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27 Cards in this Set
- Front
- Back
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why do cells divide |
-to multiply -to replace worn out cells, to grow organisms bigger |
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what is cell division called and what happens |
mitosis:
-parent cell creates an exact replica of itself, genetically identical, two daughter cells -it is a type of asexual reproduction |
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what is a chromosome |
one very long DNA molecule |
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how do cells divide |
parent cell replicates its chromosomes, producing 2 sister chromatids
each daughter cell cell receives one copy of the chromosomes (1 chromatid)
the number of chromosomes per cell remains the same |
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how do cells know when to divide |
cell division is density dependent
normal cells can sense that they are missing neighbors
will divide and then stop once the space is filled |
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what do cancerous cells do |
they don't stop dividing
if the immune system doesn't stop them, they form a tumor |
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types of tumors |
benign- stays in the same place
malignant- can spread into neighboring tissue, people with malignant tumors have cancer |
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what type of cells are the parent and daughter cells (diploid or haploid) |
diploid (double set of chromosomes) |
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what are the stages of mitosis |
interphase, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis |
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what is a human body cell called |
a somatic cell, it has 46 chromosomes
each chromosome has a twin, one from mom and one from dad called a homologous pair
each chromosome in the pair has the same genes |
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what are genes |
specific nucleotide sequence of DNA that determines which AA are produced
genes can have different alleles (dif. versions of genes) |
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which chromosomes don't have homologous pairs? |
sex chromosomes (X and Y)
females: XX males: XY |
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what does diploid mean |
-organisms have pairs of homologous chromosomes -two chromosome sets, one from mom and one from dad -the total number of chromosomes is the diploid number(2n) -humans: 2n=46
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what cells in our bodies are not diploid |
gametes: egg and sperm cells, each have 22 autosomes plus an X or a Y sex chromosome
they are haploid because they have a single chromosome set |
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human life cycle |
haploid sperm from father fuses with haploid egg from mother, fertilization
creates a zygote (diploid)
grows by mitosis and development to a diploid adult |
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how are haploid gametes made? |
meiosis
meiosis 1: diploid to haploid meiosis 2: chromatids separate |
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what is the purpose of meiosis |
to produce gametes used in sexual reproduction |
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why are offspring resulting from sexual reproduction highly variable |
3 mechanisms that lead to genetic variation:
1)independent assortment 2)random fertilization 3)crossing over
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what happens in independent assortment |
organisms produce all four combinations with equal probability
the total number of combinations of chromosomes that meiosis can produce is 2n, n is the haploid number |
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what happens in random fertilization |
humans: a random sperm fuses with a random egg
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what is crossing over |
it produces recombinant chromosomes which combine DNA inherited from each parent -occurs in prophase 1 of meiosis 2 -homologous portions of non- sister chromosomes trade places -it combines DNA from 2 parents into a single chromosome |
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what is the same and what is different between prophase in mitosis and prophase 1 of meiosis 1? |
same: chromosomes are duplicated (2 sister chromatids)
different: in prophase of mitosis each duplicated chromosome remains separate; in prophase 1 of meiosis 1 the chromosomes are associated with their homologs |
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what is the same and what is different in metaphase of mitosis metaphase 1 of meiosis 1 |
same: chromosomes align at the metaphase plate
different: metaphase of mitosis chromosomes align separately; in metaphase 1 of meiosis 1 the chromosomes align in tetrads (with their homologous pairs) |
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what is different about the end products of meiosis and mitosis |
mitosis: two diploid daughter cells
meiosis: four haploid daughter cells |
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what is nondisjunction |
when the members of a chromosome pair fail to separate -one gamete has 2 copies -other gamete has no copies |
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what is down syndrome |
an abnormal number of chromosomes usually means the affected embryo will miscarry
exception: trisomy 21 (three copies of chromosome 21) |
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what are some characteristics of down syndrome |
-shorter lifespan, more likely to get Alzheimer's
-researchers are developing a drug to prevent Alzheimer's and testing it on people with Down syndrome |
