Chromosome: a long chain of genes Genes and Chromosomes Write these down p. 74 Chromosomes are found in the nucleus of a cell. Chromosome: a long chain of genes

Chapter 3 Section 1 What is Heredity?

Austrian monk born in 1822 Son of a farmer Ordained as a priest Lived in a monastery where over many years, he performed hundreds of experiments on pea plants relating to heredity Known as the FATHER OF GENETICS

Heredity p. 74 Passing of physical characteristics from parent to offspring Mendel’s study of pea plants would forever change biology

Allele: Specific characteristics, such as stem height or seed color Remember… Different forms of a gene Allele: Write this…

Remember?? For example…

Mendel’s Experiments p. 75 Genetics: The scientific study of heredity Mendel wondered why different pea plants had different characteristics: some tall, some short, some with green seeds, some with yellow seeds…

FERTILIZATION: when egg and sperm join together MENDEL’S EXPERIMENTS Mendel “crossed” pea plants with different traits and recorded results “Crossed” means he took pollen from one plant and put it on another plant to fertilize it FERTILIZATION: when egg and sperm join together

Just listen…no need to highlight

Before we learn about Mendel’s experiments, let’s review the basics of sexual reproduction in flowering plants… Flowers have both male and female reproductive structures. The female part of the flower: pistil The pistil produces egg cells. The male part of the flower: stamen The stamen produces pollen which contains sperm cells. p. 75

The birds and the bees of plants… When pollen lands on the pistil of a flower, sperm travels down to the egg cell, and the result is fertilization Fertilization produces a tiny embryo, which is enclosed inside a seed

Pea plants are usually self pollinating Since the reproductive structures are inside the flower, the sperm of the flower will usually fertilize the egg of the same flower. Resulting embryos will have the same characteristics as their parents Even though sexual reproduction has occurred – there is only 1 parent – 2 sex cells though…

MENDEL’S EXPERIMENTS Crossing Pea Plants Mendel devised a way to cross-pollinate pea plants.

Mendel started with PUREBRED ORGANISMS PUREBRED: The offspring of many generations that have the same form of a trait Example: Purebred tall pea plants always come from tall parent plants.

Before we move on, you must be familiar with the following terms: P generation: Parent generation F1 generation: First generation of offspring F2 generation: second generation of offspring Hybrids: offspring of parents with different traits Which thumb do you put on top?

F1 Offspring p. 76 The offspring from the parent cross Filial comes from filia and filius – the Latin words for “daughter” and “son”

F1 Offspring The offspring from the parent cross – (1st generation offspring) Mendel crossed purebred tall plants with purebred short and all F1 offspring were tall.

F2 Offspring The offspring from the F1 generation (2nd generation offspring) Mendel let the hybrid tall plants from the first generation self pollinate – the result was a mix of tall and short plants. ¾ were tall and ¼ were short.

Evidently the F1 “tall” offspring must have been carrying the short trait, but it had been hidden. The short trait had been passed down to the offspring and it reappeared in the F2 generation.

Experiments with other traits Mendel studied other traits such as seed shape and color, pea pod shape and color. In all of Mendel’s crosses, he found that only one form of the trait appeared in the F1 generation. However in the F2 generation, the “lost” form of the trait always reappeared in about ¼ of the plants. Example…P generation (tall x short) F1 generation = all tall F2 generation = ¾ tall, ¼ short

Results of a Cross – figure 2 pg. 76

Results of a Cross – figure 2 pg. 76

How Do Alleles Affect Inheritance? Mendel reached several conclusions P. 77 Sets of genetic information must control the inheritance of traits The factors that control each trait exist in pairs The female parent contributes one factor, the male contributes the other One factor in a pair can mask, or hide, the other factor

Two forms for each trait:

How Do Alleles Affect Inheritance? Gene Factors that control a trait Do you know this Gene???

ALLELES Different forms of a gene EXAMPLE: The gene that controls stem height in peas has one allele for tall stems and one for short stems.

ALLELES ARE INHERITED Each pea plant inherits two alleles from its parents – one allele from MOM (the egg) and the other from DAD (the sperm) Our little sweet pea!!

ALLELES ARE INHERITED An organism’s traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive A dominant allele can cover up or mask a recessive allele

Dominant vs. Recessive Alleles Dominant alleles: trait that always shows up when the allele is present Recessive Alleles: trait that is “hidden” whenever the dominant allele is present (this trait will only show up if the dominant allele is not present)

Circle the picture of each dominant form of the trait in the P generation.

Predict: Under what conditions would the recessive form of one of these traits reappear?

Predict: Under what conditions would the recessive form of one of these traits reappear? If an offspring has two recessive alleles.

Alleles in Mendel’s Crosses Hybrid: An organism with two different alleles for a trait (1 dominant and 1 recessive) The F1 plants were all hybrids - one tall allele and one short allele The dominant allele masked the recessive allele, so all the plants were tall in the F1

Symbols for Alleles Geneticists use letters to represent alleles Dominant allele – represented by a capital letter Recessive allele – represented by a lowercase version of the same letter Example: T = tall stems t = short stems TT = tall plant Tt = tall plant Tt = short plant

Dominant and Recessive Alleles Figure 4 Fill in the missing allele symbols and descriptions. Use the word bank to complete the statements. (Terms will be used more than once). Draw the two possible ways the F2 offspring could look. T t Tall dominant t recessive Hybrid dominant dominant recessive recessive

Apply it! P. 79 WW and ww About ¾ will have long wings and ¼ will have short wings All will have long wings; Ww

Significance of Mendel’s Contribution Mendel’s discovery of genes and alleles eventually changed scientists’ minds about heredity Before Mendel, most people thought traits were just a blend of the parent’s characteristics. Mendel showed that offspring traits are determined by the individual, separate alleles inherited from each parent.

Significance of Mendel’s Contribution Known as the Father of Genetics