Chapter 5 Lesson 1 Mendel and His Peas

Gregor Mendel Young priest that worked in the garden at a monastery in Vienna. Considered the “Father of Genetics” Observed traits in hundreds of pea plants.

Mendel’s Work - Vocabulary Traits Physical characteristics of organisims Heredity Passing of traits from parent to offspring Genetics Scientific study of heredity

Mendel’s Peas Why was Gregor Mendel lucky he chose peas to study? Many traits exist only in two forms Peas produce many offspring in one generation.

How did Mendel make his crosses? White Plant Purple Plant

True Breeding (Purebred) Plant Mendel’s Experiments True Breeding (Purebred) Plant One that always produces offspring with the same form of a trait as the parent i.e. purebred short plants will only produce short offspring.

Purebred purple plants will only produce purple plants X

White flower would mean the parents are not purebred X

Mendel’s Experiments Mendel crossed plants with opposite forms of a trait i.e. purple flowers crossed with white flowers Look at Figure 3 on page 152 Explain why all offspring are purple in the first generation (F1) What happens in the second generation (F2)

Mendel’s Experiments Mendel studied flower color followed by six other “opposite” traits. Look at table 1 on page 154. What do you notice about the ratio of traits in the second generation (F2)

Let’s Look at another example

Genes and Alleles Genes Alleles Factors that control traits Different forms of a gene One allele is inherited from each parent. Alleles can be dominant or recessive

Dominant and Recessive Alleles Dominant allele Always seen if present Indicated by a capitol letter (T) Recessive allele Masked or hidden if dominant allele is present Indicated by a lower case letter (t)

Hybrid vs Purebred Hybrid Purebred Organism has two different alleles for the trait – one dominant and one recessive. Purebred Organism has two identical alleles for a trait – two recessive OR two dominant.

Alleles are represented with capitol and lower case letters. T = Tall allele (dominant) t = Short allele (recessive) Purebreds TT – two dominant alleles – plants will be tall tt – two recessive alleles – plants will be short Hybrid Tt – one dominat allele and one recessive allele – plants will be tall.

Phenotypes and Genotypes Physical appearance or visible trait Example is flower color, stem height etc. Genotype The genetic makeup or allele combination Examples are TT or Tt Genotypes determine phenotypes

Homozygous and Heterozygous An organism that has two identical alleles for a trait TT – homozygous dominant tt – homozygous recessive Heterozygous An organism that has two different alleles for a trait Tt – heterozygous – will show the dominant trait

Probability Probability Example: coin toss The likelihood that a particular event will occur Example: coin toss

Punnett Squares Punnett Squares chart that shows all possible combinations of alleles that can result from a genetic cross. Used to determine the probability of a particular outcome.

Using a punnett square Tt t T T Tt t TT Tt Tt tt Tall Tall Tall Short

Codominance Codominance – alleles are neither dominant or recessive therefore both alleles are expressed in the offspring

Codominance The heterozygous offspring will express (show) both phenotypes

What is the rabbit’s phenotype for fur color? _________ Consider a rabbit with black fur and the allele combination (Bb). What is the rabbit’s phenotype for fur color? _________ What is the rabbit’s genotype for fur color? __________ Is the rabbit heterozygous or homozygous for the fur color trait? _______________ If black is dominant over white, what genotype would produce a white rabbit? _______ If fur color in rabbits was a codominant trait instead of dominant/recessive trait, what color fur would the (Bb) rabbit have? ________________ Black (Bb) heterozygous (bb) White and black 23