11–111–1The Work of Gregor MendelThe Work of Gregor Mendel

A.A. Gregor Mendel’s PeasGregor Mendel’s Peas

B.B. Genes and DominanceGenes and Dominance

C.C. SegregationSegregation

1.1. The FThe F11 Cross Cross

2.2. Explaining the FExplaining the F11

CrossCross

Section 11-1

Section Outline

11-1 Quiz?1. Discuss who Gregor Mendel was and discuss his

contribution to biology.

2. What characteristics did he study?

3. What is the P1, F1, F2 generation?

4. What are pure plants? Give one example of self-pollination and cross pollination.

5. How did Mendel determine which of each pair of traits was the dominant trait and which was recessive?

6. Although Tall plants appear to be tall, could they be considered “pure” for the tall trait? Why or why not?

• This is the branch of biology which studies This is the branch of biology which studies heredityheredity..

White TigerWhite Tiger - This type of tiger can have yellow - This type of tiger can have yellow parents. parents. How can that happen?How can that happen? link link

What are some inherited traits for some dog What are some inherited traits for some dog breeds? (Physical and behavior)breeds? (Physical and behavior)

How do you keep producing a pure breed?How do you keep producing a pure breed?

Terms -alleles, hybrid, genes, purebred, traitsTerms -alleles, hybrid, genes, purebred, traits

GeneticsGenetics

GREGORGREGOR MENDEL MENDEL preziprezi

Mendel was a monk who lived Mendel was a monk who lived during the mid 1800’s in during the mid 1800’s in Austria. He was great in Austria. He was great in math and was a gardener at math and was a gardener at the monastery. He noticed the monastery. He noticed various things about pea various things about pea plants and their plants and their characteristics.characteristics.

He studied seven characteristics He studied seven characteristics of pea plants and noticed of pea plants and noticed what we today call what we today call inheritance inheritance or the passing or the passing of traits by heredity.of traits by heredity.

PP11- pure parent cross contrasting traits - pure parent cross contrasting traits PreziPrezi Link LinkFF11 generation generationThis generation showed only one trait from the parents This generation showed only one trait from the parents

that were crossed ( green pod, no yellow pod). that were crossed ( green pod, no yellow pod).

Mendel allowed these to self-pollinate. This is called theMendel allowed these to self-pollinate. This is called the FF22 generation. generation.

Results of this pollination showed 3/4 were green and Results of this pollination showed 3/4 were green and only 1/4 were yellow. The yellow pod trait had only 1/4 were yellow. The yellow pod trait had appeared to be lost in the Fappeared to be lost in the F11 generation, actually generation, actually reappeared in the Freappeared in the F2 2 generation. generation.

How did Mendel determine which of each pair of traits How did Mendel determine which of each pair of traits was the dominant trait and which was recessive?was the dominant trait and which was recessive?

Although Tall plants appear to be tall, could they be Although Tall plants appear to be tall, could they be considered “pure” for the tall trait? Why or why not?considered “pure” for the tall trait? Why or why not?

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1Principles of Dominance

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants

Conclusions of Mendel1. Principle of dominance and Recessiveness

One factor of a pair of alleles may mask the appearance of another. (Ex: blond hair is recessive to dark hair)

2. Principle of Segregation The two factors for a characteristic separate, during the formation of eggs and sperm.

(B - Brown, b - blue) Which allele did you get?

3. Principle of Independent Assortment- Factors for different characteristics are distributed independently to sex cells.

(curly fur /size of dog or tall plant /wrinkled seeds)

• Mendel’s most important decision was to study just a few isolated traits of the pea plants.

Section 11-1

What do the numbers mean? What is the ratio of dominant to recessive?

Parents

Long stems short stems

Red flowers white flowers

Green pods yellow pods

Round seeds wrinkled seeds

Yellow seeds green seeds

First Generation

All long

All red

All green

All round

All yellow

Second Generation

787 long: 277 short

705 red: 224 white

428 green: 152 yellow

5474 round: 1850 wrinkled

6022 yellow: 2001 green

11–2 Probability and Punnett Squares

AA.Genetics and Probability

B.Punnett Squares

C. Probability and Segregation

D. Probabilities Predict Averages

Section 11-2

Section Outline

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Punnett squares

Punnett squares

Section 11-2Tt X Tt Cross

Section 11-2

Tt X Tt Cross

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Section 11-3

Figure 11-10 Independent Assortment in Peas

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Height in HumansHeight in Humans Height in pea plants is controlled by one of Height in pea plants is controlled by one of

two alleles; the allele for a tall plant is the two alleles; the allele for a tall plant is the dominant allele, while the allele for a short dominant allele, while the allele for a short plant is the recessive one. plant is the recessive one.

What about people? Are the factors that determine height more

complicated in humans? Can you only be tall or short?

Section 11-3 Interest Grabber

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11–3Exploring Mendelian GeneticsA. Independent Assortment

1. The Two-Factor Cross: F1

2. The Two-Factor Cross: F2

B. A Summary of Mendel’s Principles

C. Beyond Dominant and Recessive Alleles

1. Incomplete Dominance

2. Codominance

3. Multiple Alleles

4. Polygenic Traits

D. Applying Mendel’s Principles

*Gene interactions(Recessive vs. Dominant) recessive genes do not produce the enzyme (protein) for a trait to be demonstrated.

Incomplete dominance - hybrids are intermediates of the parents. (Ex red x white = pink). The recessive allele can not make any pigment at all so less pigment shows up (diagram)

Codominance - both differing alleles of a gene are expressed at the same time. There is no dominance of one over the other. (Ex: roan cattle are a hybrid of a Red and White cross R xR’)

Polygenic Inheritance - traits are controlled by two or more genes. (Ex Lab retrievers have two separate genes which determine coat color)

Multiple alleles - numerous versions of a gene are possible.(eye color, blood type, etc.)diagram

Section 11-3

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

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concluded that

which is called the

which is called the

GregorMendel

Law ofDominance

Law ofSegregation

Peaplants

“Factors”determine

traits

Some alleles are dominant,

and some alleles are recessive

Alleles are separated during gamete formation

Section 11-3 Concept Map

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experimented with

Different traits separate randomly Law of

Independent assortmentwhich is

called the

1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?

3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Section 11-4Interest Grabber continued

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11–4 Meiosis

A. Chromosome Number

B. Phases of Meiosis

1. Meiosis I

2. Meiosis II

C. Gamete Formation

D. Comparing Mitosis and Meiosis

Section Outline

Meiosis• This is the division of chromosomes that creates

new cells with half the number of chromosomes (haploid)

• This type of cell division occurs in sex cells egg, sperm, pollen, spores,etc.

• They have the chromosome number of 1n • (1n + 1n = 2n) (Diploid) • Two main parts of Meiosis:

Meiosis I - Homologous Chromosomes separate into separate cells

Meiosis II - Chromatids of each chromosome are segregated into separate cells.

Meiosis I

Interphase I Prophase I Metaphase I Anaphase I

Cells undergo a round of DNA replication, forming duplicate Chromosomes.

Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Spindle fibers attach to the chromosomes.

The fibers pull the homologous chromosomes toward the opposite ends of the cell.

Section 11-4

Figure 11-15 Meiosis

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Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Meiosis I DNA replication has already happened.

Prophase I DNA condenses

into chromosomes.

Nuclear membrane disappears

Each chromosome lines up next to its homologue

These homologues twist around each other to form a tetrad and genetic material can be exchanged (crossing- over)

Metaphase I Tetrads

(Homologue) move to the middle of the cell

Anaphase I The

Homologous pairs of chromosomes separate.

One chromosome of each hom. Pair moves to each side.

The sister chromotids did not separate.

Telophase I The cytoplasm

divides, forming two new daughter cells. Each cell has one of the homologues.

Meiosis II No DNA replication has happened.

Prophase II Recoiling may

occur to form chromosomes from chromatin

Spindles form

Metaphase II Chromosomes

are moved to the middle of the cell

Anaphase II Centromeres

joining the chromatids divide

Sister chromatids are now separate

Each chromatid is moved to the opposite pole

Telophase Spindles

disappear Nuclear

membrane forms

Chromatids unwind into chromatin

Cytokinesis occurs separate from meiosis

Egg and Sperm FormationGametes - sex cells that have half the

number of chromosomes as somatic cells (body) p. 278

• Sperm are formed in the male sex organs through the process of meiosis. Four (4) new sperm are produced from this process from every “mother cell”.

• Eggs are formed in the female sex organs through meiosis. One egg cell or ootid and three (3) polar bodies are produced from every “mother cell”.

Genetic VariationSexual reproduction - fusion of gametes with different

genetic material. Offspring are genetically different than parents.

Asexual reproduction - there is no exchange of genetic material. Organism is identical to parent. Binary fission, budding, cloning.

How does genetic variety help organisms survive?

Diploid numbers for various organisms:mouse 40 rat 42 hamster 44 guinea pig 64dog 78 cat 38 frog 26 goldfish 94

garden pea 14 potato 48 corn 20 onion 16 house fly 12 grass hopper 24

What conclusion can you make from these numbers?

Section 11-4

Crossing-Over of tetrads

FYI Reduction Division reduces the number of chromosomes per daughter cell by half.

Prophase I – can last years. Human females have potential eggs which have entered prophase I by birth. Eggs remain “stuck” in this stage for decades.

Oocytes – germ cells with potential to form eggs are in follicles, found in the ovary tissue. Each follicle has a single oocyte. All germ cells are in prophase I of meiosis by birth. Oocyte grows and is packed full of nutrients for a developing embryo. Oogensis – egg forms and follicle ruptures releases the egg. Ovulation occurs. Meiosis II is completed after the fertilization of the 1 egg. 3 polar bodies are produced and disintegrate.

Synapsis – process of chromosome alignment in Prophase I. Synapsed pair of homologous chromosomes are called a tetrad. Crossing over can occur.

Sperm – produced in seminiferous tubules from stages of cells. Spermatogonia primary spermatocytes spermatidsimmature sperm

Janssens (1909) predicted crossing over leads to genetic recombination/ which increases diversity of all life.

Chiasmata- the points where two homologous chromosomes are in contact. Sites where crossing over takes place. Crossing over does not require the breakage and reunion of thick, compact chromosome pieces, but of individual DNA molecules (nucleotides+nucleotides).There are 223 combination possible in humans for to independent assort (8million possibilities)

1 in 70 million chance of having identical siblings in different pregnancies.

Pleiotrophy – product of one gene can cause many problems. (Ex: cystic fibrosis)

Epistasis – one pair of alleles (recessive) effect the genes or alleles at another loci (part of chromosome). Ex: Albinism

• 11–5 Linkage and Gene Maps

A.Gene Linkage

B.Gene Maps

Section 11-5

Section Outline

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What are some products that often come in packages containing several different colors and flavors?

What happens if you want only one flavor? What else do you get besides the color or flavor you want?

Linkage groups- these are “packages” of genes that tend to be inherited together. There is one linkage groups for every homologous pair of chromosomes.

*A human cell has about 100 000 different genes attached in a single line on each chromosome.

Crossing Over

If genes for body color and wing size are linked, why aren’t they linked all the time? Sections of the chromosomes can cross, break and reattach during Meiosis I. (see diagram)

Recombinants - individuals with new combinations of genes. It is believed that 2-3 cross-overs occurs on each pair of human homologs in sex cells.

Punnett Square - name after Reginald Punnett who studied genetics in the 1900’s.

Sutton - (1902) His Chromosome theory of heredity states that genes are located on chromosomes and each occupies a certain place. Each chromosome contains a form of the gene called an allele.

There can be two or more alleles for each gene. (see diagram)

Linked genes - they are found on the same chromosome and do not undergo independent assortment. Discovered in

fruit flies by Thomas Hunt Morgan.

What if there was no crossing-over in any organism?

Gene Mapping

Distance between genes (alleles) determines how often crossing over occurs. The farther apart- the more likely genes are to cross-over. This distance helps to “map” a chromosome and tell the probable place to find a certain gene on the chromosome.

Genes located on one of the sex chromosomes is said to be sex linked. How is the sex of offspring determined? (Review)

Crossing-Over

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Crossing-Over

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Crossing-Over

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Exact location on chromosomes Chromosome 2

Section 11-5

Figure 11-19 Gene Map of the Fruit Fly

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Earth

Country

State

City

People

Cell

Chromosome

Chromosome fragment

Gene

Nucleotide base pairs

Section 11-5

Comparative Scale of a Gene Map

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Mapping of Earth’s Features

Mapping of Cells, Chromosomes, and Genes