Mendel and HeredityMendel and Heredity

Chapter 8Chapter 8

MendelMendel

Heredity- the passing of traits from parents to offspring

Gregor Mendel- Austrian monk who worked with peas. He noticed that offspring have traits that they get from their parents.

His work with peas gave us the first rules for accurately predicting patterns of heredity

Heredity- the passing of traits from parents to offspring

Gregor Mendel- Austrian monk who worked with peas. He noticed that offspring have traits that they get from their parents.

His work with peas gave us the first rules for accurately predicting patterns of heredity

Mendel’s peasMendel’s peas

Mendel worked with peas for several reasons Peas have traits with two distinct forms- for example:

flowers are either purple or white- there is no intermediate

Stamen and pistil are in the same flower and easy to control and pollinate

Peas grow fast, mature quickly, and produce many offspring. This gives him a lot to work with.

Mendel worked with peas for several reasons Peas have traits with two distinct forms- for example:

flowers are either purple or white- there is no intermediate

Stamen and pistil are in the same flower and easy to control and pollinate

Peas grow fast, mature quickly, and produce many offspring. This gives him a lot to work with.

Mendel’s peasMendel’s peas

Traits and RatiosTraits and Ratios

Mendel worked with only ONE trait at a time conducting MONOHYBRID CROSSES

True-breeding- he would allow plants to self-pollinate for several generations and they would always produce the same trait. In animals we would call this pure-bred.

Mendel worked with only ONE trait at a time conducting MONOHYBRID CROSSES

True-breeding- he would allow plants to self-pollinate for several generations and they would always produce the same trait. In animals we would call this pure-bred.

CrossesCrosses Mendel would take two true-breeding plants with

different forms of a trait (purple and white flowers) This was his parent generation (P generation)

The offspring that were produced were called the F1 generation. He would then cross this generation with itself.

The offspring produced from a cross of two F1 parents would be called the F2 generation

Mendel would take two true-breeding plants with different forms of a trait (purple and white flowers) This was his parent generation (P generation)

The offspring that were produced were called the F1 generation. He would then cross this generation with itself.

The offspring produced from a cross of two F1 parents would be called the F2 generation

CrossesCrosses

Mendel’s resultsMendel’s results

Mendel’s work showed that one form of the trait covered up the other in the F1 generation.

When the F1 was crossed with itself, the missing trait showed up again.

Mendel also noticed that this happened in a predictable ratio of 3:1

Mendel’s work showed that one form of the trait covered up the other in the F1 generation.

When the F1 was crossed with itself, the missing trait showed up again.

Mendel also noticed that this happened in a predictable ratio of 3:1

Mendel’s ResultsMendel’s Results

Mendel’s TheoryMendel’s Theory

Each inherited trait gets two copies of a gene- one from each parent

There are alternative versions of the same trait- ALLELES When two different alleles are inherited one of them may

be completely expressed while the other if covered or hidden Dominant- the trait that hides another Recessive- the trait that is hidden by another

When gametes are formed the alleles for each gene separate independently from each other. The gametes will only carry one allele for each trait

Each inherited trait gets two copies of a gene- one from each parent

There are alternative versions of the same trait- ALLELES When two different alleles are inherited one of them may

be completely expressed while the other if covered or hidden Dominant- the trait that hides another Recessive- the trait that is hidden by another

When gametes are formed the alleles for each gene separate independently from each other. The gametes will only carry one allele for each trait

Modern TermsModern Terms HOMOZYGOUS-If two of the same alleles are

inherited by an organism. FF or ff HETEROZYGOUS- if two different alleles are

inherited by an organism- Ff GENOTYPE- the combinations of alleles that are

inherited. FF, Ff, ff PHENOTYPE- the appearance that is seen from

the allele combinations- purple flowers or white flowers, dimples or no dimples.

HOMOZYGOUS-If two of the same alleles are inherited by an organism. FF or ff

HETEROZYGOUS- if two different alleles are inherited by an organism- Ff

GENOTYPE- the combinations of alleles that are inherited. FF, Ff, ff

PHENOTYPE- the appearance that is seen from the allele combinations- purple flowers or white flowers, dimples or no dimples.

Laws of HeredityLaws of Heredity

LAW OF SEGREGATION- the alleles separate when gametes are formed

LAW OF INDEPENDENT ASSORTMENT- one allele will have no effect on another allele- for example: just because you inherit blue eyes, this does not mean that you will inherit blonde hair. Eyes and hair have no effect on each other.

LAW OF SEGREGATION- the alleles separate when gametes are formed

LAW OF INDEPENDENT ASSORTMENT- one allele will have no effect on another allele- for example: just because you inherit blue eyes, this does not mean that you will inherit blonde hair. Eyes and hair have no effect on each other.

PUNNETT SQUARESPUNNETT SQUARES

Punnett SquaresPunnett Squares

Incomplete DominanceIncomplete Dominance

The dominant allele does not completely mask the recessive resulting in a mixing of the traits

Pure red x pure white = pink

The dominant allele does not completely mask the recessive resulting in a mixing of the traits

Pure red x pure white = pink

CodominanceCodominance

Two different types of dominant alleles are expressed at the same time.

A Blood is dominant B Blood is dominant AB Blood is codominant

Two different types of dominant alleles are expressed at the same time.

A Blood is dominant B Blood is dominant AB Blood is codominant