Mendelian Genetics and Inheritance Flashcards
what is tooth agenesis?
- failure of a tooth to form
- the most common heritable disorder in humans
tooth agenesis affects ___% of the population worldwide, if ___ are excluded
- 4-7%
- 3rd molars
of the population affected by tooth agenesis, ___% are missing 3 or more teeth
1%
if 3rd molars are included in tooth agenesis stats, ___% of the population is considered to be affected by tooth agenesis
20%
mendelian genetics is a model of ___ first described by gregor mendel
inheritance
what is a phenotype?
a physical trait
mendel cross bred plants with various phenotypes and recorded the ratio of offspring across generations. this led him to formulate his ___
3 laws of inheritance
name the 3 laws of inheritance
- the law of segregation
- the law of independent assortment
- the law of dominance
what is the law of segregation?
- factors for each trait segregate, such that each gamete carries only one factor for each trait
what is the law of independent assortment?
each factor that segregates does so independently
what is the law of dominance?
some factors are dominant and some are recessive. the dominant trait will always be expressed when present
what are mendel’s heritable factors referred to as?
alleles
what are alleles?
- the different forms of a gene
- for example, flower color
law of segregation
there are ___ copies of each allele, and further, they are ___
- two
- separated
- consider meiosis: diploid (2n) cells become haploid (1n)
the law of segregation
one copy of a ___ comes from one parent, and the other copy comes from the second parent
gene (allele)
law of independent assortment
mendel concluded that not only did copies of a single allele separate, but that alleles for different traits separated ___ of one another
- independently
- for example: flower color and seed color both have an allele with 2 copies. both of these alleles will be distributed according to the law of segregation, but will do so independently of one another.
law of independent assortment
the number of ___ depends on the number of ___ we are considering
- combinations
- alleles
law of dominance
mendel observed that each trait has a ___ and ___ form
dominant and recessive
law of dominance
a ___ allele will always be expressed when present
dominant
law of dominance
what must occur in order for a recessive allele to be expressed?
both copies of the allele must be recessive
in other words, the dominant allele must not be present
describe the difference between homozygous and heterozygous
- homozygous: organisms can be either homozygous dominant or homozygous recessive, and therefore will only pass along the allele they express
- ex. AA or aa
- heterozygous: organisms will always express the dominant allele, while carrying (and passing) the recessive allele
- ex. Aa
does dominance imply normality?
no; it is simply preferred expression
dominance is not ___, but relative to an allele that is also present
inherent
T or F:
dominant traits are always the most common in a population
false:
they can actually be rare
what is a genotype?
alleles that are present
vs. phenotype, which are the traits that are expressed
in mendel’s observations from his second generation crosses, he observed a phenotypic ratio of ___:___
3 dominant : 1 recessive
in the first generation, assuming a cross between two “true breeding” or homozygous organisms, we will always get what? what laws of inheritance do we see here?
- heterozygotes, expressing the dominant allele
- 1st and 3rd laws
once we start crossing the results of the F1 generation, are we dealing with true breeding parents?
no
breeding of what generation yields mendel’s 3:1 phenotypic ratio?
breeding of the F1 generation, so the F2 generation shows the 3:1 phenotypic ratio
what is the phenotypic composition of the F2 generation when parents of the F1 generation are true breeders? which laws of inheritance are seen?
- 50% true breeding (homozygous) and 50% heterozygous organisms
- 1st and 3rd laws
- this will be the result regardless of the offspring chosen from the F1 generation
the fact that recessive genes can be carried allows the ___ of certain genes, even if they aren’t favored when expressed.
- preservation
- it will eventually allow a recessive phenotype to resurface should environmental selection pressure change
___ and ___ allows a species to resist extinction
genetic variability and selection
any patterns of inheritance which do not strictly follow the three laws of inheritance are said to be ___
non-mendelian
what are two examples of co-dominance?
- more than two possible alleles, even though each individual only carries two copies
- situations where more than one of these possible alleles are dominant, and can be expressed as a distinct co-dominant phenotype
blood groups are an example of what?
co-dominance
*non-mendelian genetics
what is incomplete dominance?
snapdragon example
- if the alleles for white flowers (recessive) and red flowers (dominant) are both present, you end up with a weaker expression of red, resulting in pink flowers
- there is no allele for pink flowers, but it is a possible phenotype when both red and white alleles are present
what is mosaicism?
- when different cells in the body have different genotypes, and thus express different phenotypes
- calico cats are an exmaple
sex-linked dominance
a __-linked trait would only be passed on to male offspring, and is relatively small so it contains ___ genes.
- Y
- fewer
sex-linked dominance
for __-linked dominant traits, inheritance depends on the relative genotypes of the parents
X
sex-linked dominance
a father with a dominant X trait will pass it to his ___ but not his ___. a mother would distribute ___% of all offspring depending on her genotype.
- daughters
- sons
- 50-100%
sex-linked dominance
which traits will predominate in males? which females will be affected?
- X-linked recessive
- females who are homozygous are affected
sex-linked dominance
___ in females can result in limited expression of an X-linked recessive trait
X-inactivation
what is extranuclear inheritance? what is an example?
- factors passed form the cytoplasm
- ex. mitochondrial DNA all comes from the ova
___ is a recombination event where DNA sequence from one homologous chromosome can replace a sequence on its counterpart.
gene conversion
gene conversion can interfere with ___
mendelian ratios
describe infectious heredity
when integrated traits introduced by a virus are passed along the germ line; this is typically passed directly along from one parent
T or F:
traits result as equal contributions from parent organisms
not always
