Molecular Biology

2

Genetics = Information Flow

Transmission Genetics =Classical Genetics = information flow between generations

Molecular Biology = Molecular Genetics = information flow within cells/organisms

DNA RNA Protein = THE CENTRAL DOGMA

3

pea plant from green seed

Data of Goss (1824)

Xpea plant from yellow seed

All seeds yellow – grow and self fertilize

Some pods with allyellow seeds – grow into plants andself fertilize

Some pods with all seedsyellow, some with green and yellow seeds

Some pods with allgreen seeds

Many pods with both yellow and green seeds

Self fertilization ofplants grown from green

All progeny plants Have pods with green seeds only

5

6

Data of Mendel (1866)

pea plant from green seed X

pea plant from yellow seed

All seeds yellow - Grow into plants and self fertilize(F1)First filial

generation

Count # of green and yellow seeds:- 8023 total seeds- 6022 yellow- 2001 green – grown into plants: self fertilization yields all green seeds

(F2)second filialgeneration

Take 519 yellow seeds – grown into plants: self fertilizationOf these 519 plants, 166 bred true (all yellow seeds), 353 did not (mixed yellow and green seeds)

7

Mendel’s modelTrue breeding yellow AA

True breeding green aa

egg cells pollen cells

x

fertilize

Aa (yellow seeds) – grow into plants and self fertilizeF1

F2AA Aa

aA aa

(pollen)

(eggs)

A

A

a

a

3:1 yellow:green__________________¼ true breeding yellow½ “impure” yellow¼ true breeding green

aA

8

Mendel’s First Law

Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).

Testing the law:- the test cross (Aa x aa) predicts new ratios- other traits tested

*Introduce modern terms: dominant, recessive, alleles, phenotype, genotype, heterozygote,homozygote

9

10

11

12

13

Results of all Mendel's crosses in which parents differed for one character

Parental phenotype F1 F2 F2 ratio

1 . Round X wrinkled seeds All round 5474 round; 1850 wrinkled 2.96:1

2. Yellow X green seeds All yellow 6022 yellow; 2001 green 3.01:1

3. Purple X white petals All purple 705 purple; 224 white 3.15:1

4. Inflated X pinched pods All inflated 882 inflated; 299 pinched 2.95:1

5. Green X yellow pods All green 428 green; 152 yellow 2.82:1

6. Axial X terminal flowers All axial 651 axial; 207 terminal 3.14: 1

7. Long X short stems All long 787 long; 277 short 2.84: 1

What happens if two character traits are followed simultaneously?

14

Fig. 13.16

15

16

Mendel’s Second Law

Second Law=The Law of Independent Assortment:

During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.

17

Mendel’s Second Law

The Law of Independent Assortment: During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.

Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).

Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).

Mendel’s First Law

18

Genes’ (alleles’) eye view of meiosis and mitosis

A / a

A a

A aA a

chromosome (DNA) replicationduring S phase prior to mitosis

A a

A aA a

A a

A a

mitotic metaphaseanaphase, telophase,cytokinesis

A

a

A

a

A

abb

BB

B

b

aa

bb

AA B

B

genotype: Aa; Bb

Meiosis I metaphase

Meiosis I product cells

replication

Meiosis I anaphase,telophase, cytokinesis

aa

bb

AA B

B

Meiosis I product cells

A B

A B

a b

a b

Meiosis II product cells

Meiosis II anaphase,telophase, cytokinesis

Meiosis II metaphase

Meiosis II metaphase

AB

AB

ab

ab

aa

bb

AA

BB

Meiosis I product cells

A

B

A

a

a

b

Meiosis II products cells

Meiosis II anaphase,telophase, cytokinesis

Meiosis II metaphase

Meiosis II metaphase

b

B

Ab

Ab

aB

aB

Figure 2-30

Pseudoachondroplasia phenotype

Figure 2-26

Red-eyed and white-eyed Drosophila

26

Eye Color Is a Sex-Linked Trait in Drosophila

female male female male

females males females males

white-eyed, normal-winged female x red-eyed, miniature winged male (wild type)

w+ mw m+

w m+

w m+

w+ m

wild type females w m+

white-eyed, normal-winged males

x

w m+

½ red-eyed, miniature winged

for male progeny, EXPECT:

w+ m

½ white-eyed, normal-winged

64% of males fell into above classes, but 36% were either wild typeOr doubly mutant !!!!!!!

w m+

w+ m

wild type females

genetic recombination = chromosomal crossing over

36% of chromosomes in meiosis I:

w m+

white-eyed, normal-winged males

x

w+ m+ w m

36% of males are either doubly mutant or wild type :

Figure 4-4Chiasmata are the sites of crossing over

Chiasmata visible inLocusta migratoria spermatogenesis

A synaptonemal complex

Chapter 4 OpenerA recombination-based map of one of the chromosomes of Drosophila

vermillion (v+ = red eyes, v = vermillion eyes)crossveinless (cv+ = normal wing veins, cv = missing crossveins)cut (c+ = normal wing margins, c = “snipped” wing margins)

v+. cv . ct x v . cv+ . ct+

v+/v . cv/cv+ . ct/ct+ x v/v . cv/cv . ct/ct (three point testcross)

phenotype # of progeny % of progeny recombinant v ..cv+ . ct+ 580 40% NRv+ . cv . ct 592 41% NRv .. cv . ct+ 45 3% v,cv ; cv,ctv+ . cv+ . ct 40 3% v,cv ; cv,ctv .. cv . ct 89 6% v,cv ; v,ctv+ . cv+ . ct+ 94 6% v,cv ; v,ctv ..cv+ . ct 3 0.2% v,ct ; cv,ctv+ . cv . ct+5 0.3% v,ct ; cv,ct

Phenotype # of progeny(T=1448) % of progeny recombinant v ..cv+ . ct+ 580 ~40% NRv+ . cv . ct 592 ~41% NRv .. cv . ct+ 45 ~3% v,cv ; cv,ctv+ . cv+ . ct 40 ~3% v,cv ; cv,ctv .. cv . ct 89 ~6% v,cv ; v,ctv+ . cv+ . ct+ 94 ~6% v,cv ; v,ctv ..cv+ . ct3 ~0.2% v,ct ; cv,ctv+ . cv . ct+ 5 ~0.3% v,ct ; cv,ct

v,cv recombinants: 45 + 40 + 89 + 94 = 268 = 18.5%v,ct recombinants: 89 + 94 + 3 + 5 = 191 = 13.2%ct,cv recombinants: 45 + 40 + 3 + 5 = 93 = 6.4%

Aha! The genes must all be on the same chromosome! (RF’s < 50%)

Hmmm…why is the measured distance between v,cv (18.5m.u.) less than the sum of the measured v,ct (13.2 m.u.) and ct,cv (6.4 m.u) distances(=19.6 m.u.)?

v ct cv13.2 m.u. 6.4 m.u.

double recombination

Hmmm…What is the expected # of double recombinants? A: 0.132 * 0.064 = .0084.0084 * 1448 = 12 expected double recombinantsBut… we got only 8 (3+5) Why?A: Interference! I = 1 - coefficient of coincidence (coc = o/e) = 0.33

v ct cv13.2 m.u. 6.4 m.u.

phenotype # of progeny % of progeny recombinant v ..cv+ . ct+ 580 ~40% NRv+ . cv . ct 592 ~41% NRv .. cv . ct+ 45 ~3% v,cv ; cv,ctv+ . cv+ . ct 40 ~3% v,cv ; cv,ctv .. cv . ct 89 ~6% v,cv ; v,ctv+ . cv+ . ct+ 94 ~6% v,cv ; v,ctv ..cv+ . ct3 ~0.2% v,ct ; cv,ct ; v,cv !!v+ . cv . ct+ 5 ~0.3% v,ct ; cv,ct ; v,cv !!

v,cv recombinants: 45 + 40 + 89 + 94 + 2(3+5) = 284 = 19.6%v,ct recombinants: 89 + 94 + 3 + 5 = 191 = 13.2%ct,cv recombinants: 45 + 40 + 3 + 5 = 93 = 6.4%

Aha! – we now realize the smallest classes of recombinants as doubles!

36

Genetic Mapping

Mapping genes in humans involves determining the recombination frequency between a gene and an anonymous marker

Anonymous markers such as single nucleotide polymorphisms (SNPs) can be detected by molecular techniques.

37

Testis Determining Factor (SRY)

Channel Flipping (FLP)

Catching and Throwing (BLZ-1)

Self Confidence (BLZ-2) - (note: unlinked to ability)

Addiction to Death and Destruction Films (T2)

Preadolescent fascination with Arachinida and Reptilia (MOM-4U)

Sitting on John Reading (SIT)

Selective Hearing Loss (HUH?)

Lack of Recall for Important Dates (OOPS)

Inability to Express Affection Over the Phone (ME-2)

Spitting (P2E)

New Genes Identified on the Human Y Chromosome

39

• effects of recombination on chromosomes within a family

• siblings inherit different chromosome regions from their parents

• grandson inheritschromosome regions

from all four of hisgrandparents’chromosomes

40

41