GENETICS Flashcards
Genetic material
Polymer of nucleotides
Each consists of Nitrogenous base, Sugar, Phosphate group
Deoxyribonucleic Acid
Reported that DNA composition varies from one species to another
Erwin Chargaff
In any species, the number of A and T bases are equal and the number of G and C bases are also equal
Chargaff’s rule
Introduced the double-helical model structure based on Rosalind Franklin’s X-ray crystallography of the DNA molecule
James Watson and Francis Crick
What rule is
adenine (A) is paired only with _____, and guanine (G) only with _______
thymine (T)
cytosine (C)
chargaff’s rule
2 strands of DNA are complementary
Each strand acts a template for building a new strand in replication
Parent molecule unwind 2 new daughter strands
Base Pairing
predicts that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand
Watson and Crick’s semiconservative model of replication
begins at particular sites called origins of replication
DNA Replication
where the two DNA strands are separated, opening up a replication “bubble”. Replication proceeds in both directions from each origin, until the entire molecule is copied
origins of replication
Y-shaped region at the end of each replication bubble where new DNA strands are elongating
Replication fork
Enzymes that untwist the double helix at the replication fork
Helicases
Bind to and stabilize single- stranded DNA
Single-strand binding proteins
corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA
strands
Topoisomerase
Enzyme for the initiation of the RNA chain
Adds RNA nucleotides one at a time
Primase
Catalyze the elongation of the new DNA at the replication fork
DNA polymerase
The antiparallel structure of the double helix affects the replication.
DNA polymerases only add nucleotides to the free 3’ end of a growing strand
Newly formed strand can only elongate in the 5’ to 3’ direction
Antiparallel Elongation
DNA strand synthesized by the DNA polymerase that moves toward the replication fork
Leading strand
DNA polymerase working on a new DNA strand away from the replication fork
Lagging strand
Segments formed from the lagging strand Later on joined by the DNA ligase
Okazaki fragments
Replicating the Ends of DNA Molecules
Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
The usual replication machinery provides no way to complete the 5’ ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends
Special nucleotide sequences found at the eukaryotic chromosomal DNA ends
Do not prevent shortening of DN molecules
Postpone the erosion of genes near the DNA molecules
Telomeres
It has been proposed that the shortening of telomeres is connected to
aging
Principles that Account for Passing of Traits from Parents to Offspring
“Blended” Hypothesis
“Particulate” Hypothesis
Genetic material from 2 parents blend together
“Blended” Hypothesis
Parents pass discrete heritable units (genes)
“Particulate” Hypothesis
Heritable feature that varies among individuals, ex flower color
Character
Each variant for a character
ex Purple or white color of flower
Trait
Plants that produce offspring of the same variety when they self- pollinate (“P generation”)
True-breeding
Mating of 2 contrasting, true- breeding varieties
Hybridization
Hybrid offspring of the P generation
F1 generation
When F, individuals self-pollinate or cross-pollinate with other F1 hybrids, what are their offsprings called
F2 generation
When Mendel crossed contrasting, true-breeding white- and purple- flowered pea plants, all of the F1 hybrids were purple
When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white
Ratio of about three to one, purple to white flowers, in the F2 generation
Purple flower color= dominant trait
White flower color= recessive trait
The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation
Law of Segregation
What Mendel called a “heritable factor” is what we now call a
gene
Alternative versions of a gene that accounts for variations in inherited characters
Allele
Determines the organism’s appearance
Dominant allele
No noticeable effect on appearance
Recessive allele
Can show the possible combinations of the sperm and egg
Punnett Square
represented by uppercase letter
Dominant allele
represented by lowercase letter
Recessive allele
Organisms with 2 identical alleles for a character
Homozygous
Organisms with 2 different alleles for the gene controlling the character
Not true-breeding
Heterozygous
used to determine gene type
test cross
physical appearance
Phenotype
genetic makeup
Genotype
A cross between such heterozygotes
Monohybrid cross
A cross between F, dihybrids
Can determine whether two characters are transmitted to offspring as a package or independently
Dihybrid cross
Developed from using the dihybrid cross States that each pair of alleles segregates independently of each other pair of alleles during gamete formation
Applied only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome
Genes located near each other on the
same chromosome tend to be inherited
together
Law of Independent Assortment
Laws of Dominance (3)
Complete dominance, Incomplete dominance, Codominance
Occurs when phenotypes of the heterozygote and dominant homozygote are identical
Complete dominance
Phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
Incomplete dominance
dominant alleles affect the phenotype in separate, distinguishable ways
Codominance
are simply variations in a gene’s nucleotide sequence
Alleles
_____ of alleles depend on the level at which we examine the phenotype
dominance/ recessiveness
Most genes exist in populations in more than two allelic forms
Multiple Alleles
Most genes have multiple phenotypic effects, a property called
Pleiotropy
ex of Pleiotropy
Sickle-Cell Disease
A gene at one locus alters the phenotypic expression of a gene at the second locus
Epistasis
ex of Epistasis
coat color of animals Depends on 2 genes
An additive effect of two or more genes on a single phenotype
Polygenic Inheritance
Polygenic Inheritance ex
human skin
includes its physical appearance, internal anatomy, physiology, and behavior
reflects its overall genotype and unique environmental history
phenotype
A family tree that describes the inter-relationships of parents and children across generations
Inheritance patterns of particular traits can be traced and described using this
can also be used to make predictions about future offspring
Pedigree
usually inherited in a recessive manner
Range from relatively mild to life- threatening
Show up only in individuals homozygous for the allele
genetic disorders
Recessive condition characterized by a lack of pigmentation in skin and hair
Albinism
disorders caused by dominant alleles, Cause lethal disease but rare and Arise by mutation
Dominantly Inherited Disorders
A form of dwarfism caused by rare dominant allele
Achondroplasia
Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components
No matter what our genotype, our lifestyle has a tremendous effect on phenotype
Multifactorial Disorders
Fetal Testing types
Amniocentesis, Chorionic Villus Sampling (CVS)
Liquid that bathes the fetus is removed and tested (days)
Amniocentesis
A sample of the placenta is removed and tested (months)
Chorionic Villus Sampling (CVS)
Explains the flow of genetic information from DNA to RNA to make a functional product
Central Dogma
genetic information from DNA to RNA to make a functional product called
protein
exaplain process of Central Dogma
Replication
DNA → RNA → Protein
Transcription Translation
