Heredity

Nucleotides

Step 1: DNA is a polynucleotide, meaning it's made of many nucleotides. Step 2: Each nucleotide has three components: nitrogenous base, sugar (deoxyribose), and phosphate. Step 3: The four types of nucleotides contain bases A, T, G, and C. Step 4: These nucleotides join together to form the DNA chain. Amino acids make proteins, fatty acids make fats, and carbohydrates are sugars - none form DNA.

O

Step 1: Universal donor can give blood to all four blood groups (A, B, AB, O). Step 2: Blood group O has no A or B antigens on red blood cells. Step 3: This means O blood won't cause immune reactions in recipients of any blood group. Step 4: O negative is especially safe as it also lacks Rh factor. Groups A, B, and AB have specific antigens that can cause reactions in incompatible recipients.

A trait that appears only when dominant trait is absent

Step 1: In a gene pair, one gene can be dominant and other recessive. Step 2: Dominant trait masks the expression of recessive trait. Step 3: Recessive trait appears only when both genes in the pair are recessive. Step 4: Example: In pea plants, dwarfness appears only when tallness gene is absent. The other options incorrectly describe dominant traits or inheritance patterns.

46

Step 1: Diploid means having chromosomes in pairs (2n). Step 2: Humans have 23 pairs of chromosomes, totaling 46 chromosomes. Step 3: This diploid number is found in all body cells except gametes. Step 4: Gametes have haploid number (23) which becomes diploid after fertilization. Options 23, 44, and 22 represent different chromosome counts but not the human diploid number.