Genetics

Campbell and Reece, Chapter 14

1865 Mendel TRANSPARENCY Fig. 14.1 - pea plants - purple vs. white flowers
P=parental, F1 first generation (filial)
TRANSPARENCY (Fig. 14.3) Since cells are diploid, there are two copies (alleles) at each locus, and they can be the same or different.
true-breeding = homozygous
hybrids = heterozygous
purple is dominant, white is recessive
TRANSPARENCY (Fig. 14.2) F2 has 3/1 ratio
units = gene separate Mendel's first law (segregation)

TRANSPARENCY (Fig. 14.4) shows haploid gametes (ova and sperm) and genotypes and phenotypes

Mutations - variation and evolution (many are bad also recessive, many are neutral, some might be good under the right environmental circumstances. They can be caused by ionizing radiation or chemicals (mutagens which are also carcinogens).

Mendel (knew about Darwin but Darwin did not know about Mendel)
"...this seems to be the one correct way of finally reaching the solution to a question whose significance for the evolutionary history of organic forms must not be underestimated."

Mendel's Second Law TRANSPARENCY (Fig. 14.7) The law of independent assortment
green-yellow, round-wrinkled
dihybrid cross (two genes each on a separate chromosome, two alleles each) fill in "Punnett square"
Independent assortment does not apply to linked genes. i.e. genes that are on the same chromosome.

Here is a picture (Fig. 14.9) TRANSPARENCY showing incomplete dominance - red vs. white snapdragon cross gives pink.

wild type (with respect to a given gene) indicated by + or capital letter
The example above is simple - usually there are many alleles, many genes, and no simple dominant and recessive relationship.

Blood groups TRANSPARENCY (Fig. 14.10)
A=B (co-dominant), O is recessive -- 3 alleles

genotypes...............phenotype.........antigens..........antibodies
IA IA or IA i...........A......................A.....................anti-B
IB IB or IB i...........B......................B.....................anti-A
IA IB......................AB....................A and B..........anti neither
ii ............................O......................none................anti both

O universal donor, AB universal recipient

Question: What is unusual about this situation? Answer: There are already antibodies even though there was no previous exposure to antigens.

Since I do research with Drosophila, and maintain a small genetic stock collection, I have mentored science projects at Gateway Middle School, and there are a number of useful figures. Drosophila are convenient because it takes only about 2 weeks for a new generation. If vials are cleared of adults, then any femal flies emerging in the next 6 hr will be virgin, and specific crosses can be set up at the experimenter's will.

Relevant to this lecture, as well as the next two outlines, there are two faculty members in biology who are especially interested in genetics and who teach our genetics course, Dr. Coulter and Dr. Tsubota.


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