chapter 10a
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Chapter 10A. Sexual Reproduction . In the dvlpt of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each w/ a different structure & corresponding function. The fertilized egg gives rise to a large # of cells through cell division - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 10ASexual Reproduction
In the dvlpt of most multicellular
organisms, a single cell (fertilized egg) gives rise to many different types of cells, each w/ a different structure & corresponding function
The fertilized egg gives rise to a large # of cells through cell division
As the cells inc. in # through this division, they also become specialized in structure & function through differentiation The various types of cells then arrange into
tissues which are organized into organs, & finally organ systems
Nearly all of the cells of a multicellular organism have exactly the same chromosomes & DNA During differentiation, only a specific segment
of the DNA is activated The segment activated deter. the function &
structure of the cell So all cells initially have the potential to
become any type of cell Once a cell differentiates, the process can’t be
reversed
Stem Cells are unspecialized cells that continually reproduce &, under the appropriate conditions, can differentiate into 1 or more types of specialized cells Embryonic Stem Cells – have this ability Adult Stem Cells are only found in certain
areas such as bone marrow**Scientists have discovered under the right
lab culture conditions, embryonic & adult, can differentiate
Chromosomes: It is a structure in the nucleus of a cell
consisting of 1 long thread of DNA that is tightly coiled
Types of Reproduction:1. Asexual reproduction – when a cell just divides
to form 2 identical daughter cells – only 1 parent In eukaryotic cells, it requires mitosis
2. Sexual reproduction – the union of a sperm and egg to form an organism that has a combination of DNA from both parents
Since the offspring produced have cells that are diploid (containing 2 sets of chromosomes – 1 from each parent), the gametes (sex cells) must be haploid (containing only 1 of each type of chromosome)
Requires meiosis
Meiosis: Purpose – to reduce the # of
chromosomes Occurs in 2 steps:
Meiosis I – Chromosome pairs replicate Results in 2 haploid daughter cells w/
duplicated chromosomes diff. from the sets in the original diploid cell
Meiosis II – The haploid daughter cells from Meiosis I divide Results in 4 haploid daughter cells called
gametes (sex cells - egg & sperm) w/ undoubled chromosomes
Meiosis I: Begins after Interphase in which cells (1)
inc. in size, (2) produce RNA, (3) synthesize proteins, & (4) replicate DNA
Meiosis I cont… Prophase I –
Nuclear membrane breaks down Centrioles separate from each other & take
up positions on the opposite sides of the nucleus
Spindle fibers are produced Chromosomes pair up & become visible as
a cluster of 4 chromatids called a tetrad
Meiosis I cont… A homologous chromosome pair consists
of 2 chromosomes containing the same type of genes One from the male & one from the female
Each chromosome consists of 2 sister chromatids attached @ the centromere
Because the homologous chromosome pairs are close to each other, crossing over can occur (the exchange of chromosome genetic material btw pairs)
Meiosis I cont… Metaphase I:
The chromosomes are attached to the spindle fiber at the centromere& are pulled into the midline (or equator) of the cell in pairs
Meiosis I cont… Anaphase I:
The chromosome pairs separate, one chromosome to each side of the cell Each daughter cell will receive only 1
chromosome from each homologous chromosome pair
Sister chromatids remain attached to each other
Meiosis I cont… Telophase I & Cytokinesis:
Chromosomes gather @ the poles, nuclear membrane may form & the cytoplasm divides
***Each of the 2 daughter cells from meiosis I contains only 1 chromsome (consisting of 2 chromatids) from each parental pair
***Each daughter cell from meiosis I proceeds to meiosis II
Meiosis II Prophase II:
Spindle fibers form in each of the daughter cells from meiosis I & attaches to the centromeres of the sister chromatids
The chromosomes progress towards the midline of each cell
The nuclear membrane breaks down
Meiosis II cont… Metaphase II:
Chromosomes, made up of 2 sister chromatids, line up across the center of the cell
Spindle fibers from opposite poles of the cell attach to 1 of each pair of chromatids
Meiosis II cont… Anaphase II:
The chromosomes separate so that 1 chromatid from each chromosome goes to each pole
Meiosis II cont… Telophase II & Cytokinesis:
Nuclear membrane forms around each set of chromosomes
The resulting daughter cells are haploid, containing 1 single chromosome from each pair of chromatids Either from father or mother contributor