Ch. 1 Mendel's Principles of Heredity

phenotype

observable characteristic

alleles

alternate forms of a gene

independent assortment

alleles of one gene separate into gametes randomly with respect to alleles of other genes

• genes for different traits will segregate independently of each other during gamete formation

gametes

reproductive cells containing only one copy of each gene

gene

the heritable entity that determines a characteristic

segregation

the separation of the two alleles of a gene into different gametes

heterozygote

an individual with two different alleles of a gene

dominant

the allele expressed in the phenotype of the heterozygote

F1

offspring of the P generation

testcross

the cross of an individual of ambiguous genotype with a homozygous recessive individual

• performed to determine if an individual with the dominant characteristic is homozygous or heterozygous

  • an individual with the dominant phenotype but unknown genotype is crossed with an individual with the recessive phenotype

genotype

• the alleles an individual has

• the genetic makeup of an organism

  • written as alleles of specific genes

recessive

the allele that does not contribute to the phenotype of the heterozygote

• controls phenotype only in a homozygote

dihybrid cross

a cross between individuals both heterozygous for two genes

homozygote

having two identical alleles of a given gene

homozygous

when both alleles of a gene are the same, the individual is _____ for that gene

• also called pure breeding

heterozygous

if two alleles of a gene are different, the organism is _____

• also known as hybrid

monohybrid cross

a cross between individuals who are both heterozygotes for one gene

3:1

ratio of progeny phenotypes in a cross between monohybrids

• Aa x Aa → 3 A- (dominant phenotype) : 1 aa (recessive phenotype

1:2:1

ratio of progeny genotypes in a cross between monohybrids

• Aa x Aa → 1 AA : 2 Aa : 1 aa

1:1

ratio of progeny genotypes in a cross between a heterozygote and a recessive homozygote

• Aa x aa → 1 Aa : 1 aa

1:0

all progeny are the same phenotype. can result from either of two cases:

• AA x — → A- (all dominant phenotype)

• aa x aa → aa (all recessive phenotype)

9:3:3:1

ratio of progeny phenotypes in a dihybrid cross

• AaBb x AaBb → 9 A-B- : 3 A-bb : 3 aaB- : 1 aabb

2, 1

remember that ___ alleles of each gene exist when describing the genotypes of individuals. but if you are describing gametes, remember that only ___ allele of each gene is in a gamete

heterozygous, dominant

you will need to determine whether a character is dominant or recessive. two main clues will help you answer this question

• if the parents of a cross are true breeding for the alternative characters of the trait, look at the phenotype of the F1 progeny. their genotype must be _______, and their phenotype is thus determined by the dominant allele of the gene

• look at the F2 progeny (the progeny of the F1 hybrids). the ¾ portion of the 3:1 phenotypic ratio indicates the ______ character

testcross

you should recognize the need to set up a ____ to establish the genotype of an individual showing the dominant character by crossing this individual to a homozygote for the recessive allele

product, sum

what are the two basic rules of probability

product rule

if two outcomes must occur together as the result of independent events, the probability of one outcome and the other outcome is the product of the two individual probabilities

• what is the probability that event 1 and event 2 will occur?

  • P(1 and 2) = probability of event 1 x probability of event 2

sum rule

if there is more than one way in which an outcome can be produced, the probability of one or the other occurring is the sum of the two mutually exclusive individual probabilities

• what is the probability that event 1 or event 2 will occur?

  • P(1 or 2) = probability of event 1 + probability of event 2

conditional probability

an event’s probability is influenced by its relationship to another event that has already occured

branched line, probabilities

punnett squares are not the only means of analyzing a cross; _____ ____ diagrams and calculations of _____ using the product and sum riles are more efficient ways of looking at complicated crosses involving more than one or two genes

dominant, recessive

when the trait is rare, look for vertical patters of inheritance characteristic of _____ traits, and horizontal patters that typify _____ traits

artificial selection

purposeful control of mating by choice of parents for the next generation

• the first applied genetic technique

• however, the results were unpredictable

homunculus, blended inheritance

what were the two misleading theories of inheritance at the time of mendel’s studies

homunculus

inherited features of offspring are contributed mainly by only one parent; many microscopists thought they saw a fully formed, miniature fetus in the sperm head

• believed that the egg was just a receptacle for humans to grow

• females had no contribution to growth

blended inheritance

parental traits become mixed and changed in the offspring

1. the time between generations is relatively short

2. can obtain large numbers of offspring in each generation

3. antagonistic pair—traits are easily distinguishable (white vs. purple)

what were the three major benefits of using the pea plants as Mendel’s experimental organism

pure breeding

organism will always make more offspring identical to itself when self fertilized over many generations

one

how many parental traits do F1 (first filial) progenies have

dominant

traist that appear in the F1 progeny is the ____ form

recessive

traits that is hidden in the F1 progeny is the _____ form

monohybrids

individuals with two different alleles for a single trait are ______

blended inheritance

each of mendel’s hybrids remembling only one of the parents disproves which theory?

homunculus

mendel performed reciprocal crosses (switching traits of male and female parents) and observed the same results, disproving what?

gamete formation

how do progeny inherit only one unit from each parent

mendel’s law of segregation

the two alleles for each trait separate during gamete formation, such that each gamete will only form one allele

diploid

two gametes, one from each parent, unite at random at fertilization to produce a (haploid/diploid) gamete

gametes

the number of different ______ = (# of different alleles for gene 1) x (# of different alleles for gene 2) x …. and so on

• Aa Bb Cc Dd → 2×2×2×2=16 kinds

• Aa BB Cc DD → 2×1×2×1=4 kinds

phenotype

a specific gene determines a specific enzyme, whose activity may affect ______

dominant

a _____ allele usually determines a normally functioning protein

recessive

a _____ allele usually does not encode a functional protein

1. long generation time

2. small numbers of progeny

3. no controlled matings

4. no pure-breeding lines

what are four reasons why determining inheritance patterns in humans might be tricky

pedigrees

orderly diagrams of a family’s relevant genetic features

vertical

a _____ pattern of inheritance indicates a rare dominant trait; e.g. huntington’s disease

• every infected person has at least one affected parent

• mating between affected person and unaffected person is effectively a testcross

horizontal

a _____ pattern of inheritance indicates a rare recessive trait; e.g. cystic fibrosis

• parents of affected individuals are unaffected but are heterozygous (carriers) for the recessive allele

1. affected children always have at least one affected parent

2. as a result, dominant traits show a vertical pattern of inheritance

3. two affected parents can produce unaffected children, if both parents are heterozygotes

what are the three key aspects of pedigrees with dominant traits?

1. affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous matings

2. all the children of two affected parents should be affected

3. rare recessive traits show a horizontal pattern of inheritance

4. recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population

what are the four key aspects of pedigrees with recessive traits?