GENETICS

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GENETICS

• CHP. 5

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GREGOR MENDEL1822-1884

• KNOWN AS THE FATHER OF GENETICS
• EDUCATED IN MATH AND SCIENCE
• WANTED TO BE A TEACHER BUT FAILED THE EXAM

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MORE ABOUT MENDEL

• HE WAS A MONK
• IN THE MONASTERY HE WAS IN CHARGE OF THE GARDEN
• HERE IS WHERE HE STARTED HIS WORK IN GENETICS

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MENDELS EXPERIMENTS

• HE USED PEA PLANTS
• HE COULD CONTROL FERTILIZATION
• WORK WITH ONE TRAIT AT A TIME
• EASY TO GROW

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MORE ON HIS EXPERIMENTS

• HE BELIEVED THAT TRAITS WERE DETERMINED BY
  INDIVIDUAL UNITS
• WE CALL THESE UNITS ALLELES
• OFFSPRING GET ONE ALLELE FOR EACH TRAIT FROM EACH
  PARENT
• FROM HIS EXPERIMENTS WITH PEAS HE DISCOVERED THE
  LAWS OF GENETICS

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LAWS OF GENETICS

• LAW OF DOMINANCE STATES THAT WHEN AN INDIVIDUAL
  IS HYBRID FOR A TRAIT, ONLY ONE ALLELE WILL
  EXPRESS ITSELF. THE ALLELE THAT EXPRESSES ITSELF
  IS CALLED DOMINANT. THE TRAIT THAT DOES NOT
  EXPRESS ITSELF IS CALLED RECESSIVE.

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LAWS OF GENETICS CONT.

• LAW OF SEGREGATION
• LAW OF INDEPENDENT ASSORTMENT

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GENETICS TERMS

• ALLELE
• DIFFERENT FORMS OF ONE TRAIT
• DOMINANT ALLELE
• ALLELE THAT IS EXPRESSED IN OFFSPRING
• REPRESENTED BY A CAPITAL LETTER

• RECESSIVE ALLELE
• ALLELE THAT IS NOT EXPRESSED IN THE OFFSPRING
• REPRESENTED BY A LOWER CASE LETTER

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MORE GENETICS TERMS

• PUREBRED
• AN OFFSPRING THAT HAS THE SAME TWO ALLELES FOR A
  TRAIT
• BOTH ALLELES ARE DOMINANT OR RECESSIVE
• EXAMPLE AA OR aa

• HYBRID
• AN OFFSPRING THAT HAS TWO DIFFERENT ALLELES FOR A
  TRAIT
• ONE ALLELE IS DOMINANT ONE IS RECESSIVE
• EXAMPLE Aa

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PUNNETT SQUARES

• IT IS USED TO SHOW ALL THE WAYS THAT ALLELES CAN
  COMBINE

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HOW TO MAKE AND USE PUNNETT SQUARES

• SELECT A TRAIT TO BE STUDIED
• LIST THE ALLELES FOR THE FEMALE ON THE TOP OF THE
  SQUARE
• LIST THE ALLELES FOR THE MALE ALONG THE SIDE OF
  THE SQUARE
• IF YOU DONT KNOW, THE 1ST ONE LISTED IN THE
  PROBLEM GOES ACROSS THE TOP
• THE 2ND ONE LISTED GOES ALONG THE SIDE
• FILL IN EACH SQUARE WITH ONE MALE ALLELE AND ONE
  FEMALE ALLELE

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TERMS FOR PUNNETT SQUARES

• GENOTYPE
• IT IS THE ALLELE COMBINATION THAT IS INHERITED
• IT IS THE LETTERS
• EX. AA, aa, Aa
• PHENOTYPE
• PHYSICAL APPEARANCE OF OFFSPRING
• DETERMINED BY DOMINANT ALLELE

• HOMOZYGOUS
• THIS MEANS THE SAME AS PUREBRED
• EX. AA, aa
• HETEROZYGOUS
• THIS MEANS THE SAME AS HYBRID
• EX. Aa

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EXAMPLE PUNNETT SQUARE

• Bird 1 has orange feathers
• Its genotype is AA

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EXAMPLE PUNNETT SQUARE

• Bird 2 has blue feathers
• Its genotype is aa

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EXAMPLE PUNNETT SQUARE

• This Punnett Square shows how we can combine the
  alleles for feather color of Bird 1 and Bird 2
• What are the possible outcomes for feather color?
• What will happen in the F2 generation?

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SEX-LINKED TRAITS

• FEMALES HAVE XX AND MALES HAVE XY
• Sex-linked traits, therefore, are traits
  determined by genes found on the X chromosome. If
  such a gene has a recessive allele it is much
  more likely to be expressed in males than females
  because they only have one copy of this gene
• EXAMPLES HEMOPHILIA, COLOR-BLINDNESS

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MUTATIONS

• THESE ARE ANY PERMANENT CHANGES IN AN ALLELE
• THEY CAN BE CAUSED
• NATURALLY BY ALLELES NOT MATCHING UP CORRECTLY
• X-RAYS, RADIOACTIVITY, CHEMICALS, DRUGS
• THEY CAN BE HARMFUL OR HELPFUL
• THEY CAUSE VARIATIONS WITHIN A POPULATION

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Genetics Since Mendel

• Incomplete dominance
• this occurs when neither trait wants to dominate
• The resulting phenotype is a combination of both
  but it is not BLENDING
• incomplete dominance Video
• Polygenic inheritance
• when a trait is controlled by more than one gene
• Ex. Hair color, eye color
• Multiple alleles
• when a trait has more than one allele
• Ex. Blood type in humans A, B, AB, O

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More on Genetics Since Mendel

• PEDIGREES
• a tool used by scientists to track a trait
  through a family
• Males are represented by squares and females by
  circles
• Lines between a circle and square mean a marriage
• Shaded in circles or squares mean that the person
  has the trait/disease
• Half-shaded circles represent a carrier
• A carrier has the trait/disease, but it is not
  showing because the dominant trait is the normal
  trait