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Introduction To Genetics- Chapter 11

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I. The work of Gregor Mendel

A. Gregor Mendel was born in 1822 and after becoming a priest; Mendel was a math teacher for 14 years and a monastery. Mendel was also in charge of the monastery garden.

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1. Mendel carried out his work with garden peas

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2. Fertilization is the fusion of an egg and a sperm.

 3. True breeding plants are plants that were allowed to self-pollinate and the offspring would be exactly like the parent.

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B. Genes and Dominance

1. The different forms of a gene is called and an alleles.

 2. The principal of dominance states that some alleles are dominant and others are recessive.

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Pinky Finger TraitsAt John Burke High School they tested dominant and recessive traits in our school population. We tested pinky finger traits, whereby, the bent

finger is dominant and the straight finger is recessive.

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C. Segregation1. Each trait has two genes, one from the mother and one from the father.

 2. Traits can be either dominant or recessive.

 3. A dominant trait only needs one gene in order to be expressed.

 

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4. A recessive trait needs two genes in order to be expressed.

 

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5. Egg and sperm are sex cells called gametes.

 6. Segregation is the separation of alleles during gamete formation.

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II. Probability and Punnett SquaresA. Genetics and Probability

 1. The likelihood that a particular event will occur is called probability.

 2. The principals of probability can be used to predict the outcome of genetic crosses.

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B. Punnett Squares1. The gene combination that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square.

 2. Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

 

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3. Each trait has two genes- one from the mother and one from the father.

 4. Alleles can be homozygous – having the same traits.

 5. Alleles can be heterozygous- having different traits.

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6. Physical characteristics are called the phenotype.

 7. Genetic make up is the genotype.

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III. Exploring Mendalian Genetics

A. Independent assortment

1. Genes segregate independently.

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2. The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

 3. Independent assortment helps account for the many genetic variations observed in plants, animals and other organisms.

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B. A summary of Mendel’s Principals

1. Genes are passed from parent to offspring.

 2. Some forms of a gene may be

dominant and others recessive.

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3. In most sexually producing organisms, each adult has two copies of each gene- one from each parent. These genes are segregated from each other when gametes are formed.

 4. The alleles for different genes usually segregate independently of one another.

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C. Beyond Dominance and Recessive alleles

1. Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

 2. Cases in which one allele is not completely dominant over another are called incomplete dominance.

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a. Example: White (W) and Red (R) is both dominate. If WW X RR the F1 generation would be WR= pink.

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3. Codominance is when both alleles contribute to the phenotype.

 Example: Feather colors

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4. Many genes have more than two alleles and are referred to have multiple alleles.

 a. This means that more than

two possible alleles exist in a population. Example: colors of rabbits see page 273.

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  5. Traits that are controlled by two or more genes are said to be polygenic traits, which means, “having many genes.”

 a. Example: eye color has many different genes.

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D. Applying Mendel’s principles 

1. Mendel’s principals do not only apply to plants.

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IV. Meiosis

A. Chromosome number 

1. Every individual has two sets of chromosomes. One from the mother one from the father. When the chromosomes pair up for the same trait they are called homologous chromosomes.

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2. A cell that contains homologous chromosomes (2 genes) is said to be diploid/ 2n.

 3. Gametes (egg /sperm) have only one chromosome and are said to be haploid/ n.

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B. Phases of Meiosis1. Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

 2. Meiosis I- ****The homologous chromosomes line up BUT then they CROSS OVER, exchanging genetic information.

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3. Meiosis II- The two cells produced by meiosis I now enter a second meiotic division. The final product = start with 1 cell with 46 chromosomes and get 4 DIFFERENT cells each with 23 chromosomes.

 Go to Internet: www.SciLinks.org code

cbn-4114 to view meiosis.

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V. Linkage and gene maps

A. Gene linkage 

1. Thomas Hunt Morgan research on fruit flies led him to the principal of linkage.

 2. Morgan discovered that many genes appeared “linked” together.

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3. It is the chromosomes, however, that assort independently not individual genes.

 4. Mendel DID miss gene linkage.

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5. Even though if two genes are found on the same chromosome this does not mean they are linked forever. Crossing over can occur.

 6. Crossing over creates genetic diversity.

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7. A gene map shows the relative location of each gene. See page 280 figure 11.9

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THE END