Mendel and Heredity Chapter 8

Mendel  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 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 peas

Traits 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.

Crosses  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

Crosses

Mendel’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 Results

Mendel’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 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 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 SQUARES

Punnett Squares

Incomplete 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

Codominance  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