1. Mode of inheritance in Drosophila

2. The Drosophila Genome
The genome of D. melanogaster (sequenced in 2000) All information are available at FlyBase database:
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 protein-coding genes)

3. Fly base

4. 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.

5. Relationship between gene, alleles, and segregation of characters.

6. 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

7. 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

8. 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

9. 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%) : (50%) : (25%)
Genotype proportion

10. 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

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

12. Indipendent assortment
RrYy x RrYy RY Ry rY ry
Possible gametes

13. Linked assortment
RrYy ry RY
Possible gametes.

14. 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

15. 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.

16. Drosophila MUTANTS

17. 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

18. Wings shape
Body color
Eye color
Eye and legs

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

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

21. 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

22. 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

23. 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

24. Direct Reciprocal X X P F1 X X F2 F2 Sex: ww ; Aut EE ww/EEAA 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