Biology: Genetics & Heredity

Distinguish between an organism's genotype and its phenotype.

The genotype refers to the specific genetic makeup or set of alleles an organism carries (e.g., Aa), while the phenotype is the observable physical or physiological expression of those genes.

What occurs during incomplete dominance in a heterozygous individual?

Incomplete dominance results in a phenotype that is an intermediate blend of the two homozygous phenotypes, such as pink flowers resulting from red and white parents.

Identify the nitrogenous base pairs in DNA and the number of hydrogen bonds between them.

Adenine (A) pairs with Thymine (T) via two hydrogen bonds; Cytosine (C) pairs with Guanine (G) via three hydrogen bonds.

What is the core principle of Mendel's Law of Segregation?

It states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.

Define Okazaki fragments and identify the strand on which they are found.

Okazaki fragments are short, newly synthesized DNA fragments formed on the lagging strand during DNA replication because DNA polymerase can only synthesize in the 5' to 3' direction.

How does codominance differ from standard Mendelian dominance?

In codominance, both alleles in the heterozygote are fully and simultaneously expressed in the phenotype, rather than one being masked or blended (e.g., AB blood type).

Explain Mendel's Law of Independent Assortment and its chromosomal basis.

It states that each pair of alleles segregates independently of each other pair during gamete formation; this applies to genes on different chromosomes or very far apart on the same chromosome.

In a Mendelian dihybrid cross (AaBb x AaBb), what is the expected phenotypic ratio of the offspring?

The expected phenotypic ratio is 9:3:3:1 (Dominant/Dominant : Dominant/Recessive : Recessive/Dominant : Recessive/Recessive).

Why are X-linked recessive traits more frequently expressed in males than in females?

Males are hemizygous for the X chromosome (XY); they only possess one X chromosome, so a single recessive allele on that chromosome will be expressed without a second X to mask it.

What is polygenic inheritance, and how does it typically manifest in a population?

Polygenic inheritance occurs when multiple independent genes have an additive effect on a single phenotypic character, usually resulting in a continuous gradient of variation (e.g., skin color or height).