Studied by 2 people
Heredity
the passing of traits from one generation to another
Genetics
the study of how traits and their variants are passed from parents to offspring in the form of genes
Gene
a functional unit of heredity. found in discrete DNA segment that encodes a functional product.
Genome
a whole set of genes (in nucleus, mitochondria and chromosomes)
Locus/loci
a particular position on a chromosome
Alleles
2 different version of the same gene
Mutation/ Variant
changes the alleles and how they arise (change of DNA sequence)
Genotype
genetic makeup of an organism… types of alleles
Phenotype
physical traits of a gene
Human gene nomenclature
all in caps + italicized in human genes
The central dogma of molecular biology describes what?
the expression of heredity information
How does one genome make all the cells in our body?
through cell specific gene expression
Basis for evolution
variation/ polymorphism
Somatic cells
all cells except germ cells, diploid, 46 total chromosomes (44 autosomes and 2 sex chromosomes)
Germ cells
gametes/ reproductive cells, 23 chromosomes (22 autosomes and X or Y sex chromosome)
Cell division
mitosis
cell death
apoptosis
Syndactyly
failure to sep digits in the womb due to no cell death
Phases of the cell cycle
G1, S, G2, prophases, pro metaphase, metaphase, anaphase, telophase, then G0 if needed
When do chromosomes replicate?
S phase
karyokinesis
nuclear separation
Outcomes of meiosis
4 genetically distinct haploid daughter cells, essential for life, makes genetic diversity
Meiosis 1 is a reductive division, why?
go from 46-23 chromosomes
When does crossing over occur?
in prophase 1 of meiosis
Synapsis
paring of homologous chromosomes
crossing over
exchange of genetic info
bivalent
chromosome pair
chiasma
place where recombination occurs
Why is meiosis 2 an equatorial division?
no DNA replication, 23 to 23 chormosomes
Do X and Y chromosnes undergo recombination?
yes, at the psuedoautosomal regions (the ends)
Gregor Mendel: the father of modern genetics
monk and scientist, 2 laws of inheritance, originally published work in 1866, was rediscovered in 1901
Self fertilization
pollen and egg from same plant
Cross-fertilization
artificially fertilized, fertilize eggs with pollen from different plants
Monohybrid cross
tracks inheritance pattern of a single trait
Phenotypic ratio of a monohybrid cross
3:1
Mendel’s first Law: The Law of segregation
during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene
True Breeding
homozygous dominant or recessive
Test cross
a way to determine the genotype of something by crossing it with a pure breeding recessive
Genetically males are
XY and are hemizygours, and the recessive X allele is not masked
Genetically females are
XX and can be homozygous or heterozygous for a sex linked trait
How is mitochondrial DNA inherited
through the egg from the mother
Dihybrids
tracks inheritance of 2 traits simultaneously
Phenotypic ratio of a dihybrid cross
9:3:3:1
The product rule
the probability of simultaneous independent events equal the product of their individual probabilities
Mendel’s Second Law: The Law of Independent Assortment
During gamete formation, the segregation of alleles of one gene is independent of the segregation of alleles of another gene
Chi-Square test
statistical test to determine whether the difference between an observed and expected outcome of an experiment is statistically significant
Pedigree
family tree of inheritance, is useful for investigating the pattern of inheritance of a phenotype whose presence or absence is determined by the genotype at a single locus
First degree relatives
share 50% of genetic info with proband- parents, siblings, and children
Second degree relatives
share 25% of genetic info with proband- half-siblings, aunts, uncles, grandparents, nieces and nephews
Third degree relatives
share 12.5% of genetic info- first cousins
Mitochondiral inheritance
maternal inheritance, severity of symptoms can vary ( if mother is affected children will be/ if father is affected chiildren won’t be)
Autosomal Recessive inheritance
appears in both sexes equally, skips generations, affected offspring born to unaffected parents, when parents are hetero ~1/4 of the offspring will be affected
Autosomal Dominant inheritance
appears in both sexes equally, both sexes transmit the trait to offspring, doesn't skip generations, affected offspring must have an affected parents, unless they have a mutation, when parent is affected (hetero) and the other not ~ ½ the offspring will be affected, unaffected parents don’t transmit the trait
X-linked Recessive inheritance
more males than females affected, affected sons born to unaffected mothers; thus the trait skips a generation, a carrier mother makes ½ affected sons, all daughters of affected fathers are carriers
X-linked Dominant inheritance
both males and females affects, often more females, doesn’t skip generations, affected sons must have affected mother, affected daughters must have either affected mother or father, affected mothers if hetero will pass the trait to ½ of their sons and daughters
Y-linked inheritance
only males are affected, passed from father to son, doesn’t skip generations
Sum Rule
the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities
Haplosufficient
the wild type allele supports wild type function in heterozygotes, Wild type allele is dominant, mutant allele is recessive
Haploinsufficient
wildtype allele does NOT support wild type function in heterozygotes, wild type allele is recessive, mutant allele is dominant
What are the functional consequences of mutation?
loss of function mutations and gain of function mutations
Null/ amorphic mutation
loss of function mutation, null alleles produce no functional product
Leaky/ hypomorphic mutation
loss of function mutation, leaky mutant allele produce a small amount of wild-type gene product
Dominant negative mutation
loss of function mutation (spoiler effect), the formation of multimeric proteins is altered by dominant negative mutants whose products interact abnormally with the protein products of other genes, leading to malformed multimeric proteins
Hypermorphic mutation
gain of function mutation, excessive expression of the gene product leads to excessive gene action.
Neomorphic mutation
gain of function mutation, the mutant allele has novel function that produces a mutant phenotype in homozygous and heterozygous organisms.
Incomplete Dominance
heterozygote phenotype is an intermediate level between the two homzygotes, no dominant or recessive allele (pink flowers)
Codominance
Heterozygote phenotype shows expression of both allele, AB blood type
Multiple Allels
a gene can have more that 2 alleles, different allele combos may produce variations in the phenotype, i.e fur color of rabbits
Lethal Alleles
genotype that causes death before an individual can reproduce, one expected genotype not observed in offspring (they are dead)
Sex-limited traits
have sex dependent phenotype, autosomal linked or X linked genera, hormone level differences, i.e beard growth, lactation
Sex-Influences traits
have variable inheritance patterns between sexes, alleles are dominant in one sex, recessive in another, again autosomal linked or X linked, hormone level difference, i.e pattern baldness, beards in goats
Phenocopy
is a phenomenon in which a trait appears to be inherited, but is caused by the environment, is not due to genotype, exposure to teratogens and infection
Pleiotropic
a gene that affects more than one trait, i.e Marfan syndrome (long limbs, caved-in chest, weakened aorta, lens dislocation)
Gene-environment
interactions that can also influence phenotype, i.e phenylketonuria, environment can be controlled by having a LOW diet of phenylalanine
Variable pentrance
all or none expression of a phenotype (polydactyly syndrome)
Variable expressivity
severity or extent of phenotype (waardenburg syndrome, hearing loss, different eye colors, white forelock, premature graying)
Cellular and organismal homeostasis requires what?
Many pathways, and mutations in any gene involved in the pathway can lead to altered phenotypes
Epistasis
the phenomenon of altered phenotypic rations due to gene interaction
No gene interaction
9:3:3:1 phenotypic ratio
Complementary gene interactions
9:7 phenotypic ratio, produced of both genes act in tandem in same pathway, both genes must have at least one wild type allele in order to have wild type phenotype
Complementation Analysis
distinguishes mutations in the same gene or different genes in a pathway
Complementation
parents have mutations in different alleles
Non-complementation
parents have mutations in the same gene
Duplicate gene action
15:1 phenotypic ratio, 2 genes encode products with redundant functions in a pathway, only need one dominant allele in either gene to produce wild type phenotype, homozygous recessive in both genes= mutant phenotype
Recessive Epistasis
9:3:4 phenotype, homozygous recessive genotype for one gene masks the genotype of another gene
Dominant Epistasis
12:3:1 phenotype, dominant allele in one gene masks the phenotypic expression of the allele in other gene
Syntenic genes
genes that are located on the same chromosome
Cis allele configuration
two dominant or two recessive alleles on each chromosome
Trans allele configuration
one dominant and one recessive allele on each chromosome
Genetic Linkage
genes that are closely spaced on the same chromosome are often inherited together
Linked genes
DO NOT assort independently UNLESS recombination occurs between them
What disrupts linkage?
recombination
Parental
(non-recombinant) have the parents allele configuration
Recombinant
(non-parental) have new combinations of alleles
Complete genetic linkage
genes extremely close together, no recombination between genes in F1 meiosis, gametes are all parental
Incomplete genetic linkage
recombination occasionally occurs between genes, more parental gametes than recombination gametes
Recombination frequency
number of recombinants/ total number, the smaller the value, the closer the genes are to each other
Two-point test cross
cross dihybrid to homozygous recessive
Genetic map
the probability genes will be separated by recombination
Physical map
distance between genes in base units
