BIOL/GEN 3130 Exam 4 Complete

pea plant

Proband

Person coming to genetics clinic first in pedigree, family history based on them

How to analyze pedigrees

Check: dominant, then x-linked recessive

Heteroplasmy

In cytoplasmic inheritance where mom has mix of different alleles → passes different mixes on to zygotes, results in different severity of traits/disease

Mendelian genetics characteristics

Complete dominance, complete viability, 2 alleles per gene, no gene interactions → actually the exception

Lethal alleles

Cause death at early stage, creats 2:1 ratio in progreny, usually

Penetrance

percentage of individuals with genotype that expressed the expected phenotype

Expressivity

Degree to which a trait is expressed

Novel phenotypes

Arise from interactions of 2+ genes

Epistasis

Genetic activity at one locus masks activity of another locus; epistatic gene masks, hypostatic is masked

Bombay phenotype

Type of blood that is recessive epistasis; hh genotype → O-like phenotype

Squash and dominant epistasis

W blocks enzyme 1, causes white; ww progresses to green, wwY progresses to yellow; dominant epistatic allele is W, hypostatic allels are Y and y because W stops enzyme ii from mattering

Complementation

Restores a wild type by crossing two mutants; indicates that mutations are on separate genes

Sex-influenced characteristics

Encoded by autosomal genes, more readily expressed in one sex (higher penetrance)

Sex-limited characteristic

On autosomal genes, only expressed in one ex, often controlled by sex hormones

Genomic imprinting

Differential expression of genetic material depending on whether it’s inherited from M or F parent; imprinted genes → allele of one parent is inactivated (methlyated on cytosine)

Epigenetics

Heritable alterations in DNA not invlving base changes but affecting expression

Igf2 genomic imprinting

Codes for a growth factor stimulating fetal development; maternal allele is silent while paternal stimulates fetal growth → siz eof fetus is determined by their combined effects

Mitochondrial cytoplasmic inheritance

Has ciruclar dsDNA, 37 genes, not packed in chromatin, 2-10 copies of mtDNA in each mitochondrion, high mutation rate; usually inherited maternally

How does mitochondrial inheritance create variation?

Cytoplasmically inherited characteristics exhibit extensive phenotypic variation b/c mitochondria segregate randomly in cell division, giving progeny cells different amounts/severity of wild-type vs. mutated mitochondria

Characteristics of cytoplasmically inherited traits

In both M and F, inherited from one parent, reciprocal crosses give diff results, lots of phenotypic variation even within a family

Human mitochondrial diseases

Mutations in mtDNA cause a # of human diseases (mostly rare): LHON = sudden bilateral blindness; Leigh syndrome = progressive loss of mental and mvmt abilities, resulting in death; symptoms can vary from person to person even in the same family

Himalayan rabbit allele

Enzyme that is needed to make dark pigment only functions below 25 degrees,but is inactivated at higher temperatures → temperature sensitive

Discontinuous characterisitcs

Relatively few phenotypes, like the ones studied by mendel, easier to predict progeny

Continuous characteristics

Continuous distribution of phenotypes, occurs when genes at many loc interact and may be influenced by environment → complex and harder to predict

Polygenic characteristics vs. pleiotropy

Polygenic = encoded by genes at many loci, while pleiotropy = one gene affects multiple characteristics

Qualitative/discontinuous characteristics

Only a few discrete phenotypes, relationship between genotype and pheno is straightforward; eg pea plant seed shape

Quantitative/continous characterisitcs w/example

Continous range of phenotypes that differ only slightly from ne another, complex relationship between genotype and pheontype; use 3^n to find number of possible genotypes for a given characteristics, but many genotypes can contribute to same phenotype

Meristic characteristics

Type of quantitative, phenotype doesn’t vary continuously, determined by multiple genetic and environmental factors, measured in whole numbers (litter size, etc.)

Threshold characteristics

Type of quantitative, phenotype doesn’t vary continously (small # of discrete phenotypic classes), multiple genetic and environmental factors, measured by presence and absence (disease susceptibility, etc.)

POlygenic inheritance

Quantitative characteristics contorlled by many genes, which individually follow Mendel’s rules, but relationship between genotype and phenotype is less obviour; different genes have ADDITIVE effect on phenotype, may have additive (active) allele or non-additive (inactive) allele which doesn’t contribute to phenotype —> genes work together to produce substantial variation in phenotype

Wheat kernel color polygenic inheritance

Have additive and non additive alleles at 2 loci, and when more additive allels in genotype, sarker purple color

(2n+1) Rule

2n+1 = total number of phenotypic classes when n is the number of genes; tells how many phenotypes in F2 progeny when alleles are unlinked, contribute equally and additively, and no significant environmental effects

What were observations made in the early 20th century that connected chromosomes to Mendel’s “unit factors”?

Light microsocopy → visualized and coutned chromosomes, early genetic studies showed some genes don’t sort independently, several genes may be ont he same chromosome

Independent assortment

All genese are on separate chromosomes

Completely linked

Genes are close togehter on the same chromosome and trasmit to the next generation as a unit

Recombination

Crossing over separates genes found on the same chromsome; creates new combinations of alleles

Crossing over in linekd genes

Leads to recombinant gametes and recombinant progeny; complete linkage → no recombinaiton

Maximum amount of recombinant progeny from a single crossover

Frequency of recombinant gametes is only half the frequency of crossing over b/c each crossover takes place between 2/4 chromatids of a homologous pair

Test crossing

Do one heterozygous for both traits with one homozygous recessive; parents should be most numerous, and crossing-over will be seen relatively rarely; each crossover → 2 crossover classes

Coupling configuration (cis)

Wild type alleles are on one chromosome, mutant alleles are on the other

Repulsion configuration (trans)

Each chromosome has one mutant and one wild-type allele

To tell whether your starting genes were cis or trans

Look at non-recombinant gene chromosomes and see what they could have come from (non-recomb are the highest proportion)

Recombination frequency

Calculated as the number of recombinant progeny/total * 100%; translate to map units in genetic mapping, and use to predict the number of offspring with different genotypes

Two-point cross limiations

TIme and labor consuming, actual distances between genes are often missed (double crossovers) or inaccurate

Three-point testcross

Mapping technique based on a testcross for 3 linked genes; easier to determine order of genes on a chromosome and DCOs

Double crossovers

Recombinant chromosomes resulting will only have the middle gene altered

How to read results of a three-point testcross

Progeny genotypes with highest number are nonrecombinant, lowest are double crossover; ID middle locus using double-crossover information

Recombination frequency in three-point cross

(SCOs+DCOs)/number of total progeny * 100 = map units between any 2 genes; either gene to the middle gene should add distances to get from end to end