Understanding Biological Inheritance

GREGOR MENDEL

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Word ListDominant Punnett

squareHomozygous

Mendel Recessive Pea plants

Genotype Hybrid Phenotype

Gene DNA Allele

Heterozygous Purebred Carrier

Heredity Chromosomes Sex-linked trait

Yellow seed coat

Blue eyes Brown hair

Gregor Mendel

Austrian monk & mathematician “The Father of Genetics”

Experimented with garden peas (Pisum sativum)

Grow & reproduce quicklyMatings can be controlledShow a number of distinct traits that are easy to observe

Studied peas for 8 years!Designed simple experiments and observed only one trait at a timeUsed math to formulate his conclusions – Mendel’s Laws

Traits that Mendel studied:

Mendel’s Big Idea!Genes are found in pairs

Characteristics are controlled by unit factors (genes) that exist in pairs in organisms and are passed from parents to offspringWhen two parents produce an offspring, each parent gives one of the factors from each pair

Mendel’s garden

Mendel’s 1st Law1. Law of Dominance:

In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. One factor is dominant and the other is

recessive

Law of Dominance (cont)

Mendel’s 2nd Law2. The Law of Segregation:

During the formation of gametes (eggs or sperm) in meiosis, the two alleles (letters) responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.When hybrids are crosses, the resulting ratio of phenotypes is 3 dominant : 1 recessive.

Mendel’s 3rd Law3. The Principle of Independent Assortment

Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This Law is easiest explained when setting up dihybrid Punnett squares in 16 boxes

Independent Assortment (cont)

Dihybrid Set Up