GENETICS

Lesson 3.06

Mendel

SC.912.L.16.1 Genetics and Heredity

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Use Mendel's laws of segregation and independent assortment to analyze patterns of inheritance.

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We are so close:

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3.06 Mendel Genetics- Quiz

3.07 Heredity Patterns- Quiz

3.08 Biotechnology- Quiz

Mod 3 Enhanced Assessment

3.10 Segment Exam-

covers Module 1, 2 and 3

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to the 9 students

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who have finished Biology!

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3.01 Cell Division

While you wait to get started…

SC.912.L.16.17 – MITOSIS AND MEIOSIS

(EOC Practice)

The cell cycle is the process that regulates cell growth and division. What are the steps to the cell cycle?

1. G1 → S Phase → G2 → Mitosis → Cytokinesis

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• S phase → G1 → G2 → Cytokinesis → Mitosis

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• Mitosis → S phase → G1 → G2 → Cytokinesis

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• Mitosis → G1 → G2 → S phase → Cytokinesis

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3.01 Cell Division

While you wait to get started…

SC.912.L.16.17 – MITOSIS AND MEIOSIS

(EOC Practice)

The cell cycle is the process that regulates cell growth and division. What are the steps to the cell cycle?

1. G1 → S Phase → G2 → Mitosis → Cytokinesis

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3.04 Meiosis

While you wait to get started…

SC.912.L.16.17 – MITOSIS AND MEIOSIS

(EOC Practice)

How is genetic variation increased during meiosis?

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1. DNA replication during interphase

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• Cell membrane formation during cytokinesis

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• Crossing over during prophase 1

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• Chromosomes going to opposite sides of the cell during anaphase

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3.04 Meiosis

While you wait to get started…

(EOC Practice)

How is genetic variation increased during meiosis?

3. Crossing over during prophase 1

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During prophase I, each pair of chromatids lines up next to its homologue. Portions of the chromatids may break off and attach to adjacent chromatids. This process is called “crossing over.” The result is that the offspring will receive a new combination of genetic information. This leads to variation in the offspring.

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Gregor Mendel was an Austrian monk who was born in 1822.

He is known as the Father of Genetics.

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He discovered three laws of genetics that would forever change biology.

The Contributions of Gregor Mendel

He conducted a series of experiments in a quiet monastery garden. Mendel spent 14 years growing and experimenting with the pea plants grown in his garden.

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• The Law of Dominance and Recessiveness

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• The Principle of Segregation

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• The Principle of Independent Assortment

Mendel's great contribution was to demonstrate that inherited characteristics are carried by genes.

Mendel gave us the three basic laws of inheritance which are still used today:

Mendel knew that these pea plants were “____________.” This means that if they are allowed to ___________, they would produce offspring ___________________.

For example: If allowed to self-pollinate, tall plants would always produce tall plants.

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Plants with yellow seeds would always produce offspring with yellow seeds.

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These true breeding plants were the cornerstone of Mendel’s experiments.

true breeding

self-pollinate

identical to themselves

Mendel’s Work

Mendel wanted to produce seeds

by joining the egg and sperm from two different plants.

To do this, he had to first prevent the possibility of self-pollination.

Tall Pea Plant

Dwarf Pea Plant

Can you roll your tongue?

Essential Vocabulary needed for Genetics

Mendel’s Experiments

1. Trait: A specific characteristic that varies from one individual to another.

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Mendel focused on seven traits found in pea plants.

Each of these traits had only two contrasting variants.

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For example: Pea plants were either tall or dwarf.

Seeds were either round or wrinkled.

Seed color was either yellow or green.

Round Seed

Wrinkled Seed

Do you have dimples?

2. Alleles:

Different versions of a gene that produce distinguishable traits in offspring

3. P generation:

Parental generation

4. F₁ generation:

First generation of offspring

5. F₂ generation:

Second generation of offspring

6. Hybrids:

The offspring of parents with different traits

Essential Vocabulary:

Mendel’s Experiments

Mendel crossed true-breeding tall plants with true-breeding dwarf plants.

Tall plants x dwarf plants 🡪

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Produces only tall offspring

1. The F₁ hybrids were all tall.

2. All of the offspring had the appearance of only one of the parents.
3. The trait of the other parent seemed to have disappeared.

Tall Pea Plant

Dwarf Pea Plant

Mendel realized that some alleles are dominant

over other alleles.

Some alleles are dominant, and others are recessive. A dominant allele can cover up or mask a recessive allele.

Principle of Dominance

and Recessiveness

Copyright ©️ Amy Brown Science

Dominant allele:

If the dominant allele is present in an offspring, the dominant trait will show up in the offspring.

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Recessive allele:

This trait will show up in the offspring only if the dominant allele is not present.

In Mendel’s experiments, the allele for tall pea plants was dominant over the allele for dwarf pea plants.

Mendel had another question:

The Principal of Segregation

Had the dwarf trait (recessive allele) disappeared, or was it still present in the F₁ offspring?

Mendel allowed the hybrid tall offspring

from the first generation to self-pollinate.

F₁ Tall x F₁ Tall 🡪

Produces offspring that are ¾ tall and ¼ dwarf

F₁ Tall Pea Plant allowed to self-pollinate

1. He found that ¾ of the offspring were tall and ¼ of the offspring were dwarf.

2. Evidently the F₁ "tall" offspring must have been carrying the dwarf trait, but it had been hidden.

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• The dwarf trait had been passed down to the offspring, and it reappeared in the F₂ generation.

F₁ Tall Pea Plant allowed to self-pollinate

F₂ Offspring

If the offspring receives a dominant allele from one parent, that dominant trait will appear in the offspring.

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Recessive traits show up in the offspring only if the offspring receives recessive alleles from both parents.

Why did the recessive allele seem to disappear in the F₁ generation and then reappear in the F₂ generation?

Mendel realized that organisms have two alleles for every trait.

These two alleles are inherited, one from each parent.

If a parent has two alleles for a trait, how does the parent pass only one allele to the offspring?

Today, we know that the answer to this lies in the type of cell division known as _______, the formation of ________.

Gametes are sex cells or egg and sperm cells.

meiosis

gametes

Each gamete has half the number of chromosomes as the parent cell. In this way, a parent passes one allele for each gene to their offspring.

The capital letter, T, represents a dominant allele.

The lower-case letter, t, represents a recessive allele.

During meiosis, the DNA is replicated and then separated into 4 gametes.

Mendel’s Principle of Segregation

Mendel’s Principle of Segregation says that every individual carries two alleles for each trait.

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These two alleles separate or segregate during the formation of the egg and sperm cells.

An offspring will inherit two alleles for a trait, one allele from each parent. The combination of alleles received by the offspring may be either homozygous or heterozygous.

Homozygous means that

the two alleles are the

same: TT or tt

Heterozygous means that the two alleles are different: Tt

Homozygous or Heterozygous?

T

T

T

t

t

t

Homozygous

Homozygous

Heterozygous

A genotype is the genetic makeup of an organism.

A phenotype is the physical characteristics of an organism or what the organism looks like.

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Phenotype: One flower is purple, and one flower is red.

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Genotypes and Phenotypes

For example, in Mendel’s pea plants, the tall allele was dominant over the dwarf allele:

Genotype

Phenotype

TT

Tt

tt

Tall plant

Tall plant

Dwarf plant

Using Probability and Punnett Squares to Work Genetics Problems

Punnett Square

1. A Punnett square is a diagram showing the allele combinations that might result from a genetic cross between two parents.
2. The alleles of the first parent will be placed across the top of the square.
3. The alleles of the second parent will be placed along the left side of the square.

A

a

a

a

Using Probability and Punnett Squares to Work Genetics Problems

4. The possible gene combinations of the offspring will be placed inside the squares.

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5. Letters will represent the alleles.

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6. A capital letter represents a dominant allele.

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• A lower-case letter represents a recessive allele.

A

a

a

a

Monohybrid Cross:

• A cross in which only one trait or characteristic is being considered.

• Monohybrid crosses use Punnett squares consisting of 4 boxes.

Mendel began his experiments using true-breeding parents. He soon discovered that the tall trait was dominant over the dwarf trait.

Cross a true-breeding tall pea plant to a true-breeding dwarf pea plant.

What is the genotype of the first parent?

What is the genotype of the second parent?

TT

tt

Place the alleles of the first parent on the top of the square.

Place the alleles for the second parent on the left of the square.

Fill in the squares to show all the possible combinations

of alleles that the offspring might inherit.

T

T

t

t

Tt

Tt

Tt

Tt

Practice Problem #1

In the above problem, none of the offspring will show the dwarf trait. As we learned earlier, Mendel wondered what had happened to the dwarf trait. He allowed the F₁ generation to self-pollinate.

Show this cross using the Punnett square below.

What is the genotype of each parent?

Tt x Tt

TT

Tt

Tt

tt

¾ Tall

¼ dwarf

Practice Problem #2

T t

T

t

1/4 TT

2/4 Tt

1/4 tt

In dogs, the allele for short hair (B) is dominant over the allele for long hair (b). Two short haired dogs have a litter of puppies. Some of the puppies have short hair and some of the puppies have long hair.

What are the genotypes of the parents?

Bb and Bb

1/4 BB

2/4 Bb

1/4 bb

¾ short hair

¼ long hair

BB Bb

Bb bb

B b

Bb

If the litter of puppies contained 12 pups, how many would you expect to have short hair?

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How many would you expect to have long hair?

¾ of the 12 should have short hair. ¾ of 12 = 9 pups

¼ of the 12 should have long hair. ¼ of 12 = 3 pups

Mendel needed to answer one more question.

When alleles are being segregated during gamete formation, does the segregation of one pair of alleles have any effect on the segregation of a different pair of alleles?

In other words, does the gene that determines if a pea plant is tall or dwarf have any effect on the gene for seed color?

The Principal of Independent Assortment

Mendel designed a second set of experiments to follow two different genes as they passed from parent to offspring.

This is known as a two-factor cross or a dihybrid cross.

One parent had peas that were round and yellow. The second parent had peas that were wrinkled and green.

The round and yellow traits are dominant.

First, Mendel crossed true-breeding parents.

Round, yellow peas

RRYY

All F₁ offspring produced round, yellow peas.

If round and yellow are dominant, what is the genotype of all of the F₁ offspring?

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RrYy

Wrinkled, green peas

rryy

X

When the first generation was allowed to self-pollinate (RrYy x RrYy), it resulted in the production of 556 seeds:

• 315 round, yellow (dominant, dominant)
• 105 round, green (dominant, recessive)
• 104 wrinkled, yellow (recessive, dominant)
• 32 wrinkled, green (recessive, recessive)

This meant that the alleles for seed shape had segregated independently of the alleles for seed color.

The alleles for one trait had no influence on the alleles of another trait.

This is known as independent assortment.

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gametes are formed, the alleles of a gene for one trait segregate independently of the alleles of a gene for another trait.

The Principle of Independent Assortment states that when

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NOTE: This is assuming that the two genes are located on separate nonhomologous chromosomes and are not linked on the same chromosome.

Using a Punnett square for a two-factor or dihybrid cross

• A dihybrid cross considers two traits at the same time.
• When two traits are being considered, the Punnett square will need 16 squares.
• Each parent will pass one allele of each gene pair to the offspring.

If the parent was AaBb:

If the parent was Aabb:

If the parent was aaBb:

If the parent was AABB:

Given the following parental genotypes, what alleles could each parent pass to their offspring?

AB, Ab, aB, ab

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Ab, Ab, ab, ab

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aB, ab, aB, ab

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AB, AB, AB, AB

Use the following Punnett square to illustrate Mendel’s experiments

True-breeding Round and Yellow (RRYY) x True-breeding wrinkled and green (rryy)

True breeding Round, yellow seed (RRYY)

True breeding Wrinkled, green seed (rryy)

16/16 RrYy

16/16 Round, yellow seeds

RY

RY

RY

RY

ry

ry

ry

ry

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

RrYy

If the offspring from the above cross are allowed to self-pollinate:

Practice Problem

Round and Yellow x Round and Yellow

RrYy x RrYy

RY

Ry

rY

ry

RY

Ry

rY

ry

1/16 RRYY

2/16 RRYy

1/16 RRyy

2/16 RrYY

4/16 RrYy

2/16 Rryy

1/16 rrYY

2/16 rrYy

1/16 rryy

Round,yellow 9/16

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Round, green 3/16

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Wrinkled, Yellow 3/16

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Wrinkled, green 1/16

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Right handedness (R) is dominant over left handedness (r). The ability to roll your tongue (T) is dominant over the inability to roll your tongue (t).

Practice Problem

What offspring might be expected from a cross involving the following parents:

RRtt x RRTt

8/16 RRTt

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8/16 RRtt

8/16 Right-handed, tongue roller

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8/16 Right-handed, nonroller

Rt

Rt

Rt

Rt

RT

Rt

RT

Rt

RRTt

RRTt

RRTt

RRTt

RRTt

RRTt

RRTt

RRTt

RRtt

RRtt

RRtt

RRtt

RRtt

RRtt

RRtt

RRtt

A Summary of Mendel’s Principles

Mendel’s principles form the basis of modern genetics. Mendel’s principles include the following:

1. The inheritance of traits is determined by individual units known as genes.

2. Genes are passed from parent to offspring.

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3. Each gene has two or more forms called alleles.

4. Some alleles are dominant, while other alleles are recessive.

A Summary of Mendel’s Principles

5. Each parent has two alleles for a particular trait that they inherited from their parents.

They will pass one allele to their offspring when the alleles are segregated into gametes.

6. The alleles for one trait segregate independently of the alleles for another trait, when the genes are located on separate, nonhomologous chromosomes.

Let’s Review Mendel’s Principles

1. The idea that different pairs of alleles are passed to offspring independently is:

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• The idea that for any particular trait, the pair of alleles of each parent separate and only one allele from each parent passes to an offspring:

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• The idea that if a cross is made between plants with contrasting phenotypes, the phenotype that appears in the first generation is dominant and the other is recessive.

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A. Principle of Segregation B. Independent assortment

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C. The Law of Dominance and Recessiveness

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B

A

C

Now what?

Complete the 3.06 Quiz.

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Get ready for tomorrow's 3.07 live lesson on

Heredity Patterns

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Biotechnology 3.08

next Tuesday

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Find the Module 3 Enhancement Assignment link in your assessments, gradebook

or click HERE

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