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| the scientific study of heredity |
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experimented w/ pea plants to understand heredity
he knew that:
-male part of each flower produces pollen (sperm)
-female part of each flower produces egg cells
he wanted to produce seeds by joining male and female reproductive cells from 2 diff plants. he cut away the pollen bearing male parts of the plant and dusted the plants flower with pollen from another plant. he was able to produce seeds that had 2 diff parents. |
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| Mendel cut away the pollen bearing male parts of the plant and dusted the plants flower with pollen from another plant. this process is called cross polination |
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| a process during sexual reproduction when the male and female reproductive cells join. fertilization produces a new cell. |
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| the seeds that are produced from self pollination inherit all of their characteristics from the single plant that bore them |
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| mendel had true breeding pea plants that, if allowed to self pollinate, would produce offspring identical to themselves |
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| a specific characteristic that varies from one individual to another |
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| parent generation. original pair (of plants in mendels case) |
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| first filial generation- offspring |
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| offspring of crosses between parents with different traits |
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| factors that determine traits and are passed from one generation to the next |
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| different forms of a gene |
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| states that some alleles are dominant and others are recessive. an organism with a dominant allele for a trait will always exhibit that trait and organisms with recessive alleles for traits will only exhibit the traits when that dominant allele is not present. |
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| the reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated, form the allele for tallness |
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| mendel suggested that the alleles for tallness and shortness in the F1 plants segregated from each other during the formation of the sex cells, also called gametes |
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| what does the F1 generation produce? |
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| when each F1 plant flowers and produces gametes, the two allele segregate from each other so that each gamete carries only a single copy of each gene. therefore, each F1 plant produces two types of gametes- those with the allele for tallness and those with the allele for shortness. |
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| the gene combinations that might result from a genetic cross can be determined by drawing a diagram called a punnett square. predict and compare the genetic variations that might result from a cross (capital letter= dominant allele, lowercase letter = recessive allele) |
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| organisms that have two identical alleles for a particular trait (true breeding) |
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organisms that have two different alleles for a particular trait (hybrid)
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| principle states that genes for different traits can segregate independently during the formation of gametes. independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms. |
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| summary of mendels principles |
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- genes are passed from parents to offspring
- if two or more alleles of the gene for a single trait exist, some forms of the gene may be dominant and others recessive
- in most sexually producing organisms, each adult has 2 copies of each gene. these genes are segregated from each other when gametes form
- alleles for different genes usually segregate independently of one another |
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| are all alleles dominant or recessive? |
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| no! many traits are controlled by multiple alleles or multiple genes |
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when one allele is not completely dominant over another. the heterozygous phenotype is between the 2 homozygous phenotypes.
red + white= pink (phenotype blends) |
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| when both alleles contribute to the phenotype. phenotype doesn't blend phenotypes like incomplete dominance but just shows both. |
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| genes that are controlled by more than two alleles are said to have multiple alleles (individual can't have more than 2 alleles but a population can) |
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| used fruit flies to advance study of genetics. decided mendels prinicples applied to all organisms. |
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| does interaction between genes and the environment help determine the characteristics of any organism? |
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| traits controlled by two or more genes |
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| mendels principles required two things: |
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1. each organism must inherit a single copy of every gene from its "parents"
2. when an organism produces its own gametes, those 2 sets of genes must be separated from each other so that each gamete contains just one set of genes |
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| the 2 sets of chromosomes are homologous, meaning that each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent |
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| a cell that contains both sets of homologous chromosomes (2N=8). contain 2 complete sets of chromosomes and 2 complete sets of genes. |
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| gametes of sexually reproducing organisms contain only a single set of chromosomes thus one set of genes (N=4) |
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| a process of reduction division in which the number of chromosomes per cell is cut in half thru the separation of homologous chromosomes in a diploid cell (includes meiosis I and II). by the end of meiosis II the diploid cell that entered meiosis has become 4 haploid cells unlike mitosis |
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| cells undergo a round of DNA replication, forming duplicate chromosomes |
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| each chromosome pairs with its corresponding homologous chromosome to form a tetrad. 4 chromatids in a tetrad. when homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in crossing over- produces new combos of alleles |
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| spindle fibers attach to the chromosomes |
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| the fibers pull the homologous chromosomes toward opposite ends of the cell |
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| telophase I and cytokenesis |
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| nuclear membranes form. cell separates into 2 which have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I |
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| no replication. each of the cell's chromosomes has 2 chromatids |
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| meiosis I results in 2 haploid daughter cells, each with half the number of chromosomes as the original cells |
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| the chromosomes line up in the center of the cell |
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| sister chromatids separate and move toward opposite ends of the cell |
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| telophase II and cytokenesis |
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| results in 4 haploid daughter cells |
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| in male animals meiosis= 4 equal sized gametes aka sperm. in females only one egg results (other 3 called polar bodies, arent involved) |
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| each chromosome is a group of linked genes so chromosomes, not genes, assort independently |
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| the farther apart 2 genes were, the more likely they were to be seperated by cross over in meiosis. created gene map that showed locations of each known gene on one of the Drosophila chromosomes. if 2 genes close together, recombination frequency between them is low cuz crossovers are rare. if far apart its high. |
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| mitosis results in production of 2 genetically identical diploid cells and meiosis produces four genetically different haploid cells |
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| can be used to study inheritance of human traits and to calculate the probability of certain traits appearing in the next generation |
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