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3/7/2016 1 MENDELIAN GENETICS Chapter 6.3 – 6.5 Gregor Mendel (1822-1884) • Genetics = the study of inheritance patterns and variation in organisms • Genes = segments of DNA that direct a cell to make a certain protein (proteins make up your traits!) I’m known as the “Father of Genetics” Mendel and Heredity Examples of Traits • Traits = characteristics that are inherited Mendel and Heredity Mendel’s Peas Mendel used pea plants to study patterns of inheritance. Why do you think he used plants instead of animals in his research? Mendel and Heredity

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Page 1: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

1

MENDELIAN GENETICS

Chapter 6.3 – 6.5

Gregor Mendel (1822-1884)

• Genetics = the study of inheritance patterns and variation in organisms

• Genes = segments of DNA that direct a cell to make a certain protein (proteins make up your traits!)

I’m known as the “Father of Genetics”

Mendel and Heredity

Examples of Traits

• Traits = characteristics that are inherited

Mendel and Heredity

Mendel’s Peas

Mendel used pea plants to study patterns of inheritance.

Why do you think he used plants instead of animals in

his research?

Mendel and Heredity

Page 2: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

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• Mendel studied 7 different traits in pea plants by cross-pollinating plants that had variations of each trait:

Mendel’s Peas

Mendel and Heredity Mendel’s 1st Experiment

• Only used “either-or” traits (ex: either tall or short…not medium)

•First experiments were monohybrid crosses (cross one trait at a time)

•Only used true-breeding (purebred) plants so he could control the outcome

X

Parents (P) First generation offspring (F1)

(F1) (F1)

X

Second generation offspring (F2)

• Allowed F1 offspring to self-pollinate to produce F2 offspring.

Mendel’s 2nd Experiment

•One particular variation of each trait showed up in offspring more often.

Mendel’s Results

Page 3: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

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Mendel’s Experiments: Mendel observed the same results every time he crossed two different forms of a trait.

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

1. Biological inheritance is determined by factors (or GENES) that are passed from one generation to the next.

• Traits are inherited from parents to offspring in patterns

Mendel’s Conclusions

2. Law of Segregation = • organisms inherit two copies of each gene, one from each parent

• organisms donate only one copy of each gene to their offspring

The Law of Segregation arose from doing monohybrid crosses

• Monohybrid = only testing only ONEtrait at a time

Mendel’s Conclusions

Example: Color

Mendel’s Conclusions

• “Principle of Dominance” – some alleles are dominant and some are recessive

•Dominant alleles are expressed over recessive alleles

** This does NOT mean that dominant is better or stronger or occurs more often in a population!

T = tall t = short

Y = yellow y = green

R = tongue roller r = non-tongue roller

• (Recessive characteristics of a trait are “hidden” if a dominant allele is present)

• •Dominant alleles use capitalized letters, recessive alleles use lower-cased letters

•Alleles = different versions of a gene

Page 4: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

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Homozygous

Dominant : AA ,GG,RR

Recessive : aa, gg, rr

Traits, Genes, and Alleles

• We use capital letters to signify dominant alleles and lower case letters to signify recessive alleles.

Alleles are identical to each other

Alleles are different from

each other

Heterozygous

Aa , Gg , Rr

Genotype

• Genome = all of an organism’s genetic material

Traits, Genes, and Alleles

•The physical appearance of a trait*what the alleles stand for

Phenotype•The genetic makeup of a particular trait

•(the alleles an organism has for a trait)

Traits and Probability

• Probability = the likelihood that an event will occur

• Probability is used to predict outcomes of genetic crosses

•Punnett Squares allow us to calculate the probability that certain traits will be passed on to offspring.

Ex: flipping a coin� What is the probability that it will land on heads?

The Punnett square yields the ratio of

possible genotypes and

phenotypes

Monohybrid Crosses – involves 1 trait

1. In pea plants tall plants (T) are dominant to short plants (t). Cross a homozygous tall pea plant with a homozygous short pea plant.

Parents: ________ x _______

Genotype Ratio= #TT : #Tt : #tt____ : ____ : ____

Phenotype Ratio = #Dominant:#Recessive ____ : ____

Genotype Percentages : ____ : ____ : ____

Phenotype Percentages: ____ : ____

Page 5: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

5

Monohybrid Crosses

2. In pea plants round seeds (R) are dominant to wrinkled seeds (r). Cross one heterozygous pea plant with another heterozygous pea plant.

Parents: ________ x _______

Genotype Ratio= #RR : #Rr : #rr____ : ____ : ____

Genotype Percentages : ____ : ____ : ____

Phenotype Ratio = #Dominant:#Recessive ____ : ____

Phenotype Percentages: ____ : ____

Monohybrid Crosses

3. Cross a heterozygous genotype with a homozygous recessive genotype

Parents: ________ x _______

Genotype Ratio= #AA : #Aa : #aa____ : ____ : ____

Genotype Percentages : ____ : ____ : ____

Phenotype Ratio = #Dominant:#Recessive ____ : ____

Phenotype Percentages: ____ : ____

A= tall a= short

Mendel’s Conclusions

3. Law of Independent Assortment– the inheritance of one gene does not influence the inheritance of another gene

In other words…just because peas are

green does not mean they

will also be wrinkled (they

could be round)

Video L of IA

R R Y Y r r y y

Dihybrid Crosses

�Involves 2 different traits

�Mendel tested many combinations of traits:

xround yellow peas wrinkled green peas

Page 6: Mendel and Heredity - Weebly · Mendel’s Conclusions • “Principle of Dominance” –some alleles are dominant and some are recessive •Dominant alleles are expressed over

3/7/2016

6

What if we crossed the F1…

RrYy RrYy

heterozygous x heterozygous

Dihybrid CrossesDihybrid Crosses

Genotype Genotypic Ratio Phenotype Phenotypic ratio

RRYY

RrYy

RrYY

RRYy

RRyy

Rryy

rrYY

rrYy

rryy

TERMS to know:Gene: Allele:

Dominant allele:

Example: _____ or _____

Recessive allele:

Example: _____

Heterozygous:

Example: _____

Homozygous:

Examples: _____ or _____

Genotype:Example: _______

Phenotype:

Example: ___________

Probability: Genome:

segment of DNA that codes for a trait

expressed when at least one copy is present; represented by a CAPITAL letter

different forms of the same gene

expressed only when 2 copies are present; represented by a lowercase letter

2 alleles are the same

physical traits

all of an organisms genetic material

the likelihood that anevent will occur

genetic makeup

2 alleles are different

Review• Gregor Mendel used peas to study how traits are inherited

• He developed 2 major conclusions:1. Law of Segregation2. Law of Independent Assortment

• Today, we simply use Punnett squares to predict the outcome (genotypes and phenotypes) of offspring

• Mendel’s principles apply to ALL sexual organisms, not just plants!

Review Video Great


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