Why are my eyes green? She has her mother’s eyes! She’s a chip of the old block! Have you ever wonder why you look the way you do? Why you are short or tall? Why your hair is straight or curly? People in a family may have things in common. They can share traits. You can inherit traits from your parents. We will further discuss this in today’s lesson: (go to next slide) Who does he look like? Mother or Father? Or both?

Genetics

Why are we learning this? To understand Genetics and Gregor Mendel’s Contribution to Heredity. To understand how traits are passed from one generation to the next.

Heredity—The passing of traits from parents to offspring Gregor Mendel An Austrian monk who worked with pea plants to develop our basic understanding of Genetics Genetics – the scientific study of how traits are passed down from parents to offspring (Heredity) Heredity—The passing of traits from parents to offspring

Mendel’s Experiments Mendel studied 7 different traits in pea plants Trait – a specific characteristic that varies from one individual to another Examples: Green seeds vs. Yellow seeds Tall plants vs. Short plants

Mendel crossed plants with different traits and studied their offspring The offspring are called hybrids Mendel saw that the hybrids had the character of only one of the parents. The character of the other parent disappeared

Mendel’s Experiments cont’d

Mendel’s Experiments cont’d Mendel then made a cross of the two hybrids and saw that the characteristic that disappeared in the first cross came back

Mendel’s Experiments cont’d

Results of Mendel’s Experiments Genes are passed from parent to offspring Genes – the genetic information that controls one trait There are different forms of a gene that create specific traits. These are called alleles Example: One allele of the gene for plant height makes it tall, the other allele makes it short

Describing Genes and Traits Most organisms have 2 copies of a gene (1 from mom, 1 from dad) Genotype – shows what type of alleles the 2 genes are Phenotype – what the organism looks like (what trait is being expressed)

Principle of Dominance Some alleles are dominant, some are recessive An organism with a: Dominant allele will always exhibit that form of a trait Recessive – only shows that form when there is no dominant form present

Dominance Represented with Upper and lower case letters: T – dominant trait for height (tall) t – recessive trait for height (short) TT = tall plant Homozygous Dominant Plant Tt = tall plant Heterozygous Plant tt = short plant Homozygous Recessive Plant genotype phenotype

What were those words again? Homozygous Dominant – 2 dominant alleles (Capital Letters TT) Homozygous Recessive – 2 recessive alleles (lower case letters tt) Heterozygous – 1 dominant and 1 recessive (one capital and one lower case Tt)

Results of Mendel’s Experiments From his observations of the pea plants, Mendel derived his first theory, the Theory of Segregation. There are four parts to the Theory of Segregation: Genes come in multiple forms, called alleles. Individuals will inherit two alleles for a given trait. Gametes, produced through meiosis, will have one allele per cell, per trait. When there are two alleles present, one will be dominant and one will be recessive.

Theory of Segregation in Action When a trait is dominant, its effects will mask those of its recessive partner. In this example, the dominant R allele produces a red pigment, while the recessive r allele produces no pigment at all.

Theory of Segregation in Action Therefore, when the plant is Rr or heterozygous, it will show a red color, but when it is homozygous recessive (rr), it will produce a white color. If a homozygous dominant and homozygous recessive plant are crossed, all the first generation (F1) offspring will be Heterozygous (Rr). If two of the F1 offspring are crossed, their offspring (second generation – F2) will be one-quarter Homozygous Dominant (RR), one-quarter Homozygous recessive (rr), and one-half Heterozygous (Rr).

Further Results of Mendel’s Experiments Mendel’s second theory was the Theory of Independent Assortment. Independent Assortment means that the traits in question aren’t linked; meaning that just because an individual is dominant for one trait, does not mean that they are dominant in another trait. This is how we can have individuals with brown hair and blue eyes, while another individual has blonde hair and brown eyes. The traits are not inherited together, meaning that the traits are on different chromosomes. “Life is like a box of chocolates………….” Forrest Gump Chromosomes are separated during meiosis.

Theory of Independent Assortment Homologous chromosomes are chromosomes that carry the same genes; one of the chromosomes will come from the mother, and one will have come from the father. During meiosis, the homologous chromosomes will go separately into each gamete. This is the process of Independent Assortment. Since each set of homologous chromosomes can be arranged into a gamete individually, when dealing with multiple chromosomes, they can all also assort independently, leading to a wide variety of potential gametes.

Incomplete dominance Heterozygous phenotype is intermediate between the two parental homozygotes.

Incomplete dominance If you cross true breeding red and white snapdragons F1 are all pink flowers F2 - 1:2:1 red:pink:white It takes 2 doses of the red allele to get red RR- red Rr – pink rr - white

Heredity—The passing of traits from parents to offspring Vocabulary Heredity—The passing of traits from parents to offspring Trait—a characteristic that an organism can pass on to its offspring through its genes Genes—factors that control traits Alleles—different forms of genes Lets review the vocabulary you will encounter.

Dominant Allele—is one whose trait always shows up in the organism when present Recessive Allele—is one that is masked, whenever the dominant allele is present Genotype—the specific set of alleles forming the genome of an individual Phenotype—visible characteristics of an individual

Tools of the Trade –Punnett Square Parent Genotype AA crossed with Aa A a AA Aa