Mendelian Genetics

I. History• Gregor Mendel conducted the

earliest genetic research and is known as the “Father or Genetics” for his discoveries of genes and inheritance

• He found organisms closely resembled their parents with slight variations and characteristics are influenced by heredity and the environment

II. Genetics• The branch of biology that studies HEREDITY,

which is the passing on of characteristics from parent to offspring during sexual reproduction

III. Conclusions Made by Mendel1. _TRAITS or physical characteristics are

influenced by GENES on chromosomeso _GENE: Segment of DNA

-1 or more genes can determine a hereditary trait

o There are two types of chromosomes, all having different genes

a. _NON-SEX chromosomes (autosomes)

b. _SEX chromosomes: X AND YLook at the Karyotype…Which are the autosomes? Which are the sex chromosomes? What is the gender?

2. Genes have alternative forms called ALLELESa. Offspring receives 1 allele from mom and dad

(One from each parent)

b. _TWO alleles determine how a trait is expressed

Allele combinations on each homologous pair:

A. HOMOZYGOUS: HAS IDENTICAL alleles that result in a dominant or recessive trait

Tall Pea Plant TT

Short Pea Plant

tt

Allele combinations on each homologous pair:

A. HETEROZYGOUS: HAS DIFFERENT alleles that result in a dominant or recessive trait

Tall Pea Plant Tt

• One allele is dominant and one is recessive• DOMINANT: observed or

expressed trait (Capital Letter)• RECESSIVE: Weaker or

hidden trait (Lower Case Letter)

Skip to Bottom of next page…A. GENOTYPE: The allele combinations of an

individual (genetic makeup)

Ex. Trait: Flower ColorRR Rr

rrred red

white

B. PHENOTYPE: The physical appearance of an individualEx. Trait: Eye ColorYou can “see” the phenotype, but you may not be sure what alleles are exactly present.