Mendelian Inheritance BIO 2215 Oklahoma City Community College Dennis Anderson
Gregor Mendel • Father of Genetics • 1823-1884 • Monk in Austria • Experimented with garden peas
Tall Tall Short
Mendel’s Hypotheses • Each parent has two factors (alleles) • Each parent gives one of those factors to the offspring • Tall has TT • Short has tt • Tall is dominant • Short is recessive
T t Tt TT tt
T T TT TT TT
t t tt tt tt
Law of Segregation • Alleles separate during gamete production • Gametes have one allele for each trait • During fertilization gametes combine at random to form individuals of the next generation
Discovery of Chromosomes in 1900 Confirmed Law of Segregation • Chromosomes are in pairs • Each chromosome has one of the allele pair
Meiosis Metaphase Chromosomes line up in a double row. T T t t Assume a T allele on each red chromatid and a t allele on each blue chromatid
Chromosomes separate Each each daughter cell gets doubled chromosomes t t T T
Allele • Member of a paired gene • One allele comes from each parent • Represented by a single letter
Dominant & Recessive Alleles • Dominant alleles are expressed • Recessive alleles are not expressed in the presence of a dominant allele • Recessive alleles are only expressed if both recessive alleles are present
Gene • A unit of heredity that controls the development of one trait • Made of DNA • Most genes are composed of two alleles
Homozygous • Both alleles alike • AA or aa
Heterozygous • Alleles are different • Aa
Genotype • Genetic make up • Represented by alleles • TT & Tt are genotypes for tall pea plants
Phenotype • A trait • Genotype determines the phenotype • Tall is a phenotype
Homologous Chromosomes • Chromosomes of the same pair • Each homologue will have one allele for a paired gene • Homologous chromosomes pair up during meiosis • Only one of each homologue will be in each gamete
Sickle Cell Anemia • RBCs sickle shaped • Anemia • Pain • Stroke • Leg ulcers • Jaundice • Gall stones • Spleen, kidney & lungs
Sickle Cell Anemia • Recessive allele s, codes for hemoglobin S • Long rod-like molecules • Stretches RBC into sickle shape • Homozygous recessive ss, have sickle cell anemia • Heterozygous Ss, are carriers
Albinism • Lack of pigment • Skin • Hair • Eyes
a A AA = Normal pigmentation Aa = Normal pigmentation aa = Albino Enzyme Amino Acids Melanin Pigment
PKU Disease • Phenylalanine excess • Mental retardation if untreated
p P PP = Normal Pp = Normal pp = PKU Enzyme Phenylalanine Tyrosine
Monohybrid Cross or One Trait A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?
AA = Normal pigmentation Aa = Normal pigmentation (carrier) aa = Albino A A a a Man = Aa Woman = Aa
A A a a Aa AA Aa aa
Aa AA Aa aa Genotypes 1 AA, 2Aa, 1aa Phenotypes 3 Normal 1 Abino Probability 25% for albinism
A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit PKU disease?
PP = Normal Pp = Normal (carrier) pp = PKU disease Pp PP Pp pp P p P p
Pp PP Pp pp Genotypes 1 PP, 2Pp, 1pp Phenotypes 3 Normal 1 PKU disease Probability 25% for PKU disease
A man with sickle cell anemia marries a woman who is a carrier. What is the chance their children will inherit sickle cell anemia?
SS = Normal Ss = Normal (carrier) ss = Sickle Cell ss Ss Ss ss S s s s
ss Ss Ss ss Genotypes 2 Ss, 2ss Phenotypes 2 Normal (carriers) 2 Sickle cell Probability 50% for Sickle cell
Dwarfism Dwarfism = D Normal height = d DD = Dwarfism Dd = Dwarfism dd = Normal height Dwarf Band
A man with heterozygous dwarfism marries a woman who has normal height. What is the chance their children will inherit dwarfism? Dwarfism is dominant.
DD = Dwarf Dd = Dwarf dd = Normal Dd Dd dd dd d d D d
Dd Dd dd dd Genotypes 2 Dd, 2dd Phenotypes 2 Normal 2 Dwarfs Probability 50% for Dwarfism
Law of Independent Assortment • The inheritance of one gene does not influence the inheritance of another gene if they are on separate chromosomes. • The gene for albinism does not affect the gene for dwarfism
Dihybrid Cross or Two Traits • A heterozygous tall plant that is also heterozygous for yellow seeds is crossed with another plant with the same genotype • Tall and yellow seeds are dominant to short and green seeds.
TY Ty tY ty What gametes can each parent produce? Tall Yellow Tall Yellow TtYy TtYy TY Ty tY ty
TY Ty tY ty 9 Tall-Yellow TY TTYY TTYy TtYY TtYy 3 Tall-Green Ty TTYy TTyy TtYy Ttyy TtYY TtYy ttYY ttYy tY 3 Short-Yellow TtYy ty Ttyy ttYy ttyy Match gametes on a Punnent Square 1 Short-Green
A man with blue eyes and normal height marries a woman with heterozygous brown eyes and heterozygous dwarfism. What are the possible phenotypes of their children? Dwarfism & brown eyes are dominant.
DB Db dB db What gametes can each parent produce? Normal height-Blue Dwarf-Brown ddbb DdBb db
DdBb Dwarf-Brown eyes DB Ddbb Dwarf-blue eyes Db dB ddBb Normal height-Brown eyes Normal height-Blue eyes db ddbb Match gametes on Punnent Square db