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Mendel & Heredity

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Mendel & Heredity. Gregor Mendel . Gregor Mendel was born in 1822 to peasant parents in what is now the Czech Republic. He became part of a monastery and was in charge of the monastery’s garden.

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Presentation Transcript
slide2

Gregor Mendel

  • Gregor Mendel was bornin 1822 to peasant parentsin what is now theCzech Republic.
  • He became part of a monastery and wasin charge of themonastery’s garden.
  • Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments.
slide3

Mendel’s Experiments

    • Over time, Mendel learned how to prevent the self-pollination of the pea plants.
  • Instead, Mendel controlled the pollination of plants by using an artist’s brush. He transferred the pollen from one flower to the flower of another selected plant.
slide4

Mendel’s Experiments

    • Mendel used this technique to breed pea plants with specific characteristics.
  • Through a series of carefully designed experiments, Mendel crossed plants with different traits to see what traits the offspring would have.
  • These offspring are called hybrids– offspring of parents with different traits.
slide5

Mendel’s Experiments: Traits Studied

  • In order to keep his experiments simple, Mendel decided to study seven isolated traits within a pea plant.
slide6

Mendel’s Experiments: F1Generation

P Generation

F1 Generation

    • One of Mendel’s first experiments crossed two plants with different seed colors (Yellow & Green).
  • These plants are called the parental generation (P Generation).
  • The offspring were all called the 1st filial generation (F1Generation).
  • The offspring (F1 Generation) of these parent plants all had yellow seeds.
slide7

Mendel’s Experiments: F2Generation

P1

F1

F2

  • Next, Mendel crossed two plants from the F1Generation
  • The offspring from this cross are called the 2nd filial generation (F2Generation)
  • After taking careful count, Mendel noticed that most of the seeds in F2 Generation were still yellow, but a small number were green.
  • After completing hundreds of more experiments with other traits, Mendel found this ratio to be approximately, 3 to 1.
slide8

Mendel to Modern Heredity

  • Mendel stated that “factors,” which do not blend together, control each trait of a living thing. Each parent contributes one of these factors to their offspring. Today, we call these factors genes.
  • A gene is a section of DNA that codes for one protein. Genes are what control & produce traits. The genes Mendel studied came in two forms (tall/short; round/wrinkled seeds; yellow/green; etc)
  • Alternative forms of the same gene are called alleles(yellow/green, wrinkled/smooth, etc).
  • 4. Some genes are dominant and some are recessive. The effects of a dominant allele are always seen if it is present. The effects of a recessive allele is not seen when the dominant allele is present.
slide9

Further Findings

  • So, each trait is controlled by a gene, and each gene has two alleles.
  • If the two alleles are the same, they are said to be homozygous. If they are different, they are referred to as heterozygous.
  • Dominant alleles are represented with a capital letter, while recessive alleles with a lower case letter.

YY

Yy

yy

HomozygousDominant

HeterozygousDominant

Homozygous Recessive

the rule of dominance
The Rule of Dominance
  • A dominant trait is the trait that will always be expressed if at least one dominant allele is present.
  • The dominant allele is always represented by a capital letter.
  • A recessive trait will only be expressed if both alleles are recessive.
  • Recessive traits are represented by a lower case letter.
slide11

Law of Segregation

Allele for purple flowers

  • This principle states that the alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.
  • Alleles are now known to be found on copies of chromosomes – one from each parent.

Locus for

Flower-color

gene

Homologous

pair of chromes

Allele for white flower

slide12

More Findings

These alleles are separated during the formation of an organism’s reproductive cells (sperm and eggs). Then, when the egg and sperm joined, each organism would have one allele from each parent.

Yy

Yy

Y

y

Y

y

YY

Yy

Yy

yy

slide13

An Example

FATHER

MOTHER

Yy

Yy

F1 Generation

YY

Yy

yy

F2 Generation

  • The law of dominance explained the heredity of the offspring of the F1 Generation
  • The law of segregation explained the heredity of the F2 Generation
slide14

Phenotypes & Genotypes

  • Phenotype – the physical appearance of an organism; the way it looks (tall/ short, green/yellow, blue or brown eyes, etc.)
  • Genotype – The genetic combination (combination of alleles) of an organism(i.e. – YY, Yy, yy)
    • Homozygous – both alleles arethe same
    • Heterozygous – each allele is different

Pea pod phenotypes

YY

yy

Pea pod genotypes

slide15

PunnettSquares: Monohybrid Crosses

Punnett Squares are a shorthand way of showing how alleles behave and a prediction of an expected genetic outcome.

Draw a big square and divide it into fours.

Place the genotype of one parent across the top and the genotype of the other on the left side.

Tt

Tt

slide16

PunnettSquares: Monohybrid Crosses

Place one allele at the side or top of each square

Populate each square with the corresponding alleles

Tt

TT

Tt

Tt

Tt

tt

slide17

Questions

How many different genotypes are present in this generation?

How many tall plants are in this generation?

Tt

TT

Tt

Tt

Tt

tt

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