Chapter 6 Introduction to Genetics

Alissa StegmanPeriod 8

Introduction to Genetics• Heredity is the set of

characteristics an organism recieves from its parents & genetics is the study of heredity.

George Mendel

• George Mendel is also refered to as the father of genetics. He was born in 1822 and died in 1884 was a monk in the czeck republic. He smoked around 20 cigars a day and used pea plants for his experiments.

Why pea plants?Why?• Small• Distinguishable traits• Quick reproductive

cycle• Produced many

offspring

Seven traits of pea plants• Seed shape• Seed color• Seed coat color• Pod shape • Pod color• Flower position• Plant heightThe traits are characteristics

that distinguish one individual from another.

Pea plants • True breeding – plants that always pass its

characteristics to the next generation• Reproduction – pea plants use their flowers to

reproduce• Pollen = male sex cell• Egg = female sex cell• A new plant is formed when pollen fertilizes an egg• Pea plants usually reproduce by self pollination

( only have one parent).

F1 Generation

• Mendel crossed true breeding plants that showed one form of a trait with true breeding plants that showed the other form of that trait

• Example : Trait = pod color, cross green podplant with a yellow pod plant.The offspring produced are called Hybrids

which are defined as an offspring of parents with different characteristics.

F1 Generation continued

• Mendel called these hybrids the F1 generation, P generation refers to the parents that were crossed.

• The results? Mendel thought that the two alternate forms of a trait will blend in the F1 generation. Example, cross a tall with a small and the offspring will be medium height.

F1 Generation continued

• This did not happen, there was no blending. Instead the traits of just one parent appeared in the offspring, the other trait seemed to vanish.

F2 Generation

• Cross F1 generation among themselves• For each of the seven traits, the form that has

vanished in the F1 generation re appeares in the F2, they appeared in ¼ of the plants.

• Genes – the unit of heredity or unit that determines traits.

• Alleles – different forms of a gene Example : height in pea plants – 2 alleles, tall & short.

F2 Generation Continued

• Dominant & Recesive • In pea plants that have both alleles (tall/short) only

the tall allele is expressed. This is the dominant allele, the short allele is not expressed this is recessive.

• Dominant allele are represented by capital letters• Example : T is the allele for a tall pea plant• Recessive allele are represented by lowercase letters• Example : t is the allele for a short pea plant

F2 Generation Continued

• Phenotype – physical appearance of an organism (adjective).

• Genotype – genetic makeup of an organism ( TT, Tt, or tt)

• Pgeneration TT x tt• Homozygous – both alleles are the same TT or tt.

• Heterozygous – two different alleles, Tt

Mendel’s principles

• Individual units, called genes, determine biological characteristics.

• For each gene, an organism receives one allele from each parent.

• If an organism inherits different alleles for the same unit, one allele may be dominant over the other.

6-2 Meiosis

Gamete

• Gamete is reproductive or sex cellplants humanpollen sperm egg egg

Gamete continued

• According to Mendel’s principles, an organism has two copies of each gene, one of these copies is passed to an offspring.

• Gametes contain half the number of chromosomes found in body cells.

• 46 chromosomes per body cell, 23 per gamete• One set of chromosomes, described as haploid (n) n = 23 humans.• Body cells (somatic) cells are described as diploid,

(2n) 2n = 46 human.

How are gametes formed?

How are gametes formed?

• Through a process known as Melosis, ( reduction division) the # of chromosomes in a diploid cell is reduced by half, producing haploid gametes.

• Melosis has two sperate cell divisions, example prophase 1 & prophase 2.

• Provides genetic veriction because chromosomes are paired and exchange genetic info, this process is known as crossing over.

6-3 analyzing inheritance

Probability or likelihood

• If we flip a coin, ½ chance chance of heads• Ace of spades out of a deck – 1/52 • 2 heads in a row = ½ x ½ = ¼• 4 heads in a row = ½ x ½ x ½ x ½ = 1/16• 4 aces in a row = 1/13 x 1/13 x 1/13 x 1/13 = 1/28561