Chapter 3 Section 1 Mendel’s Work

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? Tall Plant Short Plant

Mendel’s Experiments 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 pink plants will only produce pink 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. short plants crossed with tall plants Look at Figure 2 on page 82

Fig 2 page 82 What did Mendel get when he crossed purebred tall plants with pure bred short plants? All Tall plants What did Mendel get when he let the F1 plants self pollinate? 75% tall and 25% short.

Mendel’s Experiments Mendel studied stem height followed by six other “opposite” traits. Look at Figure 3 on page 83. What other “opposite” traits did Mendel study?

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

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 18

Probability and Genetics Chapter 3 - Section 2

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

Mendel’s Work Review Worksheet What trait in pea plants is being studied in the cross above? Plant height (short/tall) What are the two alleles for this trait? Tall (T) Short (t) Which allele is the dominant allele? Explain how you know. Dominate allele is Tall (T). Know because all offspring in F1 are tall.

Mendel’s Work Review Worksheet Which allele is the recessive allele? Explain Recessive is short (t) Know because this trait is hidden in the F1 What alleles do the F1 offspring have? Explain which allele was inherited from which parent. All F1 offspring are hybrids with the alleles (Tt) (T) was inherited from the tall parent and (t) was inherited from the short parent.

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