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1

genetics

study of..

how traits are inhereted from one generation to the next

2

basic unit of heredity

gene

3

genes composed of

4

genes are located on the

5

alleles

genes existing in more than one form

6

genotype

genetic makeup of an individual

7

phenotype

physical manifestation of genotype

8

phenotypes can correspond to a single or several of these

genotypes

9

Gregor Mendel

1860s

basic principles of genetics

garden pea experiments

10

garden pea experiment

inheritance of individual pea traits by performing genetic crosses

11

genetic crosses

mendel's pea experiments

true-breeding individuals with different traits

mated them

statistically analyzed inheretance of traits in progeny

12

mendel's first law

law of segregation

13

mendel's four postulates of inheritance

(law of segregation)

1. genes exist in alternative forms (alleles)

2. organism has two alleles for each inherited trait, one from each parent

3. two alleles segregate during meiosis ---> gametes carry one allele for any given trait

4. two alleles in individual are different - only one expressed, other is silent

14

dominant allele

allele which is expressed

15

recessive allele

allele which is silent in presence of dominant allele

16

homozygous

organisms that contain two copies of same allele

homozygous for that trait

17

heterozygous

organisms that carry two different alleles

18

Mendel's law of dominance

dominant allele appears in phenotype

19

monohybrid cross

(mendel's first law - law of segregation)

only one trait studied in particular mating 

(i.e. color)

20

Parental or P Generation

(mendelian genetics)

individuals being crossed

 

21

filial / F generation

progeny generations

22

Punnett Square Diagram

(Mendel's First Law - Law of Segregation)

used to predict genotypes expected from a cross

23

Testcross

Reasoning

(Mendel's First Law - Law of Segregation)

genotype can only be predicted from recessive phenotype

dominant phenotype - homozygous or heterozygous

24

testcross

used to

 determine unknown genotype of org with dominant phenotype

25

test cross

(aka back cross)

definition

organism with dominant phenotype of unknown genotype (Ax) crossed with phenotypically recessive organism (genotype aa)

26

results of test cross

P: AA x aa 

F1: 100% Aa; 100% dominant phenotype

P: Aa x aa

F1: 50% Aa; 50% dominant phenotype

50% aa; 50% recessive phenotype

27

Mendel's Second Law

Law of independent assortment

28

law of independent assortment

(principle)

law of segregation applies as long as genes are on separate chromosomes and assort independently

genes on same chromosomes stay together unless crossing over occurs

 

 

29

law of independent assortment

dihybrid cross

P generation:

purple flower tall pea plant (TTPP)

x

white flowered dwarf pea plant (ttpp)

F1 progeny - TtPp genotype

dominant phenotype

 

30

crossing over

(application to law of independent assortment)

crossing over may break linkage of certain pattern

i.e. redheads + freckles; sometimes blondes have freckles

31

Dihybrid Cross

F1 Generation

F1 Generation self crossed

TtPp x TtPp

4 phenotypes

9:3:3:1

(sorts as it would in monohybrid:

3:1 ratio favor dominant)

32

Non-Mendelian Inheritance

Complications with Mendelian

Genotype doesn't translate into phenotype 100% 

not 100% of recessive phenotype have 100% recessive genotype

33

Incomplete Dominance

(complications with mendelian genetics)

phenotype of heterozygote is intermediate of phenotypes of homozygotes 

34

incomplete dominance 

example:

snapdragon flowers

P: RR x rr 

(red x white)

F1 genotypic ratio: 100% Rr

F1 phenotypic ratio: Rr = pink

F1: Rr x Rr

(pink x pink)

F2 genotypic ratio: 1 RR: 2 Rr: 1 rr

F2 phenotypic ratio: 1 red: 2 pink: 1 white

35

Codominance

(non-mendelian inheritance)

multiple alleles exist for given gene

more than one is dominant

each dominant allele fully dominant when combined with recessive

two dominant alleles:

phenotype is result of expression by both dominant alleles simultaneously

36

Codominance 

example:

ABO blood groups

Blood type determined by three alleles:

IA, IB, i

only 2/3 allele present in individuals

all alleles present in human population

IA, IB - dominant

i - recessive

IAIA or IAi - blood type A

IBIB or IBi - blood type B

ii - blood type O

IAIB - blood type AB

 

37

Sex Determination

(Mendelian genetics)

for every mating event, 50% chance boy, 50% girl

38

autosomes

non sex chromosomes

22/23 chromosome pairs

39

sex chromosomes

1/23 pairs

determine sex of organism

females - XX

males XY

40

gender determination

females produce only X chromosome

male determine gender of zygote - produce X or Y

41

sex linked chromosomes

genes located on X or Y chromosomes 

42

most sex linked chromosomes carried on the ___ chromosome

X chromosome

43

Sex Linkage

(Mendelian Genetics) 

recessive genes carried on X chromosome will produce recessive phenotype in males

(only one X)

no dominant allele present to mask

recessive phenotype much more common in males

44

examples of sex linked recessives

hemophilia

color-blindness

45

sex-linkage inheritance

affected males pass on trait to all daughters (X), no sons (Y)

can be passed from father to grandson via carrier daughter

 

46

Drosophila melanogaster

helped provide explanations for mendelian genetic patterns

advantages for genetic research

47

Advantages of Drosophila melanogaster for genetic research

(5)

  • reproduce often (short life cycle)
  • reproduce large numbers
  • large chromosomes
  • few chromosomes (4 pairs; 2n=8
  • frequent mutations

48

analyses of D. melanogaster led to discoveries

(2)

pattners of embryological dev.

how genes expressed in early dev affect adult organism

49

Environmental Factors

(Mendelian Genetics)

interaction between environment and genotype produces phenotype

50

Enviornmental factors in genetics and Drosophila

with given set of wings:

crooked wings at low T

straight wings at high T

51

environmental factors in mendelian genetics in Himalayan hare

same color genes

white on warmer parts of body

black on colder parts of body

(if naturally warm parts cooled with ice, hair will grow black)

52

Genetic Problems

chromosome number and structure maybe altered by abnornal cell division

  • during meiosis
  • by mutagenic agents

53

Nondisjunction 

(genetic problems)

failure of homologous chromosomes to sep. properly during

meiosis I 

failure of sister chromatids to separate properly during

meiosis II

54

result of nondisjunction

(genetic problems)

3 copies of a chromosome - trisomy 

(somatic cells - 2N + 1)

1 copy of chromosome - monosomy

(somatic cells - 2N - 1)

55

most monosomies and trisomies result in

spontaneous abortion of embryo early in term

56

nondisjunction may also occur in sex chromosomes, resulting in

extra or missing copies of X and/or Y

57

Chromosomal Breakage

(genetic problems)

occur spontaneously

or induced by environmental factors 

58

environmental factors causing chromosomal breakage

X-rays, mutagenic agents

59

deficiency

(chromosomal breakage - genetic problems)

chromosome that loses fragment

60

Mutations

definition

(genetic problems)

changes in genetic information of a cell

coded in DNA

61

Mutations in somatic cells

can lead to tumors

62

mutations in gametes (sex cells)

transmitted to offspring

63

most mutations occur in regions of DNA that

do not code for proteins

are silent 

64

silent regions of DNA

not expressed in phenotype

65

mutations that change the sequence of the amino acids in proteins are most often

recessive

deleterious

66

Mutagenic Agents

(mutations)

mutagenic agents induce mutations

e.g. cosmic rays

X-rays

UV rays

radioactivity

chemical compounds - colchicine, mustard gas

67

mutagenic agents are generally

(mutations - genetic problems)

carcinogenic

68

colchicine

(chemical compound - mutagenic agent)

inhibits spindle formation

causes polyploidy

69

polyploidy

cells and organisms containing more than two paired (homologous) sets of chromosomes

70

carcinogenic

any substance directly involved in causing cancer

71

mutation types

(mutations - genetic problems)

gene

protein

72

gene mutation

nitrogen bases

added

deleted

subsituted

thus creating different genes

73

protein mutations

incorrect amino acid inserted in polypeptide chain

mutated protein produced

74

mutation

definition

genetic error with wrong/no base on DNA at particular position

75

examples of genetic disorders

phenylketonuria (PKU)

sickle-cell anemia

76

phenylketonuria (PKU)

definition

autosomal recessive 

genetic disorder

molecular disease

77

PKU caused by

 inability to produce proper enzyme for metabolism of phenylanine

 

78

result of PKU

degradation product (phenypyruvic acid) accumulates

can affect mental development

79

Sickle-cell anemia

definition

red blood cells become crescent-shaped because contain defective hemoglobin

80

sickle cell hemoglobin characteristic

carries less oxygen

81

sickle cell anemia caused by

substitution of valine (GUA or GUG)

for glutamic acid (GAA or GAG)

due to single base pair substitution in gene coding for hemoglobin

82

Molecular Genetics

DNA is basis for heredity

self-replication ensures that coded sequence will be passed on to successive generations

83

genes composed of

DNA

84

DNA contains 

information coded in sequence of base pairs

85

DNA provides

blueprint for protein synthesis

86

DNA reproduces via

self replication

87

DNA's ability to self-replicate is crucial for

cell division ---> reproduction

88

mutable

DNA is mutable and can be altered 

89

Changes in DNA and evolution

changes in DNA are stable and can be passed on from gen to gen ---> evolution

90

CUT PIE

cytosine, uracil, thymine

are

PYrimidines

91

PURe As Gold (Ag)

Adenine and Guanine are Purines

92

basic unit of DNA

(structure of DNA)

nucleotide

93

composition of nucleotide

deoxyribose (sugar)

bonded to:

phosphate group

nitrogenous base

94

two types of nitrogen bases

purines

pyrimidines

95

purines in DNA

adenine

guanine

96

pyrimidines in DNA

Cytosine

Thymine

Uracil

97

backbone of nucleotide

phosphate group and sugar (deoxyribose)

98

bases arranged as (on chain)

side groups

99

physicality of DNA

double-stranded helix

100

composition of double-stranded helix

sugar phosphate on outside

base pairs on inside

101

hydrogen bonding in double-stranded helix

base pairs are attracted by hydrogen bonds

2 hydrogen bonds between A = T

3 hydrogen bonds between C = G

 

the more C=G pairs, the tighter the two strands are bound

102

base pairing forms

"rungs" on interior of double helix 

links two polynucleotide chains together

103

Watson-Crick DNA Model

double-standed helix

sugar phosphate backgone

nucleotide base pairs inside

A-T; C-G

base pairs bonded via hydrogen bonding

holds together polynucleotide chains

104

DNA replication

(function of DNA)

double-stranded DNA unwinds

separates into two single strands

each strand template for complementary base-pairing

synthesis of two new daughter helices proceeds

105

each new daughter helix contains

(DNA replication)

strand from parent helix

newly synthesized complementary strand

106

semiconservative

(DNA replication)

in reference to new daughter helices complementary to parent helices

107

daughter helices are identical to

each other

parent helix

108

Language of DNA

Genetic Code

(fxn of DNA)

A,T,C,G

109

language of proteins

genetic code

20 amino acids

110

to form amino acids, DNA translated by

mRNA

111

triplet code

amino acid codons

64 different codons coding 20 amino acids

112

base sequence of mRNA translated to

codons

series of triplets

113

composition of codons

sequence of three consecutive bases

codes for particular amino acids

e.g. GGC - glycine

GUG - valine

114

genetic code is universal!

genetic code is universal!

for all organisms

115

codon possibilities

64 codons based on triplet code

20 amino acids to code for

redundancy

116

redundant codons

64 codons

20 amino acids

codon synonyms

multiple codons code for the same amino acid

each codon codes for only one amino acid

117

degeneracy 

or 

redundancy 

of the genetic code

property of 64 codons coding for 20 amino acids

118

AUG

start codon

Met (Methionine)

119

stop codons

UAA

UGA

120

RNA

(molecular genetics)

ribonucleic acid

polynucleotide structurally similar to DNA

121

RNA structure

similiar to DNA

sugar = ribose 

contains uracil (U) instead of thymine (T)

usually single stranded

122

RNA found in

nucleus 

cytoplasm

123

main types of RNA

mRNA

tRNA

rRNA

124

all types of RNA are involved in some aspect of

protein synthesis

125

mRNA

messenger RNA

fxn

carries complement of a DNA sequence and transports it from nucleus to ribosomes

(ribosomes = sight of protein synthesis)

 

126

mRNA structure

composed of ribonucleotides complimentary to "sense" strand of DNA

"inverted" complmenentary of original master DNA

e.g.

DNA - AAC (valine)

mRNA - UUG

127

monocistronic

one mRNA strand codes for one polypeptide

128

tRNA

transfer RNA

found in

cytopolasm

129

tRNA

fxn

aids in translation of mRNA's nucleotide code into sequence of amino acids

brings amino acids to ribosomes during protein synthesis

130

tRNA quantity

40 known types

at least one type of tRNA for each amino acid

131

rRNA

ribosomoal RNA

structural component of ribosomes

 

132

most abundant RNA

rRNA

133

site of rRNA synthesis

nucleolus

134

Protein Synthesis

2 events

Transcription

Translation

135

Transcription

information coded in base sequence of DNA transcribed into strand of mRNA

136

DNA is transcribted into mRNA in the ____

then mRNA ____

nucleus

leaves nucleus through nuclear pores

137

Translation

site

(protein synthesis)

cytoplasm

138

translation process

mRNA codons translated into sequence of amino acids

involves tRNA, ribosomes, mRNA, amino acids, enzymes, other proteins

139

tRNA function

(translation)

brings amino acids to ribosomes in correct sequence for polypeptide synthesis

140

in translation, tRNA recognizes

both amino acid and mRNA codon

dual function

141

tRNA structure

reflects function

one end:

contains anticodon - 3 nucleotide sequence

complimentary to one of the mRNA codons

other end: 

site of amino acid attachment

142

aminoacyl-tRNA synthetase

has active site that binds to amino acid and corresponding tRNA

forms aminoacyl-tRNA

143

ribosomes

structure

two subunits - one large, one small

consits of proteins and rRNA

subunits bind together only during protein synthesis

144

ribosome binding sites

(3)

1. mRNA

2. P site - tRNA

3. A site - tRNA

145

p site

tRNA ribosome binding site

peptidyl-tRNA binding site

binds to tRNA attached to growing polypeptide chain

 

146

A site 

tRNA

ribosome binding site

aminoacyl-tRNA complex binding site

binds to incoming aminoacyl-tRNA complex

147

polypeptide synthesis

stages

initiation

elongation

termination

148

initiation

(translation)

1. ribosome binds to mRNA near 5' end

ribosome scans mRNA until binds to start codon (AUG)

2. initiator aminoacyl-tRNA complex, methionin-tRNA (anticodon 3'-UAC-5') base pairs with start codon

149

elongation 

(translation)

1. hydrogen bonds form between mRNA codon in A site and its complementary anti-codon on incoming aminoacyl-tRNA complex

2. peptide bond formed between amino acid attached to tRNA in A site and met attached to tRNA in P site

3. ribosome carries uncharged tRNA in P site and peptidyl-tRNA in A site

4. translocation - ribsoome advances 3 nucleotides along mRNA in 5'-->3'

5. uncharged tRNA in P site expelled and peptidyl-tRNA from A site moves onto P site

6. ribosome has empty A site ready for entry of aminoacyl-tRNA corresponding to next codon

150

translocation

(translation - elongation)

ribsome advances 3 nucleotides along mRNA in 5'-->3'

151

termination

(translation)

1. stop codon arrives in A site

2. signal ribsoome to terminate translation

3. DO NOT CODE FOR AMINO ACIDS

4. frequently, polyribosome formed

152

polyribosome formation

(translation - termination)

many ribosomes simultaneously translate a single mRNA molecule forming a polyribosome

occurs during termination 

153

protein primary formation following termination

upon release from ribosome, protein immediately assumes conformation

conformation determined by primary sequence of amino acids

154

Cytoplasmic Inheritance

(molecular genetics)

heredity systems exist outside nucleus

DNA found in chloroplasts, mitochondria etc

cytoplasmic genes interact with nuclear genes ---> determine characteristics of organelles

155

plasmids

(cytoplasmic inheritance)

cytoplasmic DNA

contain 1+ genes

regulate drug resistance in micro-organisms

156

Bacterial genome

structure and location

(Bacterial genetics)

single circular chromosome located in nucleoid

may also contain plasmids

157

plasmids

(bacteria)

small circular rings of DNA 

contain accessory genes

158

episomes

plasmids

capable of intergraiton into bacterial genome

159

replication

(bacterial genetics)

begins at unique origin

proceeds in both directions simultaneously

160

Genetic Variance

3 mechanisms

(bacterial genetics)

 

transformation

conjugation

transduction

161

method of bacterial replication

binary fission

 

162

binary fission

method of bacteria cells replication

asexual process

163

transformation

(genetic variance - bacterial genetics)

foreign chromosome fragment (plasmid) incorporated into bacterial chromosome 

via recombination

164

conjugation

genetic variance - bacterial genetics

"sexual mating" in bacteria

transfer of genetic material between two bacteria that are temporarily joined

 

165

conjugation

mechanism

genetic variance

bacterial genetics

cytoplasmic conjugation bridge formed between two cells

genetic material transferred from donor male (+) to recipient female (-)

bacteria must contain plasmids - sex factors

166

Sex Factor

F factor

Conjugation

Genetic Variation

Bacterial Genetics

present in E. coli

bacteria possessing it - F+

bacteria void - F-

during conjugation bw F+/F-

F+ replicates F factor, donates copy to recipient --> converts to F+

167

Sex Factor and transfer

Conjugation

Genetic Variance

Bacterial Genetics

genes that code for various characteristics

e.g. antibody resistance

may be found on plasmids and transferred to recipient cells along with sex factors (i.e. F+)

168

Consequences of Conjugation + Sex factors

sex factor may become integrated into bacterial genome

during - entire bacterial chromosome replicates and begins to move from donor cell to recipient cell

conjugation bridge breaks before entire chromosome transferred

bacterial genes may recombine with bacteria genes already present to form novel genetic combinations

 

 

169

170

Hfr cells

 bacterium with a conjugative plasmid (often the F-factor) integrated into its genomic DNA

171

Transduction

(genetic variation - bacterial genetics)

fragments of bacterial chromosome accidentally become packaged into viral progeny produced during viral infection

virions may infect other bacteria 

introduce new genetic arrangements through recombination with the new host cell's DNA

the closer two genes are to one another on a chromosome the mroe likely they will be to transduce together

172

Recombination

genetic variation - bacterial genetics

occurs when linked genes are separated

via breakage and rearrangements of adjacent regions of DNA

when organisms carrying different genes or alleles for the same traits are crossed

173

regulation of gene expression allows prokaryotes to control their

metabolism

174

regulation of transcription is based on accessiblity of 

RNA polymerase

175

RNA polymerase

enzyme

3' --->

necessary for constructing RNA chains using DNA genes as templates (transcription)

176

gene regulation enables...

(bacterial genetics)

prokaryotes to control metabolism

 

177

another word for gene expression

(bacterial genetics)

transcription

178

regulation of transcription based on..

(bacterial genetics)

accessbility of RNA polymerase to the genes being transcribed

179

regulation of transcription directed by..

(bacterial genetics)

operon

180

operon

(bacterial genetics)

consists of

structural genes

operator gene

promoter gene

 

181

structural genes

sequences of DNA that code for proteins

182

operator gene

sequence of nontranscribable DNA 

repressor binding site

183

repressor

 DNA-binding protein

regulates the expression of one or more genes

binds to the operator and blocks the attachment of RNA polymerase to the promoter

preventing transcription of the genes

184

promoter

noncoding sequence 

intial binding site for RNA polymerase

185

regulator gene

codes for synthesis of a repressor molecule

186

in order to transcribe structural genes, RNA polymerase must

move past operator

187

regulatory systems function

prevent or permit RNA polymerase to pass on to structural genes

188

modes of regulation

inducible systems

repressible systems

189

inducible system 

basic

(transcription - bacterial genetics)

require presence of inducer

190

repressible system

basic

(transcription - bacterial genetics)

in constant state of transcription

unless corepressor inhibits 

191

inducible systems

mechanism

repressor binds to operator

forms barrier that prevents RNA polymerase from transcribing structural genes