NOTES: 14.1-14.2 - HUMAN HEREDITY; PEDIGREES Human Genes: ● The human genome is the complete set of genetic information -it determines characteristics such as eye color and how proteins function within cells Recessive and Dominant Alleles: • Some common genetic disorders are -This means that you need two recessive alleles (on any of the 44 chromosomes—NOT the sex chromosomes) to express the disease EX: • Other genetic disorders are -Only one allele is needed for the trait to be expressed EX: Autosomal Recessive Disorders: • In order to develop an autosomal recessive trait, an individual must have the genotype: “ ” • To be born with a homozygous recessive genotype, both parents must be heterozygotes (“carriers”)…or homozygous recessive themselves (although with most disorders, that is not the case)…WHY NOT?
From gene to molecule: • In both cystic fibrosis and sickle cell anemia, a small change in the DNA of a affects the structure of a protein, causing a serious genetic disorder
What makes an allele dominant or recessive? • Gene = sequence of DNA that • Usually: -Dominant alleles code for the production of that protein -Recessive alleles code for / protein production -Heterozygous condition — the normal (dominant) allele will still cause correct protein production Cystic Fibrosis: • Caused by a recessive allele on chromosome #7 -It is an autosomal genetic disorder • Causes and problems • Death around 20-30 years of age Sickle Cell Anemia: • One DNA base has been changed • Amino acid is valine, instead of glutamic acid • Result = • The abnormal hemoglobin forms crystal-like structures that change the shape of the red blood cells • The abnormal red blood cells are shaped like a “sickle” or a ; • These RBCs slow blood flow, block small blood vessels, and result in tissue damage and pain. • Three genotypes possible:
1) HH = 2) Hh = ½ healthy hemoglobin; ½ abnormal hemoglobin; ** !! 3) hh = Pedigree Chart: • Shows how a trait is transmitted from generation to generation • Each row is a generation • Circles represent • Squares represent -Shaded in: person that trait -Half shaded in: person is only a -Clear: person does that trait
Tay-Sachs Disease: • • Recessive allele results in the absence of an enzyme that normally breaks down lipids in the central nervous system • Without this enzyme, the lipids accumulate in the nervous system and the affected individual dies
Phenylketonuria (PKU): • Autosomal recessive disorder; • Absence of an enzyme to break down the amino acid phenylalanine • The accumulation of phenylalanine causes damage to the nervous system • By avoiding phenylalanine in the diet, affected infants can avoid the symptoms of the disorder
Autosomal Recessive Traits & Pedigrees: • May skip a generation • Affected individuals are born to 2 carriers • Males and • KNOWN carriers will be half-shaded in…it is not always possible to know if an individual is a carrier
What about autosomal dominant human traits? • A single dominant allele inherited from 1 parent is all that is needed for a person to show the dominant trait.
Simple Dominant Traits: • • Hair in the middle section of fingers • Unattached earlobes • Ability to taste PTC •
Autosomal Dominant Traits & Pedigrees: • Typically seen in every generation, affecting multiple people • Affected individuals are born to • Males and females affected equally • There are NO “carriers”! (you either have it – – or you don’t – ) Autosomal Dominant Disorder: HUNTINGTON’S DISEASE • ; • Results in a breakdown of parts of the brain; • Onset between the ages of 30 and 50; • No known treatment or cure; • There is a test available to see if you have it – may help with the decision to start a family; • Every child of an affected individual has a 50/50 chance of being affected (and passing it down)
• Can’t trace every human trait through a pedigree because some genes are
• Also, phenotype is influenced by your (ex: & )
REVIEW: Human Blood Groups (no need to take notes – just follow along with the slides)
ABO Blood Groups • Try this cross: Cross a person who’s genotype is IAIA with a person who is IAIB. Punnett Square:
• Give the possible genotypes and phenotypes
Genotypes:
Phenotypes:
Human Genes & Chromosomes:
Remember…
• Humans have 46 chromosomes (23 pair) • 2 of them are à they determine what sex you are -XX = -XY = • 44 of them are à they do not determine what sex you are
The Y chromosome: • If a Y chromosome is present, • X chromosomes contain genes necessary for growth / development • No cases of a person born with being 45,0Y -Probably spontaneously aborted (miscarriage)
Sex Linked Genes: • Genes carried on the X or Y chromosome are “sex-linked” because they are on the sex chromosomes • Many sex-linked genes are found on the X-chromosome • All X-linked traits are expressed in males • WHY??????? • Males only have , while females need 2 copies of the defective gene Human Sex-Linked Gene Disorders:
1. COLORBLINDNESS: • 3 human genes associated with color vision are located on the X-chromosome • In males, a defective version of any one of these produces colorblindness • Females must receive 2 copies of the allele to be colorblind
2. HEMOPHILIA • 2 important genes on the X-chromosome that code for • A recessive allele in either of these 2 genes may lead to hemophilia -“bleeders disease” -injections of normal clotting proteins prevent death
Sex-Linked Traits and Pedigrees: • only (or mostly) ; • affected males are born to “carrier” females; • typically not seen in all generations
Sex-Influenced Genes: • A person’s phenotype is affected by their sex (internal environment is different…hormones!) • Ex: Pattern Baldness
WOMEN: MEN:
BB: BB:
Bb: Bb: bb: bb:
X-Chromosome Inactivation: • Females have 2 X-chromosomes… if 1 is enough for males, how does the cell “adjust” to the extra x-chromosome in females? • One X-chromosome is -Condenses and is called a X-Chromosome Inactivation – an example: • Tortoise-shell cats: è XBY = XBXB = è XbY = XbXb = XBXb = -Can a male cat have tortoise-shell fur?