Genetics

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Genetics

• Georgia High School Graduation Test Science
  Review
• Ashley Kirby

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Introduction

• From the key vocabulary, circle the words that
  you can already define or use in a sentence.
• Write down two or three things that you think are
  important for you to know today.

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Genetics

• The study of the inheritance of traits and how
  genes pass on these traits from parents to
  offspring

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Important Genetic Vocabulary

• trait a characteristic of an organism that is
  inherited (examples eye color, hair type, etc.)
• gene basic unit of heredity made of DNA that
  determines the characteristics of a trait
• allele the two different versions of a gene for
  a particular trait (one received from each parent)

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Genotype versus Phenotype

• GENOTYPE
• an organisms genetic makeup
• includes the two alleles
• represented with two letters (example Bb)

• PHENOTYPE
• the physical appearance of a trait
• expressed by the organisms genes
• represented by description (example brown eyes)

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Dominant versus Recessive

• DOMINANT
• an allele that expresses itself while hiding the
  effects of another allele
• represented with a capital letter
• example Bb (dominant brown eyes dominates over
  recessive blue)

• RECESSIVE
• An allele whose effects are hidden by a dominant
  allele
• Represented with a lower-case letter
• example Bb (dominant brown eyes dominates over
  recessive blue)

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Homozygous versus Heterozygous

• HOMOZYGOUS
• homo- means the same
• the pairing of alleles that are the same
• examples
• BB is dominant homozygous brown
• bb is recessive homozygous blue

• HETEROZYGOUS
• hetero- means different
• the pairing of unlike alleles
• example
• Bb is heterozygous brown

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Sample Question

• Explain how traits are passed from generation to
  generation.

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Gregor Mendel

• Father of Genetics
• experimented with pea plants
• established a method for predicting how traits
  are inherited

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Mendels Laws

• The Law of Dominance a recessive trait will only
  be expressed when the organisms genotype is
  recessive homozygous (bb)
• The Law of Segregation during fertilization, new
  alleles are randomly formed one can only predict
  offspring (using Punnett squares)
• The Law of Independent Assortment each trait is
  inherited independently of other traits

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Probability and Punnett Squares

• Probability is the likelihood an event will occur
• Geneticists use Punnett squares to predict the
  probability of genetic combinations
• Example When two heterozygous brown eyes mate .
  . .

B b
B BB Bb
b Bb bb
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Theory of Inheritance

• Chromosomes are the physical basis of inheritance
  (carry DNA).
• Variability results from dominant and recessive
  alleles.
• The chromosomes in the male gamete and female
  gamete join together during fertilization to form
  a zygote.
• gamete sex cell
• zygote fertilized egg

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Sample Question

• Explain the role of DNA and RNA in heredity.

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DNA

• deoxyribonucleic acid
• found in chromosomes in the nucleus
• determines the hereditary traits of an organism
• contains all the information needed for the
  production of proteins
• protein sequences determine traits

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RNA

• ribose nucleic acid
• aids in protein synthesis in the ribosome
• 3 types
• messenger RNA mRNA carries the DNA nucleotide
  sequence for a protein from the nucleus to the
  ribosome
• transfer RNA tRNA transports amino acids
  (building blocks of proteins) to the ribosome
• ribosomal RNA rRNA makes up the structure of the
  ribosome

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Sample Question

1. Diagram and explain DNA replication.

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DNA replication

• see figure 8-5 on p.149
• self-duplication of the genetic material
• results in two new DNA molecules
• occurs during interphase (just before cell
  divides)
• proteins unwind the DNA helix and each strand
  acts as a template for a new strand
• unbound nucleotides attach . . .
• A-T (adenine binds with thymine)
• C-G (cytosine binds with guanine)

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Sample Question

1. Diagram and explain transcription.

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DNA transcription

• to transcribe is to copy
• mRNA is synthesized in the cell nucleus from the
  DNA molecule
• Just as in replication, the helix unwinds and
  free nucleotides attach to make mRNA. . .
• C-G (cytosine binds with guanine)
• U-A (uracil binds with adenine)
• Only DNA has thymine
• mRNA separates and moves out of the nucleus
• DNA double helix reforms

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Sample Question

1. Diagram and explain translation.

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DNA translation

• process of translating the genetic code to the
  amino acid sequence
• tRNA decodes the mRNA to read the DNA in order to
  make the correct protein

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Mutations

• A mutation is any change in the DNA sequence.
• A change in one nucleotide may cause a change in
  the structure of the protein.
• During pregnancy, observing a karyotype (a
  chromosome picture) can detect chromosomal
  defects.

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Discussion

• If you needed to get precise information from one
  person to another, what would you need to do? How
  would you structure the information? How would
  you store that information so that it could be
  easily retrieved?

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Lesson Summarized

• Write a sentence that explains the system
  discussed.
• Draw a graphic organizer that shows the
  relationship of the parts of the gene system to
  the whole system.