Genetics

Genetics- is the branch of biology which studies heredity and variation among related organisms. It is the science of heredity Heredity-the transmission of characteristics from parents to offspring

INHERITABLE CHARACTERISTICS Eye color Height Bone structure Hair color Skin color Foot Size

MENDEL AND PEAS Gregor Mendel: the 1st person to predict how traits are passed on Austrian (Movarian) Monk (1822-84) Interested in mathematics and botany and combined the two to make a statistical study of peas for a period of eight years (1857-65)

WHY MENDEL CHOSE PEAS: 1. Showed some definite characteristics Height: tall and short Flower color: white and various colors Seed color: yellow and green Seed shape: round and wrinkle

Peas usually self-pollinate: a. Flower is the reproductive structure in seed plants. Each flower contains stamens which produce pollen grains which form sperm nuclei Each flower contains a pistil which contains egg cells at its base. The transfer of pollen from stamens to pistil results in fertilization This called pollination

b. Self-Pollination 1. Mechanism: Pollen is transferred from stamens to pistil on the same flower or on flowers of the same plant 2. Purpose: self- pollinating plants generally breed true generation after generation

c. Cross-pollination 1. Mechanism: Pollen is transferred from one plant to the flowers of a different plant 2. Purpose: Since egg and sperm come from different plants you can study how contrasting traits are passed on in heredity

DETERMINATION OF A PURE CHARACTERISTIC Mendel planted seeds of self-pollinated plants to see if they would show the same characteristics as their parent plant. If generation after generation, the characteristic appeared, he called this a pure characteristic.

EXAMPLES Seeds from tall plants always produced tall plants Yellow seeds always produce plants that develop yellow seeds

THE LAW OF DOMINANCE Mendel then cross-pollinated a short plant with a tall plant He found that one characteristic dominated or masked the other This trait he called the dominant trait The hidden trait was called the recessive trait Tall x Short  all tall plants (dominant trait) The law of dominance states that in two contrasting characteristics (tall vs. short; wrinkled seeds vs. round seeds) that one characteristic will dominate the other

Dominant and Recessive Traits

THE F NUMBER The first generation produced by a cross is called the F1 or first filial (sons & daughters) generation The second generation after a cross is the F2 (F1 x F1) etc. The parents are designated as P generation

THE LAW OF UNIT CHARACTERS 1st generation: Mendel made a Cross of a tall and short pea plant; offspring were all tall 2nd generation: crossed 2 plants from the previous generation; offspring were 75% tall and 25% short

Law of unit characters Cont. From this observation and w/o knowing about chromosomes and genes or DNA, Mendel developed the Law of Unit Characters: States: that inherited characteristics are controlled by factors (called genes) that occur in pairs

How to determine if you are dominant or recessive for a trait Probability: likelihood that a particular trait will exist. Punnett squares: square that shows all possible combinations of alleles that may result. Male alleles go on top of square, female alleles on left side of square.

Homozygous or Heterozygous How do you determine if you use 2 capital letters, 2 lowercase letters or 1 capital and 1 lowercase letter? Homozygous: 2 identical alleles for a trait. Ex. Mom is homozygous dominant tall-TT Dad is homozygous recessive short-tt. Heterozygous: 2 different alleles for a trait. Ex. Mom is heterozygous tall-Tt Each parent will be either homozygous or heterozygous for each trait.

Phenotype: visible trait (what you see) Genotype: genetic make-up (letters) (height) Ex: Mom is TT. What is her phenotype? What is her genotype? Ex. Dad is Tt. What is his phenotype? What is his genotype? Ex. Daughter is tt.

Both parents are DOMINANT for TALL TT TT T T TT TT

Both Parents are Heterozygous 1 TT, 2Tt, 1tt so there is a 1:2:1 ratio genotypically and a 3:1 ration phenotypically

Both parents are RECESSIVE Short. t t tt tt t t tt tt

Codominance: both alleles expressed.

Incomplete dominance: neither allele is dominant or recessive (blended) neither allele is dominant or recessive (blended)

Multiple Alleles:. when there are more than 2 alleles for a gene Multiple Alleles: * when there are more than 2 alleles for a gene * in human blood types there 3 possible alleles for the ABO blood typing system IA = A antigen IB = B antigen i = no antigen " both IA and IB are dominant over i but, " both IA and IB are codominant with each other (that means, they are both expressed equally)

Multiple Alleles:. when there are more than 2 alleles for a gene Multiple Alleles: * when there are more than 2 alleles for a gene * in human blood types there 3 possible alleles for the ABO blood typing system IA = A antigen IB = B antigen i = no antigen " both IA and IB are dominant over i but, " both IA and IB are codominant with each other (that means, they are both expressed equally) Blood Typing