Mendelian Inheritance

Question 1

monohybrid cross

Answer 1

cross between two parents that differ in a single characteristic

Question 2

4 conclusions

Answer 2

1. one character is encoded by two genetic factors
2. two genetic factors separate when gametes are formed
3. concept of dominant and recessive traits
4. two alleles separate with equal probability into the gametes

Question 3

true breeding strains

Answer 3

physical appearance of offspring in each successive generation is identical to previous one

Question 4

reciprocal cross

Answer 4

two crosses are performed between a pair of individuals, but the sexes of the individuals contributing specific traits are reversed in the second cross. This approach is used to determine whether a particular trait is influenced by the sex of the parent or by sex-linked inheritance.

Question 5

mendels experiment

Answer 5

(1. prevent self fertilisation)
2. cross true breeding strains of parents to produce F1 progeny
3. performed reciprocal crosses
4. allow F1 to self fertilise to produce F2

Question 6

mendel’s findings

Answer 6

F1 progeny of a cross between plants with different traits did not breed true
in F2, the recessive trait reappeared
3:1 ratio in F2 for the traits

Question 7

what mendel concluded from his findings

Answer 7

inheritance is not blending
F1 still has information for both phenotypes
alleles segregate 50:50

Question 8

law of segregation

Answer 8

each individual diploid organism possesses two alleles for any characteristic and these two alleles segregate when gametes are formed where one goes into each gamete

Question 9

backcross

Answer 9

F1 crossed with one parent

Question 10

testcross

Answer 10

individual of unknown genotype crossed to known type

Question 11

degrees of freedom

Answer 11

number of phenotypes - 1

Question 12

incomplete dominance

Answer 12

phenotype of the heterozygous genotype is intermediate between those of the homozygous genotypes
appears like blending inheritance in F1 but parental phenotypes reappear in F2
1:2:1

Question 13

dihybrid cross

Answer 13

genetic cross between two individuals that differ in two traits, each determined by two alleles. The purpose of a dihybrid cross is to examine how alleles for two different traits segregate and independently assort during meiosis, following Mendel’s Law of Independent Assortment.

Question 14

mendels dihybrid cross

Answer 14

because of dominance, the seeds in F1 are genetically identical
F1 can produce 4 different types of gametes
9:3:3:1 because the alleles for the different traits are assorted into gametes independently of each other

Question 15

independent assortment

Answer 15

nonhomologous chromosomes can orient in either of two ways that are equally likely

Question 16

segregation ratios for two loci on the same chromosome

Answer 16

dependent on the rate of crossing over between the loci
no crossing over forms non recombinants

Question 17

dihybrid cross for linked genes, no crossing over

Answer 17

only nonrecombinant progeny produced
linked genes segregate together and crossing over produces recombination between them

Question 18

dihybrid cross for unlinked genes

Answer 18

half progeny are recombinant and half are not
due to independent assortment

Question 19

estimating crossing over rate

Answer 19

recombination frequency= (number of recombinant progeny/total number of progeny) x100
used to find order and distance between loci on a chromosome (linkage map)

Question 20

epistasis

Answer 20

effect of one locus on a phenotype depends on genotype at the second locus
gives alternative ratios to 9:3:3:1

Question 21

penetrance

Answer 21

how many individuals with a genotype show a phenotype

Question 22

expressivity

Answer 22

how variable is the degree/severity of the phenotype

Question 23

incomplete penetrance

Answer 23

Individuals with a genotype corresponding to a trait do not actually show the phenotype, either because of environmental effects or because of interactions with other genes.
The trait is either expressed or it is not.

Question 24

variable expressivity

Answer 24

A particular phenotype is expressed with a different degree of severity in different individuals.
The trait is always expressed, though the severity varies.

Question 25

what to look out for in a dominant trait in a pedigree analysis

Answer 25

check affected individuals are equalling likely to be females or males
most matings that produce affected offspsring should have only one affected parent
among matings in which one parent is affected, half the offspring should be affected
affected individuals should appear in each successive generation

Question 26

what to look out for a recessive trait in a pedigree analysis

Answer 26

again males=females
trait may skip one or more generations
individuals may have unaffected parents