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Lecture 19

BIOB11H3 Lecture Notes - Lecture 19: Mendelian Inheritance, Nuclear Membrane, Dna Replication

Biological Sciences
Course Code
Dan Riggs

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Lecture 19
Genetics and meiosis
People discovered that chromosomes exist inside a cell
There are homologous chromosomes in cells
o One from dad and one from mom = diploid
Crossing over occur and recombination and cell division generate unique chromosome
o This create diversity in the offspring
Took garden peas and looked at characters in those peas and observed some traits
appeared more frequently than other traits
He used plants with complete flowers
Heterozygote example
Mother donates a normal gene and the father donates a mutant gene
o The progeny will often exhibit normal activity
When a gene is ready to be expressed transcription and translation is expressed and you
make a protein and it’s active
But if it is recessive the mutation alters the genetic code and this results in the
production of an inactive protein or enzyme
o Although having one good copy is good enough in most cases
Mendel’s Laws
Law of segregation two alleles of gene segregate from one another into the gametes
Law of independent assortment different genes assort independently during gamete
o Two gene that segregate independently during gamete formation
Chromosomal basis of allele segregation
A heterozygote chromosome during meiosis the DNA will replicate so we get four
They swap segments during meiosis
In meiosis, there are two nuclear divisions that will ultimately turn the cell into four
haploid cells
The two alleles of a gene segregate at meiosis and half the progeny gametes contain
each allele
Chromosomal basis of independent assortment
Original organisms were heterozygous for both genes
Replication takes place and then once nuclear membrane breaks down depending on
which way the chromosomes are oriented
Left four haploid cells and two of them carry a dominant r and recessive y and 2 carry
a recessive r and a dominant y
o Depending on how the chromosomes were assorted from random orientation of
chromosome pairs you can get completely different haploids from the same
exact cells
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