Chapter 3 Flashcards
Do genes on the same chromosome generally assort independently?
- no, they are held together by the chromosome itself so it’s hard to assort independently
- most just genes on different chromosomes
How do you represent genes are on different chromosomes?
- gene pairs are separated by a semicolon
- ex: A/a;B/b
How do you represent genes on the same chromosome?
- the alleles on the homologs have no punctuation and are separated by the other homolog by a slash
- ex: AB/ab or Ab/aB
How do you represent genes that you don’t know if they’re on the same or different chromosomes?
- use a dot between the gene pairs
- ex: A/a . B/b
What are 2 common ratios found in dihybrid crosses?
- 9:3:3:1
- 1:1:1:1
What are 2 visual methods to predict genetics?
- Punnett square
- branch diagram
What are 2 calculating methods to predict genetics?
- product rule
- sum rule
What does the probability value mean for a chi squared test?
- 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
T/F: Chi squared test resulting in a p value of <0.05 means the hypothesis is true
- false- only means the results are compatible with the hypothesis
T/F: the chi squared test depends heavily on sample sizes
- true
How could you increase the proportion of homozygotes?
- repeated selfing in plants makes pure lines
- for animals selfing = mating animals of similar genotypes
What are 2 negative aspects of hybrid vigor?
- 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
By crossing autosomal and X-linked trait at the same time, what phenotypic ratio might you get?
- 9:3:3:1
What is one of the main ways an organism produces new combinations of alleles?
- independent assortment of genes at meiosis
Define meiotic recombination
- 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
Which is harder: detecting recombinants in organisms with haploid life cycles or diploid life cycles?
- 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
What are 2 ways we can infer the genotypes of diploid organisms to know if they’re recombinant?
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
What are the 2 different cellular processes that produce recombinants?
1) independent assortment of genes on different chromosomes
2) crossing over between genes on different chromosomes (ch. 4)
Why is the proportion of recombinants important? (recombination frequency)
- this value can tell us the whether genes are on different chromosomes
What is the genotypic ratio seen with genes on separate chromosomes?
- 1:1:1:1
- P:P:R:R
What’s the recombinant frequency that tells us the genes assort independently, and most likely are on separate chromosomes?
- 50%
Define law of independent assortment
- Mendel’s second law
- unlinked or distantly linked segregating gene pairs assort independently at meiosis
Define polygenes
- 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
Define dihybrid
- a double heterozygote
- ex A/a . B/b
Define dihybrid cross
- a cross between 2 individuals identically heterozygous at 2 loci
- ex AB/ab x AB/ab
Define hybrid vigor
- a situaiton in which an F1 is larger or healthier than its two different pure parental lines
Define recombination
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
Define recombinant
- refers to an individual organism or cell having a genotype produced by recombination
Define sum rule
- the probability that one or the other of 2 mutually exclusive events will occur is the sum of their individual probabilities
Define meiotic recombination
- recombination from assortment or crossing over at meiosis
