Genetics
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Genetics. AP Biology. Mendel’s Laws. Law of Segregation: Diploid cells have pairs of genes, on pairs of homologous chromosomes. The two genes of each pair are separated from each other during meiosis, so they end up in different gametes. Nondisjunction. Is a mistake

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Genetics

Genetics

AP Biology


Mendel s laws
Mendel’s Laws

  • Law of Segregation: Diploid cells have pairs of genes, on pairs of homologous chromosomes. The two genes of each pair are separated from each other during meiosis, so they end up in different gametes.


Nondisjunction
Nondisjunction

  • Is a mistake

  • Both sets of one chromosome go to the same gamete

  • Double one chromosome; missing another one



Nondisjunction2
Nondisjunction

  • Usually fatal to the gamete or zygote

  • Best cases: if it occurs in the sex chromosomes. XXY, XYY, XO, XXX can survive

  • Best case for somatic: Trisomy 21, which is Down Syndrome


Mendel s 2 nd law
Mendel’s 2nd Law

  • Law of Independent Assortment: during meiosis, each pair of homologous chromosomes (and their genes) have been separated and moved into gametes INDEPENDENTLY of other pairs.



The two laws together mean
The two laws together mean…

  • Each chromosome pair must separate during meiosis (so each gamete gets one of each type of chromosome)

  • This separation happens without being influenced by any other pairs



Crossing over
Crossing over

  • Occurs in prophase of both mitosis and meiosis

  • Why do we only see its effects in Meiosis I?


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