Genetics Flashcards
Law of segregation
follows 1 single character
- monohybrids
- monohybrids cross
monohybrids
heterozygous for one character (Pp); F1 offspring
monohybrid cross
Pp x Pp
the law of independent assortment
followed two characters; each pair of alleles segregates independently of any other pair during games formation
- dihybrids
- hypothesis of dependent assortment wrong
- law applies to genes on chromosomes that are not homologs or those far apart on same chromosome
- genes located near each other are inherited together
dihybrids
heterozygous for both characters (YyRr); crossing two true-breeding parents differing in two characters produces this
dihybrid cross
cross between F1 hybrids; determines whether two characters are transmitted to offspring as a package or independently
Mendel’s law of segregation and independent assortment reflect…
the rules of probability
the multiplication rule
the probability that two or more independent events will occur together is the product of their individual probabilities
the addition rule
the probability that any one or two or more mutually exclusive events will occur is calculated by adding together their individual probabilities
inheritance of character by single gene may deviate from simple Mendelian patterns in the following situations
- when alleles are not completely dominant or recessive
- when a gene has more than two alleles
- when a single gene produces multiple phenotype
complete dominance
occurs when phenotypes of the heterozygous and dominant homozygous are identical (PP or Pp)
incomplete dominance
the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
codominace
two equally dominant alleles, both phenotypes will show up in the heterozygote
dominant alleles are not necessarily more common in populations than..
recessive alleles
most ones exist in population in more than…
two allelic forms
- ex: IA, IB, i
pleiotropy
genes have multiple phenotypic effects
- ex: one gene causes multiple diseases
epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus
quantitative characters
are those that vary in the population along a continuum - usually indicate polygenic inheritance
polygenic inheritance
are additive effect of two or more genes on a single phenotype
- broad phenotypic range
multifactorial
genetic and environmental factors collectively influence phenotype
Why are humans not good genetic research subjects?
- generation time is too long
- humans produce relatively few offspring
- breeding experiments are unacceptable
pedigree
a family tree that describes the interrelationships of parents and children across generations
- inheritance patterns of particular traits can be traced
- can be used to make predictions about future offspring
Many genetic disorders are inherited in a recessive manner
Albinism, sickle cell disease
Carriers
heterozygous individuals who carry the recessive alleles but are phenotypically normal
- recessive disorder babies (aa) born to them
- consanguineous (close relative sex) ups chances of diseased baby
cystic fibrosis
most common lethal genetic disease in the US
- allele results in defective/absent chloride transport channels
Sickle Cell disease
homozygous, all hemoglobin is abnormal
- African, substitute of 1 AA in hemoglobin protein
- heterozygous: usually healthy but have symptoms
- less susceptible to malaria
some human disorders are caused by dominant alleles
- rare and arise from dominant alleles
- dwarfism type is an example
the timing of onset of a disease affects…
its inheritance
- Huntington’s disease is lethal but doesn’t show up until 45
____ has a tremendous effect on phenotype for cardiovascular health and other multifactorial characters
lifestyle
Sex-linked genes exhibit unique patterns of inheritance
- small X chromosome and large Y chromosome (women:XX male:XY)
- only ends of Y chromosome have regions that are homologous with corresponding regions of the X chromosome
- the SRY gene on Y is required for testes
- only for mammals
sex-linked gene
A gene that is located on either sex chromosome
- genes on Y are called Y linked genes
- genes on X are called X-linked genes
Most Y-linked genes help determine Sex but X chromosomes….
have genes for many characters unrelated to sex - X-linked genes follow specific patterns of inheritance
For a recessive X-linked trait to be expressed:
- a female needs two copies of the alleles (homozygous)
- a male needs only one copy of the allele (heterozygous)
- much more common in males
