Chapter 10 Mendel.docx

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Biological Sciences
Effiette Sauer

Chapter 10 Mendel, Genes and Inheritance 10.1 The beginning of Genetics: Mendel’s Garden Peas  Blending theory of Inheritance: popular belief which suggested that hereditary traits blend evenly in offspring through mixing of the parents’ blood, i.e. like coffee and cream  Mendel studied a variety of heritable characteristics called characters o Characters = traits  Mendel established that traits are passed to offspring in the form of discrete hereditary factors which are now known as genes  Mendel observed that rather than blending evenly many parental traits appeared uncharged in offspring, whereas some disappeared in some generations and reappeared in other 10.1a Mendel Chose True-Breeding Garden Peas for His Experiment  Mendel chose the garden pea for his research because the plant could be grown easily in the monastery garden  The male gametes are sperm found in the pollen, female gamete found in the carpel  Pea plants self-fertilize or self-pollinate, self  Cross-pollination: pollen to fertilize these flower then had to come from a different plant  True-breeding: when selfed they passed on traits without changes from one generation to the next 10.1b Mendel First Worked with Single Character Crosses  Would traits blend evenly? o Mendel took pollen from purple flowers and put them with white flowers o Preformed the reciprocal cross o Seeds were the product of the cross  F1 generation: first generation of offspring  P generation: parental generation, initial cross  F2 generation: second generation  In the F1, there was only purple flower  In the F2, there was a 3:1 ratio of purple to white flowers  In all cases he observed a uniform F1 generation, in the F2 the missing trait reappeared in definite predictable proportions among the F2 offspring 10.1c Mendel’s Single-Character Cross led to the Principle of Segregation  Mendel’s factors are genes located on chromosomes  Alleles: different versions of a gene that produces different traits of a character o Two allele for a gene o Organisms with two copies of a gene are called diploid  Mendel deduced that the trait that appeared in the F1 was the stronger allele, calling it the dominant allele  ‘If an individual’s pair of gene consists of different alleles one allele is dominant over the other, recessive allele  If an organism carries two different alleles, the dominant allele is the one that determines the appearance of the organism  The dominant allele doesn’t directly inhibit the recessive alleles  Principle of Segregation: The pairs of alleles that control a character segregate as gametes are formed, half the gametes carry one allele and the other half carry the other allele o The fusion of egg and sperm creates a zygote, the zygote receives one allele from the male gamete and one from the female gamete  Homozygote: containing one kind of allele  Homozygous: containing same allele for one gene, rr or RR  Heterozygote: contain two different allele for a gene, said to be heterozygous for that trait  Monohybrid: an F1 heterozygote produced from a genetic cross that involves a single trait  Monohybrid Cross: a genetic cross between two individuals that are each heterozygous for the same pair of alleles  Genotype: genetic constitution of an organism  Phenotype: out ward appearance of the genes  Mendel’s Crosses proved o 1) the genes that govern genetic characters are present in two copies in individuals o 2) if different alleles are present in a pair of genes, one is allele is dominant over the other o 3) The two alleles of gene segregate and enter gametes singly 10.1d Mendel Could Predict Both Classes and Proportions of Offspring from His Hypothesis  Product Rule of Probability o When two of more events are independent, the probability that they will both occur is calculated using the product rule o Product Rule: individual probabilities are multiplied o Ex. Probability that your 4 children may be all girls  ½ x ½ x ½ x ½ = 1/16  The Sum Rule in Probability o Sum Rule: when several different events all give the same outcome, that is, the probability that either event A or B or C will occur equals the probability of event A plus the probability of event B and the probability of event C  Probability in Mendel’s Crosses o Producing a PP zygote is from a monohybrid is ½
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