Review of what we know so far . . . You are Here Review of what we know so far . . .

Classical Genetics (Mendelian Genetics) Genes and alleles Dominant v. Recessive Homozygous v. heterozygous Phenotype v. genotype Punnett square v. pedigree Sexual reproduction basics Independent assortment Law of segregation (due to meiosis)

Basic Monohybrid Cross rules: (one trait) When purebreeding organisms exhibiting the alternate forms of an allele mate, a predictable ratio of offspring results: FF x ff (where F is feathery wings) produces 4:1 Ff and 4:1 feathery wings in F1 F2 genotypic is 1FF:2Ff:1ff and 3 feathery: 1 smooth wing

Basic Dihybrid Cross rules: (two traits) When purebreeding organisms exhibiting the alternate forms of two alleles mate, a predictable ratio of offspring results: FFPP x ffpp (where F is feathery wings and P is pink) produces 4:1 FfPp and 4:1 feathery, pink wings in F1 F2 phenotypic ratio is 9:3:3:1 (9 for both dominant phenotypes, 3 dom/rec, 1 recessive for both phenotypes)

The Madness 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 United Kingdom Other members of King George’s family also exhibited strange behavior with dire consequences. These included Mary Queen of Scots and her son James I both of whom were beheaded. Because madness seems to have run in the family, it is thought thought to have a genetic basis Acute intermittent porphyria seems to be consistent with the symptoms exhibited by George

Human Heredity Is Not Unique The genes of humans behave in the same way as genes of other organisms Of the estimated 35,000 human genes, most are identical in all humans The relatively small number of “polymorphic” genes in humans account for only part of the variability that we see between humans While each human (except for identical twins) has a unique set of genetic information, variation between humans also results from differences in the environment

Politics and Genetics Because we are talking about how humans are when we are talking about human genetics, there can be lots of controversy when traits are seen as relating to race, gender or other sensitive issues This is particularly true when we start to talk about the genetics of behavior

Simple Dominant/Recessive Traits Having a bent little finger is a dominant trait

Simple Dominant/Recessive Traits Many human genes are inherited as dominant or recessive traits just like the traits Mendel studied in peas Ear lobes provide an example of this: Unattached ear lobes are inherited as a dominant trait. Attached ear lobes are inherited as a recessive trait.

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

Polygenes Eye color is determined by more than one gene Thus eye color appears to vary on an almost continuous scale from brown to green to gray to blue Eye color is determined by two genes, one controls texture of the iris which refracts light to make blue. A second determines relative abundance of melanin. When a small amount of melanin is present, green eyes result while brown and black eyes result from relatively increasing amounts of melanin

Hair is multifactorial Hair color is determined by more than one gene Thus hair color appears to vary on an almost continuous scale from black to brown to blond to red The brown and black pigment is melanin The red pigment is an iron containing molecule Environmental aspects

Dominant/Recessive Human Traits Albinism - There are a number of different types of albinism, but each is characterized by an absence of pigment from the skin, eyes and hair. Albino individuals typically have very pale white skin, light blue or pink eyes, and light blond or white hair. Albinism is a recessive trait. Brown teeth - Teeth have a brown color that is not the result of poor oral hygiene or antibiotics taken as a child. White teeth are dominant.

Dominant/Recessive Human Traits Cleft chin - A noticeable indentation at the center of the chin. For examples think of Kirk Douglas and Michael Jackson (after plastic surgery). Having a cleft chin is dominant to a smooth chin. Double-jointed thumbs - This is commonly called a hitchhiker's thumb. The thumb can bend back at almost 90 degrees. Hitchhiker's thumb is a recessive trait, but it may vary in its expression.

Dominant/Recessive Human Traits Hand folding - When the hands are folded either the left or right thumb will be on top. Left thumb on top is dominant. Mid-digital hair - Hair growing from the middle section of each finger. Hair presence is dominant. PTC tasting - Phenylthiocarbamide (PTC) is a bitter tasting chemical that cannot be tasted by some individuals. PTC tasters taste PTC as bitter, non-tasters taste nothing when given PTC. Tasting is dominant to the inability to taste PTC.

Dominant/Recessive Human Traits Tongue rolling - Tongue rolling is the ability to form a tube with your tongue. Rolling is dominant. Widow's peak - A sharp point in the hairline that points toward the nose. Having a widow's peak is dominant to a smooth hairline.

Sex Influenced Human Traits Baldness - Loss of hair from the scalp following puberty. A sex influenced trait that is most commonly fully expressed (as a dominant trait) in males, but carried on an autosome Index finger shorter than ring finger - The index finger (next to your thumb) is longer than the ring finger (next to your little finger). Check the class data to see if the frequency is different for the different sexes.

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

Specific Human Traits Dimples - Round indentations in the cheeks when smiling, not lines or clefts. Freckles - Small patches of darker pigmented skin on various parts of the body and most visible in those areas commonly exposed to the sun. These may be present on both dark and light skinned individuals. Hair whorling - These may be referred to as cowlicks. Areas in which hair grows from your scalp in a whorl instead of in a given direction.

Specific Human Traits Myopia - Short sightedness, the inability to see far off objects without correction by glasses or contacts Polydactyly - Having more than five digits on each hand and foot. S-methyl thioester smeller - S-methyl thioesters are produced in the urine after consumption of asparagus. Some individuals cannot smell this substance. If you smell a strong odor on urination after eating at least 5 asparagas spears, you are an S-methyl thioester smeller.

Pedigree symbols 3 Female Male Gender unknown Deceased n P

Spontaneous abortion/Miscarriage Stillborn Spontaneous abortion/Miscarriage Termination of pregnancy elective reasons Termination of pregnancy genetic/affected condition SB

Affected individual Proband Obligate carrier Infertility 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

Generations are symbolized by Roman numerals Include below gender symbol name, maiden name if married & birthdate or age Generations are symbolized by Roman numerals Should give current date on pedigree I. John Smith 10-1-49 Current date: 08-31-06

Other Abbreviations d. 79y dx. 41y Died at 79 years of age Diagnosed at 41 years of age

I. II. III. Siblings are drawn left to right in birth order

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 52 Key Hypertension Breast cancer

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)

I. II. III. Autosomal Dominant Inheritance

Dominant Autosomal Pedigree 1 2 3 4 5 6 7 8 9 10 I II III

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

I. II. III. Autosomal Recessive Inheritance

Recessive Autosomal Pedigree

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

I. II. III. X-Linked Inheritance