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Chapter 11 Intro to Genetics Genetics- study of heredity Gregor Mendel -Austrian monk -studied science and math -taught high school and in charge of the care of monastery garden -studied garden peas -he knew that part of the flower produce pollen -pollen contains male reproductive cells or sperm -flower contains female reproductive cells or eggs -Fertilization- process during sexual reproduction, male and female cells join to form a new cell -new cell develops into a tiny embryo inside a seed -Pea flowers are normally self-pollinating -sperm cells fertilize the egg cells in the same flower -seeds produced inherit all of the characteristics from the parent plant= have single parent -Mendel had true-breeding pea plants -if allowed to self-pollinate, produce offspring identical to themselves -Ex: tall, short, green seeds, yellow seeds -Mendel wanted to produce seeds from 2 different plants -He had to prevent self pollination -cut male parts that produced pollen -dusted pollen from another plant onto that flower 1 Cross-pollination- produced seeds that had 2 different parents Mendel studied 7 different pea plant TRAITS Trait- specific characteristic, varies from 1 individual to another ex: seed color or plant height Mendel crossed plants with certain characteristics and studied their offspring P generation= (parental)= original pair of plants F1= “first filial” generation= offspring filius and filia =”son” and “daughter” Hybrids- the offspring of crosses between parents with different traits F1 hybrids Mendel’s experiment showed that all of the offspring had the character of only 1 of the parents, the character of the other parent seemed to have disappeared Mendel’s Conclusions: 1. Inheritance is determined by factors that are passed from one generation to the next genes- determines traits genes control traits alleles- different forms of a gene 2. Principle of Dominance- some alleles are dominant and others are recessive -dominant= always show trait -recessive trait shown only when dominant is not present Where did the recessive alleles go? Did they disappear or were they still present in the F1 generation? 2 Allowed F1 generation to self-pollinate (crossed F1 generation with itself) to produce F2 generation Results: recessive traits had reappeared! Segregation- separation of alleles during gamete formation (gamete= sex cell) Experiment overview: 2 parents- 1 tall, 1short (tall= dominant) F1= all plants tall When each F1 plant flowers and produces gametes, the 2 alleles segregate from each other so that each gamete carries only a single copy of the gene. Therefore, each F1 plant produces 2 types of gametes-those with the allele for tallness and those with the allele for shortness. figure 11-5 T=dominant allele; t= recessive allele *11-2 Probability and Punnett Squares Probability- likelihood that a particular event will occur ex: coin flip- 2 possibilities- heads up or tails up; probability of either outcome are equal -probability of heads up= 1 chance in 2 or ½ or 50% -if you flip a coin 3x’s in a row, what is the probability of heads up every time? ½ x ½ x ½ = 1/8 3 1 in 8 chances of flipping heads 3x’s in a row How is flipping coins related to genetics? Segregation of alleles is completely random. Punnett Squares- diagram used to predict and compare the genetic variations that will result from a cross. Homozygous- have 2 identical alleles for a particular trait; ex: TT or tt Heterozygous- have 2 different alleles for a particular trait; ex: Tt Homozygous= true breeding Heterozygous= hybrid Phenotype= physical characteristics Genotype= gentic makeup Probabilities predict averages: need LARGE sample cannot predict precise outcome of individual event -ex: flip coin twice= likely to get 1 head, 1 tail -could also get 2 heads or 2 tails -to be more likely to get the 50:50 ratio you need to flip many times 4 5