Genes are segments of DNA that contain the instructions for making proteins. These proteins are essential for the structure and function of cells.

DNA is the molecule that stores genetic information in cells. It contains the code that is used for the development and function of all living organisms.

Chromosomes are long, thread-like structures found in the nucleus of a cell, composed of DNA and proteins. They are essential for packaging DNA efficiently and ensuring its proper segregation during cell division.

A dominant allele expresses its trait even if only one copy is present and masks the effect of a recessive allele. This concept is a basic principle in Mendelian inheritance.

The genotype represents the underlying genetic code an organism carries, while the phenotype is the observable expression of that genetic code. Understanding the difference between these two is fundamental in genetics.

When two heterozygous individuals are crossed, the Punnett square shows that 3 out of 4 offspring will have at least one dominant allele. This results in 75% of the offspring displaying the dominant phenotype in a simple Mendelian trait.

Being heterozygous means that an individual has two different alleles for a specific gene. This genetic variation can influence how traits are expressed, especially when combining dominant and recessive relationships.

In the cross between a heterozygous and homozygous recessive individual, the Punnett square indicates that half the offspring receive the dominant allele. Therefore, 50% of the offspring will exhibit the tall phenotype.

X-linked recessive traits are more frequently expressed in males because they have only one X chromosome. Without a second X chromosome to mask the effect, males are more likely to display the trait.

Codominance occurs when both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that shows traits from both alleles concurrently. This is different from complete dominance where one allele masks the other.

Incomplete dominance is when the heterozygous phenotype is intermediate between the two homozygous phenotypes. This results in a blending of traits, where neither allele is completely dominant over the other.

Crossing over occurs during prophase I of meiosis when homologous chromosomes exchange segments of DNA. This exchange creates new allele combinations, contributing to genetic diversity.

Epistasis is the interaction between different genes in which the expression of one gene can mask or modify the expression of another gene. This results in phenotypic ratios that differ from those predicted by simple Mendelian inheritance.

A missense mutation is a point mutation that results in the substitution of one nucleotide for another, possibly changing one amino acid in the protein. This can alter the protein's function depending on the properties of the amino acid change.

Frameshift mutations occur when nucleotides are inserted or deleted, changing the grouping of codons in the DNA sequence. This shift usually results in a completely altered and often nonfunctional protein due to the downstream change in amino acid sequence.

For each gene, the probability of being heterozygous in a cross between heterozygotes is 1/2. Since the two genes assort independently, the combined probability is 1/2 x 1/2 = 1/4, or 25%.

A de novo mutation is a new alteration in the DNA that occurs spontaneously and is not inherited from either parent. This phenomenon can explain the appearance of a trait in an individual even when it is absent in the family history.

Genetic linkage occurs when genes are located close to one another on the same chromosome, making them likely to be inherited together. This relationship can disrupt expected independent assortment patterns.

DNA polymerase is the key enzyme responsible for adding nucleotides to a growing DNA strand during replication. Its role ensures the accurate copying of genetic material.

A silent mutation is a change in the nucleotide sequence that does not alter the amino acid sequence of the protein, due to the redundancy in the genetic code. As a result, the protein's function generally remains unchanged.