Unit 3 Chapter 13: Mendellian Genetics Flashcards
What is heredity
inheritance or the transmission of traits from parents to off spring
What is a trait
any characteristic of an individual
What is blending inheritance
one of the hypotheses to answer “what are basic patterns of transmission of traits from parents to offspring”
- claimed that the traits observed in a mother and father blend together to form the traits observed in their offspring.
- offspring traits are intermediate between mothers and fathers
What is inheritance of acquired traits
mendel’s second hypohesis
- claimed that traits present in parents are modified through use and passed on to their offspring in modified form
- kinda like natural selection in a way
Aside from practical reasons what are the 2 features of the pea that made it possible for Mendel to design his experiment were
- he could control which parents were involved in mating
2. he could arrange matings between individuals that differed in easily recognizable traits
How did Mendel control matings
cross fertilization (removed male reproductive organ from a flower before pollen formed, then transferred pollen from another pea plant to that flower’s female reproductive organ with a brush)
What is a pheneotype
what you see
What is a pure line
consists of individuals that produce offspring identical o themselves when they are self pollinated or crossed with another pure line member
What are hybrids
off spring from matings between true breeding parents that differ in one or more traits
What is continuous variation
here are a seemingly infinite number of traits for a given character. These traits fall along a continuous spectrum (i.e. height, skin color). “Blended inheritance”
What is discrete variation
there are only 2 or a few traits for a given character
ie. fur colour in mice
Does seed shape depend on whether or not the genetic determinant is in a male or female gamete
no, proven by mendel’s cross fertilization
What was Mendel’s first experiment
single trait crossed 2 individuals from round seed and wrinkled seed pure lines by taking pollen from round seed plants and putting it on the female reproductive organs of round seed plants
What were the results of Mendel’s first monohybrid cross
- produced all round peas
- proved that traits did not blend together to form an intermediate
What is a monohybrid cross
a mating between parents that each carry 2 different genetic determinants for the same traits
What are recessive traits
traits that become temporarily hidden and are only shown if an individual has 2 recessive alleles
What are dominant traits
traits that dominate over the other traits they are competing with
-always shown
What was Mendel’s second experiment
he planted the F1 generation from his monohybrid cross and allowed them to self fertilization and produce the F2 generation
What were the results of his second experiment
- 5474 round peas and 1850 wrinkled ones
- wrinkled trait reappeared
- lead to the terms dominant and recessive
What was Mendel’s third experiment
- wanted to test whether or not the sex of the parent influenced the inheritance of seed shape
- did a second set of crossed between 2 pure breeding lines but this time with pollen taken from wrinkled peas and brushed onto round organs
What is a reciprocal cross
- a set of matings where the mother’s phenotype in the initial cross is the father’s phenotype in a subsequent cross and the father’s in the initial cross is the mothers in the subsequent one
What were the results of his third experiment
- identical to his first
- proved seed shape has no dependence on sex of parents
What is particulate inheritance
- mendel’s revised hypthothesis
- hereditary determinants of traits do not blend together or acquire new modified traits through use, but they do maintain their integrity from generation to generation
- they act like discrete entities or particles
What are genes (in genetics)
hereditary determinants/units of heredity
What are alleles
different versions of the same gene
What is a genotype
alleles that are found in a particular individual, affects phenotype
What is the principle of segregation
2 members of each gene pair must segregate (separate into different gamete cells during the formation of sperm and egg in the parent)
-as a result, each gamete contains one allele for each gene
What does homozygous mean
2 copies of the same allele
What does heterozygous mean
2 different alleles for the same gene
What is the probability theory
the probability of 2 independent events is the product of the probability of each event
What was mendel’s extension of his research
- dihybrid cross
- crossed round yellow peas with green wrinkled ones (pure lines)
- hypothesis 1-law of independent assortment
- hypothesis2-dependent assortment
- predicted that F1 would be heterozygous for both genes
What is a dihybrid cross
-mating between 2 individuals that are both heterozygous for 2 traits
What is the law of independent assortment
-alleles of different genes present in each parent will separate from each other and be transmitted to offspring independently
What is dependent assortment
alleles of different genes stick together and are transmitted together
What were the results of Mendel’s dihybrid cross
- all of F1 had round yellow seeds, therefore they were heterozygous for both traits as predicted
- F2 generation made a 9:3:3:1 phenotype ratio
- concluded that the law of independent assortment holds true
What is a test cross
-uses a parent that contributes only recessive alleles to its offspring to help determine the unknown genotype of the second parent
In general, what were Mendel’s 4 accomplishments
- heredity exists as discrete units (alleles)
- units do not blend
- segregation of discrete paired genes into separate gametes
- law of independent assortment of alleles of different genes
What is a genetic locus
the physical location of a gene
Which stage of meiosis is responsible for Mendel’s principle of segregation
the separation of chromosomes/alleles in anaphase 1
What is the chromosome law of independent assortment
if the alleles for different genes are located on different non-homologous chromosomes, they assort independently in meiosis 1
What is the chromosome theory of inheritance
states that Mendel’s rules can be explained by the independent alignment and separation of homologous chromosomes during meiosis 1
What is a wild type
most common phenotype for each trait
What is a mutation
change in gene, individuals with mutations are called mutants
What is X-linked inheritance
-when a gene is only on the X-chromosome
What is Y-linked inheritance
when a gene is only on the Y-chromosome
What are X and Y linked inheritance both an example of
sex linked inheritance
What kind of inheritance do regular genes show
autosomal inheritance
What is linkage
the physical association among genes on the same chromosome
- linkage and sex linkage are NOT the same
- if 2 genes are linked they are on the same chromosome
- if a gene is sex linked it is on a sex chromosome
Is red-green colour blindess x or y linked
- x linked
- mostly in males
- affected females of affected fathers
- only males of unaffected parents are colour blind
What is a polymorphic allele
an allele that is present in more than 1% of the pop
Do linked (not sex linked) genes follow the law of independent assortment
no the law only applies to genes on different chromosomes
-unless crossing over occurs
Linked genes can be linked in cis or trans what do these mean
cis: dominant allele on one homolog and recessive on another ie. AB and ab : 50% AB gametes and 50%ab
trans; one dominant is linked to one recessive on one homolog and the other 2 on the other ie. Ab and aB; 50%Ae and 50%aB gametes
What does recombinant mean
individuals whose combination of alleles on their X chromosome is different from the combinations of alleles present in the parental generation
Why does no crossing over occur in male fruit flies
the chromosomes are not as closely associated
What is genetic recombination
- occurs when crossing over occurs
- occurs at random points on the chromsome
- the production of offspring with combinations of traits that differ from those found in either parent
- depends on how far apart the genes are on the chromsome
What is recombination rate
a measure of physical distance along the chromosome
- the more recombination the further apart the genes are
- distance (in centi morgans)= # of recombinants/divided by total # of progeny
What is a linkage group
all of the genes linked together on the same chromosome
What is incomplete dominance
when heterozygotes have an intermediate phenotype (ie. neither pure line dominates)
What is codominance
heterozygotes have the phenotype associated with each individual allele
-ie. AB blood type (both type A and B glycoproteins are present)
What is multiallelism
when more than 2 alleles are on the same gene
What are polymorphic traits
when more than 2 distinct phenotypes are present in a population due to multiple allelism
What is a pleiotropic gene
a gene that affects more than one trait (many)
What is gene-by-environment interaction
an individual’s phenotype is often as much a product of the physical environment as it is of the genotype
What is penetrance
% of individuals of a given genotype that show the phenotype at all
What is expressivity
the degree to which a phenotype is expressed
What are discrete traits
characteristics that are qualitatively different from eachother
-ie. colour, peas could be either yellow or green
What are qualitative traits
traits that exhibit quantitative variation like height or weight
What is polygenic inheritance
when each gene adds a small amount of value to the phenotype
What is gene by gene interaction
in discrete traits, the phenotype associated with an allele depends on which alleles are present at another gene
What is epistasis
the interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another
What is an allelic series
Different mutant alleles of a gene cause a range of phenotypes; each one carries a single point mutation within different regions of the same gene
What does tyrosinase do
converts tyrosine to melanin (pigment) in coat colours
