Transcript Biology Unit 5ish Notes: Mendelian Genetics

Biology
Unit 5 Notes:
Mendelian
Genetics
(1) Gregor Mendel
• Monk
• Studied genetics of pea plants.
• He noticed that:
– There were some traits which showed up all of
the time (dominant).
– There were some traits which showed up some
times (recessive).
– These traits are passed down from parents.
– You can’t tell just by looking at an organism,
which genes it has.
(2) Dominant + Recessive Traits
• Dominant Trait:
– These will ALWAYS SHOW UP if they are
present.
– Representation  Capital Letters
• Recessive Trait:
– These will ONLY SHOW UP if the organism
inherited 2 together.
– Representation  Lower Case Letters
(3) Inheriting Traits
• You inherit 2 alleles for every gene.
– Gene = Chunk of DNA.
– Allele = Variation that chunk can come in.
• “Heterozygous” = You inherited 1-Dominant and
1-Recessive allele.
• “Homozygous” = You inherited 2 of the same
alleles.
– “Homozygous Dominant” = You inherited 2-Dominant
alleles.
– “Homozygous Recessive” = You inherited 2-Recessive
alleles
(4) Ways to Describe Inheritance
• Phenotype:
– Physical Description.
– Examples:
• “White”
• “Brown”
• “White and Brown Spotted”
• Genotype:
– Genetic Description.
– Examples:
• AA or Homozygous Dominant
• Aa or Heterozygous
• aa or Homozygous Recessive
(5) What’s With These Letters?
• The letters represent the alleles an organism can
inherit.
• You should choose letters with a different Capital
+ Lower Case appearance:
– A and a
– B and b
– Bad Life Choices: S and s, X and x, C and c
• Actual Letters DO NOT MATTER:
– Heterozygous needs to be: Capital + Lower
– Homozygous Dominant needs to be: 2 Capital
– Homozygous Recessive needs to be: 2 Lower
(6) What Are Punnett Squares?
• Punnett Square = Tool used to make genetic
predictions.
• They do NOT tell you with certainty how many
offspring will have which traits!!!
• Tells you probability.
– “There is a ¼ or 25% chance that the offspring will….”
• SET-UP:
– 1 Parent’s genotype on the top
– Other Parent’s genotype on the side
(7) Setting Up Punnett Squares
• 1 Parent’s Genotype on the Top
(doesn’t matter which one).
• 1 Parent’s Genotype on the Side
(doesn’t matter which one).
• 1 Letter per Box!
• For Example:
– If one parent is AA and the other parent is aa…
A
A
Draw your Punnett Square!
a
a
(8) Filling In Punnett Squares
•
•
•
•
They get filled in like a matrix-box OR like a grid on a map.
The TOP letters copy down into each box.
The SIDE letters copy across into each box.
The dominant trait is always written in front.
• For Example:
– If one parent is AA and the other parent is aa…
A
A
a Aa
Aa
a Aa
Aa
Draw your Punnett Square!
(9) Interpreting Punnett Squares
• Each Box = ¼ or 25% chance
• For Example:
– 4/4 Boxes have Aa, so…
– There is a 4/4 or 100% chance that the offspring will be
Heterozygous.
– I could also say that there is a 100% chance that the
offspring will look dominant.
A
A
Aa
Aa
a Aa
Aa
a
Draw your Punnett Square!