Genetics Flashcards
1
Q
the basic unit of heredity is the ___
A
gene
2
Q
genes are composed of ___ and are located on ____
A
composed of DNA and are located on chromosomes
3
Q
when a gene exists in more than one form the alternative forms are called ___
A
alleles
4
Q
physical manifestation of the geneti makeup is the individuals ____
A
phenotype
5
Q
what are the 4 princples in medels 1st law of segregation
A
- Genes exist in alternative forms (alleles). A gene controls a specific trait in an organism
- An organism has teo allels for each inherited trait, one inherited from each parent
- the two alleles segregate during meiosis, resulting in gametes that carry only 1 allele for any given inherited trait
- if two alleles are different, only one is fully expressed (the dominant one) and silent one is recessive
6
Q
Monohybrid cross
A
- only looking at 1 trait
- individuals being crossed = parental or P generation
- progeny are the filial or F generation (numbered sequentially F1, F2 …)
- Pp x P produces a (1:2:1) genotypic ratio but a 3:1 phenotypic ratio
7
Q
what is a test cross
A
- used to determine genotype of an organism
- need a recessive phenotype x dominant phenotype (either homozyoug dominant or heterozygous dominant)
8
Q
explain mendel’s second law: independent assortment
A
- dihybrid cross, parents differ in two traits as long as genes are on separate chromosomes and assort independently during meiosis
- inheritance of one trait is completely independent of inheritance of the other
*the closer genes are on a chromosome the more liekly they are to be inherited together though
9
Q
Dihybrid cross
A
10
Q
what is incomplete dominance? what is codominant
A
- blends of parental phenotypes
incomplete: ie if dom = red and rec = white, heterozygous = pink
codominance: hetero = red and white spickled or blood type AB is codominant - both alleles in genotype are expressed at same time without bledning of phenotype
11
Q
explain sex determination
A
- all humans ahve 22 pairs of autosomes (pair of chromosomes), additionally women have a pair of homologous X chromosomes and men have heterologous chromosomes XY
- sex chromosomes pair during meiosis and segregate during the first meiotic division,
female can donate only X but males can donate X or Y determining the sex
- if sperm carries X or Y determines the sex, 50-50% chance
- genes located on X or Y chromosomes are sex linked, in humans most sex linked genes are located on the X
12
Q
explain sex linkage
A
- women have 2 X and men only 1, as a result recessive genes carried on X will produce recessive phenotypes whenever they occur in men bc no other dominant allele to mask
- recessive phenotypes more common in men
- men cannot pass trait to male offspring since pass on Y not the X (only female children can eb affected by the dad), but will not show trait unless get recessive gene from mother
- if this child has sons 50% will be affected (if mother is Xx sons either XY or xY)
*NOTE sex linked recessives generally affect only men, and cannot be passed from father to son but can be passed from grandfather to grandson via daughter who was a carrier
**look for skipping generation
13
Q
how to enivornmental factors effect genetics
A
- interaction between environment and genotype produces the phenotype
- temp can affect wings in drosophilia or hair type in rabbit
14
Q
what is cytoplasmic inheritance
A
- DNA also found in mitochondria and other cytoplasmic bodies
- these cytoplasmic genes may interact with nuclear genes and are important in determining characteristics of organelles
- drug resistance in mnay microorganisms is regulated by cytoplasmic DNA known as plasmids that contain one or more genes
- plasmids can be passed from one bacerial call to another via transformation
15
Q
what is nondisjunction
A
- failure of homologous chromosomes to separate proerly during meitosis I or failure of sister chromatids to separate proerly during meiosis II
- resulting zygote may have either 3 copies of that chromosome (trisomy, 2N+1) or single copy (monosomy 2N-1)
ex: trisomy on chrom 21 = down syndrome - most trisomies and monosomies are lethal cauing the embryo to spontaniously abort in early pregnancy
- can also have nondisjuction of sex chromosomes
16
Q
what are some causes of chromosomal breakage
A
- may occur spontaneously or be induced by environmental factors (mutagenic agents or X-rays)
- chromosome with a lost fragment is said to have a deficiency
- ex of mutagenic agents: cosmic rays, X-rays, ultraviolet rays and radioactivity. also compounds like cholchicine which inhibits spindle formation or mustard gas which alkylates guanine in DNA
*mutagenic agents can also be carcinogenic
17
Q
what is the diff if mutation occurs in somatic cell or in gametes
A
- if in somatic cell can often lead to tumors in the individual
- if in gemetes the mutation will be passed down to offspring
- most mutations occur in regions that do not code for proteins and are silent
18
Q
what is phenylketonuria
A
- molecular disease cause by inability to produce the proper enzyme for metabolism of phenylalanine
- degratation product (phenyl pyruvic acid) accumulates as a result
- administration of any product w. phenylalanine (such as aspartame) can be detrimental to health of individual
- PKU can be caused by a deficiency of phenylalanine hydrolase
19
Q
what is sickle cell anemia
A
- RBC become crescent shape bc contain defective hemoglobin
- these RBC carry less oxygen
- disease caused by substitution of valine (GUA or GUG) for glutamic acid (GAA or GAG) sinlge base pair substituation (missense mutation
20
Q
what does the bacterial genome consist of
A
- singular circualr chromosome located in the nucleoid ragion of the cell
- many bacteria also contain smaller circular regions of DNA called plasmids which contain accessory genes
episomes = plasmids capable of integration into the bacterial genome
21
Q
explain replication in bacteria
A
- begins at origin of replication in both directions, occuring 5’ t 3’
22
Q
how does genetic variance ocur in bacteria
A
- bacterial cells reproduce via binary fission and proliferate very rapidly under favourable conditions
- asexual process but bacteria have 3 mechanisms for increasing genetic variance: transformation, conjugation and transduction
23
Q
explain transformation
A
- process by which a foreign chromocome fragment (plasmid) is incorperated into bacterial chromosome via recombination creating new inheritable generic combinations
24
Q
explain conjugation
A
- sexual mating in bacteria
- transfer of genetic info between two bacteria that are temporarily joined via cytoplasmic conjugation between cells
- genetic info transferred from donor male (+) type to the recipient female (-) type
- only bacteria containing plasmids called sex factors are capable of conjugation (ex: F facor in ecoli, cells either F+ if have it or F- if they dont)
- genes coding for antibiotic resistance may be found on plasmids and transferred into recipient cells along with these factors
25
Q
what are Hfr cells
A
- sex factor F can become integrated into bacterial genome
- during conjugation the entire bacterial chromosome replicated and begins to move from donor cell into recipient
- conjugation bridge typically breaks before the entire chromosome is transferred but the bacterial genes that entered the cell easily recombine with genes arlready present to form novel genetic combinations
- these bacteria are called Hfr cells (high frequency of recombination
26
Q
what is transduction
A
- a bacteriophase is a virus that infects host bacterium by attaching to it
- makes a hole in bacterial cell wall and injects the viral DNA while its protein coat remains attached to cell wall
- transduction occurs when fragments of bacterial chromosome become packages into the viral progeny produced during viral infection
- these virons may infect other bacteria and introduce new genetic arrangements through recombination with host cell’s DNA
- closer the two genes are on the chromosome the more liekly they are to transduce each toher
27
Q
explain recombination
A
occurs when linked genes are separated
- occurs by breakage and rearrangement of adjacent regions of DNA when organisms carrying different genes or alleles for the same traits are crossed
28
Q
how is transcription regulated
A
- transcription is regulated ti enable prokaryotes to control metabolism
- based on accessibilty of RNA polymerase to genes being transcribed and is directed by an operon
- operon consists of structureal genes, an operator and promoter region on DNA before the protein coding genes
- structural genes contain sequences of DNA that code for proteins
- operator = non transcribable DNA that is the repressor binding site
- promoter is non coding seq that serves as binding site for RNA polymerase
- regulator gene codes for synthesis of a repressor molecule that binds to the operator and blocks RNA polymerase
29
Q
what is an inducible system
A
- requires an inducer for transcription to occur
- repressor binds to operator to form barrier preventing RNA pol
- for intracription to occur inducer binds to the repressor forming inducer-receptor complex
- complex cant bind to operator so RNA pol can transcribe
*structural genes usually code for enzyme and the inducer is the substrate, so only make the enzymes when substrate is present
30
Q
explain repressible systems
A
- repressor is inactive until is combines with a corepressor
- repressor ca bind to operator to prevent transcrition only when has formed a repressor-corepressor complex
- corepressors are typically the end product of biosynthetic pathways they control
- proteins synthesized are repressible bc they are normally synthesized unstil corepressor is synthesized
- if the operon contains a mutation or the repressor is defective it wont be able to be turned off: enzymes being synthesized will be constituative
