chapter 8-genetics Flashcards
define genetics
the study of how traits are inherited from one generation to the next
define an allele
more than one alternative form of a gene
define a genotype
genetic makeup of an individual
define a phenotype
the physical manifestation of the genetic makeup
what are the 4 principles of inheritance Mendel populated
1) genes exist in alternative forms ( alleles). A gene controls a specific trait in an organism
2) an organism has 2 alleles for each inherited trait, one from each parent
3) the 2 alleles segregate during meiosis resulting in gametes that carry only one allele for any given inherited trait
4) if 2 alleles in an indivudal organisms are different only one will be fully expressed and the other will be silent
what is a homozygous trait
2 copies of the same allele
what is a heterozygous trait
2 different alleles
what is Mendels law of Dominance
the dominant allele is expressed in the phenotype
what is a monohybrid cross
only one trait is being studied
what is the progeny of the P generation
filial ( F generation)
what is a testcross
a diagnostic tool used to determine the genotype of an organisms
with only what type of phenotype can a genotype be predicted with 100% accuracy
recessive
Mendels second law: law of independent assortment
the inheritance of one trait is completely independent of any other
when can the law of independent assortment be used
can be used to explain inheritance only for monohybrid a dihybrid crosses in which parent differ in 2 traits as long as the genes are on separate chromosomes and assort independently during meiosis
typical pattern of mendelian inheritance in a dihybrid cross between heterozygotes with independently assorting traits
9:3:3:1
why are drosophila a model organism for genetics
large number of offspring and short generation time
what is incomplete dominance
some progeny phenotypes are apparently blends of the parental phenotypes
what is codominance
multiple alleles exist for a given gene and more than one of them is dominant
- each dominant allele is fully dominant when combined with a recessive allele but when 2 dominant alleles are present the phenotype is the result of the expression of both dominant alleles simultaneously
what are autosomes
pair of regular non sex chromosomes
how many autosomes do we have
22 chromosomes
who determines the sex of a baby
a male bc his gametes are either X or Y and female is just X
true or false sex chromosomes pair during meiosis and segregate during first meitotic division
true
what are sex linked genes
genes located on the X and Y chromosomes
X or Y chromosome carry most of the sex-linked genes and why?
X bc of its size
why are recessive phenotypes are more frequently found in me
when a recessive gene is found on a X chromosome men will produce it bc there is no dominant
what is an example of sex-linked recessives in humans
goes for hemophilia and colour-blindness
what produces a phenotype ( 2 things)
interactions between the environment and genotype
what is cytoplasmic inheritance + an example
heredity system exist outside the nucleus
-ex. DNA is found in mitochondria and other cytoplasmic bodies
what is nondisjunction
failure of homologous chromosomes to separate properly during meiosis I or the failure of sister chromatids to separate properly during meiosis II
what is trisomy
+ example
- 3 copies ( somatic cells will have 2N +1 chromosomes)
- nondisjunction
- down syndrome caused by trisomy of chromosome 21
what is monosomy
+ example
- single copy of that chromosome ( somatic cells will have 2N-1 chromosomes)
- nondisjunction
turner syndrome: only viable monosomy
-monosomy of the sex chromosome resulting in the genotype XO
if a chromosome has a deficiency what does that mean
the chromosome that loses a fragment
how does chromosomal breakage occur
may occur spontaneously or be induced by environmental factors such as mutagenic agents and X rays
what is a mutation
are changes in the genetic information coded in the DNA of a cell
genetic error with the wrong base or a missing base in the DNA at any particular position
mutations in somatic cells can lead to ___
tumors
ex of mutagenic agents
cosmic rays, X-rays, ultraviolet rays and radioactivity, chemical cpds, carcinogenic
what happens with a N base is added deleted or substituted
when any of these occur inappropriate amino acids may be inserted into polypeptide chains and a mutated protein may be produced
what is a point mutation
a nucleic acid is replicated by another nucleic acid
- there are 3 possible effects on a codon bc they generally invole 1-3 nucleotides
describe silent mutation
the new codon may code for the same amino acid
describe missense mutation
the new codon may code for a different amino acid this may or may not lead to a problem with th resulting protein depending on the role of the amino acid in determining the protein structure
describe nonsense mutation
a new codon may be a stop codon which are often lethal or severely inhibit the functioning of the protein which can lead to many different problems depending on the role of the protein in organisms function
wha tis frameshift mutation
nucleic acids are deleted or inserted into the genome sequence
- this frequenly is lethal
- the length of the genome changes
what is sickle cell anemia and how is it caused
sickle cell anemia: a disease (genetic disorder) in which RBC become crescent shaped bc they contain deficient hemoglobin which carries less O2
-single base pair substitution for valine to glutamic acid
where is bacterial chromosome located
nucleoid region of the cell
what is plasmid
smaller than the single chromosome (bacterial genome) circular rings of DNA which contain accessory pigment
what are episomes
plasmids that are capable of integration into bacterial genome
where does replication begin for bacteria
at a unique origin of replication
what direction does replication occur
in both directions simultaneously
does DNA get synthesized in the 5’ to 3’ or 3’ to 5’
in the 5’ to 3’
how do bacteria reproduce
binary fission
how do bacteria increase their variance
transformation, conjugation, transduction
what is transformation
the process by which a foreign chromosome fragment (plasmid) is incorporated into the bacterial chromosome via recombination creating new inheritable genetic combination
what is conjugation and how does it work
- the transfer of genetic material between 2 bacteria that are temporarily joining
- a cytoplasmic conjugation bridge is formed between the two cells and genetic material is transferred from the donor mal (+) to the recipient female
bacteria must contain what ignorer to undergo conjugation
plasmids called sex factors are capable of conjugation
what is Hfr
High frequency of recombination
- the sex factor becomes integrated into the bacterial genome
- During conjugation the entire bacterial chromosome replicates and begins to move from the donor into the recipient
- Conjugation bridge usually breaks before the entire chromosome is transferred but the bacterial genes that enter the recipient can easily recombine with the genes already present to form novel genetic combination
what is a bacteriophage
virus that infects its host bacterium
what is transduction
Transduction: the a bacteriophage infects its host bacterium by attaching to the bacterium, boring a hole through bacteria cell wall and injecting its viral DNA while its protein coat remains attached to the cell wall
-Occurs when fragments of the bacterial chromosome become packaged into the viral progeny produced during such a viral infection
do chances of transduction increase or decrease as the 2 genes distance on a chromosome decreases
increases
recombination
occurs when liked genes are separated
-It occurs by breakage and rearrangement of adjacent regions of DNA when organisms carrying different genes or alleles for the same traits are crossed
what does an operon consist of
structural genes, an operator region and a promotor region on the DNA before the protein coding genes of DNA that code for proteins
what is regulation of transcription based on
accessibility of RNA polymerase to the gene being transcribed and directed by an operon
regulation of what enables prokaryotes to control their metabolism
transcription
what is the operator
the sequence of nontranscribable DNA that is the repressor binding site
what is the promotor
the noncoding sequence of DNA that serves as the initial binding site of RNA polymerase
what does the regulatory gene code for
codes for the synthesis of a repressor mc that binds to the operator and blocks RNA polymerase from transcribing the structural gene
how do regulatory systems function
by preventing or permitting the RNA polymerase to pass on to the structural genes
what are inducible system
- regulation may occur via them
- which are those that require the presence of a substance called an inducer for transcription to occur
what occurs in an inducible system
the repressor binds to the operator forming a barrier that prevents RNA polymerase from transcribing the structural genes
what must bind to the repressor to allow transcription to occur in an inducible system
-an inducer must bind to the repressor forming an inducer-repressor complex
what does the inducer repressor complex do if an inducer is bound to the repressor
This complex cannot bind to the operator thus removing it as a barrier and permitting transcription
what kind of genes are transcribed when the induced-repressor complex cannot bind to the operator AND what type of proteins
structural genes which encode for an enzyme
- inducible proteins
what is a repressible system
- The repressor is inactive until it combines with the corepressor
- Repressor can bind to the operator and prevent transcription only when it has formed a repressor-corepressor complex
what are corepressors
are end products of the biosynthetic pathways they control
why are the proteins produced in repressible systems said to be repressible
bc they are normally being synthesized; transcription and translation occur until the corepressor is synthesized
what is a constitutive in a repressible system
enzymes which are always synthesized
- Operon containing mutations such as deletions or whose regulator genes code for defective repressor are incapable of being turned off; their enzymes which are always synthesized
what is a pedigree
tools used by geneticists to track one phenotype in a family across generations
-Males are squares and females are circles
what shape are males and females in a pedigree
males=square and females=circle
traits of an autosomal recessive pedigree
- A personal will only be affected if he or she possess 2 copies of the recessive allele (homozygous recessive)
- Roughly affect roughly equal number of males and females
- Can skip a generation due to dominant-phenotype carriers
- when 2 unaffected individuals have offspring that are affected
traits of autosomal dominant pedigree
- a person will be affected if he or she posses one or more copies of the domiant allele ( homozygous or heterozygous)
- effect equal number of males and females
- appear in every generation
- need to have 2 affected individuals who have an unaffected offspring
traits of X linked recessive pedigree
- a person will be affected if he or she possess only affected X chromosomes
- can skip a generation
- more males are affected than females
- when 2 unaffected individuals produce offspring that is affected
