lab report

Documenting independent assortment and genetic linkage in Drosophila melanogaster

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BIOL 3251 Genetics-Section Number

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The branch of biology that is concerned with the heredity and variations is known as genetics. Mendel had succeeded where as many others had failed when it came to genetics. Mendelian inheritance illustrates that one of two possible alleles for a trait contribute by each parent, but in non-Mendelian inheritance traits do not segregate according to Mendel’s Law (Ven Hyningen and V Yeyati, 2004). Drosophila melanogasterwhich is commonly known as Fruit fly has been used in genetics for over a century due to its small size, easy to grow and short generation time. Thomas Morgan was the first one to study Drosophilaand it is one of those whose genetic make-up is known (Perrimon et al, 2016). Another reason for the importance of Drosophilais that they are dimorphic (sexually) male and female are different making it easy to differentiate between the sexes. In this project we set out to describe and study about the genetic linkage of the different mutant lines and independently assortment of these mutated genes of Drosophila melanogasterin which allele of different genes assort independently during gametes formation. Gene linkage describes about the chromosome of the eukaryotic individual that whether it constitute two or more genes on a same chromosome or not.

Three mutant lines were selected for this study, which includes Apterous wings with White eyes, Apterous wings with Sepia eyes, and Vestigial wings with Brown eyes. Gene for vestigial/ Brown wings are both located on chromosome number 2, which means we are assuming genetic linkage. Based on this we expect not to see 9:3:3:1 ratio in the F2 generation. Apterous gene is also located in the chromosomes number 2. Sepia is located on chromosome number 3, which means that the Apterous/Sepia are located on two separate chromosomes. Based on this, we hypothesized that these genes are unlinked and sorted independently, and we expect to see this with the 9:3:3:1 ratio in the F2 generation. Apterous/white One of the genes is located on X- linked chromosome, so X linked inheritance pattern is expected to be observed and the Apterous is located on chromosome number 2. As Apterous gene mutation is recessive, so hypothesized inheritance pattern for this is autosomal linked recessive (Weihe et al, 2004). Similarly, Vestigial wings gene is also located in autosomal chromosome and this mutation is too recessive, so its hypothesized inheritance pattern will also be autosomal linked recessive and a ratio of 3:1 and for X-linked a ratio of 2:1:1.

Results:

Mutant line 1: Apterous, Sepia

Observed F1 Phenotypes	Total observed
females red eyes/ normal wings	18
males red eyes/ normal wings	15

Mutant line 2: Apterous, White

Observed F1 Phenotypes	Total observed
females red eyes/ normal wings	16
males red eyes/ normal wings	13

Mutant line 3: Vestigal, Brown

Observed F1 Phenotypes	Total observed
females red eyes/ normal wings	17
males red eyes/ normal wings	22

Mutant line 1: Apterous, Sepia

F1 x F1 observed F2 Phenotypes	Females	Males	Total observed
wt, wt	27	17	38
a, wt	0	0	0
wt, s	5	9	14
a, s	0	0	0
Totals	32	26	52

Mutant line 2: Apterous, White

F1 x F1 observed F2 Phenotypes	Females	Males	Total observed
wt, wt	32	17	49
a, wt	2	6	8
wt, s	0	17	17
a, s	0	5	5
Totals	34	45	79

Mutant line 3: Vestigal, Brown

F1 x F1 observed F2 Phenotypes	Females	Males	Total observed
wt, wt	29	34	63
a, wt	4	1	5
wt, s	0	0	0
a, s	0	0	0
Totals	33	35	68