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Summary BSC 1010 Unit 4 Study Guide
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This is a comprehensive and detailed study guide on Unit 4 for BSC 1010. *Essential Study Material!!
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BIO PRINCIPLES UNIT 4I. Core Concepts
A. The features/characteristics of the organism are dictated primarily by the genes
inherited from the parents. Mendel worked out the basic concepts of inheritance
patterns. Complex interactions can occur among genes.
B. The genome of the organism is represented in each cell except for gametes (which
have half of the genome). Complex interactions among cells in tissues determine
which genes are active and where during development. That is, cells that form
bone have genes for bone development activated. Whereas cells in muscle tissue
also possess bone developing genes, but these genes are not activated. This
molecular genetics process allows for organisms to develop those features
particular to species.
C. The key to gene function is the information/instructions to produce proteins. The
genes located along the DNA must first be copied by messenger RNA, which is
translated outside the nucleus by ribosomes that produce the appropriate protein.
Mutations occur randomly and are valuable sources of variation to help create the
diversity of life.
II. Basic Concepts
A. Organismal reproduction
a. One of the most important requisites of all life, from the earliest life forms
to present-day organisms, is reproduction
b. Characteristics or traits of organisms must be passed on during
reproduction
B. Cellular Reproduction
a. Life as we know it is based on the cell, the basic unit of life
b. Cell theory states all organisms are made up of cells and come from cells
C. DNA
a. DNA (deoxyribonucleic acid) is the molecule of inheritance in ALL
cellular forms of life
D. Chromosomes
a. Eukaryotic cells possess nuclear DNA with structural and enzymatic
proteins, forming chromatin, which is visible as chromosomes during parts
of the cell cycle
b. Prokaryotic cells possess simpler DNA
c. Sexually reproducing organisms typically have pairs of homologous
chromosomes (look-alike chromosomes)
E. RNA
a. RNA (ribonucleic acid) is found in several forms, most of which are used
in protein synthesis
b. RNA is the molecule of inheritance in some viruses, which are not cell-
based life forms
F. Genes
a. Functional unit of inheritance and basis for most traits
i. Located at loci, or specific positions, on DNA; to be preserved and
transmitted
, ii. Control biological processes though production of proteins and
RNA
b. Genotype refers to the genetic composition of the organism
c. Phenotype refers to the observable inherited traits (eg physical, behavioral,
physiological characteristics); based on the inherited genotype
d. Functions
i. To be preserved and transmitted
ii. To control various biological functions through the production of
proteins (i.e., large, complex sequences of amino acids) and RNA
e. Structure
i. Deoxyribonucleic acid (DNA)
ii. Ribonucleic acid (RNA)
G. Nucleotides
a. The components of nucleic acids; made of three subunits:
i. Sugar (deoxyribose in DNA; ribose in RNA)
ii. Phosphate
iii. Nitrogenous base (one of five possible bases)
1. In DNA, the nucleic acid of chromosomes, four
nitrogenous bases are found: adenine (A), guanine (G),
cytosine (C), and thymine (T)
2. RNA consists of similar bases, except uracil (U) replaces
thymine (T)
3. DNA is a double helix molecule; that is, it is similar to a
spiral staircase or twisted ladder, with the sides formed by
repeating sugar-phosphate groups from each nucleotide,
and the horizontal portions (i.e., steps) formed by hydrogen
bonds involving A with T or C with G
4. Hereditary information: Genes found along the linear
sequence of nucleotides in the DNA molecule
H. Ploidy
a. Homologous chromosome pairs have the same loci, thus genes
b. When both chromosomes are present, for each gene there are two
representatives; this is represented by the symbol 2n or diploid condition
c. When only half of each homologous chromosome pair is present, such as
in gametes, this is represented by the symbol n or haploid
I. Alleles
a. Alternate forms of the same gene that could occupy the same locus (eg
brown versus blue eye color)
b. Homologous chromosomes possess two representatives of each gene (ie
2n)
c. Homozygous refers to the diploid condition where both alleles of the
genotype are identical (eg AA, aa)
d. Heterozygous refers to the diploid condition where both alleles of the
genotype are different (ie Aa)
, e. Dominant alleles form a phenotypic expression regardless of the other
allele on the matched chromosome of the homologue (eg “AA” or “Aa”
genotypes will both express the phenotype designated by the “A” allele)
f. Recessive alleles fail to form a phenotypic expression unless the other
allele on the matched chromosome is also recessive (eg “aa” genotype is
the only way for the phenotype designated by the “a” allele to be
expressed, assuming no other gene pairs influence inheritance)
g. Additional types of allelic interactions will be discussed in subsequent
sections
h. Determining gamete types: assuming there are no mutations, alleles
present in gametes are determined by the diploid genotypes of parents
i. For homozygous genotypes, haploid gametes will be identical for
the given traits (ie AA individual would produce “A” gametes
only; AAbb individual would produce “Ab” gametes only)
ii. For heterozygous genotypes, haploid gametes will be different for
the given traits (ie Aa individual would produce “A” & “a”
gametes; AaBb individual would produce “AB, Ab, aB, ab”
gametes–assuming two traits are unlinked)
III. Foundations of Genetics
A. “Blending Inheritance” theory
B. Gregor Mendel (1822–1884)
a. Australian monk who, through his love and interest in nature, developed
the basic ideas of genetics long before chromosomes and genes (ie
molecular biology) were discovered
i. He developed his ideas by studying plants; in particular, his most
famous work involved crosses with pea plant varieties
b. His results and interpretations contrasted with a prevailing (at that time)
theme of inheritance called “blending” –the concept that inherited traits
mixed to create a composite characteristic in offspring
c. Crosses with Pea Plant
C. Mendel’s First Law: “Segregation of Alternate Factors”
a. Specifically, Mendel discovered that with certain traits, there were
individual plants which, if only crossed with other plants just like them,
would almost always produce the exact same phenotype
i. These individuals were called true-breeders (1 allele; P generation)
ii. We now call this condition homozygous (same allele)
b. He also found that some individuals with similar appearance, when
crossed, would not have all offspring of the same kind
i. We now call this condition heterozygous
c. Mendel decided to systematically do single-trait crosses to determine the
causes for the previously states observations
d. Specifically, a parental generation (P) initiated these experimental crosses
by using two true-breeding pea plants for opposite phenotypes (eg purple
versus white flowers)
e. Offspring from this cross (F1 = heterozygous/hybrids) all showed only one
of the traits (eg purple flowers), and this trait was called the dominant trait
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