Genetics

Question 1

the basic unit of heredity is the ___

Answer 1

gene

Question 2

genes are composed of ___ and are located on ____

Answer 2

composed of DNA and are located on chromosomes

Question 3

when a gene exists in more than one form the alternative forms are called ___

Answer 3

alleles

Question 4

physical manifestation of the geneti makeup is the individuals ____

Answer 4

phenotype

Question 5

what are the 4 princples in medels 1st law of segregation

Answer 5

1. Genes exist in alternative forms (alleles). A gene controls a specific trait in an organism
2. An organism has teo allels for each inherited trait, one inherited from each parent
3. the two alleles segregate during meiosis, resulting in gametes that carry only 1 allele for any given inherited trait
4. if two alleles are different, only one is fully expressed (the dominant one) and silent one is recessive

Question 6

Monohybrid cross

Answer 6

• 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

Question 7

what is a test cross

Answer 7

• used to determine genotype of an organism
• need a recessive phenotype x dominant phenotype (either homozyoug dominant or heterozygous dominant)

Question 8

explain mendel’s second law: independent assortment

Answer 8

• 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

Question 9

Dihybrid cross

Answer 9

Question 10

what is incomplete dominance? what is codominant

Answer 10

• 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

Question 11

explain sex determination

Answer 11

• 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

Question 12

explain sex linkage

Answer 12

• 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

Question 13

how to enivornmental factors effect genetics

Answer 13

• interaction between environment and genotype produces the phenotype
• temp can affect wings in drosophilia or hair type in rabbit

Question 14

what is cytoplasmic inheritance

Answer 14

• 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

Question 15

what is nondisjunction

Answer 15

• 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

Question 16

what are some causes of chromosomal breakage

Answer 16

• 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

Question 17

what is the diff if mutation occurs in somatic cell or in gametes

Answer 17

• 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

Question 18

what is phenylketonuria

Answer 18

• 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

Question 19

what is sickle cell anemia

Answer 19

• 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

Question 20

what does the bacterial genome consist of

Answer 20

• 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

Question 21

explain replication in bacteria

Answer 21

• begins at origin of replication in both directions, occuring 5’ t 3’

Question 22

how does genetic variance ocur in bacteria

Answer 22

• 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

Question 23

explain transformation

Answer 23

• process by which a foreign chromocome fragment (plasmid) is incorperated into bacterial chromosome via recombination creating new inheritable generic combinations

Question 24

explain conjugation

Answer 24

• 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

Question 25

what are Hfr cells

Answer 25

- 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

Question 26

what is transduction

Answer 26

- 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

Question 27

explain recombination

Answer 27

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

Question 28

how is transcription regulated

Answer 28

- 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

Question 29

what is an inducible system

Answer 29

- 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

Question 30

explain repressible systems

Answer 30

- 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**