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Chapter 10.2

Mendelian Genetics

NWRC Bio 30

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vocabulary terms

When we have two capital or two lowercaseletters in the GENOTYPE (ex: TT or tt) it'scalled HOMOZYGOUS("homo" means "the

same"). Sometimes the term "PURE" is usedinstead of homozygous.

When the GENOTYPE is made up of onecapital letter & one lowercase letter (ex: Tt)

it's called HETEROZYGOUS("hetero" means"other"). A heterozygous genotype can alsobe referred to as HYBRID.

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vocabulary terms

PHENOTYPE = how the trait physicallyshows-up in the organism. The simplest wayto determine an organism's phenotype is tojust look at it. Examples of phenotypes: blueeyes, brown fur, striped fruit, yellow flowers.

ALLELES =

Alleles are alternative forms of the same

gene. Alleles for a trait are located atcorresponding positions on homologouschromosomes.

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vocabulary terms

PHENOTYPE = how the trait physicallyshows-up in the organism. The simplest wayto determine an organism's phenotype is tojust look at it. Examples of phenotypes: blueeyes, brown fur, striped fruit, yellow flowers.

ALLELES =

Alleles are alternative forms of the same

gene. Alleles for a trait are located atcorresponding positions on homologouschromosomes.

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vocabulary terms

GENOTYPE = the genes present in theDNA of an organism. We use a pair ofletters (ex: Tt or YY or ss, etc.) to

represent genotypes for one particulartrait. There are always two letters inthe genotype because (as a result ofsexual reproduction) one code for the

trait comes from mom & the othercomes from dad, so every offspringgets two codes (two letters).

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Gregor Mendel

An Austrian Monk

who did

groundbreaking work

into the theories ofheredity. According to

the textbook his work

was published in

1866.

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Mendel

Mendel discovered

some basic laws

which governed the

passage of a traitfrom one member of a

species to another

member of the same

species. Demo Mendel

http://www.dnaftb.org/dnaftb/2/concept/index.htmlhttp://www.dnaftb.org/dnaftb/2/concept/index.html

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Mendel

Why Mendel studied pea plants

This site gives us the background on how

plants self-fertilize and how they can be

cross-fertilized as well

http://www.dnaftb.org/dnaftb/1/concept/index.htmlhttp://www.dnaftb.org/dnaftb/1/concept/index.html

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Mendels Pea Plants

Monks have a lot of free time andMendel spent his time crossing peaplants. As he did this over & over &

over & over & over again, he noticedsome patterns to the inheritance oftraits from one set of pea plants to the

next. By carefully analyzing his peaplant numbers he formed hishypotheses regarding genetics.

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The original cross for the tall &short pea plants was:

parents F1

Offspring

Genotype TT X tt Tt -100%

Phenotype Tall x Short Tall 100%

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Mendels Pea Plants

While Mendel was crossing(reproducing) his pea plants(over & over & over again),he noticed somethinginteresting. When hecrossed pure tall plants with

pure short plants, all the newpea plants (referred to as theF1 generation) weretall. Similarly, crossing pureyellow seeded pea plantsand pure green seeded peaplants produced an F1generation of all yellowseeded pea plants. Thesame was true for other peatraits:

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Mendels Pea Plants

So, what he noticedwas that when theparent plants hadcontrasting forms of a

trait (tall vs short, greenvs yellow, etc.) thephenotypes of theoffspring resembled

only one of the parentplants with respect tothat trait.

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Mendels Big Surprise!

Then Mendel takes twoof the "F1" generation(which are tall) &crosses them. I wouldthink that he is figuring

that he's going get alltall again (since tall isdominant). But forsome reason he getssome short plants from

this cross! His newbatch of pea plants (the"F2" generation) isabout 3/4 tall & 1/4short.

!!!!

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The F2 Generation

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Mendel

My LAW of Segregation

says that of a pair of

characteristics only one

can be represented in agamete. What I mean

was that for any pair of

characteristics there is

only one gene in agamete even though

there are two genes in

ordinary cells.

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MendelWhat

does that

mean?

If your eyes areblue, green or grey

you have two

alleles for blue eyes

(bb) You got onefrom your mom and

one from your dad everyone comes

from 2 gametes

(egg and sperm) so

you may get 2

alleles but only one

trait is expressed.

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Monohybrid Cross

cross involved

organisms that

differed for a single

character examples in pea

tall x short,

purple x white, round x wrinkled

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Dihybrid Cross

A dihybrid cross is a

cross between two F1

offspring of two

individuals that differin two traits examples

in pea

tall x short, and

purple x white,

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Example of another dihybrid cross

SsYy x SsYy Note both maternal and

paternal alleles are heterozygous

The dihybrid cross was invented by

Mendel to discover the independent

assortment of alleles during gamete

formation.

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Mendel

My next LAW isthe law of

"IndependentAssortment". This

says that for two

characteristics the

genes are inheritedindependently.

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Mendel

My third LAW

the Law of

segregation Duringthe formation of gametes(eggs or sperm), the two

alleles responsible for a trait

separate from eachother. Alleles for a trait arethen "recombined" at

fertilization, producing thegenotype for the traits of the

offspring.

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Mendel

Suppose one of your parents had the genotypeAABB then you would have inherited AB fromthis parent. Suppose also that your other parenthad the genotype aabb then you would haveinherited ab from this parent. The combinationsofAB and ab are parental types. Your genotypeis AaBb and some of your children will inheritthese parental types eitherAB orab from you.

However, it is also possible for some of yourchildren to inherit new combinations called "re-combinants from you. These are Ab and aB.

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What does that mean in real

terms?

Lets say A is a tallness allele so a would beshortness

B is brown eyes and b is blue eyed

one of your parents had the genotype AABB sothat parent (well call him dad) is TALL andBrown eyed

your other parent (called Mom) had the

genotype aabb (Short and blue eyed) Your genotype would be AaBb

What would you look like???

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What does that mean in real

terms?

Your genotype would be AaBb

So you would have the dominant trait for

tallness and the dominant trait for brown

eyes.

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Mendel!

Dominant Genes review

http://www.dnaftb.org/dnaftb/4/concept/index.htmlhttp://www.dnaftb.org/dnaftb/4/concept/index.html

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Review Questions

1. Which cross would best illustrate Mendel'sLaw of Segregation?

A. TT x ttB. Hh x hh

C. Bb x Bb D. rr x rr The right answer is C because - both parent

show dominant trait, but some recessive

offspring will be produced (each parentcarries a "b")

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Review Questions

2. In the cross Yy x Yy, what percent ofoffspring would have the same phenotype asthe parents?

A. 25%B. 50%C. 75%D. 100%

C is right - in the completed p-square, 3 of 4boxes will have at least 1 "Y", producing thedominant phenotype (same as parents)

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Review Questions

In a certain plant, purple flowers are dominant to redflowers. If the cross of two purple-flowered plantsproduces some some purple-flowered and some red-flowered plants, what is the genotype of the parent

plants? A. PP x PpB. Pp x Pp

C. pp x PP

D. pp x pp

answer B is right - for any offspring to be recessive,each parent MUST have at least one "p"

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Chapter Questions

1.

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Chapter Questions

The Law of SegregationGoes like so: During the formation of gametes(eggs or sperm), the two alleles responsible

for a trait separate from each other.Alleles for a trait are then "recombined" atfertilization, producing the genotype for the traits of the offspring.

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2 Continued

The Law of Independent AssortmentAlleles for differenttraits are distributedto sex cells (& offspring) independently ofone another.Mendel noticed during all his

work that the height of the plant and theshape of the seeds and the color of thepods had no impact on one another. Inother words, being tall didn'tautomatically mean the plants had to have

green pods, nor did green pods have tobe filled only with wrinkled seeds, thedifferenttraits seem to be inheritedINDEPENDENTLY.

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3.

R r

r

r Rr rr

rrRr