1/23/2012 Genetics

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Mendel  postulated 3 important ideas from his results.

Dominate and recessive traits vs “blending theory”

Particulate theory of Inheritance (genes that govern traits as discrete units and remain unchanged) – because the white that was completely lost in the F1 generation reappeared in F2. 

Genetic determinants segregate from each other during the process that gives rise to gametes.



Mendelian Genetics Today

-Chromosomes contain short segments of DNA that function as units of heredity called genes.

-Most eukaryotes species have pairs of chromosomes (one from each parent)

-Each pair of chromosomes may have identical or different forms of a gene (alleles).  Eye color, skin pigment and many others have multiple alleles. (multiple genes acting together)

-Homozygous: individual with the same form (allele) of a gene on both chromosomes dominant(BB) or recessive (bb)

-Heterozygous: individual with different forms (allele) of a gene on each chromosome (Bb). Multiple alleles = write allele as exponent

-Genotype: genetic makeup or composition of an individual (BB, Bb, bb)

-Phenotype: observable trait of an individual (ex Brown hair)

-Two genotypes = BB, Bb

-One phenotype= brown hair


Law of Independent Assortment

“Two different genes will randomly assort their alleles during the formation of haploid reproductive cells.”  Ex. Crossing over, random paternal/maternal metaphase alignment


Punnett Square- Reginald Crundall Punnett (1875-1967)

-English Zoologist who helped establish a genetics program at Cambridge university

-Worked with William Bateson to incorporate statistics into Mendelian genetics (eg. Punnett square)

-Worked with mathematician G. H. Hardy inspiring what later became as the Hardy-Weinberg equation.

-Genophagy??- eventually will all become one dominant trait.  Blondes extinct?



Chapter 3 Reproduction of Chromosome Transmission

Basic Terminology

-Cytologist vs. Geneticist

-Cytologist- completely with chromosomes, bigger picture, disorders  having to do with chromosomes (forest)

-Geneticist- wants to look at the genes itself, nucleotide sequence, mutations, transposons  (trees)

-Prokaryotic vs. Eukaryotic

-Prokaryotic- chromosomes are circular, nucleoid

-Eukaryotes- linear chromosomes, nucleus

-Somatic vs. Gamete

-Somatic- 2n, body, diploid

-Gametes- n, sperm or egg, haploid

-Karyotype: photographic representation of the chromosomes found within actively dividing cell. In karyotype, the homologues are arranged by largest to smallest.


Homologues: nearly identical members of paired chromosomes. Mom and dad.

Locus (plural= loci)- physical location of a gene

-p represents short arm of chromosome

-q represents long arm of chromosome


Example: Sex determining region: Yp11.3

-Y- which chromosome

-p- short arm

-11.3- position on chromosome


Cell Division

Chromosomes must be:

-Copied (replicated)



Cell division is necessary in asexual reproduction & for muilticellularity (growth)


Binary Fission (Bacteria)

-Does not involve the fusion of gametes.

-Asexual Reproduction


Eukaryotic Cell Division

-Goal: Two daughter cells with the same number and types of chromosomes as mother cell.

-Walter Flemming(1843-1905)

-In 1882 first to describe chromosomes and mitosis. (looked like colored pieces of thread)

Posted on January 23, 2012, in Genetics. Bookmark the permalink. Leave a comment.

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