10-02 Lecture Notes

7/30/2019 10-02 Lecture Notes

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Dihybridcrosses,MitosisandMeiosis

Todays

questions:

I. Howareallelesfromdifferentgenestransmittedto

o spr ng toget er,or n epen ent yo eac ot er

II.WhatisthephysicalbasisofMendelsrules?

a.Mitosis:Howcellsdivideduringasexual

repro uct onan

ur ng

growt

b.Meiosis:Howcellsdividepriortoformationofeggs

an sperm sexua repro uc on


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Y=yellow,y=green R =round;r=wrinkled

F1sallmakeyellow,roundseeds(YyRr)

WhenF1sareselffertilized,phenotypesofF2 offspringare:

yellowround:

greenround:

yellowwrinkled

greenwr n e


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Note:othercombinationsoftwotraitsbehavedthe

sameway.

Mendelsconclusion:Thesegregationofallelesof.

Thisis

the

principle

of

independent

assortment.

ote:


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Ratio is a comparison of numbers of the same kind. Expressed in X:Y.A comparison of numbers of the same kind, but expressed in percentages

or decimals.Law of independent assortment is a sometimes rule. It happens only

sometimes.


5/20

TounderstandthephysicalbasisofMendelsrules

andhowgeneticvariationisgeneratedin

popu a ons,wenee oexam ne wo ypeso ce

divisionthat

were

first

described

in

the

late

1800s.

I.Mitosis:Theprocessresponsibleforasexual

reproductionand

growth

in

multicellular

organisms.

Howdoesithappen?

Focusonchromosomes(colored

o es ns e enuc eus


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Chromosomescomeindifferenttypes,distinguished

bysizeandshape(morphology)

Inmanyorganisms,thereare2ofeachtypeof

Pairsofsimilarchromosomesaresaidtobe


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Keynotation:

Usen toindicatethenumberofdifferenttypesof

chromosomesfoundinaspecies

Useanumeralbeforethen toindicatethenumberof

.

Whichis

the

ploidy?

Whichisthehaploidnumber?

Andwhatsthedifferencebetweena

chromosomeand

achromatid?


8/20

Use n to indicate the number of different species types of chromosome found in a species. n=23 in humans, this is the haploid number. Use a numeral before the n to indicate the number of each type present. 2n=46, this is the ploidy. 2n indicates diploid. The difference between chromosome and chromatid: -There are sister chromatids after replication.


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10/20


11/20

Drawahaploidsetof

unreplicated chromosomesin

aspec esw eren = .

Drawtheunreplicated

chromosomes

of

a

diploid

cell

in

, .

Drawthe

replicated

chromosomesofadiploidcellin

aspecieswheren =3,2n =6.


12/20


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Anoverviewofmitosis

n =2;2n =4

Chromosomesreplicate

Chromosomeslineup

Sisterchromatids separate

Ce ivi es

Overview of Mitosis


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Overview of Mitosis


15/20


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AnoverviewofmeiosisI

n =2;2n =4

Chromosomesreplicate

Crossingoveroccurs

Homologs lineup

Homologs pullapart

Celldivides

Only one

of each

type linedup. It is

haploid.


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AnoverviewofmeiosisII

(sameinbothdaughters)

Chromosomesline

up

Sisterchromatids

pullapart

Celldivides


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Whatare

the

consequences

of

mitosis

and

meiosis?

Mitosis Meiosis

Start:

End:

Chromosomes

sameordifferent

asparent

cell?

23 Replicated.

1 cell.Diploid.

2n=46, n is still 232 cells with diploids.

23unreplicated.

1 cell.Diploid.

Still 23.

four cells with haploid.

Same as parent cells. Different from parent cells.


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Use end of chapter questions,use study questions, use practice exam.What happens to meiosis if homologues are not paired?-

Crossing over happens during meiosis causes genetic variation. Because they allow


20/20

g pp g g y

exchange of alleles. Genetic variation among chromosome.Independent assortment also allows for genetic variations because it allows alleles to go

to different areas. For humans, with 23 chromosome and only two allele for each gene,you could have 2^23 different combinations. That's over 8 billions, more than the human

population themselves. Genetic variation within chromosome.

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10-02 Lecture Notes