Understanding Meiosis and the Sexual Life Cycle in Heredity
This chapter introduces the fundamental concepts of heredity and genetics, emphasizing the differences between asexual and sexual reproduction. It explores how genes, which are segments of DNA, play a critical role in passing traits from parents to offspring. Key concepts include the structure of chromosomes, the process of meiosis, and the mechanisms contributing to genetic variation in sexual reproduction. The chapter also covers the human life cycle, gamete formation, and the results of meiosis, which generates genetic diversity essential for evolution.
Understanding Meiosis and the Sexual Life Cycle in Heredity
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Presentation Transcript
Chapter 13 notes Meiosis and sexual life cycle
An Introduction to Heredity Heredity: the transition of traits from one generation to the next Along w/ similarities, there is also variation- offspring differ somewhat in appearance from parents to offspring Genetics: the study of heredity and hereditary variation
An Introduction to Heredity Parents pass information to offspring through coded hereditary units called genes. - 30 to 40 thousand genes in humans - genes are segments of DNA
Concept 13.1 Two types of reproduction: Asexual reproduction: single parent passes copies of all its genes to offspring; “like begets like.” Sexual reproduction: two parents give rise to offspring; results in greater variation
Concept 13.2 Life cycle: generation-to-generation sequence of stages in the reproductive history of an organism The human life cycle - each somatic cell has 46 chromosomes (23 pair); 2 copies of each pair are called homologous chromosomes
Concept 13.2 - chromosomes can be displayed through a karyotype - pairs 1-22 are called autosomes - pair 23 are called sex chromosomes - XX = female; XY = male - we inherit one chromosome of each pair from each parent
Concept 13.2 - gametes, or sex cells, contain 22 autosomes and 1 sex chromosome; a cell with a single chromosome set is called a haploid cell. - haploid cells are abbreviated 1n (n = 23) - the combining of gametes forms a zygote; becomes a diploid cell (2n)
Concept 13.2 - The only cells of the human body not produced by mitosis are gametes - this process is a form of cellular division called meiosis; meiosis reduces the chromosome number in half
Concept 13.2 The variety of sexual life cycles Animal cells - after meiosis, the gametes undergoes no division before fertilization Fungi - after meiosis, mitosis occurs and produces a 1n multicellular organism; forms 1n gametes that then fertilize
Concept 13.2 Plants (alternation of generations) - has both diploid (sporophyte) and haploid (gametophyte) multicellular stages;
Concept 13.3 Meiosis, like mitosis, is preceded by the replication of chromosomes; however, the single replication is followed by 2 consecutive divisions (meiosis I and meiosis II)
Concept 13.3 Meiosis I - during prophase I, chromosomes pair up in synapsis; 4 chromatids form a tetrad - during metaphase I, homologous pairs line up on equator - during anaphase I, chromosomes, not chromatids, separate to poles
Concept 13.3 Meiosis II - goes through the same steps as meiosis I, but does not replicate DNA Meiosis outcome is 4 1n gametes from a single cell
Concept 13.4 3 mechanisms contribute to the genetic variation arising from sexual reproduction Independent assortment of chromosomes -each homologous pair of chromosomes is positioned independently of the others; variation is 223 or about 8 million
Concept 13.4 Crossing over - when chromosomes line up along the equator, parts of chromatids can combine genes from parents Random fertilization - even w/out considering crossing over, any two parents will produce a zygote with any of 70 trillion combination (223 x 223)
