Biology Chapter 11 Introduction to Genetics: Mendel and Meiosis

Biology Chapter 11

Introduction to Genetics: Mendel and Meiosis

IQ #1

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 11-4: Meiosis

I. MEIOSISA. Meiosis= process of

_________________________ in which the number of chromosomes per cell is cut in 1/2 and the homologous chromosomes that exist in a diploid cell are separated. (and produce haploid cells)

B. Purpose=

Reduction Division

Form gametes (egg and sperm)

II. DIPLOID AND HAPLOID CHROMOSOME NUMBER

A. During ________________ the genetic material from one parent combines with genetic material from another

Example: A fruit fly has 8 chromosomesA set of 4 came from the female flyA set of 4 came from the male fly

B. The two sets of chromosomes are said to be

fertilization

homologous = a female chromosome has a corresponding male chromosome.

C. =contain both sets of homologous chromosomes

D. = contain 1 set only

Male gamete

Female gamete

Diploid (2n)

Haploid (n)

Sperm (n) = 23 chromosomes

Egg (n) = 23 chromosomes

Question: If we start with a diploid cell, how do we get an organism that produces haploid gametes?

Answer: Example: what if:

46

44

8

44

8

16

8

23 2323

46

92

46

Meiosis (aka: reduction division)1 replication; 2 divisions

23

Human Fruit fly

Duplicatedchromosomes

Duplicated

chromosomes

III. PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES: MEIOSIS I & II

INTERPHASE: growth, DNA synthesis, protein production, organelle production

A. Meiosis I 1. homologous chromosomes pair up (Form tetrads)

2. nucleoli disappear 3. nucleus disappears 4. crossing-over occurs:

portions of chromatids exchange genetic material

2n (diagram 277)

prophase I

Crossing-Over

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Crossing Over: exchange of genetic material between homologous chromosomes

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Crossing Over

Crossing-Over

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Crossing Over

2. spindles attach to chromosomes independent assortment occurs

1. homologous pairs (tetrads) line up at the equator

metaphase I

anaphase I

Key point: homologous pairs separate, cell now haploid

1. spindles pull the homologous chromosomes toward opposite ends of the cell

Telophase I

2. cell begins to separate into two new haploid cells

3. 2 haploid daughter cells

1. Nuclear membranes reform

n n

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 I






Section 11-4


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Meiosis I






Section 11-4


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Meiosis I






Section 11-4


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Meiosis I

B. Meiosis II (similar process as mitosis; no replication)

n

n

n

n

***RESULT: 4 haploid daughters that are genetically different!!

Prophase II

Metaphase II

Anaphase II

Telophase II/Cytokinesis

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.

Figure 11-17 Meiosis II

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Meiosis II


Prophase II Metaphase IIAnaphase II Telophase IIThe

chromosomes line up in a similar way to the metaphase stage of mitosis.



Section 11-4


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Meiosis II


Prophase II

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




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Meiosis II


Prophase II Metaphase II Anaphase IITelophase IIThe




Section 11-4


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Meiosis II


Prophase II Metaphase II Anaphase IITelophase IIThe




Section 11-4


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http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.htmlMeiosis II

IV. GAMETE FORMATION (refer to page 278)A. Males1. 2. male gametes produced by a process called _________________ B. Females1. 4 haploid cells are produced but only 1-haploid cell is a 3-produce 2. female gametes produced by a process called _______________

The 4 haploid cells (gametes) = sperm

spermatogenesis

viable egg polar bodies caused by uneven cytoplasmic division

oogenesis

(a) In the male, all four haploid products of meiosis are retained and differentiate into sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg cell and three (in some cases, only two) small cells called polar bodies that do not give rise to functional gametes. Although not indicated here, the mature egg cell has usually grown much larger than the oocyte from which it arose.

V. COMPARING MITOSIS AND MEIOSIS A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. http://biologyinmotion.com/cell_division/

Mitosis Meiosis

Number of daughter cells

Type of cells produced

Number of divisions

Number of replications

Purpose of division

2 diploid cells

1

1

Growth, replacement, repair, asexual reproduction

gametes

2

1

4 haploid cells

Sexual reproduction

Body cells

Section 11-1Standards addressed: CA 3.b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment. National 7 2.c. Students know an inherited trait can be determined by one or more genes. 7.2.d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining phenotype while the other is recessive. B1. 2.d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).

Key Ideas: What is the principle of dominance?What happens during segregation?

INTRODUCTION TO GENETICS I. The work of Gregor Mendel

A. : the scientific study of heredity

B. Heredity: II. Gregor Mendel's Peas

A. In the 1800's, _____________________________ (an Austrian Monk) conducted the first scientific study of heredity using pea plants.

B. Pea plants contain both

male (pollen:sperm) and female (eggs) reproductive parts.

Genetics

Passing genes from generation to generation

Gregor Mendel

Flowering Plant Structures: Pea Plant

C. _______________ = Joining of male and female reproductive cellsFertilization

D. _________________= a pea plant whose pollen fertilizes the egg cells in the very same flower.

1. Mendel discovered that some plants ___________ for certain traits

2. Trait=

Example: seed color, plant height

3.True breeding (a.k.a. pure)=

Example: Short plants that self pollinate for

generations always produce offspring that were pure for shortness.

Self-pollination

“Bred True”

Specific Characteristics

Peas that are allowed to self-pollinate produce offspring identical to themselves

Cross Pollination

Self pollination

E. _______________= male sex cells from one flower pollinate a female sex cell on a different flower.

Cross-pollination

F. Mendel manually cross pollinated pea plants, removing the male parts to ensure no self-pollination would occur. Through a series of experiments, Mendel was able to make discoveries of basic principles of heredity.

1. principle of

2. principle of

3. principle of

Dominance

Independent Assortment

Segregation

A. Mendel studied __ different traits in pea plants each with 2 contrasting characters. (refer to page 264) B. Each trait Mendel studied was controlled by one gene. C. Different forms of a gene (trait) = Example: Gene for plant height has 2 alleles

Alleles

Dominant: T = tall Recessive: t = short

7

III. Experiments Mendel performed

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

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Mendel’s Seven Crosses on Pea Plants

Parent Offspring

pure bred tall x pure bred tall TT X TT

All plants are

pure bred short x pure bred short tt X tt

All plants are

Pure bred tall x pure bred short X

All plants are

Mendel Experiment #1:

TALL

SHORT

TT tt TALL

· individual factors (now known as _________) · the factors

________________________________= some alleles are dominant (expressed trait;written as a capital letter; ex. T) some are recessive (hidden/masked trait; written as a lower case letter; ex. t) From these conclusions, Mendel wanted to continue his experiments to see what happened to the recessive trait

genes

did not blend

Principle of Dominance

Conclusion:

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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Section 11-1


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Section 11-1


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3 tall : 1 short

Conclusion:· ___________________________: The reappearance of the recessive allele indicated that at some point the allele for shortness separated from the allele for tallness. Mendel suggested that the alleles separated during the formation of the sex cells (gametes)….During meiosis.

Principle of Segregation

A. Probability =

B. Probability=

Example #1: If you flip a coin, what is the probability of landing on heads? Probability= (side that has a head on it) ( opportunities on a coin; head or tails) Example #2: If you flip a coin 3 times what is the probability of landing on heads? Probability=

The likelihood that a particular event will occur

# of times a particular event occurs# of opportunities for the event to occur (# of trials)

122

½ x ½ x ½ = 1/8

IV. PROBABILITY AND PUNNETT SQUARES

A. Each flip is

B. The C. The principles of probability can be used to

independent of the next. Past outcomes do not affect future ones. Similar to alleles that segregate randomly, like a coin flip.

larger the number of trials the closer you get to the expected outcomes

predict the outcomes of genetic crosses.

IV. PUNNETT SQUARES Use of Punnett squares help determine the probable outcomes of genetic crosses.· New vocabulary to help with Punnett squares -Homozygous = -Heterozygous= -Genotype= -Phenotype= -Hybrids=

Having 2 identical alleles (TT, tt)Having 2 different alleles (Tt)

Genetic makeup of an organism (TT, tt, Tt)Physical appearance (tall or short)

The offspring resulting from a cross between parents of contrasting traits

· Example of a Punnett square: Parent (P) cross

homozygous tall( ) x homozygous short( )

Probability of producing homozygous tall offspring?

Probability of producing hybrid?

TT tt

0/4

4/4

F1

offspring

t t

Tt

T

T

TtTt

Tt

IV. PROBABILITY AND SEGREGATIONA. For fun, lets cross F1’s to see if Mendel’s assumptions

about segregation are correct:

Tt x Tt

If the alleles segregate during meiosis, then the probable outcomes will be:

TT= Tall=Tt= Short=tt= Ratio tall:short=

1/42/4

1/4

31

3:1

t

T

T t

TT Tt

Tt tt

Conclusion:

IV. PROBABILITY AND INDEPENDENT ASSORTMENT

A. Mendel wondered if one pair of alleles affected the segregation of another pair of alleles. B.The two factor cross: Mendel crossed RRYY x rryy (P)(aka:two trait cross)

All offspring are

Mendel was correct in his assumptions about Segregration

Do round seeds have to be yellow?

Hybrid (RrYy) (F1)

A. Then he crossed the hybrids (F1):

RrYy x RrYy· Punnett square formatting rules for 2 trait crosses 1. Determine the possible gametes produced by the parents. 2 methods: a. F- RrYy O- I- L-

irst twoutside two

nside twoast two

(RY)(Ry)(rY)(ry)

a. Use a punnett square. One trait on top and the other trait on the side.

Parent 1: RrYy Parent 2: RrYy

Possible gametes Possible gametes

RyRY

ryrY ryrY

RyRY

r

R

yY yY

R

r

2. Place one parent’s gametes at the top of a 16-Punnett square and the other parent’s gametes on the side of the 16-Punnett square.

RY

RY

Ry

Ry

rY

rY

ry

ry

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Section 11-3

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Probability: RY (round and yellow)= Ry (round and green =rY (wrinkled and yellow)= ry (wrinkled and green)= Phenotype Ratio= Conclusion=

9/163/16

3/161/16

9:3:3:1

Alleles for seed shape independently assort.

****This is true if the traits you are studying Just by chance all 7 of Mendel’s traits were on different chromosomes.

Genes for different traits can segregate independently during the formation of gametes

are located on different chromosomes

Independent assortment

1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.3. In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.4. The alleles for different genes usually segregate independently of one another.

**Summary of Mendel’s Principles**

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

experimented with

Summary of Gregor Mendel’s Work

Key idea: Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

Ex. Four O’clock flowers (see next slide)

Beyond Dominant and Recessive Alleles

Incomplete Dominance in Four O’clock Flowers

Incomplete Dominance: One allele is _______________ dominant over another. Therefore the phenotype in the heterozygous is somewhere __________ the two homozygous phenotypes.

not completely

in between

Incomplete Dominance in Four O’clock Flowers

Codominance: both alleles contribute _________ to the phenotype. Ex. Cholesterol

Mutliple Alleles: Genes that have _____________

alleles.This does not mean an individual can have more than two alleles, but that there are more than two alleles in the _______________ for a given trait.

Ex. Rabbit coat color, blood type

equally

more than two

population

BO

BB

Multiple Alleles and Codominance

3 Alleles: iA, iB, I

iA and iB are codominant

iA, iB both dominate over i

Blood Type/Phenotype

Polygenic Inheritance: The interaction of many genes controls one trait.

It is usually recognized in traits that show a ____________________ such as skin color, height, and body weight.

range of phenotypes

Applying Mendel’s Principles. Mendel’s principles do not apply only to plants. Thomas Hunt Morgan1. In the early ________, Morgan (a nobel prize winning geneticist) decided to look for a model organism to advance the study of genetics.2. He studied the _____________, Drosophila melanogaster.3. This specimen was a good choice because: _______ and can be kept in a small place produce ___________ of offspring has only _________ of chromosomes they can produce a new _______________ every 4 weeks

1900’s

fruit fly

tiny hundreds 4 pairs

generation

Fruit Flies (Drosophila melanogaster)

Genes alone ______________________ the characteristics of an organism. The interaction between genes and the ________________are necessary. Ex. Consider the height of a sunflower. Genes provide a plan for the development of a sunflower but the condition of the soil, climate, and water availability will also influence the height of the sunflower.

do not determine

environment

Genetics and the environment

11-5: Gene Linkage and Gene MapsStandards addressed: CA B1 3.b students know the genetic basis forMendel’s laws of segregation and independent assortment. *B1 3.d. Students know how to use data on frequency of recombination at meiosis to estimate genetic distances between loci and to interpret genetic maps of chromosomes. Key concept: What structures actually assort independently?

Actually ________________________ do assort independently just as Mendel had suggested but the _______ on the chromosomes can be ____________.

A. Linked genes1. Genes located on the _________ chromosome2. Inherited _____________3. Do not undergo ___________________; they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes...none were linked.)

the chromosomes

genes linked together

same

together independent assortment

B. Linkage group= all the genes on a _____________

* If there are ___ pairs of chromosomes then there are ____ linkage groups. Humans have ____ pairs of chromosomes therefore ____ linkage groups

chromosome

4 4 23

23

III. Crossing OverA. If two genes are found on the same chromosome, does it mean that they are linked forever? NO! Crossing over produces ___________________

B. Recombinants= individuals with _________________ of genes

recombinants.

new combinations

IV. Gene Mapping

A. Sturtevant stated that: crossing over occurs ________________ along the linkage groups. the _______________ the genes are from each other the ______________ they will cross over using the _______________________ (how often crossing over occurs), a gene _______ can be made for each chromosome

randomly

further more likely

frequency of recombination

map

B. Gene map= the __________________ on a chromosome Example: gene a and gene b cross over 20%

gene a and gene c cross over 5% gene b and gene c cross over 75%

chromosome:

positions of genes

C A B

Exact location on chromosomes Chromosome 2

Figure 11-19 Gene Map of the Fruit Fly

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Biology Chapter 11 Introduction to Genetics: Mendel and Meiosis