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 Short Tall
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
TT tt Tt t T
TT TT TT T T
tt tt tt t t
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
Doubled Chromosomes Separate in Second Meiotic Division
Each gamete will have a T allele or a t allele
Allele Member of a paired gene Represented by a single letter 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 Enzyme Amino Acids Melanin Pigment AA = Normal pigmentation aa = Albino
PKU Disease Phenylalanine excess Mental retardation if untreated
p P Enzyme Phenylalanine Tyrosine PP = Normal Pp = Normal pp = PKU
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 Man = Aa Woman = Aa A A a a
A a A Aa AA a Aa aa
AA Aa aa Genotypes Phenotypes Probability 1 AA, 2Aa, 1aa 3 Normal 1 Abino Probability 25% for albinism
A man & woman are both carriers (heterozygous) for PKU disease 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 P p PP Pp pp P p
PP Pp pp Genotypes Phenotypes Probability 1 PP, 2Pp, 1pp 3 Normal 1 PKU disease Probability 25% for PKU disease
A man with sickle cell anemia marries a woman who is a carrier 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 S s s Ss ss s
Genotypes ss Ss Phenotypes Probability 2 Ss, 2ss 2 Normal (carriers) 2 Sickle cell Probability 50% for Sickle cell
Dwarfism DD = Dwarfism Dd = Dwarfism dd = Normal height Dwarfism = D Dwarf Band
A man with heterozygous dwarfism marries a woman who has normal height 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 d d D Dd dd d
Genotypes Dd Phenotypes dd Probability 2 Dd, 2dd 2 Normal 2 Dwarfs 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.
What gametes can each parent produce? Tall Yellow Tall Yellow TtYy TtYy TY TY Ty tY ty Ty tY ty
Match gametes on a Punnent Square TY Ty tY ty TtYy TTYY TTYy TtYY TTyy Ttyy ttYY ttYy ttyy 9 Tall-Yellow TY Ty tY ty 3 Tall-Green 3 Short-Yellow 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.
What gametes can each parent produce? Normal height-Blue Dwarf-Brown ddbb DdBb db DB Db dB db
Match gametes on Punnent Square db DdBb Ddbb ddBb ddbb Dwarf-Brown eyes Dwarf-blue eyes Normal height-Brown eyes Normal height-Blue eyes DB Db dB db
The End