Sexual Reproduction

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Sexual Reproduction

• We will be discussing heredity (genetics) for the
  next 6 weeks- get used to hearing the words above
  without snickering!

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Say What?

• Give me your best estimated definition for the
  following words
• 1. haploid
• 2. allele
• 3.heterogeneous
• 4. diploid
• 5. homogeneous
• 6. meiosis
• 7. gene
• 8.hybrid
• 9. co-dominance
• 10. genotype

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Sexual Reproduction and Meiosis

• During sexual reproduction two sex cells (called
  an egg and a sperm) come together
• This process is called fertilization and the
  result is called a zygote
• See figure 9 on page 218 for a good visual
  representation of this

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Diploid vs. Haploid

• Diploid cells are body cells and have 46
  chromosomes- paired together to make 23 pairs
• Haploid cells are sex cells and they have only 23
  chromosomes
• ??How many chromosomes are in each egg cell??

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Genes

• NOTE- if you spell this JEANS it is a completely
  different thing and points will be taken away.
• Genes are a section of chromosomes on DNA- book
  definition
• Genes are what make you.you and are handed down
  from your parents through sexual reproduction
  (meiosis)-my definition

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Mutations

• Because meiosis is such a complicated process,
  sometimes things go wrong.
• For instance, if an extra chromosome is copied or
  if one is left off a mutation will occur.
• Many times this is a natural occurrence but
  studies have shown that x-rays, sunlight and
  other chemicals have been shown to produce
  mutations.
• Please note, not all mutations are
  life-threatening or even bad. Some mutations can
  help- any ideas?

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Now on to the Principles of Genetics-drum roll
please

• The 6 basic principles of genetics are as
  follows
• 1. Traits or characteristics are passed on from
  one generation to the next.
• 2. The traits of the organism are controlled by
  genes.
• 3. Organisms inherit genes in pairs, one from
  each parent
• 4. Some genes are dominant and some are recessive
• 5. Dominant genes hide recessive genes when both
  are inherited by an organism.
• 6. Some genes are neither dominant or recessive.
  These genes show incomplete dominance.

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Some definitions to know

• Heredity- passing of traits from parent to
  offspring
• Genetics- the study of how traits are inherited
  through interactions of alleles.
• Allele- the different forms of a trait that a
  gene may have (example having dimples vs. not
  having dimples)

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Genetics and Probability

• Probability is the possibility/likelihood that a
  particular event will take place. (the result of
  one event does not affect the results of future
  outcomes)
• Probability can be used to predict the results of
  genetic crosses.

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The Father of Genetics

• Gregor Mendel-Austrian Monk who studied Math and
  Sciencesubject studied was pea plants
• It took him 8 years of using very exact and
  calculated Scientific methods to report his
  findings about how traits are passed from one
  generation to the next.

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Hybrids vs. Purebreds

• Hybrids have information from both parents- if
  crossed either allele may be shown
• Purebreds have no variation when offspring is
  produced. For example, tall pea plants that
  generation after generation produce only tall pea
  plants.

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Genetic Crosses- Punnett Squares

• A Punnett square is a chart that shows all of the
  possible combinations of alleles that can result
  from a genetic cross.
• Punnett squares are used to show the possible
  outcomes of genetic crosses and to determine the
  probability of a particular outcome.

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Dominant vs. Recessive

• Dominant traits (alleles) cover-up all other
  traits (they dominate!) In a Punnetts square the
  dominant traits are represented by an Upper-case
  letter
• Recessive traits are hidden by dominate traits.
  In a Punnetts square the recessive traits are
  represented by a lower-case letter

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Now on to all of the fun words

• Genotype- the letter representation of a trait
• For example, TT for tall or Dd for dimples
• Phenotype- the way an organism looks or behaves
• For example, the appearance of being tall or
  having dimples
• Homozygous- an organism with 2 alleles that are
  the same TT for the tall dominant trait or tt
  for the short recessive trait
• Heterozygous- an organism with 2 alleles that
  differ
• In Mendels experiments, the pea plants were
  heterozygous for height Tt.

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How do Punnett Squares Work?

• They are simply a way to organize your
  information. The genotype of one parent goes on
  the top, the genotype of the other parent goes on
  the side. You then cross them, and a possible
  outcome is predicted.
• If you stay organized, it is a simple way to
  understand the concept!