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