Mendel, Morgan and Beyond Mendel, Morgan and Beyond I. Mendelian Genetics A. Gregor Mendel and the Garden Pea Experiments

B. Garden Pea and the Seven Traits Studied in the Garden Pea Plant

C. Flower Structure and Function A. Carpel Structure B. Stamen Structure C. Pollination D. Fertilization

II. Mendel’s Genetic Crosses A. Producing Purebred Garden Pea Plants

B. Monohybrid Crosses

T = tall stem; t = short stem TT x tt parental generation (P) cross pollination

T T t t gametes

Tt first filial generation (F1)

Tt x Tt F1 self fertilization

T t T t gametes

second filial generation (F2) 3:1 phenotypic ratio

C. Dihybrid Crosses

R = round seed, r = round seed; Y = yellow seed, y = green seed RRYY x rryy P cross pollination RY RY ry ry gametes

RrYy F1

RrYy x RtYy F1 self pollination

RY Ry rY ry RY Ry rY ry F1 gametes

F2 phenotypic ratio 9:3:3:1

III. Genetics Mendel Missed A. Incomplete Dominance- neither allele dominant 1. New phenotypes emerge in the F1 not found in parents 2. Four o’clock flower inheritance r = red flower color, w = white flower color rr x ww P cross pollination r w gametes

rw F1

rw X rw self pollination of F1

r w r w F1 gametes

F2 phenotypic ratio 1:2:1

Examples of incomplete dominance in four o-clock flowers

1:2:1 phenotypic ratio White - Pink - Red flowers

B. Codominance- both alleles are dominant 1. Both phenotypes appear- neither is dominant 2. Blood types in humans A B AB O

Codominance in tulips and cattle

Bicolor tulip Hybrid roan cattle

C. Multiple Alleles 1. Exists when there are more than two alleles for a given trait 2. Blood typing in humans is an example of multiple alleles 2. Three blood type alleles: A, B and O alleles 3. When doing genotyping for blood types, I stands for

immunoglobulinandthe superscript the blootd type allele A A A B B B A B

I I I i I I I i I I i i A A B B AB O

D. Pleiotrophy 1. Pleiotropy occurs when one gene influences multiple phenotypic traits 2. Sickle cell trait

E. Epistasis 1. The gene whose phenotype is expressed is called epistatic, while the phenotype altered or suppressed is called hypostatic 2. Labrador retriever coat color B = black, b = chocolate; E = color deposition, e = no color deposition

BBEE BbEE BBEe BbEe bbEE bbEe BBee Bbee bbee (no color deposited even though the color coat gene is present)

F. Penetrance

1. The likelihood a given gene will result in disease 2. If half (50%) of the people with the polydactyly have the disease, the penetrance of the polydactyly gene is 0.5

G. Expressivity

1. Variable expressivity shown by 10 grades of piebald spotting in beagles 2. Each of these dogs has the allele responsible for piebald spots in dogs

H. Polygenic Inheritance 1. More than one set of genes determine a characteristic 2. Skin pigmentation in humans displays polygenic inheritance

Genes A, B, C determine skin color in humans

Genotypic combinations:

AABBCC AaBBCC AABbCC AABBCc aaBBCC aaBbCC aaBBCc aabbcc

IV. Thomas Hunt Morgan

A. The Morgan “Fly Lab” at Columbia University 1. Following the rediscovery of Mendelian inheritance in 1900, Morgan's research moved to the study of mutation in the fruit fly, Drosophila melanogaster 2. In “Fly Room” at Columbia University, Morgan was able to demonstrate that genes are carried on chromosomes and are the mechanical basis of heredity 3. Awarded the Nobel Prize in Physiology or Medicine in 1933 for discoveries relating the role the chromosome plays in heredity

B. Why Drosophila melanogaster? - short life cycle- 10-14 days -inexpensive to culture -sexes easily discerned -only four pairs of chromosomes - need little room to culture -sexes easily discerned

Female fruit fly layer an egg

C. Sex Linkage and Sex Chromosomes 1. Chromosomes of Drosophila melanogaster 2. Examples of sex-linkage -white eye color in fruit flies -color blindness in humans -hemophilia

D. Determination of eye color in Drosophila 1. Eye color mutants (clockwise): brown, sepia, cinnabar, vermilion, white, and apricot 2. Eye color is determined by two biochemical pathways which makes the many colors found in Drosophila eye color mutants

E. Sex Determination and Chromosomes

1. X-Y System in Mammals 2. X-0 System in Grasshoppers, Cockroaches, and other Insects 3. Z-W System in Birds, Some Fishes, and Some Insects 4. Haplo-Diploid System in Bees and Ants F. Nondisjunction 1. Can lead to abnormal chromosome numbers

G. Chromosome Map of Drosophila

E. X Chromosome Inactivation 1. Barr body phenomenon

2. Calico cat are all female due to the orange and black coat color gene residing on the X chromosome only

Tortoise shell cat

VI. Chromosome Aberrations A. Aneuploidy 1. Abnormal number of chromosomes B. Trisomy 1. 2n + 1 C. Monosomy 1. 2n – 1 D. Sex Chromosome Abnormalities 1. Klinefelter’s syndrome XXY 2. Turner’s syndrome XO 3. Trisomy X

Trisomy X XYY

Klinefelter’s syndrome

Turner’s syndrome

E. Down’s Syndrome

VII. Sex Chromosomes and Inheritance A. Sex-Linked Traits 1. Hemophilia 2. Red-green color blindness B. Sex-Limited Traits 1. Genes present in both sexes of sexually reproducing species but turned on in only one sex 2. Sex-limited genes cause the two sexes to show different

phenotypes 3. These genes are responsible for sexual dimorphism

C. Sex-Influenced Traits

Male Female

VIII. Autosomal Recessive Genetic Disorders A. Sickle Cell Anemia B. Cystic Fibrosis C. Tay-Sachs Disease D. Phenylketonuria IX. Autosomal Dominant Genetic Disorders A. Familial Hypercholesterolemia B. Huntington's Disease 1 in 15,000 C. Achondroplasia