Sex determination in Drosophila

Drosophila has 8 chromosomes: three pairs of autosomes and 1 pair of sex chromosomes. It inherited 1 haploid set of autosomes and 1 sex chromosomes from each parent. The Y chromosome does not determine maleness instead, each fly’s sex is determined by a balance between genes on autosomes and genes on X-chromosome. This type of sex determination is called genic balance system. The X-chromosome contains genes with female producing effects, whereas the autosomes contain a gene with male-producing effects. Thus, a fly’s sex is determined by X: A ratio, = the no. Of X-chromosome/ the no. Of the haploid set of autosomal chromosome.

X:A = 1 (female) ; X:A= 0.5 (male) ; X:A = <0.5. (male phenotype but sterile, metamales); X:A = 1.0 between 0.5 (intersex fly, both features); X:A = >1.0 female phenotype (metafemale)

Normal females contain (XX,AA) (1.0)

Normal males (XY,AA) (0.5)

(XXY,AA) (fully fertile female)

(XO,AA) (sterile male)

Thus, Y chromosome does not determine sex.

XX	AA	1	Female
XXY	AA	1	Female
XY	AA	0.5	Male
XO	AA	0.5	Male
XXX	AA	1.5	Metafemale
XXXY	AA	1.5	Metafemale
XX	AAA	0.67	Intersex
XO	AAA	0.33	Metamale
XXXX	AAA	1.3	Metafemale

difference between Microevolution and macroevolution

Microevolution	Macroevolution
1. Intra-species genetic change	1. Changes leads to formation of a completely new species.
2. Occurs over small-time scale.	2. Occurs over large time-scale.
3. Genetic information that already exists is put in new arrangement, altered or lost.	3. New information is added to the existing genetic structure.
4. Changes in the gene pool of a population.	4. Macroevolution is the result of a lot of microevolution over a long period of time.
5. E.g., new breeds of dogs	e.g., Amphibians to reptiles

Pedigree analysis

Autosomal recessive traits

• Appear with equal frequency in males and females.
• Appear when a person inherits two alleles for a trait, one from each parent.
• When both parents are heterozygotes, ¼ of the offspring express the trait.
• Appear more in consanguinious couples.
• Affected children are commonly born to unaffected parents (carrier)
• Tend to skip generation
• E.g., tay-sach

Autosomal dominant trait

• Doesn't skip generation
• Appear equally in both sexes
• Affected child has an affected parent
• If one parent is heterozygous for the trait and other is unaffected, ½ of the offspring will be affected.
• E.g., familial hypercholesterolemia

X-linked recessive trait

• Appear more frequently in males than female
• Affected males are born to unaffected mother
• Tend to skip generation
• Heterozygous mother gives ½ sons affected and ½ daughter as unaffected carriers.
• Not passed from father to son
• E.g. hemophilia A

X-linked dominant trait

• Appear equal in male and female but affect more female than male
• Must affected parents
• Do not skip generation
• Affected father pass trait to all daughters and none of the son.
• Affected mother pass to ½ sons and ½ daughters.
• E.g hypophosphatemia I or familial vitamin D resistant rickets.

Y-linked traits

• Only males are affected
• Trait is passed from father to son .
• Does not skip generation
• E.g. maleness

Penetrance and Expressivity

Penetrance	Expressivity
1. It is the % of individual organism having a particular genotype that express the expected phenotype.	1. It is the extent of a given genotype, expressing at the phenotypic level.
2. Quantitative measurement.	2. Qualitative measurement.
3. It explain how often the gene is expressed.	3. It explains at which extent gene is expressed.
4. Incomplete penetrance difficults the genetic analysis.	4.  Variable expressivity difficults the genetic analysis.
5. Describe the expression of single gene	5. Describe the expression of characters.
6. It shows whether the disease show or not.	6. It explains how a disease show up.

CHEMICAL PRESERVATIVES:

CHEMICAL PRESERVATIVES:

The food additives which are specifically added to prevent the deterioration or decomposition of food have been referred to as chemical preservatives.

Preservatives may inhibit microorganisms by interfering with their cell membrane, their enzyme activity or their genetic mechanisms.

Factors that influence the effectiveness of chemical preservatives:

·     Concentration of a chemical

·     Temperature

·     Time

·     Kind, number, the age of organisms

·     Chemical and physical characteristics of the substrate (moisture, pH, kind and amount of solute etc.)

Ideal antimicrobial preservative:

·     Non-toxic to human beings or animals.

·     Have a wide range of antimicrobial activity

·     Not effect flavor, taste or aroma of food

·     Not encourage the development of resistant strains

·     Economical

·     Kill rather than inhibit microorganisms

·     Should not be inactivated by food

SUGAR AND SALT:

·     these compounds lower the water activity (aw)

·     NaCl is used in brine and curing solution.

·     Salts have the following effects:

·     Causes high osmotic pressure and hence plasmolysis of cells.

·     Reduces solubility of oxygen in moisture.

·     Interfere with the action of proteolytic enzymes.

·     Ionizes to yield Cl ion ( oxidizing agent)

·     Dehydrates food by drawing out moisture hence, dehydrates microbial cells.

·     Sugars (glucose or sucrose) make water unavailable to the organism by the osmotic effect.

·     E.g.., sweet condensed milk, jellies, fruits

ORGANIC ACID AND THEIR SALTS:

·     They are added to foods by fermentation.

·     Lactic, acetic, propionic and citric acids or their salts may be added to foods or developed in foods by fermentation.

·     Citric acid is used in syrups, drinks, jams, and jellies as a substitute for fruit flavors and for preservation.

·     Lactic and acetic acids are added to brines of various kinds, green olives etc.

·      

·     (A)  benzoic acid and parabens

·    

·     Sodium benzoate was the first chemical preservative approved by FDA.

·     Mainly inhibitory against yeasts and molds

·     The antimicrobial activity of benzoate is related to pH, greater at low pH (2.5-4) and essentially ineffective at neutral pH.

·     Undissociated acid is an effective agent.

·     It is corporate into jams, jellies, beverage, salads, pickles, fruit juices etc.

·     Two esters of p-hydroxybenzoic acid, methyl paraben, propyl paraben are extensively used in foods

·     Similar to benzoic acid but can be effective at higher pH because of the esterification of carboxyl group.

·     More effective in molds than yeasts.

·     Mode of action: the undissociated form is soluble in the cell membrane and act apparently as proton ionophores. They facilitate proton leakage into cells and thereby increase the energy output of cells to maintain their usual internal pH. With the disruption of membrane activity, amino acid transport is adversely affected.

·     It blocks the oxidation of glucose and pyruvate at acetate level. Inhibit germination of outgrowth during endospore germination.

CITRIC ACID:

·     Found in citrus fruits.

·     Widely used in carbonated beverages and as an acidifying agent of foods because of its unique flavor properties.

·     Highly soluble in water, unlimited acceptable intake

·     Less effective than other acids.

·     Used in Fruit juices, and jams.

ETHYLENE OXIDE:

·     Acts as a sterilant. Kills all microorganisms

·     Acts as strong alkylating agents attacking labile hydrogen.

·     The H atom attaches itself to oxygen, forming hydroxyl ethyl radical, CH2CH2OH.

·     This radical blocks reactive groups within microbial proteins, resulting in inhibition.

·     Ethylene and Propylene oxide: used as sterilants for packaging materials, fumigation of warehouses. 'cold sterilization’ of numerous plastics, chemicals, pharmaceuticals, syringes, and hospital supplies.

·     Use of ethylene oxide is restricted to spices and other processed natural seasonings.

NITRATE AND NITRITES:

·     combination of these salts used in curing solution and curing mixture for meats.

·     Curing is a food preservative and flavoring process with the aim of drawing moisture out of food by the process of osmosis.

·     Nitrites decompose to nitric acid which forms nitrosomyoglobin when reacts with pigments in meats i.e., myoglobin in reducing condition and thereby forms a stable red color.

·     Nitrites react with secondary and tertiary amines to form nitrosamines, which are carcinogenic.

·     Inhibits Clostridium botulinum in meat products along with Staphylococcus aureus and Bacillus sp.

·     Inhibits Clostridium botulinum by interfering with Fe-S enzymes such as ferredoxin and thus preventing the synthesis of ATP from pyruvate.

·     Nitrous oxide is a powerful reducing agent causing disruption of cell metabolism and inhibiting germination and outgrowth of endospores.

·     Nisin (bacteriocin) can be used along with nitrites.

·     Nitrite levels of 100 ppm in presence of NaCl (3-5%) is sufficient to impart adequate flavors, color, anti- botulism activities.