Mendelian Genetics and Punnett Squares

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Mendelian Genetics and Punnett Squares

• Genetic Continuity, Gregor Mendel and monohybrid
  crosses

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Lesson Objectives

• Weekly Learning Goals
• Minds ON
• Reports (Bacteria / Parasites) handed back
• Pre-March Break Recap
• Mendel, Punnett Squares and Monohybrid Crosses
• Group Assignment Sign Up
• Homework

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Learning Goals for This Week

• We are learning to use the Punnett square method
  to solve basic genetics problems involving
  monohybrid crosses, incomplete dominance,
  codominance, dihybrid crosses, and sex-linked
  genes (D2.3)
• We are learning to investigate monohybrid and
  dihybrid crosses, and use the Punnett square
  method and probability rules to analyse the
  qualitative and quantitative data to determine
  the parent genotype (D2.4)
• We are learning to explain the concepts of
  genotype, phenotype, dominance, incomplete
  dominance, co-dominance, recessiveness, and sex
  linkage according to Mendelian laws of
  inheritance (D3.3)
• We are learning to explain the concepts of
  genotype, phenotype, dominance, incomplete
  dominance, codominance, recessiveness, and sex
  linkage according to Mendelian laws of
  inheritance (D3.3)

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Minds ON

• With the people around you, try to unscramble
  these genetic words. (Note these are terms we
  have already discussed in class). You have 3-5
  min.
• Soiemis
• Lellaes
• Tsamgee
• Tpgeyeno
• Tpheyone
• Soimtsi
• Zhymoouogs
• Treoheoguzy

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Minds ON

1. Meiosis
2. Alleles
3. Gametes
4. Genotype
5. Phenotype
6. Mitosis
7. Homozygous
8. Heterozygous

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Reports Handed Back

• Overall, well-done!!
• Some things to note for next time
• Hypothesis needs a specific direction or scope
  go out on a limb and take a guess (DONT state
  the obvious). The prediction is supposed to back
  up that belief.
• Report writing involves the use of headings.
• List of sources References, not Bibliography
  or Works Cited (MLA)
• References need to be alphabetical.
• Follow instructions carefully.
• Introductions can stand alone as one paragraph
  that includes purpose, hypothesis and prediction.
• When in doubt, use citations if its not your
  idea, give credit to the owner!
• Embedded or in-text citations using citations
  within a text e.g. (Smith, 2014)
• Hypotheses are supported or not supported ---
  NOT proven or disproven A future experiment
  could yield different results!

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The Week Before March Break Recap

• Mitosis

• Meiosis

• Purpose Growth and repair
• Divisions 1
• Parent Cell 2n diploid
• Daughter Cells 2 cells 2n identical to parent
  cell
• Product Somatic cells (body cells)

• Purpose Sexual reproduction
• Divisions 2
• Parent Cell 2n diploid
• Daughter Cells 4 cells 1n not identical to
  parent cells
• Product Gametes (sex cells, germ cells)

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The Week Before March Break Recap

• Alleles
• Variations of a certain gene (i.e. eye colour
  many possibilities)
• Dominant Traits
• If present, will always be shown (BB)
• Homozygous dominant Individual has two dominant
  pairs of alleles (BB) dominant trait expressed
• Heterozygous dominant Individual has a dominant
  and recessive allele (Bb) dominant trait
  expressed
• Recessive Traits
• If present, will only be expressed if both
  parents give a recessive pair (bb)
• Heterozygous recessive Individual has two
  recessive alleles (bb) recessive trait expressed
• Genotype
• The DNA makeup demonstrated by letter
  combination cant be seen (BB, Bb, bb)
• Phenotype
• The physical trait expressed (brown eyes, blue
  eyes)

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Gregor Mendel The Father of Genetics

• 19th century Moravian monk
• Born Johann Mendel, in Austria (1822)
• Studied science to become a high school teacher
  at the University of Vienna
• Demonstrated laws of heredity using pea plant
  Pisum sativum.
• Completed his experiments from 1856-1868 and was
  elected Abbot of the monastery
• Died of a kidney disorder (1884)

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His Work

• Mendel was able to demonstrate laws of heredity
  by crossing his pea plants thousands of times to
  support his hypothesis that certain traits could
  be predicted.
• Mendel used pure breeds of pea plant Pisum
  sativum.
• Looking at this diagram, why do you think he
  would choose a pea plant rather than a mouse or a
  bee?

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Why the Pea?

• Mendel chose to use peas for a variety of
  reasons
• The pea plant can self pollinate, so Mendel could
  control the parental crosses by cutting off the
  stamens (male reproductive organ in plants) of
  one plant and using the pollen of another plant
  to fertilize the first plant.
• Pisum sativum grows, matures and reproduces
  quickly, yielding a high number of seeds. This
  allows for many generations to be observed over a
  relatively short period of time.
• These pea plants produce several pairs of obvious
  and contrasting characteristics.

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Figuring Out the Pea Parental (P1 Generation)

• First, Mendel self-pollinated the pea plants over
  several years in order to establish pure bred
  plants.
• Next, he took two pure bred individuals and
  crossed (bred) them for a certain trait (i.e.
  colour). Purple is dominant for colour (PP) for
  and white plants are recessive for colour (pp).
• When they mate, their offspring become the first
  filial generation (F1 generation).
• Using a Punnett Square the possible outcomes can
  be predicted (see figure).
• If the resulting offspring mate, they will create
  a monohybrid cross.

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Monohybrid Crosses

• F2 Generation (Pp x Pp)
• Two heterozygous dominant (Pp) peas are crossed
  and 3 of the offspring have a purple phenotype
  and 1 of the offspring has a white phenotype
  because both parents were heterozygous dominant.
• Genotypic ratio
• 121 (PPPppp)
• Phenotypic ratio
• 31 (Purplewhite)

• F1 Generation (PP x pp)
• Two purebred (homozygous recessive (pp)/dominant
  (PP)) peas crossed and ALL the offspring would
  have a purple phenotype because they have
  heterozygous dominant genotypes (Pp)
• Genotype ratio
• 040 (PPPppp)
• Phenotypic ratio
• 40 (Purplewhite)

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Mendels First Three Principles of Inheritance

• Genetic characteristics are controlled by unit
  factors (alleles) that exist in pairs in
  individual organisms
• -Three possible combinations because there are
  two types of alleles (i.e. HH, Hh, hh)
• When two unlike unit factors (alleles)
  responsible for a single character are present in
  a single individual, one unit factor is dominant
  over the other, which is said to be recessive
• -i.e. H is dominant over h
• -Dominant and recessive also refer to designated
  traits (i.e. Tall stems are dominant over dwarf
  stems)
• During the formation of gametes, the paired unit
  factors separate or segregate randomly so that
  each gamete receives one or the other with equal
  likelihood
• - i.e. If your father is heterozygous for height
  (has a tall allele a short allele), you have a
  50 chance of getting either one

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Lets Try a Punnett Square

• The presence of horns (H) is dominant to not
  having horns (h).
• Use a Punnett Square to determine the possible
  outcomes of the offspring.

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Lets Try a Punnett Square

• Prediction of offspring
• As a phenotypic ratio
• 40 horned
• As a genotypic ratio
• 40 Hh
• As a phenotypic percent 100 horned

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Figuring Out Unknown Parental Genotypes F2
Generation

• Test Cross Occurs when an individual of an
  unknown genotype is crossed with an individual
  that is homozygous recessive for a certain trait.
• This allows for the determination of the unknown
  individuals genotype.

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Group Assignment Sign Up

• This is the culminating activity for the genetics
  unit.
• It is a group assignment.
• In groups of 3, you will pick from the list of
  topics on your sheet.
• Read page 226 Ethics and Genetics
• Prepare a 5 minute power point including all the
  aspects on the rubric.
• Once you have chosen a topic, split the different
  aspects you need to include up and create a group
  assignment contract so I can see who has done
  what and so that if a person in your group fails
  to pull their weight, you wont be affected.
• First come, first serve basis for signing up!

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Homework

• Hybrid Cross Sheet
• Genetics Terms Sheet
• A little video clip
• http//www.youtube.com/watch?vMehz7tCxjSE