UCLA Genetics

Genome

total or an organism’s genetic information

 gene of model org

• Eukaryotes: Homo sapiens, M.musculus (bc quick reproduction when we cross one genotype to another to examine offspring with altered gene), D. melanogaster (developmental genetics, veins, stripes on abdomen, bristles on body; different gene mutations lead to Δ phenotype), A. thaliana, S. cerevisiae “brewer’s yeast”, (Euk, linear chromosome, single celled org, how cell operates with nucleus, fast repro)

• Prokaryote: E.coli (circular chromosome, practical in lab)

• More complex orgaism have higher genome size, but lower gene density (# of genes in an area is lower than in bacteria) → bacteria 1 chromosome, yeast 16, fruit fly 4 chromo

Chromosome:

genetic structures consisting of DNA

Genes:

basic unit of genetic information; often coding for a protein

Nucleotide:

• a subunit of DNA (or RNA) ex. A,T,C/U,G

Proteins:

polymers which carry out most biological functions

Amino acids:

building block of proteins (20 main amino acids, but can be infinite)

Polypeptide / proteins:

• chain of amino acid joined by peptide bonds

  • (Proteins often dont act as we want, often form concert complex structure ex. Hemoglobin alpha form hemoglobin complex)

  • (conserved  = similar protein sequence —> sequence is crucial for protein function)

Forward Genetics

• start with phenotype, have a random change, infer the gene, GOAL = identify gene

(Mutation methods: x-ray radiation, UV radiation, transposons, base analogs)

Reverse genetics

Direct mutagenies of specific gene —> see change in phenotype —> used to understand gene function

Mutation methods: homoglogus recombination, Gene knockouts, Directed viral transformations, CRISPR

4 types of inherited traits

• Continuous (contains decimals): height, cropy yields

• Discrete (one or the other):  presence of Rh factor, Animal coat color (black or light brown coat)

• Complex (affected by variety of factors): disease susceptiblity, longetivity, height 

• Simple: either have traits or not. —> seed shape, free earlobes, dimples or no dimple

Incomplete dominance

heterezygotes show an intermediate blended phenotype & 1:2:1 ratio, effect of dosage

Codominance

offspring show both phenotypes, gene no effect on each other; 1:2:1 ratio

Pleiotropy:

• single gene may determine multiple traits   

  • (Ex. Marfan syndrome —> unusually tall, thin fingers, heart problems)

Epistatic gene

interaction between allele of diff genes only. when the gene masks the effects of the other gene Ex. black fur color encoded by gene A but gene B states that the color is masked.

(Recessive epistatis = dominant alleve of 2 gene have same pathway function, result = common outcome ex. B & E = black hair, ee gene determines yellow labrador dogs

dominant epistatis = dominante allee of 2 gene have opposite functions. (A-) det squash color yellow, chicken feather as white —> gene B prevent pigmentation generated by gene A

reciprocal / Redundant allele = same result ex. AA BB both code for long broad maize leaf)

 Monomorphic vs. polymorphic

•  Monomorphic: one wild type allele

• Polymorphic: multiple wild type alleles    ex. Human hair color

recessive lethal

• Homozygous/recessive lethal: an allele which results in the death of an organism when homozygous

  • Embryonic lethal = that individual will never be born or hatched

Complementary gene action

• Two genes are necessary for the wild type phenotype to be seen.

Epistasis:

Two genes affecting the same phenotype, where one may mask the phenotype of the other.

Heterogeneous trait:

•  A trait in which many different mutant genes may give rise to the same mutant phenotype.

Complementation test:

• determining if two mutations are in the same gene or different genes.

Penetrance:

• What percentage of those with a certain genotype will show the associated phenotype.

Expressivity:

• The amount of variation of intensity of a phenotype in a certain genotype

Parallel pathways:

: independent pathways taken by a gene, protein but have same result

Complementary gene action:

2 parents with the same recessive mutant phenotype breed —> create wildtype offspring b/c mutant is on different gene, so they exchange and rescue each other

Ex. aaBB x AAbb

Mutation complement = reside on different gene

Fail to complement = on same gene

Redundant genes

• gene duplications thatleadto multiple copies of same gene, if all retain theirfunction then they are redundant genes. Redundant gene requires all copies to be recessive allele for trait to be expressed (may express incomplet dominance)

Heterogenous trait

trait where many diff mutant gene can give rise to same mutant phenotype (seen in complementation yeast amino acid test)

Chi-square test for goodness of fit

 det if two genes are linked by comparing progeny of exp. Class and then the expected null of them being unlinked genes.

(Degree of freedom = # of diff classes - 1

p < 0.05 = rejectnull hypoth)

(PD = NPD ---> means assort independently  

• linked gene PD >>> NPDs 

• two gene far apart on single chromosome PDs = NPDs)

Homologous chromosome vs. nonhomologous

Homologous chromosome: Chromosomes that match (e.g. two

chromosome 3s)

• Nonhomologous chromosome: Chromosomes in the same genome

that do not match

Sister chromatid:

completely Identical copies of a chromosome, immediately following replication (ex. Both sister chromatids both have A allele)

Autosome:

Chromosomes not involved in sex determination

 Barr body

inactive X chromosome condensed into Barr body —> male and female onlyexpress one X chromosome in somatic tissue

Homogametic Sex vs. heterogametic

Homogametic: Sex determined by having two of the same sex chromosome

Heterogametic Sex: Sex determined having two different sex chromosomes

Chromosomes

thread-like structures containing genes thatreside in the nucleus. It segregates into daughter cells during cell division and sexual dimorphism (male and female have differences based on their sex. Ex. male taller than females)