human genetic traits

Question 1

in coupling vs in repulsion

Answer 1

Dominant genes on same chromosome in F1 are said to be “in coupling” (cis arrangement)

Dominant genes on separate chromosomes are said to be “in repulsion” (trans arrangement)

Question 2

If the middle gene is swapped, that indicates that there was a ____

Answer 2

double crossover

Question 3

3 point test cross

Answer 3

following three genes.

ex: ‘prj’

Question 4

test cross +++prj x prj results; how many unique offspring?

Answer 4

notation +++/prj means that the +’s are the dominant form of p,r and i. Cross with homozygous recessive tester to form gametes.

unique gametes = 2 ^n

3 heterozygous genes: (n=3). 2^n =8

Question 5

how do you identify the parental types in a 3 point test cross?

Answer 5

The big numbers are the parental types, the ones that have the chromosomes just as they appear in the first generation, and since crossing over is relatively rare, the #’s that get the chromosomes intact will be highest.

Question 6

how do u identify the double crossovers in a 3 point test cross

Answer 6

these will be the smallest numbers

Question 7

how do you evaluate in a 3 point cross which gene was switched?

Answer 7

Then, compare the results you see in the least frequent classes (the double crossovers) with the parental phenotypes to find the arrangement. Where do you see a difference? Here, the difference is in the “juicy” gene, that was switched. That tells us that the juicy gene is the one that’s in the middle of the three.

Question 8

expected ratio offspring of NON LINKED genes?

Answer 8

2 non parental phenotype : 2 parental phenotype

(50% non parental)

Question 9

expected phenotypic ratio of completely linked genes

Answer 9

0 non parental/2 parental (1:1 heterozygous, homozygous)

Question 10

expected phenotypic ratio linked genes

Answer 10

something crazy! like 165:162:5:5 or something.

Question 11

do linked genes show independent assortment

Answer 11

genes that are not on separate chromosomes do not show independent assortment

Question 12

If recombinants are forming 10% of the time we say these genes are __ map units (mu) apart

Answer 12

10

Question 13

when would you use a Chi Square test

Answer 13

If you do a dihybrid test cross with genes that you expect are on separate chromosomes, you would expect to get the phenotype in a 1:1:1:1 ratio.

However, if the data shows differences, ppl use chi square test

Question 14

how do you use a chi square test?

Question 15

Allelic frequency:

Answer 15

frequency of just the single ‘W’ or ‘w’ result. a measure of the relative frequency of an allele on a genetic locus in a population. shows the genetic diversity of a species population

Question 16

Genotypic frequencies

Answer 16

frequency of WW, Ww, or ww.

Question 17

Phenotypic frequencies

Answer 17

• percent of the population showing the dominant vs the recessive phenotype

Question 18

Hardy + Weinberg equation for allelic frequencies

Answer 18

(p+q)^2=1.

p^2+ 2pq+ q^2=1.

why 2? b/c we’re diploid.

Question 19

Population of 100 cats. 84 black, 16 white. Black as dominant B, b as recessive form. Calculate frequency of phenotypes.

Answer 19

84% black, 16% white

Question 20

84 black cats, 16 white cats. calculate allelic frequencies

Answer 20

Probability of having B is p, b is q.

p^2+ 2pq+ q^2=1.

• 1.* Q^2 = 0.16 . q=0.4. (allelic ratio)
  2. P=1-q. 1-0.4. p=0.6.

Question 21

84 black cats, 16 white cats. calculate GENOTYPIC frequencies.

Answer 21

p^2+ 2pq+ q^2=1

q^2 = 0.16. q=0.4 . p=1-0.4. p=0.6

now: p^2: 0.36 : 36% BB
2pq: 0.48 : 48% Bb

q^2: .16: 16% bb.