Ch. 5 – Inheritance Patterns, Phenotype Variability, and Allele Frequencies.

%%What is a gene? What is the proper way to write human gene names? Do you have two alleles for every gene? Why or why not?%%

^^Gene^^: a specific sequence of DNA that encodes a particular protein
^^Allel:^^ a version of a gene (they exist in the same ==locus== (location) of a chromosome)

Human gene names: * ALL CAPS and in italics * example: CFTR

}}What does it mean for a trait to be mono-genic or multifactorial? What is Mendelian inheritance?}}

3 laws of Mendelian inheritance * ^^Law of segregation:^^ Offspring inherit one genetic allele form each parent * ^^The law of Independent Assortment:^^ the inheritance of one trait is not dependent on the inheritance of another * not always the case: * monogenic: only one gene influences the observed characteristic * eye-color 👁️ * Multifactorial traits: multiple genes and environmental factors influence observed trait * skin color * ^^Law of Dominance:^^ An organism with alternate forms of a gene will express the form that is dominant

}}What does it mean for a trait to be mono-genic or multifactorial? What is Mendelian inheritance?}}

monogenic: only one gene influences the observed characteristic * eye-color 👁️
Multifactorial traits: multiple genes and environmental factors influence observed trait * skin color
Mendelian inheritance → always monogenic

%%Dominant and recessive phenotypes are not the only phenotypes. What are some other examples?%%

Incomplete Dominance: the phenotype of a heterozygote is intermediate between the two homozygotes * example: *
Co-dominance: both dominant alleles contribute equally to the phenotype * example: * eggplant * ABO blood group system *
Epistasis: the expression of one gene modifies the phenotype during the presence of one or more other genes *

%%Be able to read and interpret which of the five basic inheritance patterns a pedigree is depicting.%%

**Pedigrees (**stammbäume): Graphical representation of a family tree with standardized symbols
Types: * Autosomal dominant * Autosomal recessive * X-linked dominant * X-linked recessive * Y-linked (patrilineal) * Mitochondrial (matrilineal)
Vocabulary : * Proband proposito=male proposita=female family member whom the family is first ascertained: brought to the attention of health care professionals * Kindred Extended family covering many generations * Sib (sibling) brother or sister * Sibship: a series of brothers and sisters *

%%Be able to calculate the frequency with which autosomal dominant and recessive disorders are inherited given the carrier/affected status of parents. How do offspring of consanguineous fair?%%

%%What is consanguinity? How is the coefficient of relationship calculated?%%

%%Explain how men are constitutionally hemizygous for most genes on the X-chromosome and women are functionally hemizygous. Why most genes and not all genes? True or False?: Males are never heterozygous for Y-linked sequences. Be able to explain.%%

constitutionally hemizygous → if you only have one X chromosome
functionally hemizygous → in females, due to X-inactivation
FALSE: because men only have one Y chromosome therefore they are hemizygous

%%What are examples of patrilineal and matrilineal inheritance? What is heteroplasmy?%%

patrilineal inheritance: passing down traus from the father to son * example: Y-linked traits ability to produce sperm
matrilineal inheritance: passing down the trait from mother to offspring( all sexes) * example: mitochondrial DNA
Heteroplasmy: the presence of more than one type of mitochondrial DNA within an individual cells * due to mutations in mitochondrial DNA during cells division resulting in a mixture of normal and mutated mitochondria DNA \n

%%Why is the ascertainment bias high for recessive conditions?%%

Ascertainment bias: when a particular trait is overrepresented in a pedigree ( normally recessive disease but more than 1/4 of people have the disease)
Disease is more common in family than in population

%%How can two affected parents (of autosomal recessive disease) produce an unaffected child? What is locus heterogeneity? Allelic heterogeneity? Phenotypic heterogeneity? (see also see p. 556 and glossary)%%

different locus heterogeneity → the mutations from parents are on a different location on chromosome *
Allelic heterogeneity refers to the presence of different mutations within the same gene that can cause the same phenotype * a different mutations of Cystic fibrosis all cause cystic fibrosis
Phenotypic heterogeneity refers to the same genotype results in different phenotype * example muscular dystrophies *

%%What is penetrance? Why do we not always see 100% penetrance?%%

Penetrance: the likelihood of an individual with a particular genetic mutation developing the condition associated with that mutation * example, allergies * age-related penetrate due to * incremental tissue death * loss of function of the normal protein and toxic accumulation of mutant version( pre-diabetic) * inability to repair some sort of environmental damage * second mutation ( two-hit)
expressivity: the degree of severity or extent of expression

%%What is the difference between a mosaic organism and a chimera? How could each occur?%%

mosaic organisms: mutation during embryonic development resulting in some cell having the mutations while others do not
chimera: when a person has at least two distinct genotypes within their body due to a fusion of two embryos during development

mosaicism vs chimera

%%What are assumptions made by the Hardy-Weinberg Law?%%

The law states that under certain conditions, the frequencies of alleles and genotypes in a population will remain constant from generation to generation.
Allele frequencies are not changing * The population size is infinite * Mutations are not occurring * Mating is random * There is no purifying selection * There is no gene flow

%%Be able to explain how genetic drifts, bottle necks, the founder effect influence allele frequencies.%%

geneflow: the transferring of genetic diversity among populations resulting in a change on allele frequencies

genetic drift: the random fluctuations of allel frequencies within a population

bottleneck event: an event that causes a severe reduction in population size and the next generation only has the alleles of the small population

founder effect: a type of genetic drift when small group in populations establishes new population and normally less frequent alleles become more common in new population

%%Why do some genetic mutations remain in the population? Are high mutation rates and unstable genes enough to explain why harmful disease alleles persist? What is balancing selection?%%

because mutations are not harmful to current environment or press after giving birth to children * tumors
most disease are in ressiev forms → carries
must mutations are neutral
some mutations are advantages to enviriment * malaria and sickle cell anemia
Balancing selection: a type of natural selection which maintains genetic diversity → heterozygous genotype has higher fitness ( due to better adaptation) than homozygous genotypes leading to maintenance of both alles in population

%%Be able to explain selective sweeps, “hitchhiking alleles” and loss of heterozygosity. (more in 11.4)%%

selective sweeps: occur when beneficial mutations arise in a population and rapidly increase due to positive selection. While the mutation spreads it sweeps out or eliminates nearby genetic variation
hitchhiking alleles: when an allele changes frequency not because it itself is under natural selection but because it is near another gene that is undergoing a selective sweep and that is on the same DNA chain.
loss of heterozygosity: Heterozygosity refers to the presence of different alleles at a given locus or gene in an individual, and loss of heterozygosity occurs when one allele becomes fixed in the population due to positive selection. This results in a loss of genetic variation at the affected locus or gene.