Monday, March 24th, 2008

Chapter 14:

 

Homework problems posted on RAM CT under "SECTION 3"

Will post the answers on friday.

On friday will also post the practice exam.

Next Friday we'll have the next exam - Friday the 4th.

 

GENETICS!

 

Genetics: the study of heredity and variation.

Heredity: the transfer of properties from one generation to the next.

(genetics study how these properties are transfered, but heredity is the transfer in itself.)

(what we study is called traits.... we don't really separate traits from Characters but the book does... equivalent in this class)

Traits(ie charcter): - a heritable feature that varies among individuals.

Genes: a segment of DNA that codes for a specific trait. (usually a single protein) Genes are located on chromosomes.

Locus: the position or location of a genes on a chromosome.

Alleles - variants of the same gene.

 

we are diploid therefore at every locus every gene site we have two alleles - one from mother other from father. If two are the same, . The two alleles are...

Homozygous = the two alleles for the same gene are identical in an organism.

Homozygote - singular locus

 

Heterozygous = the two alleles for the same gene are different.

Heterozygote - singular locus

 

Phenotype: the physical (or physiological) traits that are expressed in an organism. -- blonde hair, (the way you look)

Genotype: the genetic make up of an organism. Usually Genotype determines phenotype.

 

 

AREAS OF GENETICS

1. Classical genetics - Mendel, chronosomes, (Cytogenetics)
2. Molecular genetics - DNA sequence & the related areas. (Studying proteins, as well as sequences. coding, etc)
3. Population (Evolutionary) genetics.

Gregor Mendel - 1850's to 1860's

true breeding parent - they always always ALWAYS give the same trait -- homozygous at that level.
IE. Purple + White = ALWAYS ALWAYS ALWAYS PURPLE.

 

Prarental generation = PGeneration = true breeding unless specifically state "you're parents are different" assume this.

P = purple allele = Dominant

p = white allele = recessive

Always keep the same letter because we could have more traits and it gets confusing.

 

PP x pp =

P     p  --> eggs and sperm

/    /

Pp = heterozygous    // F1 = 1st filial generation (hybrid)

 

Punnet square

Everytime we see the recessive phenotype we know its homozygous.

 

MENDEL'S MODEL

 

1. Alternative versions of a gene account for the variation in inherited traits = different alleles.
2. For each trait, an organism inherits two alleles - one from each parent.
3. If the two alleles differ, then the dominant allele determines the organisms appearance or phenotype; the other allele has no noticable effect on the phenotype.

4. Law of Segregation: two alleles for a heritable charcter separate (segregate) during gamete formation & end up in different gametes. (anaphase I of meiosis)

    

Model's done an excellent job in standing the test of time.

He looked at a variety of charcters.

 

• Why are recessive alleles recessive?

Usually recessive alleles are notfunctional.

 

Another cross: Assume black & white mice.

we get all black mice when crossed.

Therefore black is dominant.

• assign big B's for Dominant (black) and little b's for white.

 

Monohybrid Cross = mono = one trait. Hybrid = Homozygous.

Test Cross = how to find out if an organism with the dominant penotype is homozygous or heterozygous.

• we could cross it with the homozygous recessive?

Dihybrid Cross - more than one trait.

2 genes are on different chromosomes (non homologous chromosomes)

Law of independent assortment - Each pair of alleles segregates independently of every other pair of alleles during gamete formation.

(Happening during Meiosis I)