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28 Cards in this Set
- Front
- Back
Meiosis |
a reduction division of the nucleus to form haploid gametes |
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When does DNA replication occur? |
In the S-phase of interphase before meiosis |
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Crossing over |
the exchange of DNA material between non-sister homologous chromatids |
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What does crossing over do? |
It produces new combinations of alleles on the chromosomes of haploid cells |
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Chromatid |
one of the replicated chromosomes still connected to the other by the centromere |
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How are bivalents formed? |
Homologous pairs (attached to their replications) associate with each other via synapsis during prophase I |
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Chiasma (pl. chiasmata) |
the X-shaped, microscopically visible region representing non-sister homologous chromatids that have exchanged genetic material through crossing over during meiosis |
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What must happen for crossing over to function correctly? |
Identical breaks must occur at exactly the same position in adjacent non-sister chromatids |
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When do homologous chromosomes separate? |
Meiosis I (Anaphase I) |
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When do sister chromatids separate |
Meiosis II (Anaphase II) |
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What does random orientation refer to? |
The behaviour of homologous chromosomes (meiosis I) or pairs of sister chromatids (meiosis II) |
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What does independent assortment refer to? |
The behaviour of alleles of unlinked genes as a result of gamete production |
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When are gene loci considered linked? |
When they are on the same chromosome |
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How do linked genes work? |
The linked genes are on the same chromosome and are close together, reducing the chance of them being separated in crossing over. This means they are more likely to be inherited together. |
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Mendel's Law of Independent Assortment |
The presence of an allele of one of the genes in the gamete has no influence over which allele of another gene is present. |
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Name an example of discrete variation |
Dry versus wet earwax |
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Name an example of continuous variation |
Human height |
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What are polygenic characteristics? |
Characterisitics influenced by multiple genes |
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Do phenotypes of polygenic characteristics tend to show continuous or discrete variation? |
Continuous |
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What is Drosophila? |
A genus of fruit fly |
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Why did Morgan use Drosophila in his experiments? |
They reproduced quickly - every two weeks |
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What did Morgan discover? |
His results showed non-Mendelian ratios, and from them he discovered linked genes |
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What can also influence polygenic traits? |
Environmental factors |
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Gene pool |
the total collection of different alleles in an interbreeding population OR all the genetic information present in the reproducing members of a population at a given time |
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Large gene pool |
Lots of variation |
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Small gene pool |
Little variation |
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Allele frequency |
a measure of the proportion of a specific variation of a gene in a population |
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What is allele frequency expressed as? |
A proportion or a percentage |