Mizzou Genetics Exam 3

single nucleotide polymorphisms (SNPs)

single base-pair differences between individuals, may result in a loss/addition of a restriction site

PCR

detects SNPs or mutations that affect restriction sites

PCR step 1

design primers to amplify a region containing the point mutation

PCR step 2

digest the amplified fragment with the RE

PCR step 3

use gel to determine the sizes of fragments produced

PCR step 4

mutant DNA will give a different digestion pattern

restriction fragment length polymorphism (RFLP)

caused by different restriction patterns

Short tandem repeats (STRs)

aka microsatellites; contain very short tandem repeats (one after the other); distributed widely in the human genome; many are polymorphic and used for forensics; different individuals have different numbers of repeats; usually typed by PCR w primers flanking the sequence; individuals can be homozygoud or heterozygous

variable number of tandem repeats (VNTRs)

aka mini satellites; longer than STRs; fewer VNTR loci than STR loci in the human genome; PCR is generally not used for their detection (bc they are so long), use RE digest + Southern blot instead; can be used for paternity testing

VNTR procedure

- DNA is digested w a restriction enzyme that cuts sequences flanking the VNTR

- fragments are electrophoresed and blotted to a filter

- the blot is probed with the VNTR repeating sequence

unique VNTR and multicopy VNTR

two types of VNTR

unique VNTR

only one copy is present in the haploid genome

multicopy VNTR

many copies scattered around the genome, a probe that detects a family loci may reveal multiple bands in an autoradiogram

Gregor Mendel

father of genetics; Czech monk who began his work in 1854 with the garden pea by cross-breeding plants with different traits/characteristics

grow easily, produce large numbers of seeds quickly, self-fertilize

why did Mendel use the garden pea?

Mendel's experimental design

first grew strains of peas using self-fertilization to be certain that the traits of interest were unchanged in subsequent generations (genetics, not environment)

seed coat/flower color (grey/purple vs white/white), seed color (yellow vs green), seed shape (smooth vs wrinkled), pod color (green vs yellow), pod shape (inflated vs pinched), stem height (tall vs short), flower position (axial vs terminal)

7 traits Mendel studied:

pure-breeding strains

true breeding, homozygous plants

monohybrid cross

cross-fertilization between pure-breeding strains that have alternative phenotypes of a single trait, offspring resemble only one parent

both smooth and wrinkled seeds (3:1)

results of F1 plant cross

the principle of segregation (1st mendelian law)

recessive characters, which are masked in the F1 from a cross between 2 pure-breeding strains, reappear in a specific proportion (3S_:1ss) in the F2

Punnett Square

diagram that can be used to predict the genotype and phenotype combinations of a genetic cross

branch diagram

diagram that can be used to predict the genotype and phenotype and their relative frequencies; practical accounting of all possibilities using the multiplication rule of probability.

dihybrid cross

crosses involving 2 pairs of traits; traits are inherited independently of one another (they segregate independently);

principle of independent assortment (2nd mendelian law)

the factors for different traits assort independently of one another; genes on different chromosomes behave independently in gamete production and the 2 different genes transmit independently

testcross

cross between an organism with an unknown genotype and an organism with a recessive genotype/phenotype to determine the genotype of the unknown organism

pedigree analysis

the study of the phenotypic records of a family over several generations

generation

roman numeral

individual

arabic numeral

autosomal recessive traits

non-sex chromosome; parents of most affected individuals (aa) have normal phenotypes but are heterozygous (Aa-->carriers); allele may skip generations if it is rare

autosomal dominant traits

non-sex chromosome; affect individuals have at least one affected parent, recessive mutants often have normal parents; the trait is usually present in every generation; since dominant mutant alleles are rare most affected individuals are heterozygous and will likely mate with a homozygous normal individual

sex chromosomes

females have XX and males have XY; fusion results in half XX/female and half XY/male; male decides gender of offspring

Morgan (1910)

mutant white-eyed male fly; showed gene for eye color is located on the X chromosome; the white gene is X-linked

hemizygous

instead of having 2 alleles, there is only 1

X-linked recessive

traits occur much more frequently among males; female expresses recessive trait only if she were homozygous recessive; affected fathers + non-carrier mothers = all daughters express recessive allele, no sons do; father-to-son transmission doesn't occur; female carrier + normal male = 1/2 sons show trait, 1/2 daughters will be carrier

X-linked dominant

heterozygous females show the trait; since females have twice the number of X chromosomes these occur more frequently in females; affected male + normal female = all daughted and non of the sons are affected; heterozygous female + normal male = 1/2 sons show the trait and 1/2 daughters show the trait

Y-linked

a trait resulting from a mutant gene that is located on the Y chromosome but has no counterpart on the X; only shown in males; when affected male reproduces all the sons and none of the daughters are affected

multiple alleles

not all genes have only two forms/alleles; however, no matter how many alleles for the gene exist, a diploid individual will only have two alleles (one on each homologous chromosome)

ABO blood groups

3 alleles: IA, IB, and i

4 phenotypes: A, B, AB, and O

IA

makes A antigen

IB

makes B antigen

i

makes no antigen

antigen

antibody generating substance; a molecule that is recognized as foreign by an organism; stimulates the production of protein molecules called antibodies which bind to the antigens and tag them for destruction by the immune system; an organism doesn't attack its own

blood type A

genotypes IAIA or IAi; A antigens on their RBCs; no antibodies against A antigens (anti-A antibodies); have antibodies against B antigens (anti-B antibodies) which clump any RBC that have the B antigen; can give blood to A and AB, can accept blood from A and O

clumped cells

cannot move through fine capillaries and thus cause blockage

blood type B

genotype IBIB or IBi; have B antigens on their RBCs; have anti-A antibodies but no anti-B antibodies; can give blood to B, AB; can accept blood from B,O

blood type AB

universal recipients; genotype IAIB; have both A and B antigens on their RBCs; have neither anti-A nor anti-B antibodies; can give blood to AB; can accept blood from A, AB, B, O

blood type O

universal donors; genotype ii; have neither A nor B antigens on their RBCs; have both anti-A and anti-B antibodies; can give blood to A, B, AB, O; can accept blood from O

glycolipid

polysaccharide/sugar + lipid ; recognized as the A antigen

molecular basis of ABO

- IA and IB encode enzymes that add extra sugars to existing polysaccharides on the glycolipids

- IA gene product transferase converts the H antigen to the A antigen (adds alpha-N-acetylgalactosamine sugar)

- IB gene product converts the H antigen to the B antigen (by adding a galactose sugar)

- both enzymes are present in IAIB individuals (some H antigens are modified to the A antigen while others are modified to the B antigen. some H remain unmodified)

- neither enzyme is present in ii individuals (H antigen remains unmodified, it is not considered foreign since it is basic component of A and B antigens)

Rhesus factor (Rh)

2 antigen types: + (presence 90%) and - (absence 10%)

- people have anti-Rh antibodies

8

How many overall blood types are there? (including Rh)

complete dominance

one allele is completely dominant over another, such that the heterozygote exhibits the dominant phenotype

incomplete dominance

the heterozygote exhibits a phenotype intermediate between the two homozygotes; heterozygote: the recessive allele is not expressed, one dominant allele is unable to produce the full phenotype and the result is a new intermediate phenotype (plumage feather color in chickens)

codominance

the heterozygote phenotype includes the phenotypes of both homozygotes; NOT an intermediate of the two homozygotes; ABO blood series; both alleles make a produced producing a combined phenotypes

lethal alleles

mutations in essential genes (genes required for life) that may result in death (yellow body color gene in mice -- AY is dominant for yellow coat and recessive for death)

epistasis

gene interaction, the interaction between 2 or more genes to control a single phenotype; the expression of a gene at one locus can mask the expression of a second gene at another locus; often involves genes from the same pathway and produces modifications in the familiar 9:3:3:1 dihybrid ratio

9:7 (see notes for methods)

fruit color in sweet peas ratio

15:1 (see notes for methods)

fruit shape in shepherd's purse plant ratio

9:4:3 (see notes for methods)

coat color in mice ratio

12:3:1 (see notes for methods)

fruit color in summer squash ratio

discontinuous traits

only have a few distinct phenotypes (pea pod -- green or yellow)

continuous traits

have a continuous range of phenotypes (birth weight, adult height, wheat kernel color); could be attributed to the involvement of multiple genes/alleles and their interaction w the environment

quantitative trait loci (QTLs)

(collectively) the genes that contribute to the variation of a continuous trait

Identifying individual QTLs (via mapping)

- identifying regions of genomes containing genetic markers that are linked to QTLs

- tells us the number of genes involved and their locations

more genes are involved; alleles don't contribute equally

traits are more complex if: