Download Genetics Review: What is genetics? Genetics is what makes me

Genetics Review:
What is genetics?
● Genetics is what makes me different from a tomato
● Heredity: transmission of traits from parent to offspring. Involves reproduction.
● Genetics explains the mechanism for variation that we see in organisms.
Reproduction:
● Asexual
● Sexual: crossing of two organisms to make offspring. Way more variation.
○ A cell needs chromosomes they are normally distributed evenly between
cells.
Terms:
●
●
●
●
●
●
●
●
●
●
●
●
Gene: a unit of hereditary information
Traits: hereditary characteristics passed from parent to offspring.
Pure: offspring that is always genetically identical to parents.
P1 or P: parental generation, usually genetically pure to start
○ F1: first filial generation of offspring from mating two parents.
○ F2: second filial generation after self mating of F1.
Dominant: a trait that dominates another factor or trait.
Recessive: a trait that is dominated usually in the F1 of a heterozygous mating.
Homozygous: Both alleles of a pair of homologous chromosomes are alike.
Heterozygous: Two alleles in a pair of homologous chromosomes are different.
Allele: each of several alternative forms of a gene on homologous chromosomes.
○ Lots of alleles are possible in one spot.
Phenotype: a manifestation of genes. Appearance of organism due to traits
expressed by a particular genotype.
Genotype: the genetic makeup that is controlled by an organism’s alleles.
Locus: the physical location of a gene on a chromosome.
Mendel’s Laws:
● Law of Dominance: In a cross between two pure contrasting traits only one of
these traits appears in the next generation. This is the dominant trait and the nonappearing one is recessive.
○ Best shown by TT x tt, the dominant trait is always the phenotype.
● Law of Independent Assortment: When dihybrid plants are crossed, the factor for
each trait is distributed independently of factors for all other traits.
○ Traits do not influence each other.
○ Best illustrated by: AaBb x AaBb
○ Only applies if alleles are on different chromosomes exception is linkage.
●
Law of Segregation: During gamete formation, the two genes responsible for each
trait separate from each other so each gamete only contains one gene for each
trait.
○
Explains the reappearance of recessive trait in the F2 after the F1 produces
100 percent dominant.
○ Best shown by Tt x Tt because the recessive phenotype shows up.
● Incomplete dominance: hybrid is different from both purebred parents.
Theory of the Gene:
1. Genes in a chromosome are arranged in a row
2. Traits inherited together are located on the same chromosome.
3. Linkage groups may be broken by crossing over.
4. Position of genes on a chromosome may be determined.
●
●
Non-sex chromosomes = autosomes
Sex-linked inheritance: traits carried by sex chromosomes
Chromosome Mutations:
● Ploidy: homologous chromosomes fail to separate resulting in diploid gametes.
● Nondisjunction: only one pair of homologous chromosomes fail to separate.
Resulting gametes have an extra or missing chromosome. Fertilization of a “n” +with an “n” results in body cells with an extra chromosome.
●
Causes of Gene Mutation:
● Xrays, radioactive isotopes, cosmic rays, other radiation, chemical mutagens.
Factors Promoting Offspring Variation:
● Independent assortment of chromosomes, chance mating of different sperms/eggs,
crossing over of different portions of chromatids, mutations.
Why use the Statistical Method?
● Probability methods examine the formation of fertilized zygotes by gametes but
look at the contribution of one trait at a time. This allows a consideration of many
indirect non allelic loci in predicting genotypic outcomes. Most efficient way.
Autosomal Recessive:
● A = Normal, unaffected
● a = NOT OK, affected
● A/anything = normal unaffected
● a/a = affected
● “Hidden potential” in carriers, healthy parents can pass to child
Autosomal Dominant:
● A = NOT OK, affected
● a = Normal, unaffected
● A/anything = normal unaffected
● a/a = affected
● much easier to pass because only one allele needed, phenotype usually appears in
every generation.
X-Linked Recessive:
● XA= unaffected
● Xa = affected
● y=y
● XA XA= female unaffected
● Xa Xa = female affected
● XA Xa = female unaffected (carrier)
● XA Y = male unaffected
● Xa Y = male affected
● Fathers can’t pass to sons because mother carrier and affected father is only
combination that yields affected female.
X-Linked Dominant:
● XA= affected
● Xa = unaffected
● y=y
● XA XA= female affected
● Xa Xa = female unaffected
● XA Xa = female affected (carrier)
● XA Y = male affected
● Xa Y = male unaffected
● Gender specificity. Affected males don’t pass to sons. Affected females pass to
half sons.
Incomplete dominance: a form of intermediate inheritance in which one allele for a
specific trait is not completely dominant over the other allele. This results in a combined
phenotype.
Codominance: A form of inheritance in which both alleles are equally shown.
● Good example of codominance is blood types.
○ IA/IA, IA/i = A blood type
○ IB/IB, IB/I = B blood type
○ IA/IB = AB blood type
○ i/i = O blood type
Epistasis: one gene function stands upon another.
9:3:4:
●
●
recessive epistasis: one product super cedes another in a pathway
One recessive homozygous pairs phenotype overrides presentation of the other
pair’s phenotype.
● A/_ B/_ will produce 9/16 phenotype for example (blue)
●
●
A/_ b/b will produce 3/16 phenotype for example (magenta)
a/a B/_ will produce 3/16 and a/a b/b will produce 1/16 of phenotype (white)
○ Even if B is there it wont’ be expressed because A supersedes it.
9:7:
●
●
Both dominants at both loci bus t be there for pigment to be made.
Involved gene products interact in the same pathway. Complementation of these
genes allows certain phenotypes to be rescued by backup genes.
● A/_ B/_ will produce 9/16 phenotype.
● A/_ b/b, a/a B/_, and a/a b/b will produce the same phenotype.
12:3:1:
●
●
●
●
●
The presence of a dominant gene prevents further events in a pathway.
Two unlinked gene sets interact.
A_/B_ and A_/bb produce 12/16 phenotype
aa/B_ produces 3/16 phenotype.
aa/bb produces 1/16 phenotype.
Linked Genes:
● RF < 50 % = linkage
● RF >= 50 % = linkage is ruled out they must be on different chromosomes.
● 1 M.U. = RF OF 1%
5’ ATG GAC 3’ Sense DNA
3’ TAC CTG 5’ Antisense DNA (Sense to Anti = replication)
5’ AUG GAC 3’ mRNA (Antisense to mRNA = transcription)
3’ UAC CUG 5’ tRNA (mRNA to tRNA = translation)
N MET ASP C (Protein made by ribosome)
PCR: polymerase chain reaction. Simple amplification of DNA bounded
by two target sequences. Temperature is key, also need heat stable
polymerase.
Griffith and Avery: Isolated DNA as element of heredity. Characterized
its potential. Watson, Crick, Wilkins, Franklin: DNA structural
characteristics.
Beadle and Tatum: Central dogma, one gene = one polypeptide.
Jacob and Monod: gene regulation, how DNA/Genes are controlled to
express proteins.
Chargaff: base pair rules