LECTURE                                                            GENETICS

In this lecture you will learn about:

HOMOLOGOUS PAIRS
One chromosome is derived from the father and the other from the mother. 

Humans have 22 homologous pairs and 1 non-homologous pair, the XY set. 

ALLELES -  an alternative form of a gene that is located at a specific position on a specific chromosome (LOCUS).

These variations between the same gene are called ALLELES, and the term used to describe alternate forms of the same gene is called ALLELIC VARIATION. Alleles occur when there is a difference in the DNA sequence between pairs of genes. One example is sickle cell anemia which is caused by a change of only one BASE PAIR. There may be 2, 3 or more alleles for any gene. Strictly speaking, alleles refer to alternate forms of genes, but it is used when referring to alternate forms of non-gene DNA.

MULTIPLE ALLELES EXIST FOR MANY TRAITS
GO HERE TO LEARN ABOUT THE ALLELES FOR EYE COLOR

PUNNETT SQUARE
GENOTYPE VS PHENOTYPE, 3/4 phenotype is purple, 1/4 pheno is white, the genotype is 1/4, ½, 1/4
PP x Pp  = work out
-- long (S, dominant) or short (s, recessive) stems.
PPSS X ppss
F1 = all purple flowers/long stems
-- F2  purple-long (probability 9/16), white-long (probability 3/16), purple-short (probability 3/16), or white--short (probability 1/16).
when did Mendel do this important research?
Mendels results are "perfect" meaning he fudged the data.. fortunately, he got it right
 
 
 
GENE INTERACTIONS
DOMINANT
-- one ALLELE dominates
-- brown eyes are dominant over blue eyes

RECESSIVE
phenotype doesnt show up if the dominant gene is present

CODOMINANCE
  both alleles contribute to the phenotype of the heterozygote

------ example is ABO blood group

INCOMPLETE DOMINANCE
--  heterozygous condition is seen as an intermediate phenotype between the two parental phenotypes

-- example, red flower x white flower =  pink


 
RANDOM ASSORTMENT aka INDEPENDENT ASSORTMENT

 
 
 

THIS ONLY OCCURS DURING MEIOSIS in the eggs and sperm

It only occurs when there are multiply chromosomes, not in bacteria. 

 

When there ISNT random assortment certain traits will show up repeatedly in tandem.  Often lethal traits are linked and seen because they are so obvious.  And very often they are sex linked because there is no corresponding part on the X so recessive genes are seen. 
 

LINKAGES BETWEEN GENES  leads to theorizing about crossing over.  The genetics of ear wax

White "Persian" blue eyed male cats have a higher incident of deafness. Deafness seems to be linked to the male chromosome, white fur and blue eyes
Sex linked genes - hemophilia

Inbreeding

GENE TESTING

SAMPLE OF REVIEW QUESTIONS:
What are ALLELES?
What is the difference between genotype and phenotype.
Explain how a single point mutation can cause disease.
What is the principle of independent assortment?  Give an example.  Draw an example.
How many pairs of somatic chromosomes do humans have? How many pairs of sex chromosomes?
Name a couple sex linked characteristics or diseases.  Why do these happen?
Describe how a sex linked disease brought down the monarchy of Russia.
What does dominance, recessive, codominance and incomplete dominance mean and give an example of each.
ABO blood group is an example of what kind of gene interaction.
Coat color in lab retrievers is an example of what kind of gene interaction.