Chapter 11- Introduction to Genetics BIG IDEA: How does biological info. pass from one generation to another?

11.1 The Work of Gregor Mendel Genetics is the science of heredity, or how traits are passed through each generation. Gregor Mendel is considered the father of genetics: Austrian monk Worked with pea plants Why might someone choose to work with pea plants to study genetics? Peas are small and easy to grow. They provided Mendel with the “model system” to carry out his experiments. Peas can reproduce much more quickly than larger organisms such as humans, so it is easy and quick to see changes through generations.

Fertilization occurs when the male and the female sex cells join together to form a new cell. Traits are genetic characteristics (ex: hair color, eye color, height, etc.) -To prevent plants from self-pollinating he cut the male parts from the flower and dusted pollen from them onto the desired flowers. (Cross pollination) Mendel wondered what caused his pea plants to be different color, texture, and height from each other. He prevented the plants from self-pollinating in order to know which exact traits he was trying to cross. He took true-breeding plants (homozygous, would only produce plants like themselves from generation to generation). Cross pollination allowed mendel to breed plants w traits different from those of their parents, and then study the results.

The different forms of each gene are alleles Mendel’s Principles of Inheritance: 1. The factors that pass from one generation to the next are called genes The different forms of each gene are alleles In Mendel’s experiments tall plants were dominant to short plants, smooth plants were dominant to wrinkled, and yellow seeds were dominant to green.

2. Some alleles are dominant and some are recessive Dominant traits mask recessive traits and are seen if 1 of the 2 alleles present are dominant

3. Allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. - A trait may not show up in an individual but can still be passed on to the next generation.

Generations in crossing P generation= Parental generation, each being true-breeding (SS or ss) F1= 1st generation cross. Cross between 2 true-breeding organisms F2=2nd generation cross. Cross between two F1 offspring. The generation where recessive alleles may re-appear

During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only 1 allele for each gene http://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?method=vlo&internalId=301310100000102&isHtml5Sco=false&fromTab=DONETAB# See if link works??

11.2 Applying Mendel’s Principles Probability is the likelihood that a particular event will occur. The principles of probability can be used to predict the outcomes of genetic crosses. Homozygous organisms have 2 identical alleles (Ex: TT/tt) Heterozygous organisms have 2 different alleles (Ex:Tt)

Probabilities predict averages/ratios: F1 produce all tall plants, or 4:0, or 100% F2 produce mostly tall plants, or 3:1, or 75%:25%

Phenotype: physical traits Genotype: genetic makeup Example: Tt=genotype, tall=phenotype

Punnett squares are used to predict the genotype and phenotype combination in genetic crosses. How to for 1 factor and 2 factor crosses: pg. 316 http://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?method=vlo&internalId=301310100000103&isHtml5Sco=false&fromTab=DONETAB#

To test if certain traits were linked to each other Mendel performed a “Dihybrid” cross, involving 2 traits. -F1- rryy x RRYY, all offspring were heterozygous for each trait -F2 generation produced approximately 9:3:3:1 He found out that seed shape and color are not related Independent assortment states that genes for different traits can segregate independently.

A summary of Mendel’s Principles: -Genes are passed from parents to offspring -2 or more alleles exist for each trait, they may be dominant or recessive -Genes segregate from each other when forming offspring -Alleles for diff. genes usually sort independently

11.3 Other Patterns of inheritance There are some exceptions to Mendel’s principles Some alleles are neither dominant or recessive -Incomplete dominance shows the heterozygous phenotype to be an intermediate between the 2 dominant parental phenotypes Many traits are controlled by more than 1 gene.

Codominance produces offspring that show both dominant phenotypes at the same time Ex: Roan cow

Many genes exist in several different forms and are therefore said to have multiple alleles Polygenic traits are the traits that are produced by the interaction of several genes. -Ex: height, skin color The phenotypes of all individuals are determined by a combination of both their genetics AS WELL AS their environment!

Environmental conditions can affect gene expression and influence genetically determined traits. Examples: different temperatures, diets, toxins

11.4 Meiosis How many sets of genes are found in most adult organisms? All offspring receive 1 chromosome from each parent, forming homologous pairs. Diploid (2n)=2 sets Haploid (1n)=1 set The diploid cells of most adult organisms contain 2 complete sets of inherited chromosomes and 2 complete sets of genes. Meiosis only occurs w/ sex cells. Meiosis produces 4 1n daughter cells. Mitosis produces 2 2N daughter cells. Body cells

Meiosis is the process by which the # of chromosomes per cell is cut in ½ through the separation of homologous chromosomes in a diploid cell Remember: PMAT Prophase I: Each replicated chromosome pairs w/ its corresponding homologous chromosome. Crossing-over produces new combinations of allleles

Metaphase I: Paired homologous chromosomes line up across center of the cell Anaphase I: Spindle fibers pull each homologous chromosome pair toward opposite ends of the cell Telophase I: Nuclear membrane forms around each cluster of chromosomes. Cytokinesis follows, forming 2 new cells

Meiosis I

Prophase II: Chromosomes become invisible Metaphase II, Anaphase II, Telophase II: Similar to meiosis I, but the result is 4 haploid daughter cells Fertilized egg= zygote The results of meiosis 1 are 2 daughter cells, but neither has acomplete set of chromosomes b/c they were shuffled. Next we go into meiosis 2, but unlike our 1st division the chromosomes are not replicated before division. Each of the 4 daughter cells produced receive 2 chromosomes.

Meiosis vs. Mitosis Produces sex cells Produces body cells Result= 4 1N cells Reduces chromosome number by half Produces body cells Result=2 2N cells No change in chromosome number

Alleles of different genes tend to be inherited together from one generation to the next when those genes are located on the same chromosome. Genes that are far apart assort independently, genes that are linked are on the same chromosome. Genes that are close together on a chromosome are NOT likely to cross-over. The frequency of crossing over between genes can determine the distances those traits are from each other on chromosomes. = Gene mapping