Genetics Flashcards
(40 cards)
Mendel’s Laws of Inheritance:
- Law of Segregation: Alleles separate during the formation of gametes. Each gamete carries only one copy of each allele such that offspring inherit two alleles—one from each parent.
- Law of Independent Assortment: Alleles of different genes are distributed into gametes independently because homologous chromosome pairs align randomly during metaphase I of meiosis.
- Law of Dominance: a dominant allele masks the expression of a recessive allele
Penetrance vs expressivity
Penetrance: the probability that an organism with a specific genotype will express the corresponding phenotype (e.g. likelihood that a gene for baldness will cause a bald phenotype).
Expressivity: describes the level of expression of a phenotype for a specific genotype (e.g. gene for body hair → people with the same genes may express different amounts of body hair due to different levels of expressivity).
Not all inheritance follows simple Mendelian patterns. What are the types non-Mendelian inheritance?
- Incomplete dominance: more than one dominant allele. Heterozygote with two dominant alleles shows a blended phenotype.
- Codominance: both inherited dominant alleles are completely expressed. Heterozygote with two dominant alleles shows both phenotypes simultaneously.
- Multiple alleles: more than two possible alleles for a gene (e.g. blood type, eye color).
- Epistasis: one gene’s expression masks the phenotypic expression of another (e.g. baldness gene masks hair color gene).
- Pleiotropy: a single gene affects multiple phenotypic traits (e.g. a single plant gene determines height, color, and texture).
- Polygenic inheritance: many genes determine one phenotypic outcome (e.g. height, skin color).
Pleiotropy vs polygenic inheritance
Both are types of non-mendelian genetic inheritance.
Pleiotropy: a single gene affects multiple phenotypic traits (e.g. a single plant gene determines height, color, and texture).
Polygenic inheritance: many genes determine one phenotypic outcome (e.g. height, skin color).
Sex-linked vs sex-influenced genes
Sex-linked genes: genes located on the sex chromosomes; either X-linked or Y-linked.
*Color blindness is X-linked recessive. Men only have one X chromosome, so they express colorblindness with just one affected allele.
*Only men can have Y-linked genes (e.g. webbed toes).
Autosomal genes are located on autosomal (non-sex) chromosomes.
Individuals with a dominant condition carry an affected allele and express the affected phenotype. For recessive conditions, a heterozygous individual (a carrier) carries the affected allele but still displays a normal phenotype.
*All males with X-linked conditions must have inherited it from their mother. Fathers pass only the Y chromosome to their sons (not the X chromosome).
Sex-influenced genes: expression is influenced by the sex of the individual. Gene is not necessarily on a sex chromosome.
* E.g. a sex-influenced gene for baldness may result in males being bald, but females unaffected
Genomic imprinting
the deactivation of one copy of a gene depending on which parent it came from (allelle expression affected)
- affects autosomal chromosomes
- only a few genes undergo this process
What is the cause of calico cats being like that?
X-inactivation: a female phenomenon in which one of the two X chromosomes (randomly chosen) condenses down into an inactivated Barr body. Expressed genes come from the remaining X chromosome.
Note: not ALL genes on that x-chromosome are shut off, its still important
In these cats, cells randomly inactive one of the X-chromosmes, and different X-linked colour alleles are expressed in different cells
In X-inactivation, we only shut off one of the X-chromosomes, not remove it. What would happen if we removed it?
Turners Syndrome
- a complete or partial absence of X chromosomes
What is the heterozygote advantage?
When the heterozygous genotype has an advantage over homozygous dominant or recessive (e.g. heterozygotes for sickle-cell anemia have malaria resistance without suffering from disease).
Example:
Autosomal dominant (AA):
- no sickle cell disease
- susceptible to malaria
Heterozygote (Aa):
- no sickle cell disease
- resistant to malaria
Autosomal Recessive (aa):
- has sickle cell disease
- resistant to malaria
Recombination frequency
Recombination frequency: the percentage likelihood that two genes will be separated by crossing over.
- Linked genes have a low recombination frequency
50% recombination frequency for the whole distance of the chromosome
Describe the key characteristics when looking at a pedigree to determine whether the disease is:
- Autosomal dominant
- Autosomal recessive
- X linked dominant
- X linked recessive
Steps:
1. dominant/recessive?
- recessive if unaffected parents have affected children
- X-linked or autosomal?
For dominant:
- Autosomal dominant: two unaffected parents cannot have affected offspring
- X-linked dominant: all daughters of an affected father will be affected
For recessive:
- Autosomal recessive: two unaffected parents having affected offspring
- X linked recessive: affected mothers = affected sons. normal father NEVER has affected daughter. these conditions are more often in sons since they only got one x chromosome
What are some cancer-causing agents, and some compounds that prevent unregulated cell growth?
Cancer-Causing Agents:
*Viruses: insert genetic information into the genome and disrupt the genes responsible for regulating normal cell growth, allowing cancer to develop.
*Mutagenic agents: include radiation, carcinogenic compounds, and certain infectious agents.
Compounds that prevent:
- colchicine (prevents microtubules from stabilizing, which prevent mitotic spindle formation and mitosis cant proceed)
- chemotherapeutic agents (kill these cells)
Examples of autosomal dominant conditions
Huntington’s disease: nervous system degeneration
Anchondroplasia: dwarfism
Hypercholesterolemia: excess choleserol in blood that progresses to heart disease
Examples of autosomal recessive conditions
Phenylketonuria: phenyalanine breakdown inability, leading to phenyl pyruvic acid accumulation
Cystic fibrosis: fluid buildup in respiratory tracts
Tay-sachs: inability to breakdown lipids, affecting brain function
Sickle-cell anemia: defective hemoglovin due to substitution
Galactosemia: cannot breakdown galactose properly
Sex-linked recessive conditions examples
Hemophilia: abnormal blood clotting
Color blindness: inability to see color, primarily seen in males
Duchenne’s muscular dystrophy: progressive loss of muscle
Chromosomal (aneuploidy) disorders examples
Down syndrome: trisomy 21, extra copy of chromosome 21
Turner’s syndrome: partially or completely missing X chromosome
Klinefelter’s syndrome: extra X chromosome
Cri du Chat: piece of chromosome 5 missing
Maternal Effect Genes
genes which when mutated in the mother, cause a phenotypically normal mother who produces mutant offspring, regardless of offspring genotype.
(e.g. defective mRNA or proteins in egg cell leads to a disrupted embryonic environment).
mRNA processing (post-transcriptional modification) occurs in eukaryotes, prokaryotes, or both? What is it?
ONLY eukaryotes.
- mRNA is further modified before being translatedinto a protein product.
- 5’ capping: a GTP molecule is added to the 5’ end of the mRNA to provide stability by preventing degradation. Ribosomes bind to the 5’ cap to begin translation.
- Poly-A Tail: many adenine nucleotides are added to the 3’ end of the mRNA to provide stability by preventing degradation.
- RNA splicing: spliceosome complex removes introns from the mRNA, and connects exons together.
- Introns: RNA sequences that are removed from the transcript before RNA gets translated.
- Exons: sequences that are retained in the transcriptand translated into protein.
- Alternative Splicing: RNA splicing allows different mRNA strands to be generated from one original RNA transcript, allowing one gene to code for multiple different proteins through different arrangements of exons.
RNA World Hypothesis. What is it, What evidence is there to support this?
“RNA existed first”
States that self-replicating RNA molecules were the earliest precursor to life (before DNA and proteins existed).
* Evidence:
- RNA can store genetic information, like DNA.
- RNA can catalyze chemical reactions, like proteins/enzymes.
The most effective way to prevent gene expression is to __________________. What are some other ways too?
Delete the promoter region = no transcription
MicroRNA (miRNA) & small-interfering RNA (siRNA) can also be used for RNA interference and gene silencing:
- siRNA degrades target mRNA
- miRNA inhibits translation (blocks pol)
Prokaryote vs eukaryote ribosomes
Prokaryote:
- Large subunit = 50S
- Small subunit = 30S
Eukaryote:
- Large subunit = 60S
- Small subunit = 40S
In both, translation occurs in cytosol across ribosomes
What is an exception to the central dogma?
Reverse transcriptase!
- RNA –> DNA
- NOT performed by living organisms
Hayflick limit
- running out of telomeres over time
- limited # of times a cell can divide due to shortening telomeres
- Reached when telomeres become too short to allow further cell division.
Transcriptome and proteome
Transcriptome: entire set of expresssed mRNA (exon, intron)
Proteome: entire set of expressed protein
- Humans have more proteins than genes –> Multiple proteins can be synthesized from the same gene (via alternative splicing).
