Monohybrid Cross
A cross between two true-breeding (Homozygous dominant and homozygous recessive) parents with different variants for a given character to follow one character from generation to generation.
Monohybrid Cross Generations
P: Tall x Dwarf
F1: All tall
F2: 3 Tall: 1 dwarf
Dihybrid Cross
Track two traits that are inherited independently
F2 ratio of a dihybrid cross
9:3:3:1
Gene
unit of heredity that may influence outcome of a trait in an organism
Trait
characteristics of an organism
Dominant allele
allele that determines the phenotype in the heterozygous condition
recessive allele
allele masked by the presence of a dominant allele
True breeding
organism is homozygous for selected trait(s)
Homozygous
diploid individual with two identical alleles of a gene
Heterozygous
two different alleles for a particular trait
genotype
The genetic makeup of an organism
phenotype
The observable characteristics of an organism
Law of segregation
During gamete formation, the alleles for a trait separate from each other, so each gamete carries only one allele for that trait.
When does the law of segregation occur in cell divison?
Anaphase of Meiosis I
What experiment led to the creation of the law of segregation?
Mendel’s monohybrid cross with a 3:1 ratio.
Law of Independent Assortment
Two different genes will randomly assort their alleles during the process that gives rise to gametes.
When does the law of assortment occur?
Metaphase of meiosis I
What experiment led to the law of independent assortment?
Mendel’s dihybrid cross with 9:3:3:1 ratio.
Prophase of mitosis
Chromosomes condense and become visible. Nuclear membrane dissolves. Spindle fibers form and attach to chromosomes.
Metaphase of mitosis
Sister chromatids align in the middle and are attached to both poles by microtubules
Anaphase of mitosis
sister chromatids separate and move towards opposite poles of the cell, pulled by spindle fibers.
Telophase of mitosis
Chromosomes reach opposite poles and nuclear envelope reforms around each set of chromosomes.
Prophase of meiosis I
chromosomes condense and pair up, forming tetrads. Nuclear envelope breaks down, spindle fibers form, and homologous chromosomes cross over.
metaphase of meiosis I
Pairs of sister chromatids align at the metaphase plate.
Anaphase of meiosis I
The two pairs of sister chromatids separate and migrate to a pole
Telophase of meiosis I
the nuclear envelope reforms around the separated chromosomes.
Cytokinesis of mitosis
resulting in two daughter cells
Cytokinesis of meiosis I
results in two daughter cells containing half the number of chromosomes as the parent cell
prophase of meiosis II
Same as prophase of mitosis
metaphase of meiosis II
Same as metaphase of mitosis
Anaphase of meiosis II
Same as anaphase of mitosis
Telophase of meiosis II
Chromosomes reach respective poles and decondense while the nuclear membrane reforms.
Cytokinesis of meiosis II
results in 4 haploid cells
testcross
used to determine the genotype of an individual displaying a dominant trait by crossing the individual with a homozygous recessive individual
wild-type allele
the most common or naturally occurring form of a gene in a population
mutant allele
altered version of a gene that can cause changes in an organism's phenotype
Why can heterozygotes display the same phenotype as a homozygous dominant individual when they only have a single copy of the dominant allele?
half of the enzymes is sufficient or the dominant copy is upregulated
Complete dominance
dominant allele is fully expressed, while the recessive allele remains hidden
codominance
both alleles in a gene pair are fully expressed, resulting in a phenotype that shows traits from both alleles
X-linked inheritance
Genetic inheritance pattern where the gene responsible for a trait or disorder is located on the X chromosome.
Y-linked
Y-linked refers to genes located on the Y chromosome. These genes are passed down exclusively from fathers to their sons.
Sex-influenced inheritance
expression of traits that varies between sexes due to hormonal difference
reciprocal cross
helps determine if the inheritance pattern is influenced by parental sex
incomplete penetrance
a situation in which an allele that is expected to cause a particular phenotype does not
expressivity
degree to which a gene or trait is expressed in an individual
incomplete dominance
intermediate phenotype is expressed when both alleles are present
overdominance
a heterozygote has greater reproductive success than either of the corresponding homozygotes
Codominance
When both alleles of a gene are fully expressed in the phenotype, resulting in a heterozygous individual displaying traits of both alleles
pleiotropy
a single gene influences multiple traits or characteristics in an organism
epistasis
one gene masks or modifies the expression of another gene
Chi-Square formula
Σ((O - E)^2 / E)
gene mapping steps
determine parentals
determine double crossovers
determine middle gene
find short map distances
find long map distance
Formula used for map distance
recombinants/ total number of offspring
Three ways scientists can organize and classify chromosomes
size, location of centromere, and g-banding
deletion
region of a gene is lost
insertion
genetic mutation where a nucleotide is added to a DNA sequence, altering the genetic code.
duplications
a region of a gene is repeated
inversions
a region of a gene is reversed
simple translocations
part of one chromosome is attached to another chromosome
reciprocal translocations
swapping regions in two different chromosomes
When will deletions result in phenotypic effects?
when they remove or alter necessary genes
When will duplications result in phenotypic effects?
when they involve a large piece of a chromosome or occur in multiple generations
When will inversions result in phenotypic effects?
when the location of a gene changes and causes a change in expression
When will translocations result in phenotypic effects?
when they have position effect, break up an essential gene, or are imbalanced
Which type of chromosomal abnormality results in the formation of gene families?
Duplications
Why are gene families evolutionarily important for a species?
allow for the evolution of new gene functions while preserving essential ones to increase diversity
Balanced translocations
when segments from two different chromosomes swap places without any loss or gain of genetic material
Unbalanced translocations
when exchange of genetic material between chromosomes is unequal, resulting in an abnormality
Between balanced translocation and unbalanced translocation, which is more like to have a phenotypic effect?
unbalanced translocation
Non-homologous crossing over
DNA segments from non-homologous chromosomes exchange places due to the two chromosomes having the same repetitive sequences
Homologous crossing over
when two homologous chromosomes exchange piece
Euploid
when chromosomes are divided into equal sets
Diploid
two sets of chromosomes (2n)
triploid
three sets of chromosomes (3n)
tetraploid
four sets of chromosomes (4n)
Aneuploidy
total number of chromosomes cannot divide into equal sets
Trisomy
an additional chromosome (2n + 1)
monosomy
lacking a chromosome (2n - 1)
Experiment performed by Griffith
Showed that genetic material can be transferred between bacteria. Live harmless bacteria transformed into deadly bacteria when exposed to heat-killed bacteria.
Experiment from Avery, McCarty, and McCloud
Determined DNA as the genetic material. They used enzymes to destroy proteins, RNA, and lipids in a bacteria sample. Transformation only occurs when DNA is intact, proving it carries genetic information.
Experiment from Hershey and Chase
Demonstrated that DNA, not protein, is the genetic material. Bacteriophages were labeled with radioactive isotopes (sulfur for proteins and phosphate for bacteria), infecting bacteria. Only DNA was found inside the bacteria, supporting the conclusion that DNA carries genetic information.
Chemical structure of a nucleotide and the parts that make it up
At least one phosphate group, a pentose sugar, and a nitrogenous base
position of a phosphodiester bond
Attachment of a phosphate to the 3’ carbon in one nucleotide and to the 5’ carbon in another
function of a phosphodiester bond
Essential for the formation of the DNA double helix and the stability of the RNA molecule.
Four nitrogenous bases
Adenine (A), Thymine (T) Guanine (G) and Cytosine (C)
Purines
adenine (A) and guanine (G)
Pyrimidines
thymine, uracil (RNA), and cytosine
importance of hydrogen bonding to the structure of DNA
Stabilizing the double-stranded structure of the DNA
RNA polymerase II
reads DNA from 3’ to 5’ and produces it from 5’ to 3’
DNA helicase
an enzyme that separates the two strands of DNA by breaking hydrogen bonds
Topisomerase
travels in front of the helicase to relieve tension by cutting. untwisting, and ligating DNA back together
Primase
synthesizes short RNA primers during DNA reproduction.
DNA Ligase
catalyzes the formation of a covalent bond within the backbones of two DNA strands
End-replication problem
the ends of our chromosomes get a little bit shorter because a primer cannot be made upstream from the 3’ end
Telomerase
Maintains the length of telomeres by acting as a protective cap to help prevent DNA degradation
What cells express telomerase?
Stem cells
Euchromatin
Less condensed form of chromatin that is actively transcribed and accessible for gene expression
Heterochromatin
highly compacted regions of chromosomes in which DNA is transcriptionally inactive
Constitutive heterochromatin
always heterochromatin and permanently transcriptionally inactive