(And why was his work so important?) Who was Gregor Mendel? (And why was his work so important?)

Gregor Mendel Gregor Mendel was a monk who lived in the 1800s

Mendel’s Mind Wandered… Mendel wondered how the same species of plants could have different characteristics Characteristic is a trait that makes the plant (and you) look a certain way

Mendel began to think… Mendel wondered about the Characteristics that appeared with each generation He wondered if they were “heritable features” – “Heritable” means they are inherited (passed down) from parents to children Some traits seemed to appear more often…

Pea Plants Mendel performed an experiment and chose pea plants to use He chose pea plants because he could identify seven pairs of contrasting traits found among  typical garden peas:  Seed color (yellow or green) Seed shape (smooth or wrinkled) Pod color (yellow or green) Pod shape (inflated or pinched) Flower color (purple or white) Flower position (middle or end) Stem height (tall or short)

Either or…. One or the other… Easy to see AND collect data!

Watching the plants grow… For two years, Mendel grew different varieties of peas to make sure that their offspring were always the same This meant that the 
plants he used were 
purebred Purebred means an 
organism always 
produces the same 
traits in its offspring

Think about purebred dogs… When you purchase a purebred dog, you receive a record of their family tree so you know who their parents and grandparents and great grandparents were! Proof that the dog is purebred.

Patience is a virtue After recording his observations over a couple 
of years, Mendel decided to breed different 
varieties together to make hybrids Hybrid means it’s a “mix” - a “cross” - of different traits (Think… Hybrid cars!) He made these hybrids by cross-pollinating 
plants with different characteristics Cross-pollinating means “mating” (crossing) two 
different plants of the same species White flower x Purple flower Smooth pea x Wrinkled pea

Cross-pollinating (making hybrids) Mendel brushed the 
pollen off yellow pea 
plants and put it on 
green pea plants He did the same for 
plants with each of the 
seven pairs of traits He then grew 
generation after 
generation of hybrids 
and tracked the 
appearance of the 
different traits

Crossing Hybrids gives a 3 to 1 ratio of traits in offspring! His Findings… Crossing Hybrids gives a 3 to 1 ratio of traits in offspring!

Crossing Characteristics Mendel crossed many different traits and 
 carefully recorded the traits of the offspring He determined that each parent supplies one 
 “unit” or “factor” for each different trait… Somehow… Some traits seemed to disappear in the first generation but reappear later…

Recessive and Dominant The traits that disappeared in the first 
generation of hybrids he called “Recessive.” He called those that always appear,
“Dominant.” In later generations the recessive traits reappeared in a predictable pattern. For example, later generations of plants had 
 one green pea for every three yellow peas. 
  The same ratio appeared for all seven pairs of traits.

Pea Soup Anyone? Mendel grew an estimated 28,000 pea plants 
over eight years. He recorded the traits of parent generations 
 (P) as well as the traits of the first generation 
(F1) (F1) is the “First Filial” generation: the first 
offspring to be born Can you guess what the second generation 
was listed as? _____________

What Mendel Discovered Mendel discovered that 
traits are inherited And it occurs in a 
consistent pattern Mendel used math to figure 
out what was going on in the cell and how the “factors” (traits) would be passed on.  See????? Math IS useful!!!!

The “Father of Genetics” He published his results, observations and 
conclusions These are now known as Mendel’s Laws Mendel's laws of heredity work with other 
organisms as well They form the basis of modern genetics Even though Mendel knew nothing about genes and DNA, we call him the “Father of Genetics”

Now called “Genetics” Mendel used the terms “unit”, “factor” and “element” to describe how traits are inherited (passed) from parents to offspring Today, we call these “units” GENES (DNA) Genes are found on our chromosomes (in the nucleus of our cells) and are made up of DNA (which is made of nucleotides!)

What are Genes, Anyway? Genes are the basic “unit” of heredity They are a sequence of DNA that causes a 
 certain characteristic to appear in an organism Genetics is the science of genes, traits and heredity Genetics is the study of how traits are inherited (through genes) from one generation to another

The Punnett Square Mendel found out that every trait is controlled by two “elements” (genes) One from one parent and one from the other parent Now, the “Punnett Square” is used to show how different traits are passed from one generation to the next This is called Probability The chance that a given event will occur

Predictable Ratios Mendel repeated his experiments over and over and the F2 generation always had a 3:1 ratio of yellow to green or round to wrinkly Mendel then crossed plants that differed in 
 more than one trait: round, yellow peas with wrinkled, green one, or tall, violet- flowered plants with short, white-flowered ones These traits appeared in predictable ratios, too

Dominant & Recessive Mendel determined that, in order to show-up, 
 a Dominant trait needs only one trait “unit” from one of the parents A dominant trait can “cover up” (mask) a 
 recessive trait Dominant is stronger, more powerful The Recessive trait needs two “units”, from 
 both parents, in order to show up in the next generation Recessive is “weak”, possessing little power/influence

Mendel’s Laws of Inheritance Mendel came up with these important 
conclusions known as Mendel’s Laws: The Law of Dominance states that some unit characters can mask the expression of others. The Law of Segregation states that each unit character separates into a different sex cell. The Law of Independent Assortment states that genes segregate (separate) according to chance.

The Vocabulary of Genetics The genetic make-up of an organism is called 
its “genotype”  It is the type of genes found in the cell The appearance of the organism that is 
determined by its genotype is called its 
“phenotype”  It is how the organism looks (appears) on 
 the outside

Homologous Pairs When making a new organism, one gene 
from the mother matches up with a 
“similar” gene from the father These genes are called “homologous” pairs Homologous means similar (in length, 
size, genetic make up, etc…) The homologous “genes” are found on 
chromosomes – so, if homologous genes 
pair up, they create homologous 
chromosomes!

Genes Vs. Alleles A gene is a section of DNA which codes for a certain characteristic, such as height. Genes, however, can have variations and this is 
where alleles come in…  Height can be either tall or short Alleles are different versions of a gene. For example, a tall allele or a short allele. They are the different sequences of DNA that 
determine a single characteristic (height). They occur in pairs (one from one parent, one from the other) and can be classified as recessive or dominant.

More Vocab! Homozygous means that the two alleles 
(genes) for an organism are exactly the same 
(TT or tt). Also known as Purebred… Heterozygous means that the two alleles for 
an organism are different (Tt). Also known as Hybrid…

Heredity Heredity is the passing of traits from one 
 generation to another”. Inherited traits are passed (genetically), from the parent generation to the offspring

How do Geneticists figure it out? Geneticists use letters to represent alleles. The same letter is used to indicate both alleles. A capital letter = a Dominant trait A lowercase letter = a Recessive trait Examples: Flower color: P= purple, p= white Seed color: Y= yellow, y = green Seed shape: W = wrinkled, w = round

In humans…. Widow's peak: W = widow's peak, w = continuous hairline Freckles: F = freckles, f = no freckles Earlobes: E = unattached, e = attached Thumbs: H = hitch-hiker, h = non-hitch-hiker Cleft chin: C = cleft chin, c = no cleft chin Hair on Fingers: F = hair, f = no hair Spock Fingers: S = spock yes, s = spock no Handedness: R = right handed, r = left handed

Genes & Mutations Each gene carries a separate piece of information DNA codes for all genes Changes in the sequence of the DNA molecule (and therefore the gene) are called mutations  A mutation may change the manner in which a trait is expressed by an organism. So, a mutation in the genotype, changes the phenotype  Remember that not all mutations are bad!