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Heredity and gene transfer
- Offspring acquire traits from parents.
- Inheritance of chromosomes with Genes.
- -Genes are segments of DNA that include specific nucleotide sequence (code for proteins/enzymes)
- Traits are the cumulative effect of proteins, meaning different genes, different traits.
- Copying of DNA required so genes can be passed to offspring
- -Egg and sperm transmit these genes (sexual reproduction)
- Offspring get genes from both parents. DNA is subdivided into chromosomes, except mitochondrial and chloroplast DNA.
- A single individual is the sole parent that passes its genes to offspring and produces clones (genetically identical)
- mitosis and asexual reproduction
- Single-cell organisms divide by copying DNA equally. Somatic products of multicellular organism (buds, fragmentation by mitotic divisions)
Sexual reproduction and meiosis
- Sexual reproduction results in greater variation and traits than asexual.
- Two parents create different gene combos which requires meiosis to create sperm and egg.
Have same length, centromere position
Homologous chromosomes have genes that control same characters except femails have homologous x and x (xx) males have one x and one y (xy) and only small parts of x and y are homologous.
- X and Y.
- Men: XY
- Women: XX
All other chromosomes besides X and Y.
Human Life cycle and meiosis
- Somatic cell chromosomes include 46 from two sets of 23. Diploid cells produced from mitosis
- Gamete cell chromosomes. Single set of 23. Haploid cells produced by meosis.
a reducing cell division. Halves the number of chromosomes. Occurs in ovaries and testes.
Homologous chromosomes are separated. 1 cell->2 cells
- Homologs attatched along length
- Produces tetrad- cluster of 4 chromatids
- Chromatids cross.
- Trade segments of DNA with eachother
- Metaphase 1: Homologs align at plate. Orientation of homologs is random. 2 posibilities for each maternal/paternal pair. 50/50 chance daughter cells get either.
- Possible number of combinations of maternal/paternal chromosomes in gametes 223 ≈ 8 x 106
- Sister chromatids are separated. 2 cells -> 4 cells
- Prophase II-spindle forms and attachs to chromosomes
- Metaphase II chromosomes align at metaphase plate
- Anaphase II- sister chromatids separated, move to poles
- Telophase II and cytokinesis- Nuclei form at opposite poles. Four haploid daughter cells produced.
Products of mitosis vs. meiosis
- Meiosis: chromosome number reduced in daughter cells
- Mitosis: chromosome number stays the same in daughter cells
- Meiosis: 4 daughter cells genetically different from parent and from eachother
- Mitosis: 2 daughter cells genetically identical
Unique events of meiosis
- Synapsis- duplicated chromosomes with homologs. Tetrad: four associated chromatids. Chiasmata: crossing of non-sister chromatids.
- Metaphase 1: Homologs align in pairs at metaphase plate.
- Anaphase 1: Each homolog moves to opposite pole (sister chromatids remain attached)
Sources of Genetic Variation
- Interdependent assortment of chromosomes: position of homologs at metaphase 1 is random.
- Crossing-over: Exchange of DNA occurs with chiasmata
- Random Fertilization: Fusion of one egg and one sperm (out of many). Each egg and sperm genetically different.
- Dependent on genetic variation. Individual variation required for population evolution.
- Individuals with favorable traits will survive (dependent on environment). Fittest survivors likely to create more offspring. (traits passed on)
Differential survival changes population. Population changes over time=Evolution.