Who was Gregor Mendel? - PowerPoint Presentation

Slide1

Who was Gregor Mendel?

(And why was his work so important?)

Slide2

Gregor Mendel

Gregor

Mendel was a monk who lived in the 1800s

Slide3

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

Slide4

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 appeared more often with

the same

parent plants

Mendel wondered why…

Slide5

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)

Slide6

Either or….

One or the other…

Easy to see AND collect data!

Slide7

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

Slide8

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.

Slide9

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

Slide10

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

Slide11

His Findings… Crossing Hybrids gives a

3 to 1 ratio of traits in offspring!

Slide12

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

…

S

omehow

…

Some traits seemed to disappear in the first generation but reappear later…

Slide13

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.

Slide14

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? _____________

Slide15

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!!!!

Slide16

The “Father of Genetics”

He published his results, observations and 
conclusions

These are now known as

Mendel’s Laws

Me

ndel'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”

Slide17

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!)

Slide18

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

Slide19

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

Slide20

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

Slide21

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

Slide22

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.

Slide23

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

Slide24

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!

Slide25

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.

Slide26

More Vocab!

Homozygous

means that the two alleles 
(genes) for an organism are exactly the same 
(TT or

tt

).

Also known as Purebred…

Hete

rozygous

means that the two alleles for 
an organism are different (Tt).

Also known as Hybrid…

Slide27

Heredity

Heredity is the passing of traits from one 
 generation to another”.

Inherited traits are passed (genetically), from the parent generation to the offspring

Slide28

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

Slide29

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

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Slide33

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!