Chapter 10
Section 1
Mendel’s Laws of Heredity
Mendel’s Laws of Heredity
Focus Questions
• Who was Gregor Mendel?
• Why did Mendel choose pea plants?
• What was Mendel’s monohybrid crosses and what did he
learn from them?
• What is the “rule of dominance?”
• What is the law of segregation?
• What is the difference between phenotype and genotype?
• What is a dihybrid cross?
• How & why are Punnett Squares used?
• What is probability and what role does it have in genetics?
Who was Gregor Mendel?
• “Father of Genetics”
• Austrian monk who studied pea
plants – 1800’s
• Studied heredity
• 1st person to successfully predict
how traits are passed from one generation
to the next
Why did Mendel choose pea plants?
• Reproduce sexually (male and female gametes)
• Male and female reproductive organs found in
same flower (no contamination)
• Fast generations
• 7 different traits can be studied
What is a monohybrid cross?
• Both parents are different in ONLY one
trait (ex: parent pea plants are identical for
6 of the 7 traits…only different in 1 trait)
• Simplest way to test for
dominance/recessiveness
What is the “rule of dominance?”
• Rule of dominance – for every trait, there are 2 possible
alleles (dominant or recessive)
• Alleles are represented by letters (capital for dominant,
lowercase for recessive)
• There are three possible combinations of alleles
example:
» dominant – dominant (TT) (look dominant)
» dominant – recessive (Tt) (look dominant)
» recessive – recessive (tt) (look recessive)
What is the law of segregation?
• Both parents have two alleles for a trait
(one from each of their parents)
• Law of segregation – each allele
separates and the offspring gets one allele
for that trait from each parent
What is the difference between
phenotype and genotype?
• Phenotype – what the organism looks like for
that trait (ex: red flower)
• Genotype – what alleles does the organism
have for that trait (ex: Rr)
• Dominant – allele will mask the other allele (BIG
LETTER)
• Recessive – allele will only be seen if both
alleles are recessive (little letters)
• Homozygous – alleles are the same (BB or bb)
• Heterozygous – alleles are different (Bb)
What is a dihybrid cross and what
did he learn?
• Both parents are different in ONLY two
traits (ex: parent pea plants are identical
for 5 of the 7 traits…only different in 2
traits)
• Law of independent assortment - traits are
passed to offspring independently of one
another
What & why are Punnett Squares used?
• Chart to help determine probability of
passing on traits/alleles to offspring
dihybrid
monohybrid
What is probability and what role does
is have in genetics?
• Probability – likelihood that something will
happen