Mendel and His InGene-ius Idea…
Big Idea 3: Living systems store,
retrieve, transmit, and respond to
info essential to life processes.
Essential Knowledge
• 3A3: The chromosomal basis of
inheritance provides an understanding
of the pattern of passage of genes
from parent to offspring.
•… “particulate”
hypothesis is the idea
that parents pass on
discrete heritable units
(genes)…
Gregor Mendel
1822-1884
Mendel’s Peas…
• Planned
experiments
using
characters
(flower color)
and traits
(purple/white)
He Experiments…
• Mendel mated 2 contrasting, true-breeding
varieties  hybridization
• True-breeding parents = P generation
• Hybrid offspring of P generation = F1
generation
• When F1 individuals self-pollinate = F2
generation is produced
Purple =
dominant
White =
recessive
3:1 Ratio
Mendel’s heritable factor = gene
Alternate versions =alleles
IA Video
Law of Segregation and I.A. apply to genes
on diff. chromosomes.
• Genes near
each other
on same
chromosome
tend to move
as a unit
• Probability of
segregation
is a fxn of
the distance
b/t them.
Dominant vs Recessive
• Use Punnett Squares
to predict heredity
outcomes.
• Dominant alleles:
Use upper case. Ex: S
• Recessive alleles:
Use lower case. Ex: s
• Homozygous:
alleles for a trait
are same. Ex:
SS or ss or TT
(true breeding)
• Heterozygous:
alleles for a trait
are different. Ex:
Ss or Tt
Ratios
• Receive 2 types of
info: genotype and
phenotype.
• Genotype: genetic
trait that you cannot
see (genes)
• Phenotype: trait or
behavior you can
see physically.
Genotype
Phenotype
Use probability to analyze passage of
single gene traits from parent to offspring
Punnett
Squares!!
One Factor Punnett Square
• One trait =
monohybrid cross.
• Ex: Cross a tall
dominant
homozygous pea
plant (TT) w/ short
recessive
homozygous pea
plant (tt).
Monohybrid Cross
TT is a parent
who is Tall
tt is a parent
who is Short
Both are
homozygous
that make
heterozygous
offspring.
Ratios to Know
TT x tt = 100% Dominant, but heterozygous
Tt x Tt = 75% Dominant, 25% Recessive, 3:1
Two factor Punnett Square
• Cross 2 traits =
dihybrid cross.
• Example: Cross a
dominant green,
smooth pea plant
(GGSS) with a
recessive yellow,
wrinkled pea plant
(ggss)
Ratios to Know
SsTt x SsTt = 9:3:3:1
9 dominant in both traits
3 dominant in one trait or the other trait
1 recessive for both traits
Human Genetic Disorders
• Can be received by inheriting a single gene trait or
specific chromosomal change
• Ex: Tay-Sachs Disease: Mutation on Chrom. 15
causing deterioration of nerve cells.
What’s This??
Punnett Square Sample Probs