Chapter 12- Meiosis
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Chapter 12- Meiosis
What is fertilization?
when a sperm and egg unite
What is a karyotype?
the number of types of chromosomes present.
what is a homologous chromosome?
Chromosomes of the same type
What is a gene?
a section of DNA that influences hereditary traits
What does it mean to be haploid?
one of each type of chromosome
What does it mean to be diploid?
two of each type of chromosome
What does it me to be polyploid?
3 or more versions of a chromosome
What happens before meiosis occurs (Interphase)?
each chromosome is diploid parent cell is replicated forming sister chromatids
In animals, daughter cells become what?
2 haploid gametes fuse during fertilization to become what?
5 phases of meiosis 1
What happens in early prophase 1?
nuclear envelope breaks up
homologous pairs synapse forming a tetrad
What happens in late prophase 1:
-non sister chromatids begin to seperate
-exchange or crossing over occurs when chiasmata are formed during this stage
What happens during metaphase 1:
pairs of homologs line up at metaphase plate
What happens in Anaphase 1?
paired homologs seperate and begin to migrate to opposite ends
What happens in Telophase 1/Cytokinesis?
homologs finish migrating to opposite poles then cytokinesis occurs
end result of meiosis 1?
one chromosome of each homologous pair is distributed to a different cell
What happens during prophase 2?
Spindle apparatus forms and attaches to chromosomes?
What happens during metaphase 2?
replicated chromosomes consisting of 2 sister chromatids line up at metaphase plate
What happens during Anaphase 2?
sister chromatids seperate and begin moving to different poles
What happens during telophase 2/Cytokinesis?
Chromosomes finish moving to opposite poles and then the cell divides
End result of meiosis 2?
4 haploid cells form from one dipolid cell
what is the key difference between mitosis and meiosis?
homologs pair in meiosis, not in mitosis
What happens during the synape of prophase 1?
2 pairs of sister chromatids are held together by a network of proteins called synaptonemal complex
What does crossing swap?
Swaps segment of paternal and maternal chromosomes
What is a gene?
provides instructions for specifying what particular trait might be in an indivdual
how many genes are there on each chromosome?
hundreds or thousands
How many different combinations of chromosomes can humans produce?
crossing over is a form of what?
crossing over produces what?
new combinations of alleles on the same chromosome
What is outcrossing?
gametes from different individuals combine to form offspring
how does outcrossing increase genetic diversity?
because chromosomes of 2 different parents are combined
What is self-fertilization?
when gametes from the same individual combine
What does John Maynord Smith's mathematical model predict?
asexually reproducing organisms should reproduce faster and outcompete similar organisms in sexual reproduction
What is the purifying selection hypothesis?
Natural selection occurs against damaged alleles
What does the Changing Environment Hypothesis state?
Offspring that are different from their parent are more likely to survive through environmental changes
What is nondisjunction?
failure of homologous chromosomes to seperate
what is a trisomy?
2 gametes having an extra copy of a chromosome
what is monosomy?
2 gametes lacking a chromosome
what are aneuploid zygotes?
those with too few or too many chromosomes
Where are the most cases of aneuploidy chromosomes found?
sex chromosomes and chromosome 21