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Bio 100 - Exam 2


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Without Sex by single-celled or mulitcellular organisms. the offspring are genetic replicas of the parent
Asexual Reproduction
With Sex by multicellualar organismas. requires fertilizatino of an egg by a sperm
Sexual Reproduction
What makes up chromosomes?
DNA & Histone Proteins
the DNA and protein molecul;es that make up a chromosome
The region where the two chromatids are joined together
the two copies of a chromosome that contain identical genes
Sister Chromatids
Microtubules that begin to appear during prophase
Spindle Fibers
the process in which the cytoplasm splits after a clevage furrow and two daughter cells form
The maternal and paternal chromosome pair
the 2 homologous chromosomes that cross over and line up during prophase
the diploid result of fertilzation
fusion of gametes
these are haploid (1n), produced in germ tissue (gonads) via meiosis
(2n) humans have 46 chromosomes (23 homologous pairs) body cells
(1n) sperm and egg cells
tetrads separate and chromosomes move to seperate poles during anaphase
a standardized arrangement of a cell showing the pairs within them
a non dividing phase, chromosomes appear as chromatin, chromosome duplication occurs
chromatin become visible short chromosomes, centrosomes/centrioles begin moving towards opposite Ends of the nucleus, spindle fibers(microtubules) begin to appear, nuclear envelope disappears
chromosomes align along equator of spindle apparatus, spindle fibers attached to the centromere of each Chromosome
centromeres of each chromosome divide and chromatids now separate, sister chromatids become Daughter chromosomes, spindle fibers begin to move daughter chromosomes towards opposite poles
nuclear envelope reappears around two new daughter nuclei, chromosomes revert to the diffuse Chromatin condition, cytokinesis occurs
What is the end product of mitosis?
2 haploid daughter cells identical to mother and to each other, 1 division
What is the end productin of meiosis?
4 haploid daughter cells, 2 divisions, it has gametes
What are three types of asexual reproduction?
Binary fission- ex. amoebas
Budding- ex. Yeast
Vegetative reproduction- ex. Strawberries, Bermuda grass, ferns
chromosomes line up with homologs to form tetrads, crossing over occurs between chromatids Of homologous chromosomes, crossing over means chromosomes are different from parent cell’s
Prophase I
tetrads align along equator of the cell, spindle fibers attached to centromeres of chromosomes
Metaphase I
disjunction- tetrads separate and chromosomes move to opposite poles, here is where the Number of chromosomes are reduced
Anaphase I
2 haploid nuclei undergo mitosis to produce 4 haploid daughter cells
Meiosis II
occurs in cells of the ovary- oocytes, 4 haploid daughter cell produced, 1 daughter cell develops in a Gamete called ovum (egg), and other 3 become small nonfunctional polar bodies
occurs in testes cells- spermatocytes, 4 haploid daughter cells produces, daughter cells develop into mobile gametes called spermatozoa
What is the importance of meiosis?
keeps diploid number constant b/c of haploid gametes -a source of genetic variation
zygote has an additional chromosome for a homologous pair (2n+1)
zygote is missing 1 chromosome of a homologous pair (2n-1)
What process produces a trisomy or a monosomy and what is it?
Non-disjunction: abnormal separation of chromosomes during meiosis, occurs during anaphase I or II
Trisomy 21, extra 21st chromosome, most common serious birth defect in US (1 in 700), related to age of Mother, characteristics- mental retardation, heart defects leukemia, short stature, etc.
Down's Syndrome

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