Bell Ringer: (5 min.)

Section 11-3: Exploring Mendelian Genetics

Independent Assortment

• Mendel wanted to know:– Does the segregation of one pair of alleles affect

that of another?• For example: Does the allele for seed color effect the

shape of the seed?

• 1. To find this Mendel created a two factor cross and followed two different genes as they passed from one generation to the next.

The Two Factor Cross: F1

• Crossed true breeding plants for round (RR) yellow (YY)peas– 2. Genotype (RRYY)

• With true breeding plants for wrinkled (rr) green (yy) peas– 2. Genotype (rryy)

• And proceeded to observe the offspring

The Two Factor Cross: F1

ry ry ry ry

RY RrYy RrYy RrYy RrYy

RY RrYy RrYy RrYy RrYy

RY RrYy RrYy RrYy RrYy

RY RrYy RrYy RrYy RrYy

The F1 Results:

• 3. This shows that the dominant alleles are present:– Phenotype:

• Heterozygous• Round Yellow Seeds

– Genotype:• RrYy

• 4. Does this result show if genes segregate independently?– Nope

The Two Factor Cross: F2

• 5. Mendel took the F1 generation (heterozygous) and crossed them.

• He wanted to see if the two traits would separate independently of one another or if dominant would stick with dominant and recessive stay with recessive.

• Was very curious of the possible outcomes.

10. The Two Factor Cross: F2RY Ry rY ry

RY

Ry

rY

ry

The F2 Results:

• 6. & 8. There was a total of 556 seeds produced:– Round Yellow: 315– Round Green: 105– Wrinkled Yellow: 104– Wrinkled Green: 32– 7. There were seeds that displayed combinations not

found in the parents (RRYY and rryy)• Did Independent assortment occur?– YES!

Let’s Look at the Numbers Again:

• 9. Count up the Phenotypes, what is the ratio?– 9:3:3:1

• Round Yellow: 9– RRYY, RrYy

• Round Green: 3– RRyy, Rryy

• Wrinkled Yellow: 3– rrYY, rrYy

• Wrinkled Green: 1– rryy

11. Independent Assortment

• The alleles for a given trait segregate independently of one another and do not influence each other’s inheritance.

12. A Summary of Mendel’s Principles

• The inheritance of biological characteristics is determined by genes that are passed down from parents to their offspring

• 13. Two or more forms of a trait may exist (ex: Dominant and Recessive)

• The copies of genes are segregated from each other when gametes are formed

• The alleles for different genes usually segregate independently from one another

Beyond Dominant and Recessive

• 14. There are some alleles that are neither dominant or recessive, and many traits:

• Genetics tends to be a bit more complicated than that:– The majority of genes have more than two alleles,

and important traits are controlled by many different genes.

15. Incomplete Dominance

• Cases in which one allele is not dominant over the other– The heterozygous phenotype is somewhere

between the two homozygous phenotypes– Ex:• Strawberry Blonde• 4 ‘o Clock Plants

15. Codominance

• Both alleles contribute to the phenotype– Both alleles will be shown in the offspring

• Ex:– Erminette Animals• Black feathers is codominant with white• Offspring show both colors

– Humans• Proteins synthesis

15. Multipe Alleles

• Genes that have more than two possible alleles

• This does not mean that an individual can have more than two alleles for a gene– It means that there could be more than two

possibilities in a population– Ex:• Rabbit fur color• Blood Types in humans

Multiple Alleles

15. Polygenic Traits

• Traits that are controlled by two or more genes– Many traits are produced by the interaction of

several genes– Ex:• Human Skin Color• 4 genes control skin color• Human Eye Color

Applying Mendel’s Principles

• Thomas Morgan- Geneticist that worked with Fruit Flies to test Mendel’s Principles of Segregation– 16. Chose Fruit Flies because:

• Small in size• Easy to take care of in a lab setting• Capable of producing large numbers of offspring very quickly

• 17. The conclusion:– Mendel’s Principles apply to not just pea plants, but

other organisms as well

Genetics and the Environment

• 18. Genes are not the only factor for determining characteristics of an organism

• The Environment plays a role as well– Ex: Sunflower Height is determined by the genes,

but this will change depending on factors such as climate, water availability, and soil composition

Exit Slip

X

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Katy Perry Wolverine

Hair Color:-B: Black-b: Blue

Claws:-C: No Claws-c: Claws

Solve the Cross:Bbcc

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