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Review of what we know so far . Review of what we know so far . . .. .

Classical Genetics Classical Genetics (Mendelian Genetics)(Mendelian Genetics) Genes and allelesGenes and alleles Dominant v. RecessiveDominant v. Recessive Homozygous v. heterozygousHomozygous v. heterozygous Phenotype v. genotypePhenotype v. genotype Punnett square v. pedigreePunnett square v. pedigree Sexual reproduction basicsSexual reproduction basics

– Independent assortmentIndependent assortment– Law of segregation (due to meiosis)Law of segregation (due to meiosis)

Basic Monohybrid Basic Monohybrid Cross rules: (one trait)Cross rules: (one trait) When purebreeding organisms When purebreeding organisms

exhibiting the alternate forms of exhibiting the alternate forms of an allele mate, a predictable ratio an allele mate, a predictable ratio of offspring results: FF x ff (where of offspring results: FF x ff (where F is feathery wings) produces 4:1 F is feathery wings) produces 4:1 Ff and 4:1 feathery wings in F1Ff and 4:1 feathery wings in F1

F2 genotypic is 1FF:2Ff:1ff and 3 F2 genotypic is 1FF:2Ff:1ff and 3 feathery: 1 smooth wingfeathery: 1 smooth wing

Basic Dihybrid Cross Basic Dihybrid Cross rules: (two traits)rules: (two traits) When purebreeding organisms When purebreeding organisms

exhibiting the alternate forms of two exhibiting the alternate forms of two alleles mate, a predictable ratio of alleles mate, a predictable ratio of offspring results: FFPP x ffpp (where F is offspring results: FFPP x ffpp (where F is feathery wings and P is pink) produces feathery wings and P is pink) produces 4:1 FfPp and 4:1 feathery, pink wings in 4:1 FfPp and 4:1 feathery, pink wings in F1F1

F2 phenotypic ratio is 9:3:3:1 (9 for both F2 phenotypic ratio is 9:3:3:1 (9 for both dominant phenotypes, 3 dom/rec, 1 dominant phenotypes, 3 dom/rec, 1 recessive for both phenotypes)recessive for both phenotypes)

The Madness of King George The Madness of King George IIIIII Partly as a result of the erratic behavior of King George III Partly as a result of the erratic behavior of King George III the American colonies decided to break away from the the American colonies decided to break away from the United KingdomUnited Kingdom

Other members of King George’s family also exhibited Other members of King George’s family also exhibited strange behavior with dire consequences. These included strange behavior with dire consequences. These included Mary Queen of Scots and her son James I both of whom Mary Queen of Scots and her son James I both of whom were beheaded.were beheaded.

Because madness seems to have run in the family, it is Because madness seems to have run in the family, it is thought thought to have a genetic basisthought thought to have a genetic basis

Acute intermittent porphyria seems to be consistent with Acute intermittent porphyria seems to be consistent with the symptoms exhibited by George the symptoms exhibited by George

Human Heredity Is Not Human Heredity Is Not UniqueUnique The genes of humans behave in the same way as The genes of humans behave in the same way as

genes of other organismsgenes of other organisms Of the estimated 35,000 human genes, most are Of the estimated 35,000 human genes, most are

identical in all humansidentical in all humans The relatively small number of “polymorphic” genes The relatively small number of “polymorphic” genes

in humans account for only part of the variability that in humans account for only part of the variability that we see between humanswe see between humans

While each human (except for identical twins) has a While each human (except for identical twins) has a unique set of genetic information, variation between unique set of genetic information, variation between humans also results from differences in the humans also results from differences in the environmentenvironment

Politics and GeneticsPolitics and Genetics

Because we are talking about how Because we are talking about how humans are when we are talking about humans are when we are talking about human genetics, there can be lots of human genetics, there can be lots of controversy when traits are seen as controversy when traits are seen as relating to race, gender or other relating to race, gender or other sensitive issuessensitive issues

This is particularly true when we start This is particularly true when we start to talk about the genetics of behaviorto talk about the genetics of behavior

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits Having a bent little finger is a Having a bent little finger is a

dominant traitdominant trait

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits Many human genes are inherited as Many human genes are inherited as

dominant or recessive traits just like dominant or recessive traits just like the traits Mendel studied in peasthe traits Mendel studied in peas

Ear lobes provide an example of this:Ear lobes provide an example of this:

Attached ear lobes are inherited as a recessive trait.

Unattached ear lobes are inherited as a dominant trait.

White forelock -White forelock - A white patch of hair at the A white patch of hair at the front of the scalp.front of the scalp.

Specific Human TraitsSpecific Human Traits

PolygenesPolygenes

Thus eye color appears to vary on Thus eye color appears to vary on an almost continuous scale from an almost continuous scale from brown to green to gray to bluebrown to green to gray to blue

Eye color is determined by two Eye color is determined by two genes, one controls texture of the genes, one controls texture of the iris which refracts light to make iris which refracts light to make blue. A second determines relative blue. A second determines relative abundance of melanin. When a abundance of melanin. When a small amount of melanin is present, small amount of melanin is present, green eyes result while brown and green eyes result while brown and black eyes result from relatively black eyes result from relatively increasing amounts of melaninincreasing amounts of melanin

Eye color is determined by more Eye color is determined by more than one genethan one gene

Hair color is determined Hair color is determined by more than one geneby more than one gene

Thus hair color appears to Thus hair color appears to vary on an almost vary on an almost continuous scale from continuous scale from black to brown to blond to black to brown to blond to redred

The brown and black The brown and black pigment is melaninpigment is melanin

The red pigment is an iron The red pigment is an iron containing moleculecontaining molecule

Environmental aspectsEnvironmental aspects

Hair is Hair is multifactorialmultifactorial

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits AlbinismAlbinism - There are a number of different types of - There are a number of different types of

albinism, but each is characterized by an absence albinism, but each is characterized by an absence of pigment from the skin, eyes and hair. Albino of pigment from the skin, eyes and hair. Albino individuals typically have very pale white skin, light individuals typically have very pale white skin, light blue or pink eyes, and light blond or white hair. blue or pink eyes, and light blond or white hair. Albinism is a recessive trait.Albinism is a recessive trait.

Brown teeth -Brown teeth - Teeth have a brown color that is not Teeth have a brown color that is not the result of poor oral hygiene or antibiotics taken the result of poor oral hygiene or antibiotics taken as a child. White teeth are dominant.as a child. White teeth are dominant.

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits Cleft chin -Cleft chin - A noticeable indentation at the center A noticeable indentation at the center

of the chin. For examples think of Kirk Douglas of the chin. For examples think of Kirk Douglas and Michael Jackson (after plastic surgery). and Michael Jackson (after plastic surgery). Having a cleft chin is dominant to a smooth chin.Having a cleft chin is dominant to a smooth chin.

Double-jointed thumbs -Double-jointed thumbs - This is commonly called This is commonly called a hitchhiker's thumb. The thumb can bend back at a hitchhiker's thumb. The thumb can bend back at almost 90 degrees. Hitchhiker's thumb is a almost 90 degrees. Hitchhiker's thumb is a recessive trait, but it may vary in its expression.recessive trait, but it may vary in its expression.

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits Hand folding -Hand folding - When the hands are folded either the When the hands are folded either the

left or right thumb will be on top. Left thumb on top is left or right thumb will be on top. Left thumb on top is dominant.dominant.

Mid-digital hair -Mid-digital hair - Hair growing from the middle section Hair growing from the middle section of each finger. Hair presence is dominant.of each finger. Hair presence is dominant.

PTC tasting -PTC tasting - Phenylthiocarbamide (PTC) is a bitter Phenylthiocarbamide (PTC) is a bitter tasting chemical that cannot be tasted by some tasting chemical that cannot be tasted by some individuals. PTC tasters taste PTC as bitter, non-tasters individuals. PTC tasters taste PTC as bitter, non-tasters taste nothing when given PTC. Tasting is dominant to taste nothing when given PTC. Tasting is dominant to the inability to taste PTC.the inability to taste PTC.

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits

Tongue rolling -Tongue rolling - Tongue rolling is the ability Tongue rolling is the ability to form a tube with your tongue. Rolling is to form a tube with your tongue. Rolling is dominant.dominant.

Widow's peak -Widow's peak - A sharp point in the hairline A sharp point in the hairline that points toward the nose. Having a that points toward the nose. Having a widow's peak is dominant to a smooth widow's peak is dominant to a smooth hairline.hairline.

Sex Influenced Human Sex Influenced Human TraitsTraits

BaldnessBaldness - Loss of hair from the scalp following - Loss of hair from the scalp following puberty. A sex influenced trait that is most puberty. A sex influenced trait that is most commonly fully expressed (as a dominant trait) in commonly fully expressed (as a dominant trait) in males, but carried on an autosomemales, but carried on an autosome

Index finger shorter than ring finger -Index finger shorter than ring finger - The index The index finger (next to your thumb) is longer than the ring finger (next to your thumb) is longer than the ring finger (next to your little finger). Check the class finger (next to your little finger). Check the class data to see if the frequency is different for the data to see if the frequency is different for the different sexes.different sexes.

Sex Linked Human Sex Linked Human TraitsTraits

Color blindness -Color blindness - Inability to distinguish Inability to distinguish between colors of the same intensity. There may between colors of the same intensity. There may be two types, red green color blindness in which be two types, red green color blindness in which individuals perceive red and green as the same individuals perceive red and green as the same color, and complete color blindness in which all color, and complete color blindness in which all colors are perceived as being the same and colors are perceived as being the same and vision is the functional equivalent of black and vision is the functional equivalent of black and white television. Both types of colorblindness white television. Both types of colorblindness are sex linked traits.are sex linked traits.

Dimples -Dimples - Round indentations in the cheeks when Round indentations in the cheeks when smiling, not lines or clefts.smiling, not lines or clefts.

Freckles -Freckles - Small patches of darker pigmented skin Small patches of darker pigmented skin on various parts of the body and most visible in those on various parts of the body and most visible in those areas commonly exposed to the sun. These may be areas commonly exposed to the sun. These may be present on both dark and light skinned individuals.present on both dark and light skinned individuals.

Hair whorling -Hair whorling - These may be referred to as These may be referred to as cowlicks. Areas in which hair grows from your scalp cowlicks. Areas in which hair grows from your scalp in a whorl instead of in a given direction.in a whorl instead of in a given direction.

Specific Human TraitsSpecific Human Traits

Myopia -Myopia - Short sightedness, the inability to see far Short sightedness, the inability to see far off objects without correction by glasses or contactsoff objects without correction by glasses or contacts

Polydactyly -Polydactyly - Having more than five digits on each Having more than five digits on each hand and foot.hand and foot.

S-methyl thioester smeller -S-methyl thioester smeller - S-methyl thioesters S-methyl thioesters are produced in the urine after consumption of are produced in the urine after consumption of asparagus. Some individuals cannot smell this asparagus. Some individuals cannot smell this substance. If you smell a strong odor on urination substance. If you smell a strong odor on urination after eating at least 5 asparagas spears, you are an after eating at least 5 asparagas spears, you are an S-methyl thioester smeller.S-methyl thioester smeller.

Specific Human TraitsSpecific Human Traits

Pedigree symbols

Female

Male

Gender unknown

Deceased

3

n

P

Stillborn

Spontaneous abortion/Miscarriage

Termination of pregnancy elective reasons

Termination of pregnancy genetic/affected condition

SB

Affected individual

Proband• 1st person in family to

come to medical/genetic attention

Obligate carrier

Infertility

Constructing the Pedigree

Relationship or marriage

Break in relationship

Consanguineous relationship

Monozygotic twins• (Identical)

Dizygotic twins• (Fraternal)

Adoption into a family

Adoption out of a family

Include below gender symbol name, maiden name if married & birthdate or age

Generations are symbolized by Roman numerals

Should give current date on pedigree

John Smith

10-1-49

I.

Current date:

08-31-06

Other Abbreviations

d. 79y

dx. 41y

Died at 79 years of age

Diagnosed at 41 years of age

Siblings are drawn left to right in birth order

I.

II.

III.

Rules of Thumb

Always include a key At least 3 generations Use birth dates or ages Sign and date Include ancestry with oldest generations

Causes of death or health problems should be noted on the pedigree or explained by a key

Key Hypertension

Breast cancer

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Autosomal Dominant Inheritance

Each affected individual has one affected parent

Males and females may be affected Pattern of inheritance is vertical (passed

from generation to generation)

Autosomal Dominant Inheritance

I.

II.

III.

1 2 3 4 5 6 7 8 9 10

1 2

I

1 2 3 4 5 6

II

III

Dominant Autosomal Pedigree

Autosomal Recessive Inhertance Do not need a parent who is affected;

each parent must be a carrier of the recessive gene

Males and females may be affected Pattern of inheritance is horizontal

(usually seen in siblings) Offspring of parent with the condition

are obligate carriers

Autosomal Recessive Inheritance

I.

II.

III.

Recessive Autosomal Recessive Autosomal PedigreePedigree

X-Linked Inhertance

Gene is located on X chromosome Female is usually clinically normal and

disorders are typically seen more often in males than females

Absence of male-to-male transmission

X-Linked InheritanceI.

II.

III.