Mode of inheritance in Drosophila

The Drosophila Genome The genome of D. melanogaster (sequenced in 2000) All information are available at FlyBase database: http://flybase.org/ Four pairs of chromosomes: an X/Y pair, and three autosomes labeled 2, 3, and 4. The genome is 165 million bases and contains approximately 13,767 protein-coding genes, which comprise ~20% of the genome. (human have 23.000 protein-coding genes)

Fly base http://flybase.org/

Sex determination in Drosophila In Drosophila, sex determination is achieved by a balance of female determinants on the X chromosome and male determinants on the autosomes. If there is one X chromosome and 2 autosomes (1X:2A), the fly is male. If there are two X chromosomes and two autosomes (2X:2A), the fly is female. Thus, Drosophila with one X chromosome and no Y (X0) are sterile males. In flies, the Y chromosome is not involved in determining sex. Rather, it contains genes active in forming sperm in adults.

Relationship between gene, alleles, and segregation of characters.

Few terms -Genes reside on chromosomes. -Alleles are different versions of the same gene -An individual with two identical alleles is termed homozygous -An individual with two different alleles, is termed heterozygous -Genotype refers to the specific allelic composition of an individual -Phenotype refers to the outward appearance of an individual

Segregation of characters -Heredity -Monohybrid: variants of a single trait -Dihybrid: segregation of two characters -Trihybrid: segregation of three characters For two or more characters you can have: linked or independent assortment spermatozoids eggs 2 2 spermatozoids eggs Also: characters can be linked to sex or autosomal chromosomes

Mendel Law of segregation (first law) The two copies of a gene (alleles) segregate from each other during transmission from parent to offspring Law of indipendent assortment (second law) Two different genes will randomly assort their alleles during the formation of haploid cells

Mendel’s law of segregation first low The two copies of a gene segregate from each other during transmission from parent to offspring. P F1 F2 X Tall Small 1 (25%) 3 (75%) : Punnet square Allows you to predict the types of offspring the parents will produce and the proportion of the trait in the offspring. Male gametes P T T P generation TT x tt Haploid gametes T x t F1 tT homozygous t Cross between tall and short Female gametes Male gametes heterozygous F1 generation tT x tT Haploid gametes T or t x T or t F1 T t F2 Self fertilization tt tT TT T t Female gametes Phenotypic proportion 1 (25%) : 2 (50%) : 1 (25%) Genotype proportion

Two factor crosses or dihybrid crosses Mendel’s law of segregation second low Two factor crosses or dihybrid crosses Crossing individual plants that differ in two traits For example Trait 1 = Seed texture (round vs. wrinkled) Trait 2 = Seed color (yellow vs. green) There are two possible patterns of inheritance for these traits

Two possible scenario Independent assortment Linked assortment X P Generation X 2 2 spermatozoids eggs spermatozoids eggs F1 Generation Determine the F2 generation

Indipendent assortment RrYy x RrYy RY Ry rY ry Possible gametes

Linked assortment RrYy ry RY Possible gametes.

Predicted results if Independent Assortment Hypothesis is correct Predicted results if Linked Assortment Hypothesis is correct RrYy x RrYy RrYy x RrYy RY Ry rY ry Haploid gametes RY ry Haploid gametes RrYy RY Ry rY ry RRYY RRYy RrYY RrYy RY ry RY ryry ryRY RYry RYRY RRYy RRyy Rryy RY ry RrYy Ry RrYy RrYY RrYy rrYY rrYy rY RrYy Rryy rrYy rryy ry 3 : 1 9 : 3 : 3 : 1

Mendel law of independent assortment During meiosis, chromosomes assort randomly into gametes, such that the segregation of alleles of one gene is independent of alleles of another gene. This is stated in Mendel's Second Law and is known as the law of independent assortment. The law of independent assortment always holds true for genes that are located on different chromosomes, but for genes that are on the same chromosome, it does not always hold true.

Drosophila MUTANTS

Mutations Many Characteristics: Shape and color of eye Color of the body Shape and size of the head Shape and size of wings Color of the wings behavior

Wings shape Body color Eye color Eye and legs

Wild type Wild type vermillion yellow white Bar forked white apricot crossvein crossveinless

We can study the mode of inheritance FIRST assignment Mode of inheritance of two mutant phenotypes Direct and reciprocal crosses

Remember that mom and Dad are pure lines ? Mom and dad genotypes? F1 All females are Wild type All males show the mutation All males and female show the mutation All female show the mutation All males are Wild type All males and females are Wild type X X 2 2 X Y 2 2 X X 2 2 X Y 2 2 X X 2 2 X Y 2 2 X X 2 2 X Y 2 2 F2

Your mutants B = bar (bar eye) ap = apterus (no wing) w = white eye wa = apricot m = short wings y = yellow body sc = missing one or more bristle in scutellum dp = dumpy wings Se = brown eye (seppia) f = curly bristles vg = curly wings gl = reduced eye with different texture

The goal of this experiment is for you to be able to understand if your mutations are: - Inked to sex chromosomes - Autosomal - Dominant or recessive

Direct Reciprocal X X P F1 X X F2 F2 Sex: ww ; Aut EE ww/EE AA X Y AA X X AA X Y A A Sex: ww ; Aut EE ww/EE Sex: W0 ; Aut ee w0/ee Sex: WW ; Aut ee WW/ee Sex: w0 ; Aut EE w0/EE We 0e wE Ww/Ee w0/Ee WE 0E We Ww/Ee W0/Ee F1 X X W w E e w E e E e w W E e W X X AA X Y AA X X AA X Y AA Sex: Ww ; Aut Ee Ww/Ee Sex: w0 ; Aut Ee w0/Ee Sex: Ww; Aut Ee Ww/Ee Sex: W0; Aut Ee W0/Ee F2 F2