Chapter 3

Question 1

what are dihybrid crosses used for?

Answer 1

to study the simultaneous transmission of two traits

Question 2

what ratio was F1 if two pure breeding individuals mate in a dihybrid cross, and how many phenotypes are possible?

Answer 2

1:1:1:1
-4 phenotypes are possible

Question 3

if genes assort independently, what is the phenotypic ratio of the F1 offspring?

Answer 3

1:1:1:1

Question 4

what ratios did the dihybrid cross produce for F2, and how many possible phenotypes?

Answer 4

a 3:1 ratio for each trait and a 9:3:3:1 ratio for the combined phenotypes, and 16 possible phenotypes

Question 5

in dihybrid crosses, can you examine single traits?

Answer 5

yes because these traits are independent of each other

Question 6

what is the law of independent assortment?

Answer 6

mendel’s second law: During the formation of gametes, segregation of alleles at one locus is
independent of segregation of alleles at another locus

Question 7

What is the chi-square test?

Answer 7

a statistical way to check scientific results

Question 8

What is the null hypothesis?

Answer 8

there is no difference between the observed and expected values–>Any difference we see between observed and expected is just due to chance.

Question 9

how do you determine the degrees of freedom?

Answer 9

the number of outcome classes minus 1.

Question 10

what does the p-value tell us?

Answer 10

the probability that the outcome was due to chance.

Question 11

what does it mean if the chi-squared value is very small?

Answer 11

because the differences are small, we can not reject the null hypothesis and there is no difference between observed and expected
values.

Question 12

for what p-value do we usually reject the null?

Answer 12

when p<0.05 because this means to reject the null, there has to be less than 5% chance that the outcomes are due to chance

Question 13

what are organelle genes, and what is a key characteristic?

Answer 13

-DNA in mitochondria and organelle genomes
-inheritance is independent of the nucleus

Question 14

What are 3 characteristics of maternal inheritance?

Answer 14

1. Organelles exist in cytoplasm
2. Eggs contribute the bulk of cytoplasm
3. None of the organelle DNA is from father

Question 15

what does a pedigree for an organelle disease look like?

Answer 15

-if mom has trait, all offspring have it
-if dad has trait and mom doesn’t. none of the offspring have it

Question 16

what is cytoplasmic segregation?

Answer 16

multiple copies of organelle DNA in a cell

Question 17

What are 2 characteristics of human mitochondrial DNA (mtDNA) mutations

Answer 17

1. Mutations arise in only 1 mitochondrion and proliferate through cell division
2. Some of the mutations in human
   mitochondrial genes can lead to disease when, by random drift or cytoplasmic segregation, they rise in frequency to such an extent that cell function is impaired

Question 18

stages of meiosis?

Answer 18

interphase: chromosomes are unpaired
prophase: chromosomes and centromeres have replicated, but centromeres have not split
prophase: homologs synapse
anaphase: centromeres attach to spindle and are pulled to poles of cell
telophase: two cells form
second anaphase: new spindles form, and centromeres finally divide
end of meiosis: four cells from each meiosis(meaning allelic combinations for which version of meiosis it goes through are equally frequent)