Human genetics exam review Flashcards
Polyploidy
Cells and organisms containing more than two complete paired (homologous) sets of chromosomes
Mendels first law
Principle of segregation- each individual diploid organism possesses two alleles for any particular characteristic and only one is passed to offspring
Epigenetics
Alterations in DNA that do not include changes in base sequence, but alter the way in which the gene is expressed
How did mendel reveal the principle of independent assortment and what does it result from
Examining the behavior of two traits simultaneously using a dihybrid cross
Results from independent separation of chromosomes in anaphase I of meiosis
x linked recessive diseases
Fragile x Color blind Hemophilia Duchennes Glucose-6-phosphate dehydrogenase deficiency
Penetrance can be affected by
Whether you inherited from mom or dad, whether you are a male or female
Heredity and heritability refer to
Populations, not individuals
Heredity
The passing on of physical or mental characteristics from one generation to the other
X-linked dominant traits
Affected males pass on to all their daughters and none of their sons Affected females (heterozygous) pass to about half of their daughters and sons Doesn't skip generations
Genetic linkage
The tendency of alleles that are located close together on chromosome to be inherited together
Linked genes do not obey mendels second law (independent assortment)
First mechanism generating genetic variation in new gametes is
Crossing over during prophase I of meiosis
Dicentric chromosome produced how
Crossing over takes place in individual heterozygous for paracentric inversion
A double crossover between two linked genes produces
Only nonrecombinant gametes. Second crossover cancels effects of first
Translocation carriers and downs syndrome
Translocation carriers are at increased risk for producing children with downs syndrome
Deletion mapping can be used to
Determine the chromosomal location of a gene
GINA
Genetic information nondiscrimination act
Illegal to discriminate against employees or applicants because of genetic information.
Insurers cannot deny coverage to healthy person or charge them higher solely based on a genetic predisposition
Single crossover will result in
Half nonrecombinant gametes, half recombinant
Cohesin and shugoshin
Cohesin holds sister chromatids together. Shugoshin protects cohesion from degradation at the centromere. Shugoshin must be degraded before cohesin can be
Epigenetic modifications in germ cells
Epigenetic modifications are erased and parent specific modifications are established
Negative of crossing over
Can result in unequal exchange of genetic material producing chromosomes with deleted or duplicated regions
Why do 1/3 of women carrying hemophilia (x-linked recessive gene) experience bleeding episodes
Skewed x-inactivation- greater than 80% of X chromosomes showing preferential inactivation of one chromosome. Good chromosome may be inactivated
Model organism characteristics
Short generation time
Numerous progeny
Ability to carry out controlled genetic crosses
Ability to be reared in a lab environment
Availability of multiple genetic variants
Accumulated body of knowledge about their genetic systems
Genetics definition
The study of genes, heredity, and genetic variation in living organisms
Heterozygous vs homozygous inversions
Inversions in heterozygous often have non functional gametes due to large deletions
Homozygous have no problems
Complex inheritance of traits
Many genetic traits don’t follow simple inheritance patterns. Some are produced by the interplay of many sets of genes (polygenic traits)
Example of recessive epistasis
Bombay phenotype.
People with hh recessive mutation are bound to end up with blood type O
-Therefor, genotypes at both the H locus and ABO locus determine ABO blood type
Why are sex chromosome aneuploids more common than autosomal aneuploids
No mechanism of dosage compensation for autosomal chromatids. Autosomes carry more genes. Most autosomal aneuploids are spontaneously aborted
Aneuploidy
the loss or gain of chromosomes
How is incomplete dominance different from blended inheritance
If you cross F2, you can restore parental phenotype. This is not possible with blended inheritance
Allele definition
One of two or more alternative forms of a gene that arise through mutation and are found at the same place on the chromosome
Metacentric
Submeta
Telo
Acro
Meta-middle
Submeta- just off-center, one arm longer
Telo- no short arm visible
Acro-very short arm
Lamarckianism
Inheritance of acquired characteristics
-Acquired traits become incorporated into hereditary info (i.e. giraffe necks)
GWAS
Genome wide association studies
Can give hints on what variants might be important, but further testing must be done to confirm
Proband
The person from who the pedigree is initiated
Pleiotropy
When one gene influences two or more seemingly unrelated phenotypes
Cystic fibrosis, sickle cell
Sex influenced traits
Controlled by genes on autosomes, hence such genes are present in both sexes but their expression is different in males vs females. (usually due to different responses to androgens or estrogens)
Y linked traits
Appear only in males and are passed from a father to all sons
Sex chromosome, gene and protein
Y chromosome
SRY gene
TDF- testis determining factor (protein)
Heritability
The proportion of total variation between individuals in a given population that is due to genetic variation
Heterogametic
Sex produces 2 different gamete types with two different sex chromosomes
Other effects of deletions besides sterility
Imbalances in gene product
Recessive gene is expressed
Haploinsufficiency
Molecular genetics
Studies the structure and function of genes at the molecular level
After G1/S checkpoint
Cell is committed to cell cycle
Heterosis
The improved or increased function of any biological quality in a hybrid offspring of pure bred strains (opposite of inbreeding depression)
Mendels third law
Concept of dominance- when two different alleles are present in a genotype, only the trait encoded by one of them- the dominant allele- is observed in the phenotype
Germ-plasm theory*
All cells contain a complete set of genetic information
Inheritance in multicellular organism takes place by means of germ cells
Haplotype
Set of DNA variations that tend to be inherited together
Genome definition
A complete set of genetic instructions for any organism
DNA or RNA
Anticipation
A genetic trait becomes more strongly expressed or is expressed at an earlier stage as it is passed from generation to generation
i.e. huntingtons
Concordance
The presence of the same trait in both members of a pair of twins. However, the trait may not be exactly the same phenotypically due to differences in penetrance or environment
Recombination frequency equation
RF= (# recombinant progeny/Total # progeny) x100%
Inversion/deletions/duplications can often lead to
Sterility
Epistasis
When the effect of one gene is dependent on the presence of one or more “modifier” genes
Mosaicism
Cells within same person have different genetic make-up. e.g. When different X chromosomes are inactivated in neighboring cells
Genetic maps are determined by
Recombinant frequency
Homologous chromosome definition
Similar but not identical. Each homolog carries the same genes but the alleles for each trait may differ
Epigenetic trait*
A stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence
Linkage disequilibrium
The non-random association of alleles at different loci. When the frequency of association of their different alleles is higher or lower than what would be expected if they were separating independently
Interference
When the first crossover inhibits or impacts a second crossover
Physical maps are determined by
Nucleotide position
Complex disorders characteristics compared to single gene disorders
Multiple gene products instead of only one
Environment plays important role in phenotype
Often older age of onset
Disease risks for relatives are less predictable, but usually have lower risk
More common than single-gene disorders
Mendels second law
Independent assortment- alleles segregate independently when gametes are formed
Common rule
Requirements for assuring compliance by research institutions
Requirements for researchers obtaining and documenting informed consent
Requirements for IRB membership, function, operations
Additional protection for certain vulnerable research subjects (pregnant women, prisoners, children)
Second mechanism generating genetic variation in new gametes is
Random distribution of chromosomes into newly divided cells during anaphase I
Complete linkage leads to ___ – crossing over has what affect on this
All nonrecombinant gametes and progeny
Crossing over disrupts linkage and leads to recombinant gametes and progeny
Hermaphrodite
Monoecious
Dioecious
Herm- both sexes in same organism
Mono- both reproductive systems in save organism
Dio- either male or female reproductive but not both
Three point testcross can be used
To map three linked genes
Pangenesis
Genetic info travels from different parts of body to reproductive organs
False
Genomic imprinting
Different expression of genetic material depending on whether it is inherited from the male or female parent
Primary spermatocyte/oocyte vs secondary
Primary = 2n Secondary = 1n
G2/M checkpoint
Only passed if DNA is replicated/undamaged
What causes the difference between genetic and physical maps
Recombination rates vary between different chromosomes
Difference b/w spermatogenesis and oogenesis
Spermatogenesis generates 4 functional gametes while oogenesis generates 1
Paracentric vs Pericentric inversion
Paracentric inversion- breakpoints are confined to one arm of the chromosome
Pericentric- breakpoints occur on both arms- span the centromere
Prokaryotes
No nucleus
One circular DNA usually
No membrane-bound organelles
Multiple testing correction
When testing for multiple different variables (bp, heart rate, etc..) we may need to increase the threshold to reach significance. i.e. the P value may need to be
