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The scientific study of heredity and variation
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| the transmission of traits from one generation to the next |
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| is demonstrated by the differences in appearance that offspring show from parents and siblings |
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| the units of heredity, and are made up of segments of DNA |
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| Genes are passed to teh next generation through these reproductive cells (sperm and eggs) |
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| The certain chromosomal location for each gene |
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It is packaged into chromosomes annd one set of chromosomes is inherited form each parent
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| One parent produces genetically identical offspring by mitosis |
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a group of genetically identical individuals from the same parent
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| Two parents give rise to offspring that have unique combinations of genes inherited from the two parents |
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the generation-to-generation sequence of stages in teh reproductive hsitory of an organism
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| (Any other cell than a gamete) have 23 pairs of chromosomes |
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| an ordered display of the pairs of chromosomes from a cell |
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| two chromosomes in each pair, or homologs |
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| The 22 pairs of chromosomes that do not determine sex |
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| (2n) Has two sets of chromosomes. For humans Diploid number is 46 (2n=46) |
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| A gamete (sperm or egg) contain a single set of chromosomes which is called a haploid |
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| The union of gametes (the sperm and the egg) |
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| The fertilized egg is called a zygote an dhas one set of chromosomes from each parent. Zygote produces somatic cells by mitosis and develops into an adult |
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| Gametes are the only types of human cells produced by meiosis, rather than mitosis. Meiosis results in one set of chromosomes in each gamete (4 haploids) |
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| Meiosis produces gametes, which undergo no further cell division before fertilization. Gametes are the only haploid cells in animals. Gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicelullar organism |
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| The Plants and some Algae Life Cycle |
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| Most fungi and some protists Life Cycle |
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| Only diploid stage is the single-celled zygote; there is no multicellular diploid stage. Zygote produces haploid cells by meiosis. Each haploid cell grows by mitosis into a haploid multicellular organism. Haploid adult produces gametes by mitosis |
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| The diploid organism which makes haploid spores by meiosis |
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| Haploids made by sporophytes by meiosis |
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| Each spore grows by mitosis into a haploid multicellular organism called a gametophyte |
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| The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis, each with only half as many chromosomes as the parent cell |
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| Homologues chromosomes separate and results in two haploid daughter cells with replicated chromosomes; It is called teh reductional division |
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| Sister chromatids separate and results in four haploid daughter cells with unreplicated chromosomes; it is called the equational division |
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| Chromosomes are replicated to form sister chromatids; Sister chromatids are genetically identical and joined at the centromere. The signle centrosome replicates, forming two chromosomes |
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Occupies more than 90% of the time required for meiosis.
Chromosomes begin to condense
Synapsis Occurs
Crossing over occurs
Each pair of chromosomes forms a tetrad
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| Homologous chromosomes loosely pair up, aligned gene by gene (only occurs in Prophase I) |
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| X-shaped regions where crossing over occured |
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| When each pair of chromosomes forms a group it is a group of four chromatids |
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Tetrads line up at the metaphase plate.
Microtubules from each poles are attached to teh kinetochore |
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Pairs of homologous chromosomes separate.
One chromosome moves toward each pole, guided by teh spindle apparatus. (sister chromatids remain attached at the centromere and move as one unit toward the pole) |
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| Each half of the cell has a haploid set of chromosomes; Each chromosome still consists of two sister chromatids. |
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Occurs simultaneously, forming two haploid daughter cells.
In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms
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| Spindle apparatus forms. Chromosomes (each still composed of two chromatids) move toward teh metaphase plate |
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| Sister chromatids are arranged at the metaphase plate. (no longer genetically identical because of crossing-over) |
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| Sister chromatids separate toward opposite poles |
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Chromosomes arrive at opposite poles.
Nuclei form, and the chromosomes begin decondensing |
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| Separates teh cytoplasm. End of meiosis, there are four daughter cells, each with a haploidset of unreplicated chromosomes |
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Mitosis conserves the number of chromosome
sets, producing cells that are genetically identical
to the parent cell Meiosis reduces the number of chromosomes sets
from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell |
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| Three events unique to Meiosis |
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- Synapsis and crossing over in prophase I:
Homologous chromosomes physically connect
and exchange genetic information
– At the metaphase plate, there are paired
homologous chromosomes (tetrads), instead of
individual replicated chromosomes
– At anaphase I, it is homologous chromosomes,
instead of sister chromatids, that separate |
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| Protein complexes that keep sister chromatids of a single chromosome to stay together through meiosis I. Broken up in Anaphase I and II |
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| Protects cohesins at the centromere at anaphase I, thus maintainig the attachment between sister chromatids and ensuring that they separate properly during meiosis II |
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| (chanes in an organism's DNA) are the original source of genetic diversity. Creates different versions of genes called alleles. Reshuffling of alleles during sexual reproduction produces genetic variation |
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| Three mechanisms contribute to genetic variation: |
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- Independent assortment of chromosomes
- Corssing Over
- Random fertilization |
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| Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the otehr pairs |
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| Possible cominations of chromosomes |
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Formula: 2^n
For humans (n=23), there are more than 8 million (2^23) possible combinations of chromosomes |
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| Produced by crossing over and they are combined genes inherited from each parent |
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Homologous portions of two nonsister chromatids trade places.
Combines DNA from two parents into a single chromosome
(only occurs in Prophase I) |
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Adds to genetic variationb ecause any sperm can fuse with any ovum (unfertilized egg).
The fusion of two gametes (each with 8.4 million possible chromosome combinations) produces a zygote with any of about 70 trillion diploid combinations |
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| Natural selection results in... |
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| the accumulation of genetic variations favored by the environment. Sexual reproduction contributes to this genetic variation in a population. |
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