Chapter 3

Question 1

Do genes on the same chromosome generally assort independently?

Answer 1

• no, they are held together by the chromosome itself so it’s hard to assort independently
• most just genes on different chromosomes

Question 2

How do you represent genes are on different chromosomes?

Answer 2

• gene pairs are separated by a semicolon

- ex: A/a;B/b

Question 3

How do you represent genes on the same chromosome?

Answer 3

• the alleles on the homologs have no punctuation and are separated by the other homolog by a slash
• ex: AB/ab or Ab/aB

Question 4

How do you represent genes that you don’t know if they’re on the same or different chromosomes?

Answer 4

• use a dot between the gene pairs

- ex: A/a . B/b

Question 5

What are 2 common ratios found in dihybrid crosses?

Answer 5

• 9:3:3:1

- 1:1:1:1

Question 6

What are 2 visual methods to predict genetics?

Answer 6

• Punnett square

- branch diagram

Question 7

What are 2 calculating methods to predict genetics?

Answer 7

• product rule

- sum rule

Question 8

What does the probability value mean for a chi squared test?

Answer 8

• the probability of observing a deviation form the expected results at least as large as on the basis of chance if the hypotehsis was right

Question 9

T/F: Chi squared test resulting in a p value of <0.05 means the hypothesis is true

Answer 9

• false- only means the results are compatible with the hypothesis

Question 10

T/F: the chi squared test depends heavily on sample sizes

Answer 10

• true

Question 11

How could you increase the proportion of homozygotes?

Answer 11

• repeated selfing in plants makes pure lines

- for animals selfing = mating animals of similar genotypes

Question 12

What are 2 negative aspects of hybrid vigor?

Answer 12

• each season the parental plants need to be grown separately, making hybrid seeds more expensive
  (its more inconvenient than just letting the plant self)
• once the hybrid plants have grown the seeds aren’t as good because they have gone through meiosis (independent assortment) so ~1/2 are homozygous and not as god as the heterozygotes

Question 13

By crossing autosomal and X-linked trait at the same time, what phenotypic ratio might you get?

Answer 13

• 9:3:3:1

Question 14

What is one of the main ways an organism produces new combinations of alleles?

Answer 14

• independent assortment of genes at meiosis

Question 15

Define meiotic recombination

Answer 15

• any meiotic process that generates a haploid product with new combinations of the alleles carried by the heploid genotypes that united to form the meiocyte
• compare inputs with outputs

Question 16

Which is harder: detecting recombinants in organisms with haploid life cycles or diploid life cycles?

Answer 16

• diploid life cycles because their inputs and outputs are gametes, so you need to figure out the genotype
• in haploid life cycles the input and output are the genotypes of individuals, not the gametes, so it can be inferred directly from the phenotype

Question 17

What are 2 ways we can infer the genotypes of diploid organisms to know if they’re recombinant?

Answer 17

1) to know the input gametes- use pure-breeding diploid parents b/c they can produce only 1 gametic type
2) to detect recombinant output gametes- testcross the diploid individual and observe progeny

Question 18

What are the 2 different cellular processes that produce recombinants?

Answer 18

1) independent assortment of genes on different chromosomes

2) crossing over between genes on different chromosomes (ch. 4)

Question 19

Why is the proportion of recombinants important? (recombination frequency)

Answer 19

• this value can tell us the whether genes are on different chromosomes

Question 20

What is the genotypic ratio seen with genes on separate chromosomes?

Answer 20

• 1:1:1:1

- P:P:R:R

Question 21

What’s the recombinant frequency that tells us the genes assort independently, and most likely are on separate chromosomes?

Answer 21

• 50%

Question 22

Define law of independent assortment

Answer 22

• Mendel’s second law

- unlinked or distantly linked segregating gene pairs assort independently at meiosis

Question 23

Define polygenes

Answer 23

• quantitative trait locus
• a gene whose alleles are capable of interacting additively with alleles at other loci to affect a phenotype (trait) showing continuous distribution

Question 24

Define dihybrid

Answer 24

• a double heterozygote

- ex A/a . B/b

Question 25

Define dihybrid cross

Answer 25

• a cross between 2 individuals identically heterozygous at 2 loci
• ex AB/ab x AB/ab

Question 26

Define hybrid vigor

Answer 26

• a situaiton in which an F1 is larger or healthier than its two different pure parental lines

Question 27

Define recombination

Answer 27

1) in general, any process in a diploid or partially diploid cell that generates new gene or chromosomal combinations not previously found in that cell or in its progenitors
2) at meiosis, the process that generates a haploid product of meiosis whose genotype is different from either of the 2 haploid genotypes that constituted the meiotic diploid

Question 28

Define recombinant

Answer 28

• refers to an individual organism or cell having a genotype produced by recombination

Question 29

Define sum rule

Answer 29

• the probability that one or the other of 2 mutually exclusive events will occur is the sum of their individual probabilities

Question 30

Define meiotic recombination

Answer 30

• recombination from assortment or crossing over at meiosis