Genetics Summary
I.
How the structure of DNA allows genetics information to serve as the blueprint for an organism and
be passed down through generations.
a. Double-stranded molecule with two complementary strands joined with weak hydrogen bonds,
allowing it to “unzip” and be replicated.
b. Information is stored in the order of nitrogen bases (A, T, C, and G).
II.
How genetic material is used to build and maintain an organism through the synthesis of proteins
(transcription and translation)
a. During transcription, mRNA makes a copy of a gene (a segment of DNA that codes for one
protein) in the nucleus. Messenger RNA will then leave the nucleus.
b. During translation, mRNA and a ribosome meet up in the cytoplasm. tRNA molecules bring
amino acids that correspond to the codons on mRNA. The amino acids are joined together to
form a protein.
c. Proteins are used to build and maintain living cells.
d. Different genes are used by different cells based on their cell type and needs. For example, a
liver cell uses different genes than a muscle cell.
III.
How physical characteristics (phenotype) are determined for organisms.
a. Genes are the unit of heredity; they are passed from parent to offspring. In sexually reproducing
organisms, offspring receive two copies of each gene, one from each parent.
b. Types of inheritance:
i. Simple (mendelian) dominance: In this type of inheritance, there are two versions of each
gene (alleles), one dominant and one recessive. The dominant masks/hides the recessive
gene. Examples include tongue rolling, widow’s peak, and attached ear lobes.
ii. Polygenic inheritance: Polygenic traits are controlled by two or more genes. Examples
include: Skin color, hair color, eye color, and height.
iii. Incomplete dominance: In this type of inheritance, no allele is dominant over the other,
leading to a blending of traits. Example: red, white, and pink flowers.
iv. Codominance: In this type of inheritance, more than one allele is dominant, and they
both show up separately in a heterozygous individual. Examples: roan cows, blood types
1. Blood Types: A, B, AB, and O are the four possible blood types. This results
from different combinations of three different alleles, IA, IB, and i. Type O is the
universal donor due to no antigens on red blood cells. Type AB is the universal
recipient due to A and B antigens on red blood cells.
v. Sex-Linked: Sex-linked genes are carried on the X chromosome. Patterns of inheritance
are different because females have XX and males have Xy when it comes to sex
chromosomes. Because of this, males are more susceptible to a sex-linked condition,
such as red-green color blindness and hemophilia.
c. Pedigrees can be used to interpret patterns of inheritance across generations and determine how a
trait is inherited.
IV.
How genetic diversity arises in sexually reproducing organisms
a. During meiosis (the formation of sex cells), crossing over and random assortment of
chromosomes lead to very genetically diverse gametes.
b. Offspring have genetic material from two different parents contributing to their genome.