Mendelian Inheritance

Gregor Mendel

• 1822-1884• Austrian Monk• Grew up on a farm, worked

as a gardener• Studied physics and became

a physics teacher• Worked on breeding plants

and bees• Known as the “Father of

Modern Genetics”• Published his findings in 1866• Gene 1909• DNA 1944, structure 1953

Mendel’s Laws explain patterns of inheritance

What is inheritance?

Law of Segregation

• When gametes form (meiosis) the chromosome copies separate so each gamete has only one copy.

• A gamete either gets one allele or the other

EXCEPTION:Nondisjuntion

• Do Punnett Squares still work if meiosis doesn’t work properly?

• Are Punnett Squares always true, or can they sometimes give you a false result?

Law of Independent AssortmentGenes sort themselves independently from each other during meiosis.

EXCEPTION:Linked Genes

Probability

• A woman is pregnant. What is the probability she will have a girl?

Ms. Macway’s Family

Ms. Macway has 3 sisters and no brothers. But probability says that offspring should be half (50%) boys and half (50%) girls.

If her parents have another child,what is the chance it will also be a girl?