8/9/2019 L1Bio261F2014

1/36

Molecular and General Genetics 2014 Biol261/2

8/9/2019 L1Bio261F2014

2/36

The science of genetics is relativelynew.

Modern breeding designs andmolecular capabilities have acceleratedthe pace and scope of understanding thenature of genes and characterexpression, promising a biologicalrevolution

But, the fabric of this revolution isbuilt using an ,applies various causaloperating at different levels of

(organismal andmolecular) that are at well integratedin .

8/9/2019 L1Bio261F2014

3/36

DEFINITIONSGenetics is defined as:

(1) The studyofgenes(2) The studyof inheritance. (Griffiths et al. 9e)The study ofall aspects of genes(Griffiths et al. 10e)(3)Genetics is the study ofheredity and variation(Lewontin 1974)

Genetics is studied on different natural scalesof organization: molecular, chromosomal,transmission genetics, population and evolutionary

genetics, genomics.

Consequently, for example, definitions of a gene differwith the scale and nature of the study.

8/9/2019 L1Bio261F2014

4/36

ClassicalGeneticsModel I involve genes (only) governing theexpression of a character or phenotype:genetic determination- a

set of instructions for turning undifferentiated environmentalmaterials into making a specific organism, regardless of theenvironment.

GeneticDeterminism

8/9/2019 L1Bio261F2014

5/36

Model II:Environmental determinism Expressed DNAcontains the information, but the local environment (internal orexternal)determines the actual course of development or theexpression of a character state. For example, gene expressionmay be governed by chromosomal tags or intervening sequences,sex in turtles and crocodiles is determined by eggdevelopment temperature.

8/9/2019 L1Bio261F2014

6/36

Model III:genotype - environment interaction - The courseof development, or phenotypeexpression depends on the

genes an individual inherits from its parents and thesequence of specific environments an individual encountersduring development.

8/9/2019 L1Bio261F2014

7/36

Figure 1-18

Genes and the environment both influenceeye size in Drosophila

8/9/2019 L1Bio261F2014

8/36

Our understanding of Genetics, summarized by the authors ofyour text book, pre-eminent geneticist of our generation, is.. Genescannot generate or even dictate the structure of an organism bythemselves. The environment (internal or external) has a crucial

ongoing effect and sometimes it is a controlling component ofexpression. Ch 1, Griffiths et al 9thedition.

Nonetheless: Many write, talk and act as if genes alonedetermine phenotype expression.

In some cases this appears correct, in others this may be amisleading characterization.

8/9/2019 L1Bio261F2014

9/36

Development variation unrelated to known or controlled allelic orenvironmental variation, may produce asymmetrical or highly

variable characters. Thisdevelopmental noisecauses variability

not related to specific environments or genes

8/9/2019 L1Bio261F2014

10/36

Textbooks:

An Introduction to Genetic AnalysisGriffiths et al. 10thedition - required.

Solutions Manualfor An Introduction to

Genetic Analysis -suggested

I clicker - required

8/9/2019 L1Bio261F2014

11/36

8/9/2019 L1Bio261F2014

12/36

WEB Site for Molecular and General Genetics:

https://www.myconcordia.caChoose Course websites (Moodle)

Lecture slidesRecommended Problems

Course outline and grading scheme

The text book publisher, W.F. Freeman has a web sit

www.whfreeman.com

with study aids including animations.

8/9/2019 L1Bio261F2014

13/36

Mandatory tutorialsmeet once a week for 2 hr,beginning next week

A teaching assistant will reviewthe previous weeksmaterial, discussillustrative problems, and a week later,testyou and other students on the lecture material.

Each week, a section is covered in 2 lectures,say section A. The following week, problems related tosection A are solved in tutorial. Student teams of 4-5 willpresent the solution to a pivotal selected problem.

In the next week section A will be the subject of the quiz.

Your tutorial grade will be largely based on your quiz marksand yourpresentation scores.

8/9/2019 L1Bio261F2014

14/36

The readings in the text and the assignedproblems are in the dates reading andproblems EXCEL file

(Biol 261 Schedule.xls)

For example,Week 1

ReadCh: 1, 2.0-2.2, 2.4-2.6

PrintCh 2: 15, 18, 28,31,33,34,40,43,50,51,61,63,64

8/9/2019 L1Bio261F2014

15/36

Grading:

20% Tutorial

40%

2 Midterm Exams40% Final

8/9/2019 L1Bio261F2014

16/36

SECTION 1 : Classic Genetics

Mendelian Genetics 1 gene, 2 alleles

8/9/2019 L1Bio261F2014

17/36

Scientific genetics beganwith Gregor Mendelwho in

the 1850s used differentpure-breeding strains in acontrolled breedingexperiment to test their mode

of inheritance.

See C. Stern and E.R. SherwoodThe Origin of Genetics a MendelSource Book

The laws of inheritance were independentlyrediscovered in 1900 by Hugo de Vries,

Carl Correns, and Erich von Tschermak.

8/9/2019 L1Bio261F2014

18/36

Single Gene Inheritance

During Mendels university education inbotany, breeding and physics,physicists were

interested in the atomic nature of matter.

John Dalton is considered the originator ofmodern atomic theory. But Daltons atomichypothesis did not specify the size of atoms.

Therefore it was a major landmark when in1865 Johann Josef Loschmidtmeasured thesize of the molecules that make up air.

Loschmidtwas also from the Czech Republic aprofessor of Physics in Vienna inevitably part

of Mendels education.

So it was not surprising that Mendel set out to lookfor the atoms of inheritance.

8/9/2019 L1Bio261F2014

19/36

A) Experimental Control. Start with a

population, any sexual populationis

defined by the extent ofpotentially

interbreeding individuals. In Mendels

case he restricted breeding individuals

to the strains he used within his garden

plot below.

The more control you have over its

ecology, you decrease the influence

of chance effects of the environmenton inheritance and expression.

But, there are always other levels of

chance variation.

B) Statistics One of Mendels

conceptual breakthroughs in dealingwith this variation was his statistical

approach, the larger the sample size

(statistical) , and the more factors

you control (experimental), the

smaller the influence of chance

effects on the experimental

outcome.

Foundations Experimental Control and Statistics

8/9/2019 L1Bio261F2014

20/36

Inbred,pure breeding (selfed or bred withan individual from the same strain),

colored (Purple ish), Psium sativumParental line

X

X

Inbred Strain

8/9/2019 L1Bio261F2014

21/36

X

X

Second (white) pure breeding,inbred Parental line

8/9/2019 L1Bio261F2014

22/36

Alternative Hypotheses:(1)Discrete categorical inheritance or

(2) Blending continuous inheritance

Test: crossing inbred white and purple-floweredpea strains, are colors retained in hybrids,

through several generations or are they lost,changed or otherwise altered (blended) indifferent offspring generations?

Methods:(1) define the character-flower color(white, purple with no intermediates), then

(2) the breeding design.

8/9/2019 L1Bio261F2014

23/36

Controlfor differences

in the cross of pure-breeding parentalstrains

Reciprocal CrossesMale purple pollen to

white stigma (shown),and male white pollentopurple stigma (notshown).

8/9/2019 L1Bio261F2014

24/36

XParentals

(F1)

Discrete or Blending Inheritance?

Breeding design: Reciprocal Monohybrid Cross

Inbreed or self fertilize the (F1).

In the first generation: there was no blending butthere was evidence of possible character loss.

first filial generation

50% 50%

8/9/2019 L1Bio261F2014

25/36

Parental Cross

F1:observations?Interpretation

X

X

Count224 white (0.24 total)705 purple (0.76 total)

(1: 3.15)

F2:observations

Odd fact -the ratiochanged from 50/50 in the

parentals, 100% purple inthe F

1 to 3:1 in the F

2?

Interpretation

8/9/2019 L1Bio261F2014

26/36

F2

225 white, 705 purple or 3:1

Test the particle variation by inbreeding F2plants

8/9/2019 L1Bio261F2014

27/36

F2

F3

Inbreed (self)

(pp) (pP) (PP)

Dominance hides the frequency of different particles,gametes or alleles -actually 50% p /50%P

Dominance is an empirical description, anempirical fact without a specific mechanism.

8/9/2019 L1Bio261F2014

28/36

Causality of phenotypic variation inMendel s experiment is best described as:

a)Genetic determination

b)

Environmental determination

c)

Gene-environment interaction

d) Developmental noise

8/9/2019 L1Bio261F2014

29/36

8/9/2019 L1Bio261F2014

30/36

Mendels other hybrid crosses confirm the 3:1 characterorphenotype ratio in inbred dominant and recessive charactercrosses

Mendels data demonstrates that genetic facts are

statistical facts. You can not predict a exact phenotypebut in a breeding design you can assign an expected

probability .

8/9/2019 L1Bio261F2014

31/36

MENDELS FIRST LAW: EQUAL SEGREGATION OF ALLELES

Mendels Model

(1)

Inherited germinal or pollen particles for each character orgenesmayhavegenes in different states calledalleles(variation)

(2) Individuals have 2 copies of each gene (gene pairs). If thestates of each gene are the same they are calledhomozygotes(pp or PP), if alleles are different they are calledheterozygotes(Pp).

(3) Each parental gene segregatesrandomly into a gamete(spermor eggs) or individuals in a pair are segregated into different

gametes.(4) Parental sex causesgene copies to recombineforming the F1and F2 offspring, which have allele pairs from both parents.

(5) Individual offspring have two copies of each allele, either oneof which may or may not be dominant (P) or recessive (p).

8/9/2019 L1Bio261F2014

32/36

P

p

0.5 purple gametes inbreeding population

P: Monohybrid Cross : white (pp) and purple (PP)flowers

0. 5

wh

ite g

am

et e

sin

b re

ed

ing

p o

p u

latio

n

Punnett SquareModel of equal segregation andrandom recombination

The breeding population consists of equal numbersof white and purple parents, hence,

you expect 50% p alleles, 50 % P in the F1

F1

8/9/2019 L1Bio261F2014

33/36

0.5 P

0.5 p All Ppdiploids

purple gametes in thebreeding population

P: Reciprocal monohybrid cross (pp x PP)

whi t

ega

m e

tes

b re

ed

ing

p o

p u

latio

n

Punnett SquareModel

F1 Offspring Expectationbased on equal segregationand random recombination. All heterozygotes

8/9/2019 L1Bio261F2014

34/36

P p

P

p

0.5 1/2

0.5

1/2

Pp x Pp

F1 PunnettSquare

Inbreed (heterozygote)individuals

F2expected

values

8/9/2019 L1Bio261F2014

35/36

P p

P

p

PP1/4

Pp1/4

Pp1/4

pp1/4

0.5 1/2

0.5

1/2

Pp x Pp

F1 PunnettSquare

Inbreed (heterozygote)individuals

F2

8/9/2019 L1Bio261F2014

36/36

Terms to define: Monohybrid cross, genes, alleles, allele

frequency, dominance, monohybrid, homozygote,heterozygote genotype, breeding design, inbreeding andoutbreeding.

Know: genetic models (I-IV);Mendel 1: the monohybrid cross breeding design, includingthe meaning of inbreeding and outbreeding, first and secondfilial crosses; Mendels first law -what it means, PunnettSquare.

Monohybrid breeding design - Parentals, expectations F1, F2