Genetics – the branch of biology that studies heredity Heredity – the passing on of traits from parent to offspring Chromosomes – the genetic material that is passed from generation to generation Genes – segment of DNA that codes for a trait Alleles – different forms of genes 2 Types of Alleles Dominant observed trait, or the trait that is expressed Capital Letter (T) Recessive trait that is masked or hidden Lower Case Letter (t)

You inherit 2 alleles for each gene. One from mom and one from dad. Homozygous – two same alleles for a trait Homozygous Dominant – 2 dominant alleles (TT) Homozygous Recessive – 2 recessive alleles (tt) Heterozygous – 2 different alleles for a trait (Tt)

Two organisms can look alike but have different gene combinations Phenotype – the trait you see Genotype – the actual gene combination You can’t always know an organisms genotype simply by looking at its phenotype Genes are lined up on chromosomes A chromosome can contain a thousand or more genes

11-1 The Work of Gregor Mendel Gregor Mendel Carried out the first important studies of heredity Father of genetics He was a monk in an Austria Monastery that was a great scientific research center First person to predict how traits are transferred from generation to generation

He studied pea plant traits Pea plants reproduce sexually and contain both male and female gametes Self Pollination – male and female gametes from the same plant unite Pure-Bred – the offspring of 1 parent and has identical genes (clone) Cross Pollination – male and female gametes from different plants unite Hybrid – the offspring of 2 parents that have different forms of a trait Mendel carefully controlled his experiments and only studied one pea trait at a time One trait he studied was height of a pea plant

Tall Pea PlantShort Pea Plant Self Pollinate Tall Pea PlantShort Pea Plant Cross Pollinate 4 Tall Pea Plants Self Pollinate 3 Tall and 1 Short P generation F1 generation F2 generation Monohybrid Cross – a genetic cross involving one trait

From this monohybrid cross Mendel concluded… Pea plant had two alleles of the gene that determined its height The allele for Tall is Dominant - T The allele for short is recessive - t If the plant was tall its genotype was TT or Tt If the plant was short its genotype was tt

The Law of Segregation To explain why in the F1 generation the trait for shortness disappeared and then reappeared in the F2 generation Mendel formulated his Law of Segregation He concluded that the F1 plants had a allele for tallness and an allele for shortness Because they have two different alleles they can produce 2 different types of gametes (tall and short) During fertilization these gametes randomly pair to produce 4 possible combinations of alleles Law of Segregation – the members of each pair of alleles separate when gametes are formed Punnett Square – used to predict and compare the genetic variations that will result from a cross

Alleles separate during gamete formation. Tt T T t t

Mendel's Cross Tt TTTTt t tt Mom’s genotype: Tt Dad’s genotype: Tt Genotypic Ratio: TT – 1, Tt – 2, tt – 1 Ratio: 1:2:1 Phenotypic Ratio: Tall - 3, Short - 1 Ratio: 3:1

Mendel’s Dihybrid Crosses Mendel did another cross which he used pea plants that differed from each other in two traits rather than one Dihybrid Cross – a cross involves two traits Will the two traits stay together in the next generation or will they be inherited independently of each other?

Round Yellow Pea SeedWrinkled Green Pea Seed Self Pollinate Round Yellow Pea SeedWrinkled Green Pea Seed Cross Pollinate 16 Round Yellow Pea Seeds Self Pollinate 9 Round Yellow 3 Round Green 3 Wrinkled Yellow 1 Wrinkled Green P generation: F1 generation: F2 generation:

The Law of Independent Assortment Law of Independent Assortment – genes for different traits can segregate independently during the formation of gametes The gametes, R (round), r (wrinkled), Y (yellow), and y (green), will separate from each other and recombine in 4 different ways RY, Ry, rY, and ry If the alleles were inherited together, only two kinds of pea seeds would have been produced RY (round yellow) and ry (wrinkled green) This Law does not hold true all of the time. If the genes are on different chromosomes it is true, but if they are on the same chromosome it is not true.

Beyond Dominant and Recessive Alleles Not all genes show simple patterns of dominant and recessive alleles In most organisms genetics is more complicated, because the majority of genes have more than two alleles. Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

Incomplete Dominance Incomplete Dominance – the phenotype of the heterozygote is intermediate between the dominant and recessive Ex. Red Snapdragon (RR) x White Snapdragon (WW) Pink Snapdragon (RW) Neither allele is completely dominant over the other

Codominance Codominant Alleles – the phenotypes of both homozygotes are produced Both allele are expressed equally Example White Horse WW X Tan Horse TT Roan Horse WT

Multiple Alleles It is common for more than two alleles to control a trait in a population Multiple Alleles – traits controlled by more than two alleles Example 1- A rabbit's coat color is determined by a single gene that has at least four different alleles.

Different combinations of alleles result in the colors shown here. KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles

AIbino: cc Himalayan: c h c, or c h c h Chinchilla: c ch c h, c ch c ch, or c ch c Full color: CC, Cc ch, Cc h, or Cc

Example 2 - ABO Blood Groups Human blood types are determined by the presence or absence of certain molecules on the surface of red blood cells The best known are ABO groups and Rh groups

ABO Groups 3 Alleles for blood types I A (A), I B (B), i (O) I A (A), I B (B) are dominant i (O) is the recessive 4 Blood Types Blood Type Possible Allele Combinations AI A I A or I A i O BI B I B or I B i O ABIAIBIAIB OiOiOiOiO

Blood TypeCan Give Blood ToCan Get Blood From AA, & ABA, & O BB, & ABB, & O AB A, B, AB & O (Universal Recipient) OA, B, AB, & O (Universal Donor) O

Rh Groups Stands for rhesus monkey + allele is dominant - allele is recessive

Universal Donor – O blood and is most common Universal Recipient – AB blood and is rare If blood types are not matched during a blood transfusion, the red blood cells will clump together causing death Blood typing is also useful in determining parentage