Chapter 12 Who Was Gregor Mendel? Gregor Mendel was a monk, born in 1822 in Austria. He performed many scientific experiments in the monastery garden. Discovered the principles of heredity, the passing of traits from parents to offspring. “Father of genetics” Chapter 12

Mendel’s experiments Mendel used garden pea plants for his experiments. Self-Pollinating Peas have both male and female reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower. stigma anther Pistil

Pea plants can also cross-pollinate Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant. The image shows cross-pollination and self-pollination.

Mendel studied the characteristic of peas. A characteristic is a feature that has different forms in a population. Ex. Seed shape, eye color Different forms of a characteristic are called traits. Ex. Round or wrinkled.

A Great Idea Mendel knew that factors that affect traits exist in pairs. The instructions for an inherited trait are called genes. RR= gene for round peas The different forms of a gene are alleles. You get two for each gene. One from mom and one from dad. R = round

Mix and Match Mendel would pollinate wrinkled seed plants with round seed plants to see what would happen. RR rr

White flower gene disappears Mendel’s Discoveries One trait was always present in the first generation, and the other trait seemed to disappear. Ex. Only purple flowers form, white would disappear. Parents (P) pp PP White flower gene disappears Offspring (F1)

Mendel called the trait that appeared the dominant trait. The trait that disappeared was called the recessive trait. Parents (P) pp PP recessive Dominant

Dominant traits occur most often and masks the expression of other alleles. A recessive trait or allele is expressed only when two recessive alleles for the same characteristic are inherited. (P) Parents dominant recessive + Kid (F1)

B b + Dominant allele gets a capital letter. recessive + Bb Dominant allele gets a capital letter. Recessive gets a lower case. B b gene

Phenotype An organism’s appearance is known as its phenotype Phenotype An organism’s appearance is known as its phenotype. Genes affect the phenotype. What you see hair height nose ears

BB = brown hair bb = red hair Genotype The combination of inherited alleles together form an organism’s genotype. BB = brown hair bb = red hair genotype Phenotype

A person with two dominant or two recessive alleles is said to be homozygous. A person that has the genotype Bb is said to be heterozygous. bb= blond Bb= black homozygous heterozygous purebred hybrid

Recessive gene disappears Recessive gene reappears Mendel’s Final Discovery pp PP Parents (P) Offspring (F1) Offspring (F2) purebred Recessive gene disappears Recessive gene reappears Lost trait always reappears in 2nd generation offspring

Punnet Squares

Punnett Squares are used to organize all the possible genotype combinations of offspring from particular parents. Parents pp PP

True-breeding = homozygous P= purple, dominant p=white, recessive * All heterozygous hybrids Female Male Possible offspring 1. Pp 2. Pp 3. Pp 4. Pp True-breeding = homozygous P= purple, dominant p=white, recessive

Possible offspring 1. PP 2. Pp 3. Pp 4. pp Heterozygous = Pp Flower pollinating itself

What Are the Chances? Probability is the mathematical chance that something will happen. Probability is most often written as a fraction of percentage.

Flower pollinating itself Possible offspring 1. PP 1/4 2. Pp 3. Pp 4. pp 1/4 Heterozygous = Pp Flower pollinating itself 1/2

True-breeding = homozygous P= purple p=white Female Male Possible offspring 1. Pp 2. Pp 3. Pp 4. Pp True-breeding = homozygous P= purple p=white 100% Genotypic ratio

Gene Interactions and Variations Incomplete Dominance Researchers have found that sometimes one trait is not completely dominant over another. One Gene, Many Traits Sometimes one gene influences more than one trait. Many Genes, One Trait Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together.

Phenotype vs. Genotype Genotype Pp P P p Pp Pp Phenotype Pp Pp Purple flower Pp P P p Pp Pp Phenotype Pp Pp

The Importance of Environment Genes aren’t the only influences on traits. A combination of things determine an individual’s characteristics. Your environment also influences how you grow. Lifestyle choices can also affect a person’s traits.

Sex Chromosomes carry genes that determine sex. Human females have two X chromosomes. Human males have one X chromosome and one Y chromosome.

Sex-Linked Disorders The genes for certain disorders, such as colorblindness, are carried on the X chromosome. Genetic Counseling Genetic counselors use pedigrees to trace traits through generations of a family. These diagrams can often predict if a person is a carrier of a hereditary disease. Selective Breeding In selective breeding, organisms with desirable characteristics are mated.