Chapter 11: Mendel and Meiosis

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Chapter 11 Mendel and Meiosis

• Mendels Laws of Heredity
• Meiosis

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Chapter 11 Vocabulary

• Genetics
• Heredity
• Traits
• Gregor Mendel
• Alleles
• Dominant
• Recessive
• Genotype
• Phenotype
• Homozygous
• Heterozygous

• Monohybrid Cross
• Dihybrid Cross
• The Law of Independent Assortment
• Punnet Square

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Chapter 11 Concept Map p. 272-273
Heredity
Traits
Genetics
Gregor Mendel
Gametesp. 278
Pollination
Fertilization
True Breeding
2nd Generation
1st Generation
The Law of Segregation
Alleles
Dominant
Recessive
The Principle of Independent Assortment
Phenotype
Genotype
Homozygous
The Principle of Dominance
Heterozygous
Gene Linkagep. 279
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Chapter 11 Concept Map p. 267-271
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic traits
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Chapter 11 Concept Map p. 267-271
Principle of Probablility
Reginald Punnett
Punnett Square
Dihybrid Cross (Two Factor Cross)
Monohybrid cross
Genes, Chromosomes and numbers (12.2)
Diploid Cell
Haploid Cell
Homologous chromosome
Crossing Over
Gene Map
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Chapter 11 Concept Map p. 275-277
Phases of Meiosis 1 2
Heredity
Telophase I II
Interphase
Prophase I II
Anaphase I II
Metaphase I II
Tetrad
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Mendels Laws of Heredity

• Genetics is the branch of Biology that studies
  the topic of Heredity, or the passing of
  characteristics from parents to offspring.
• Traits Inherited characteristics.
• True Breeding means self pollination
• Lets Review

http//www.writing.ucsb.edu/faculty/samuels/dna.jp
g
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Review

• Gametes The sex cells found in an individual-
  egg or sperm.

• Zygote A fertilized egg- the first cell in a
  new organism.
• Pollination Transfer of male pollen grains to
  the female pistil.
• Can be Self or Cross
• Fertilization The uniting of male and female
  gametes.

• Hybrid Has desired traits from both parents,
  usually done on purpose by man.

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Mendels Laws of Heredity

• Pea plants usually self-pollinate.
• Why is this important to genetic study?

http//www.nature.com/nsu/030616/images/gm_180.jpg

• Gregor Mendel (1822-1884) An Austrian monk. He
  wanted to know how traits were passed from parent
  to child and then to future generations.
• He knew a lot about pea plants so he decided to
  study them to answer his questions and develop
  his research.

http//www.wcer.wisc.edu/step/ep301/Spr2000/Brian-
B/images/medel.gif
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Mendels Laws of Heredity

• Mendel started out with plants that he knew were
  only tall or short.
• The tall ones had no short plants in their
  family.
• The short ones had no tall plants in their
  family.
• He mated short plants with tall plants.
• All the offspring were tall!! Hmmmmmm
• What was going on???

http//www.mhhe.com/biosci/esp/2001_gbio/folder_st
ructure/ge/m2/s2/assets/images/gem2s2_1.jpg
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Mendels Laws of Heredity

• First, you must know this-
• The parental generation of plants is called
  theP1 generation (P for Parental)
• The first generation of offspring is called
  theF1 generation (F for Filial)
• The second generation of offspring is called
  theF2 generation
• Usually we dont go as far as an F3 generation

http//www.fastplants.org/graphics/genetics/parent
_F2.jpg
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Mendels Laws of Heredity

• In order to find out what was going on, Mendel
  had the new tall offspring (F1 plants)
  self-pollinate so he could observe this second
  generation (F2 Plants).
• The resulting F2 plants were tall ¾ of the time,
  and short ¼ of the time!
• It was as if the short trait in the original
  plants (P1 Plants) was coming out two generations
  later in the F2 plants!

http//www.biology.arizona.edu/mendelian_genetics/
problem_sets/monohybrid_cross/graphics/02Q.gif
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Mendels Laws of Heredity

• Mendel concluded that there must be two factors
  in each organism that determine trait
  inheritance.

• He called them unit factors.
• We call them alleles.
• Alleles A particular form of a gene, one comes
  from the mother, one from the father.
• Ex. If the gene is for height, the allele could
  be tall or short.
• If the gene is for eye color, the allele could be
  light or dark.

http//ghs.gresham.k12.or.us/science/ps/sci/soph/g
enetics/alleles.gif
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The Rule or Principleof Dominance

• If there are two alleles, and only one observed
  trait, which allele is dominant?
• A dominant allele is always expressed whether
  with another dominant allele, or with an
  unexpressed allele.
• A recessive allele is never expressed when in the
  presence of a dominant allele, but it is
  expressed when paired with another recessive
  allele.

http//wellspring.isinj.com/bio/principlesI/Images
/segregation.jpg
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The Rule or Principle of Dominance

• Remember, Mendel said there were two alleles, one
  from the female and one from the male for every
  trait, or gene.
• He then said that for the height gene, the allele
  TTall and the allele tShort.
• We now know that T is dominant to t which is
  recessive.

http//web.grcc.edu/biosci/revhand/genetic/wp0002
.jpg
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PRINCIPLE OR LAW OF SEGREGATION

• 1ST of Mendels 2 laws on heredity
• States All plants/animals have two alleles for
  each gene.
• If these alleles are different, then the
  organisms can produce
• two different types of gametes. These gametes
  randomly pair
• during fertilization to produce four possible
  combinations of alleles.

Each F1 has a tall and short allele (for the gene
for height) that it can pass on to its offspring
(F2)

• Example (Pea Plants) F1 (Tt) X F1 (Tt)

F2 TT Tt Tt tt

• What is the genotypic ratio? Phenotypic ratio?

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The Rule or Principle of Dominance

• If T is dominant, then
• TTTall, TtTall, and ttShort.
• In this case TT, Tt, or tt is called the genotype
  of the height trait.
• GenotypeThe gene combination (or combination of
  alleles) an organism has for a trait.
• Phenotype The expression of the gene itself.
• Blue eyes, straight hair, smooth pea, wrinkled
  pea are all phenotypes.

http//web.grcc.edu/biosci/revhand/genetic/wp0002
.jpg
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Mendels Laws of Heredity

• Homozygous Two of the same allele for a trait.
• Ex. TT or tt.
• Heterozygous Two different alleles for one
  trait.
• Ex. Tt.
• TT is homozygous dominant.
• tt is homozygous recessive.
• Tt is heterozygous.

http//www.biologie.uni-hamburg.de/b-online/ge08/0
1.gif
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Mendels Laws or Principles of Heredity

• P1 TT x tt Forced Mating Tall x Short
• ? ?
• F1 All Tt Self-pollinate All Tall
• ? ?
• F2 TT Tt Tt tt Count 3 Tall1 Short

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Dihybrid Crosses (2 Factor Cross)

• So far we have only looked at single or lone
  traits like height.
• The crossing of these plants when only looking at
  one gene or trait is called a monohybrid cross.
• What would happen if we looked at two traits and
  their alleles at the same time?
• Ex. Wrinkled and yellow peas or round and green
  peas
• This is called a dihybrid cross (2 factor cross).
• Mendel did this so lets see what happens

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Phenotypes Dihybrid Cross

• P1 Round Yellow x Wrinkled Green
• F1 All Round and Yellow
• F2 Round Yellow (9) Round Green (3) Wrinkled
  Yellow (3) Wrinkled Green (1)
• 4 Possibilities

http//campus.queens.edu/faculty/jannr/Genetics/im
ages/dihybridtestcross.gif
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Punnett Squares

• Based on The Law of Independent Assortment. This
  law states that alleles are inherited
  independently of each other.
• If an organism has a genotype of RrYy (its
  phenotype is yellow round peas), when it passes
  on its alleles to its offspring, they could be in
  any combination possible (think of the face lab,
  when you did eye color).
• RY, Ry, rY, or ry

http//www.ndsu.nodak.edu/instruct/mcclean/plsc431
/mendel/mendel3.htm
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Punnett Squares

• These crosses are getting too complicated! It
  cant be this difficult!
• Lets use a Punnett Square
• Original P1 Monohybrid Cross (Tall x Short)

Male T T
Tt Tt
Tt Tt
Female t t
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Genotypes Dihybrid Cross

• P1 RRYY x rryy
• F1 All RrYy
• F2 RRYY, RRYy, RRyy, RrYY,
• RrYy, Rryy,
• rrYY, rrYy,
• rryy
• 9 possibilities

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Phenotypes - Dihybrid Crosses

• RRYY, RRYy, RrYY, RrYy Round Yellow
• rrYY, rrYy Wrinkled Yellow
• RRyy, Rryy Round Green
• rryy Wrinkled Green

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Punnett Squares

• As you can see, they are most useful when doing a
  dihybrid cross.
• See p. 267 Fig. 10.
• Do practice problems.
• Remember Punnett Squares are only a prediction
  of the ratios that will be seen in the F2
  generation. They are not completely exact at all
  times!

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Summary of Mendels Principles

• Genes are passed from parents to their offspring
• Some genes are dominant, some are recessive
• Each adult has 2 copies of each gene, one from
  each parent, these genes are segregated from each
  other when gametes are formed
• Alleles for different genes usually segregate
  independently of each other.

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Breaking the Rules

• What happens when the rules of dominance and
  recessiveness are blurred?
• What happens when there arent just two possible
  alleles for a trait but three? How about four,
  five, six or 100?
• Its time we found out.

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Incomplete Dominance

• Incomplete Dominance The heterozygote is an
  intermediate form of both alleles for a trait.
• Ex. Red snapdragons crossed with white
  snapdragons produce pink ones.
• Notation is R and R instead of R and r.
• RR is Red, RR is pink, RR is white.

http//www.allensfarmandfloral.com/Images/132002.j
pg
http//www.weddingsolutions.com/articles/snapdrago
n.jpg
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CuriosityFarmMed.jpg
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Codominance

• Codominance Both alleles are expressed equally.
• Notation is B and W instead of B and b.
• B for black, W for white
• BB-black, BW-white and black, WW-white.
• Ex. Chickens.

BW
WW
BB
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uk/insideout/east/series2/images/chicken_rare_bree
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/east/series2/
http//www.curlytailz.co.uk/black_chicken2.jpg
http//www.americanmountedgamebirds.com/Chicken200
2/smSpeckledSussex.jpg
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Multiple Alleles

• Multiple Alleles more than two alleles exist for
  any one gene or trait.
• Only two alleles are found in an individual, but
  there can be many different alleles that exist in
  a population.
• Ex. Blood type. A, B, or O are all alleles.
• ABType AB, AOType A, BOType B, OOType O.

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Polygenic Inheritance

• Polygenic Inheritance The inheritance pattern of
  a trait that is controlled by more than one gene.
• Genes may be on the same chromosome or different
  chromosomes.
• Ex. Skin color (remember baby lab).
• Very often, the more dominant alleles that are
  involved, the more the trait is expressed.
• Ex. 1 dominant allele light skin, 2 darker,4
  very dark, etc.

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http//www.cabrinihigh.com/faculty/gcano/webprojec
t1/kim/j.20lo205.jpg
http//www.georgwa.demon.co.uk/aretha_franklin.htm
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Environmental Factors

• An organisms external and internal environment
  affects its genetic development.
• External
• Temp., light, nutrition, chemicals, etc.
• Internal
• Hormones or age.
• Baldness in males, horn production in sheep, and
  vibrant feather coloring in birds are all hormone
  related.

http//www.cool.co.cr/usr/turtles/turtles7.jpg
http//home.pages.at/kgirsch/florida98/images/ali2
.jpg
http//www.topshot.com/dh/pix/bald.jpg
http//www.sweetdreamfarm.com/images/manlyheadon-S
IZED.jpg
http//members.tripod.com/zdoll2/animal/parot.jpg
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Meiosis

• Why Meiosis?
• Mitosis produces cells with exactly the same
  amount of chromosomes as the original cell.
• If this was the only means of cell division,
  offspring would end up with twice as many
  chromosomes as the parents.
• Ex. Pea plant has 14 chromosomes each plant
  produces gametes with 14 chromosomes
• Egg (14 chrom.) Sperm (14 chrom.)
  Offspring (28)

F1 Egg (28) F1 Sperm (28) F2
Offspring (56)
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Meiosis

• In order to produce offspring with the same
  number of chromosomes as the parents, the
  organism must produce gametes with only half the
  number of chromosomes as the parents body cells.
• Haploid cell with one of each kind of chromosome
  (n)
• Organisms produce gametes that are haploidegg
  and sperm
• Diploid cell with two of each kind of chromosome
  (2n)
• Body cells of animals/plants have chromosomes
  that occur in pairsone from each parent
• To produce haploid gametes, organisms undergo
  meiosis

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Meiosis

• Meiosis has 2 separate divisionsMeiosis I and
  Meiosis II
• Meiosis I begins with a Diploid cell2n
• Meiosis II finishes with 4 Haploid cells (1n)
• These 4 Haploid cells are Gametes (Egg or Sperm)
• With Fertilization, Sperm (23) and Egg (23)..
  Haploidcome together to produce a Zygote
  (46)..Diploid

• This pattern of reproduction that involves the
  combining (fusion) of haploid gametes is called
  Sexual Reproduction

• Homologous Chromosomes Paired chromosomes, each
  with genes for the same traits. These exist in
  Diploid cells and are what determine how an
  individual looks.
• See pg. 276-277

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Interphase
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Prophase I pg. 276
Crossing Over can occur
Each pair of homologous chromosomes come together
to form a four-part structure called a Tetrad
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Metaphase I
In Meiosis, the Tetrad of homologous chromosomes
lines up down the middle
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Anaphase I
This step insures that each new cell will only
receive one chromosome from each homologous pair
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Telophase I
At the end of Meiosis I the two new cells are
still Diploid
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Prophase II
Meiosis II is identical to Mitosis
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Metaphase II
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Anaphase II
45
Telophase II
Each Haploid cell has one chromosome from each
homologous pair
4
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Genetic Variation

• Meiosis shuffles chromosomes so that the
  offspring are not identical to the parentsthis
  is genetic variation
• HOW??
• Gene combinations vary depending on how each pair
  of homologous chromosomes lines up during
  Metaphase Ithis is completely random
• Crossing Over can occur anywhere at random

• Genetic Recombination reassortment of
  chromosomes and genetic information they carry,
  either by crossing over or independent
  segregation of homologous chromosomes

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Gene Linkage

• Thomas Hunt Morgans
• Research on fruit flies led him to the principle
  of linkage
• Showed linkage groups assort independently not
  individual genes
• Gene Maps a map of distances between genes
• Determined by the rate at which linked genes are
  separated and recombined
• See pg. 280

http//www.uky.edu/Agriculture/Entomology/entfacts
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