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 1822-1884 The monk who worked with?

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

WHY PEA PLANTS? EASY TO GROW REPRODUCE IN A SHORT TIME GET RESULTS QUICKLY ONLY 7 TRAITS EACH TRAIT ONLY HAS 2 FORMS MALE & FEMALE PARTS on flowers allow for SELF-FERTILIZATION OR MENDEL could CROSS FERTILIZE them

HOW MENDEL CROSS FERTILIZED

FLOWERS & THEIR PARTS

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. White recessive offspring Purple Dominant

How to fill & label a punnett cross 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 Phenotype white flower alleles Phenotype Purple flower Genotypes of 4 offspring are ?___ What is the phenotype of offspring?___

How to do a punnett square http://nortonbooks.com/college/biology/animations/ch10p02.htm How to do a punnett square http://www.zerobio.com/videos/monohybrid.html

MENDEL’S OBSERVATIONS OF OF 1ST PURE-BRED CROSS 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 letters 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.

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

MENDEL’S 2ND 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 2nd Experiment Ratios

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

DI-HYBRID CROSSES http://www.siskiyous.edu/class/bio1/genetics/dihybrid_v2.html

MENDEL’S HYPOTHESIS Mendel’s Theories 1. EACH TRAIT IS CONTROLLED BY A FACTOR… 2. MANY FACTORS HAVE 2 FORMS 3. ONE IS DOMINANT OVER ANOTHER 4. EACH PARENT CONTRIBUTES 1 FACTOR 5. FACTORS SEPARATE WHEN GAMETES FORM, & JOIN TO MAKE A PAIR for a ZYGOTE 6. SOME TRAITS DISAPPEAR IN A GENERATION, THEN REAPPEAR. What we know About 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

INDEPENDENT ASSORTMENT http://bcs.whfreeman.com/thelifewire/content/chp10/1002001.html

ABILITY TO PREDICT FUTURE EVENT PROBABILITY http://nortonbooks.com/college/biology/animations/ch10a05.htm 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 It 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 Example 2 Example 1 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.