Mendel’s Laws of Heredity

10.1

Gregor Mendel

An Austrian monk who studied heredity through pea plants

“Father of Genetics”

HeredityThe passing on of characteristics from parents to offspringTraits Characteristics that are inherited

Genetics

The branch of biology that studies heredity

Gametes

Male and female sex cells (egg and sperm)

Fertilization

The process in which the male gamete unites with the female gamete

Zygote

The fertilized cell that develops into a seed, baby, etc.

Pollination

The transfer of pollen grains from a male reproductive organ to a female reproductive organ in plants

Hybrid

Offspring formed by parents having different forms of a trait

Ex tall and short height

Monohybrid Cross

Mendel crossed parent plants of different heights

(mono = single trait)

Original parents (true breeding plants) are the P1 generation

Offspring of the parent plants are known as the F1 generation (filial)

Cross two F1 plants with each other and their offspring are

known as F2

generation

Alleles

Different gene forms

Come in pairs

DominantThe observed trait of an organism that masks the Recessive form of a trait

Dominant = capital letter

Recessive = small case letter

Mendel’s 1st Law of Inheritance

Law of Segregation

Gametes receive only one allele for a trait from each parent

Phenotype

The expression of a gene (The way an organism looks/behaves)

Genotype

The actual genetic make-up of an organism (TT)

Genotypes…

TT=the plant has 2 alleles for tallness

Tt=1 allele for tallness and 1 allele for shortness

tt=2 alleles for shortness

Homozygous

If the two alleles for the trait are the same

TT = homozygous dominant (for height)

tt = homozygous recessive (for height)

Heterozygous

The 2 alleles for a trait are different

Tt=1 allele for tallness and 1 for shortness

(for height)

Dihybrid Cross

A cross where two different traits are used

Di means two

Mendel’s 2nd Law

Law of Independent Assortment

Distribution of alleles for 1 trait into the gamete doesn’t affect distribution of alleles for the other trait

Punnett Square

A shorthand way of finding the expected ratios of possible genotypes in the offspring cross

The gametes that each parent forms are listed on the top and left side of the square

Probability

The likelihood that something will occur

Punnett Squares aren’t exact results because genetics is by chance (like flipping a coin)