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NATS 1690 (39)


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York University
Natural Science
NATS 1690
Barbara Czaban

Gregor Mendel (1822-1884) - Law of segregation  Single trait inheritance - Law of independent Assortment  Two trait inheritance - Mendelian Genetics  Incomplete dominance  Multiple alleles  Codominance  Pleiotropic effects  Polygenic inheritance  Epistasis  Environmental contributions to gene expression  Gene linkage  Crossing over  Sex-linked inheritance - Variation  Mutations  Chromosomal aberrations  Gene duplication - Genetics problems Meiosis - 2 cell divisions - Result in 4 haploid daughter cells - Starts off diploid to end haploid* - 2n = 4 – first step- contains two homologous pairs of chromosomes - Second step - DNA replication – during interphase forms two copies of each chromosome, and the copies remain attached. - Third step – Meiosis 1 – homologous chromosomes separate into two haploid cells, each containing one member of each homologous pair - Fourth step - Meiosis 2 – Sister chromatids separate and four haploid daughter cells are formed that will develop into gametes. - Keeps chromosome number constant through generations  Haploid gametes – sperm and egg cells  Fertilization restores diploid number - Increases genetic variability in the population through genetic recombination  Crossing over  Independent assortment - Failure of chromosomes to separate creates cells with extra or missing chromosomes  Nondisjunction Meiosis 1 - Duplicated homologous pair of chromosomes align and separate  Result in 2 haploid daughter cells  2 chromatids/chromosomes - Reduction Division Meiosis 2 - Duplicated chromosomes align and separate  Result in 4 haploid daughter cells  1 chromatid/chromosomes Germ Cells – diploid (2n) - Found in gonads – ovary, testis, anther - Each cell has pair of homologous chromosomes - Formed by mitosis - Undergo meios
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