlindnessBlindness

8% of United States 8% of United States males affectedmales affected

Red and green colors Red and green colors look like shades of look like shades of brownbrown

Are you color blind?Are you color blind?

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Hemophilia is Hemophilia is characterized by characterized by delayed blood delayed blood clotting.clotting.– Common in Royal Common in Royal

Families of Europe Families of Europe due to due to intermarriageintermarriage

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Polygenic TraitsPolygenic Traits

Poly = many; genic = genesPoly = many; genic = genes Many genes needed to determine a traitMany genes needed to determine a trait Most human traits are polygenicMost human traits are polygenic

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Environmental InfluencesEnvironmental Influences

Environment has an influence on Environment has an influence on phenotypephenotype

Sunlight: without enough sunlight Sunlight: without enough sunlight most flowering plants do not bear most flowering plants do not bear flowersflowers

Water: many plants lose their leaves Water: many plants lose their leaves in response to lack of water.in response to lack of water.

others: diet, exerciseothers: diet, exercise

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Environmental InfluencesEnvironmental Influences

Temperature: Temperature: Siamese cat’s tail, Siamese cat’s tail, feet, ears and nose feet, ears and nose are dark in are dark in response to cooler response to cooler temperatures; the temperatures; the black pigment black pigment production is production is responsive to responsive to temperaturetemperature

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Helps scientists separate genetic contributions from environmental contributions

Traits that appear frequently in identical twins are at least partially controlled by heredity.

Traits expressed differently in identical twins are strongly influenced by environment.

Interesting information from identical twins separated at birth in Minnesota Twin Studies

Twin StudiesTwin Studies

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HeredityHeredity

11.3 Chromosomes and 11.3 Chromosomes and Human HeredityHuman Heredity

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Karyotype StudiesKaryotype Studies

Karyotype is a micrograph (picture) of Karyotype is a micrograph (picture) of chromosomes at metaphase arranged by chromosomes at metaphase arranged by size in homologous pairs. size in homologous pairs.

Twenty-two pairs of autosomes are the Twenty-two pairs of autosomes are the same for males and females.same for males and females.

Males have one X chromosome and one Y Males have one X chromosome and one Y chromosome (not paired) and females chromosome (not paired) and females have two X chromosomes (paired).have two X chromosomes (paired).

Karyotypes are useful for detecting Karyotypes are useful for detecting chromosome abnormalitieschromosome abnormalities

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Karyotype StudiesKaryotype Studies

Chromosome smear

Karyotype

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TelomeresTelomeres

Telomeres protective Telomeres protective end caps on the end caps on the chromosomes made of chromosomes made of DNA and proteins.DNA and proteins.

Short repetitive Short repetitive nonessential DNA nonessential DNA sequencessequences

Prevent one Prevent one chromosome form chromosome form binding to another binding to another chromosome (not chromosome (not sticky)sticky)

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TelomeresTelomeres Absolutely essential for Absolutely essential for

chromosome functionchromosome function Telomeres decrease in Telomeres decrease in

size (length) as an size (length) as an organism ages and organism ages and may play a role in may play a role in aging and cancer.aging and cancer.

Cancer cells have Cancer cells have increased length of increased length of telomeres compared to telomeres compared to adult cells.adult cells.

Telomere function is Telomere function is an intense field of an intense field of researchresearch

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NondisjunctionNondisjunction

Failure of chromosomes to separate Failure of chromosomes to separate during cell divisionduring cell division

Results in one cell getting too many Results in one cell getting too many chromosomes and one cell not getting chromosomes and one cell not getting enough.enough.

If nondisjunction occurs during If nondisjunction occurs during meiosis the resulting gametes could meiosis the resulting gametes could form an organism with every cell form an organism with every cell having an incorrect chromosome having an incorrect chromosome number.number.

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Down SyndromeDown Syndrome

Results of parental gamete Results of parental gamete nondisjunction resulting in trisomy (three nondisjunction resulting in trisomy (three chromosomes ) of chromosome #21.chromosomes ) of chromosome #21.

Symptoms include: mental retardation, Symptoms include: mental retardation, distinctive facial features, short stature, distinctive facial features, short stature, heart defects, sexually underdeveloped, heart defects, sexually underdeveloped, sterile, more likely to develop leukemia sterile, more likely to develop leukemia and Alzheimer's, shorter life spanand Alzheimer's, shorter life span

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Down SyndromeDown Syndrome

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Down SyndromeDown Syndrome Incidence of Down Incidence of Down

Syndrome increases Syndrome increases with increasing age with increasing age of the motherof the mother

Risk increases to Risk increases to 6% for mothers over 6% for mothers over age 45age 45

Recommended fetal Recommended fetal testing for mother’s testing for mother’s age 35 and olderage 35 and older

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Other TrisomysOther Trisomys

Patau syndrome: trisomy 13; 1/5000; Patau syndrome: trisomy 13; 1/5000; serious eye, brain and circulatory serious eye, brain and circulatory problems; lifespan less than 1 yearproblems; lifespan less than 1 year

Edward’s syndrome: trisomy 18; Edward’s syndrome: trisomy 18; 1/10,000; effects every body organ; 1/10,000; effects every body organ; lifespan less than 1 yearlifespan less than 1 year

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Nondisjunction of Sex Nondisjunction of Sex Chromosomes MaleChromosomes Male

Klinefelter syndrome: (XXY); 1/2000; Klinefelter syndrome: (XXY); 1/2000; males sex organs, testes abnormally males sex organs, testes abnormally small; sterile; feminine body small; sterile; feminine body characteristics (breast enlargement, characteristics (breast enlargement, fat deposition); normal intelligencefat deposition); normal intelligence

(XYY); taller than average male; not (XYY); taller than average male; not characterized by a “syndrome”; characterized by a “syndrome”; some suggest increased aggressionsome suggest increased aggression

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Nondisjunction of Sex Nondisjunction of Sex Chromosomes FemaleChromosomes Female

(XXX): 1/1000; normal due to X (XXX): 1/1000; normal due to X inactivitation; only distinguishable by inactivitation; only distinguishable by karyotypekaryotype

Turner syndrome Monosomy X (XO): Turner syndrome Monosomy X (XO): 1/5000; female with no maturation of 1/5000; female with no maturation of sex organs; no secondary sex sex organs; no secondary sex characteristics; short; sterile; normal characteristics; short; sterile; normal intelligence with spatial learning intelligence with spatial learning disabilitiesdisabilities

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Fetal TestingFetal Testing

AmniocentesisAmniocentesis: : removal amniotic removal amniotic fluid with sloughed fluid with sloughed fetal cells at 14fetal cells at 14thth - -1616thth week; for week; for diagnosis of diagnosis of chromosomal chromosomal abnormalities; 1% abnormalities; 1% risk of risk of complicationscomplications

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Chorionic villus Chorionic villus samplingsampling: removal : removal of placental sample of placental sample at 8at 8thth -10 -10thth week; week; quicker results; quicker results; less accurate; less less accurate; less than 1% risk of than 1% risk of complicationscomplications

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Fetal blood Fetal blood samplingsampling: sample of : sample of fetal blood; can fetal blood; can detect increased detect increased number of genetic number of genetic abnormalities; abnormalities; medication can be medication can be given to fetus given to fetus before birth; before birth; greater risk to fetusgreater risk to fetus

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Chapter 11 Complex Inheritance and Human Heredity