Patterns of Heredity and Human Genetics :Patterns of Heredity and Human Genetics By: Mr. B. del Rosario 3rd Quarter BIOLOGY Paref-Southridge School


How to Construct a Pedigree? :How to Construct a Pedigree? Symbols and Rules: Male = Female = Affected = Unaffected = Carrier = Link parents together with a line and then make a vertical line to connect to offspring.


Pedigree :Pedigree helps geneticists map the inheritance of genetic traits from one generation to the next looks very similar to a family tree allows identification of males, females, offspring, siblings, etc. who maybe affected by a certain condition


Things to remember… :Things to remember… A carrier is a heterozygous individual for a particular trait Horizontal line connecting a square and a circle represent the parents. Vertical line connects parents to offspring. Generation – horizontal row; Roman numerals Most recent generation at the bottom.


Simple Recessive Heredity :Simple Recessive Heredity common genetic disorders; caused by recessive alleles as the name implies includes PKU, Tay-Sachs disease, cystic fibrosis, sickle cell anemia, etc.


Medical Genetics :Medical Genetics Simple recessive The disease appears in male and female children of unaffected parents.


Examples of Simple Recessive Disorders :Examples of Simple Recessive Disorders Congenital Deafness Diabetes Mellitus Sickle Cell anemia Albinism Phenylketoneuria (PKU) – Inability to break down the amino acid phenylalanine. Requires elimination of this amino acid from the diet or results in serious mental retardation. Galactosemia – enlarged liver, kidney failure, brain and eye damage because can’t digest milk sugar Cystic Fibrosis – affects mucus and sweat glands, thick mucus in lungs and digestive tract that interferes with gas exchange, lethal. Tay Sachs Disease – Nervous system destruction due to lack of enzyme needed to break down lipids necessary for normal brain function. Early onset and common in Ashkenazi Jews; results in blindness, seizures, paralysis, and early death.


Simple Dominant Heredity :Simple Dominant Heredity These traits are inherited just as the rule of dominance would predict. A single dominant allele is all that is needed for a person to show the dominant trait. Ex: cleft chin, widow’s peak hairline, freely hanging earlobe, etc.


Medical Genetics :Medical Genetics Autosomal dominant Affected males and females appear in each generation of the pedigree. Affected mothers and fathers transmit the phenotype to both sons and daughters. Ex: Huntington’s disease


Examples of Simple Dominant Disorders :Examples of Simple Dominant Disorders Dwarfism Polydactyly and Syndactyly Hypertension Hereditary Edema Chronic Simple Glaucoma – Drainage system for fluid in the eye does not work and pressure builds up, leading to damage of the optic nerve which can result in blindness. Huntington’s Disease – Nervous system degeneration resulting in certain and early death. Onset in middle age. Neurofibromatosis – Benign tumors in skin or deeper Familial Hypercholesterolemia – High blood cholesterol and propensity for heart disease Progeria – Drastic premature aging, rare, die by age 13. Symptoms include limited growth, alopecia, small face and jaw, wrinkled skin, atherosclerosis, and cardiovascular problems but mental development not affected.


Complex Patterns of Inheritance :Complex Patterns of Inheritance Incomplete Dominance Codominance Multiple Phenotypes from Multiple Alleles Sex Determination Sex-linked Inheritance Polygenic Inheritance


Slide 12:Incomplete Dominance – the phenotype of heterozygotes are intermediate between those of the two homozygotes.


Codominance :Codominance Heterozygous individuals express the phenotypes of both homozygotes.


Slide 14:Codominance The human ABO blood group illustrates another genetic phenomenon – codominance. Codominance occurs when the phenotype associated with each allele is expressed in the heterozygote. The AB phenotype (genotype IA IB) is an example of codominance.


Multiple Phenotypes from Multiple Alleles :Multiple Phenotypes from Multiple Alleles occurs when a new allele is formed after a mutation in a nitrogenous base happens


Slide 16:Multiple Alleles Many genes are present in 3 or more versions (alleles) – this is known as multiple alleles. The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.


Sex determination :Sex determination


Sex-linked inheritance :Sex-linked inheritance Sex chromosomes contain genes for the so-called sex-linked traits. Eye color in fruit flies is the most famous example of an X-linked trait. “Y-linked traits are passed only from a male to male offspring.”


Sex-linked inheritance :Sex-linked inheritance


Polygenic inheritance :Polygenic inheritance A trait is controlled by two or more genes. These genes may be on the same or different chromosomes. Each gene may have two or more alleles. NOTE: We used to know only two alleles per gene. Ex: human skin color and height


Environmental Influences :Environmental Influences Influence of external environment Influence of internal environment


Codominance in Humans :Codominance in Humans seen in individuals who are heterozygous to the sickle-cell allele. (phenotype?)


Multiple Alleles Govern Blood Type :Multiple Alleles Govern Blood Type Type A – IAIA; IAi Type B – IBIB; IBi Type AB – IAIB Type O – ii * The alleles IA and IB are dominant to i.


Sex-linked Traits in Humans :Sex-linked Traits in Humans


Sex-linked Traits in Humans :Sex-linked Traits in Humans include red-green color blindness & hemophilia (X-linked traits) Duchenne’s muscular dystrophy (Y-linked)


Polygenic Inheritance in Humans :Polygenic Inheritance in Humans includes skin, eye, and hair color light-skinned X dark-skinned F1: offspring have intermediate skin colors F2: skin color range from light to dark skin color of the grandparents Children have intermediate skin color.


Polygenic Traits… :Polygenic Traits… 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


Polygenic Traits… :Polygenic Traits… 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


Changes in Chromosome Numbers :Changes in Chromosome Numbers usually a result of accidents in meiosis not uncommon to observe abnormal phenotypic effects Ex: abnormal numbers of autosomes, Down syndrome (Trisomy 21), abnormal number of sex chromosomes (XXY, XYY, XXX)


Klinefelter’s Syndrome (XXY) :Klinefelter’s Syndrome (XXY)


XYY Syndrome :XYY Syndrome often no unusual physical features or medical problems taller than average increased risk of learning disabilities and delayed speech and language skills behavioral problems