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Lec10notescomplete - Bio1A Lecture 10 Complete Notes...

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Bio1A Lecture 10 Complete Notes 1 Chapter 13: Meiosis and Sexual Life Cycles Hereditary Similarity and Variation E Living organisms are distinguished by their ability to reproduce their own kind E Genetics is the scientific study of heredity and variation E Heredity is the transmission of traits from one generation to the next E Variation shows that offspring differ in appearance from parents and siblings Inheritance of Genes E Genes are the units of heredity. Genes are segments of DNA E Each gene has a specific locus on a certain chromosome E One set of chromosomes is inherited from each parent E Reproductive cells called gametes (sperm and eggs) unite, passing genes to the next generation Comparison of Asexual and Sexual Reproduction E In asexual reproduction, one parent produces genetically identical offspring by mitosis E In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents E A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism E Fertilization and meiosis alternate in sexual life cycles Fig. 13-2 Sets of Chromosomes in Human Cells E Each human somatic cell (any cell other than a gamete) has 46 chromosomes arranged in pairs E A karyotype is an ordered display of the pairs of chromosomes from a cell E The two chromosomes in each pair are called homologous chromosomes , or homologues E Both chromosomes in a pair carry genes controlling the same inherited characteristics Fig. 13-3 Sex Chromosomes E The sex chromosomes are called X and Y E Human females have a homologous pair of X chromosomes (XX) E Human males have one X and one Y chromosome E The 22 pairs of chromosomes that do not determine sex are called autosomes Diploid cells E Each pair of homologous chromosomes includes one chromosome from each parent E The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father E The number of chromosomes in a single set is represented by n
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Bio1A Lecture 10 Complete Notes 2 E A cell with two sets is called diploid (2n) E For humans , the diploid number is 46 (2n = 46) Replicated chromosomes E In a cell in which DNA synthesis has occurred, each chromosome is replicated E Each replicated chromosome consists of two identical sister chromatids Fig. 13-4 Haploid cells E Gametes are haploid cells, containing only one set of chromosomes E For humans, the haploid number is 23 (n = 23) E Each set of 23 consists of 22 autosomes and a single sex chromosome E In an unfertilized egg ( ovum ), the sex chromosome is X E In a sperm cell, the sex chromosome may be either X or Y Behavior of Chromosome Sets in the Human Life Cycle E At sexual maturity, the ovaries and testes produce haploid gametes E Gametes are the only types of human cells produced by meiosis , rather than mitosis E Meiosis results in one set of chromosomes in each gamete E Fertilization
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