Early Belief about Inheritance Blending Theory Children were a mixture of both parents But, if this were true over time what would we see? A reduction in variety of traits.

GREGOR MENDEL Look at your diagram on Plant traits The monk who worked with?

MENDEL’S GOAL EXPLAIN the PATTERN of HEREDITY from PARENT to OFFSPRING

WHY PEA PLANTS? EASY to GROW REPRODUCE offspring in a SHORT TIME Get offspring results quickly Only 7 traits (genes) Each TRAIT HAS 2 FORMS (physical) –Avoid any confusion in results MALE & FEMALE parts on flowers allow for –SELF-FERTILIZATION OR MENDEL could control breeding with CROSS FERTILIZING

HOW MENDEL CROSS FERTILIZED

FLOWERS & THEIR PARTS Use your worksheet Sexual Reproduction In Plants Male flower parts Female flower parts

How to fill & label a punnett crosspunnett The letters pp or PP are called ALLELES. Each parent CONTRIBUTES one ALLELE to their offspring Therefor there are 2 ALLELES for each TRAIT, one from each parent The alleles are genes. So we call the combination of alleles, genotype, think Genes When we look at the physical characteristics the genotype creates this is called a phenotype, think Physical. Purple, white flowers alleles Phenotype Purple flower Phenotype white flower Genotypes of 4 offspring are ?___ What is the phenotype of offspring?___

MENDEL’S FIRST TRAIT EXPERIMENT- Flower Color We use a punnett square to show the results: Two purebred parents are crossed One parent has PP it has purple flowers The other has pp white flowers A dominant trait is a capital letter P A recessive trait is a small letter p The offspring are all purple. Because they have one dominant gene P. Even though they have a p gene. Purple Dominant White recessive offspring

Mendel’s Discovery HW assignment Breeding Pea ColorPea

MENDEL’S OBSERVATIONS OF OF 1 ST PURE-BRED CROSS Use your worksheet-”Genetic Explanation of Formation of Hybrids” The PARENT’s generation uses the code P. They are PUREBRED plants. They had 2 genes that were both represented by the same letters, either PP for purple flowers or pp for white flower color. We also call purebreds Homozygous for a trait. Two alleles that are the same- PP or pp. The OFFSPRING generation uses the code F-1 In this example the offspring are Hybrids or Heterozygous, Pp. They have 2 genes, one dominant and one recessive. Because the offspring have one dominant gene P they have purple flowers.

If someone believed in the Blending Hypothesis they would have predicted that the offspring of a purple and white flower … LIGHT PURPLE But they were not. Mendel therefore called the purple color a Dominant trait.

ALL OFFSPRING had DOMINANT, purple flowers None had the white flowers, or Recessive trait. MENDEL’S OBSERVATIONS OF 1ST PURE-BRED CROSS

MENDEL’S 2 ND EXPERIMENT SELF-FERTILIZATION CROSS He bred the F-1GENERATION Remember the F-1 were HYBRIDS, Pp –They had two genes, one dominant and one recessive. But Mendel did not realize this. He only saw that they had purple flowers. So he expected to see? All purple offspring when they were bred with each other

F-2 RESULTS However, he had SOME PURPLE & also some White flowered plants appear HOW WAS THIS POSSIBLE?! THE RECESSIVE TRAIT was always there in the genes of the flowers. To get a white flower two recessive genes had to come together in an offspring to show up. pp The phenotype ratio of offspring he had by flower color was 3:1 Three purple to one white. The genotype ratio he got was 1 PP, 2Pp, 1 pp it is written at 1:2:1

Mendel’s 2 nd Experiment Ratios

Mendel’s 1 st exp. Mendel’s 2 nd experiment Crosses purebreds Crosses hybrids

Tutorials on how to do Punnett Squares Use your worksheet Expected & Observed Results Zero Bio site with narration narration Tutorial with description, step by stepTutorial

DI-HYBRID CROSSES Use your Worksheet Di-hybrid Crosses If you need help, go to this tutorialtutorial

MENDEL’S Discoveries Mendel’s Theories 1. EACH TRAIT IS CONTROLLED by a FACTOR… 2. FACTORS are DUPLICATED 3. ONE is DOMINANT over ANOTHER 4. EACH PARENT CONTRIBUTES 1 FACTOR 5. FACTORS SEPARATE WHEN GAMETES FORM, & JOIN to as a PAIR to form a ZYGOTE 6. SOME TRAITS DISAPPEAR in a GENERATION, then REAPPEAR. How Theory contributed to Genetics A factor is a GENE A gene has two copies (chromosomes) DOMINANT/RECESSIVE 1 GENE MEIOSIS and Fertilization A PARENT can have a Recessive TRAIT & not EXPRESS it physically & can pass it onto their child

Law of Dominance & Recessive Traits Some traits are dominant over others Some traits may not be expressed unless inherited on both genes

Principle of Segregation For any particular trait, the pair of alleles from each parent separate and only one allele passes from each parent on to an offspring. Which allele is inherited is a matter of chance.

PRINCIPLE OF INDEPENDENT ASSORTMENTINDEPENDENT different pairs of alleles are passed to offspring independently of each other Look at the possible allele combinations to the right. Some offspring may not resemble their parents.

PROBABILITY ABILITY TO PREDICT FUTURE EVENT PREDICT THE FREQUENCY OF OFFSPRING TRAITS EXAMPLE A COIN TOSS WHAT are the CHANCES of GETTING HEADS with 1 COIN? ½, one side is heads, the other is tails WHAT are the CHANCES of getting HEADS with 2 COINS? ½ x ½ =? ¼!

TEST CROSS When you are not sure what the GENOTYPE is for a dominant trait, example –a black dog can be HOMOZYGOUS BB or HETEROZYGOUS Bb You would breed the dominant trait organism with a HOMOZYGOUS RECESSIVE bb mate since they have no dominant genes This mate can only give recessive genes to the offspring This is what a breeder would do to determine if the dominant organism’s phenotype is homozygous or heterozygous

TEST CROSS Cross your dominant organism w/a recessive organism HOMOZYGOUS genotype HETEROZYGOUS genotype t All offspring are heterozygous then the unknown parent must be a purebred, or homozygous dominant 2 offspring are heterozygous, 2 are recessive. Therefore, the parent is not a purebred. Example 1 Example 2 tt