BIS 101 Lecture Notes - Lecture 2: Dihybrid Cross, Chromosome Segregation, Mendelian Inheritance
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Which of these statements is incorrect?
Syntenic genes are located on the same chromosome. |
Independent assortment results in recombinant chromosomes. |
You can reliably predict the relative genetic distance fromgenesâ physical distance on a chromosome. |
Linked genes are always syntenic. |
What is the relative genetic distance between two linked genesif the recombination frequency is 0.49?
0.49 cM |
4.9 cM |
49 cM |
490 cM |
What statement best explains the distortion in Mendelian ratiosobserved by Bateson & Punnett in 1905? (Reminder: they found anoverrepresentation of F2 offspring showing both dominant orrecessive phenotypes, and an underrepresentation of offspringdisplaying one dominant and one recessive phenotype)
Human error: they should have been more careful about theirexperimental setup. |
Gene linkage: Genes for flower color and pollen shape arephysically close on the same chromosome, leading to a breakdown inthe independent assortment of the alleles for these traits. |
Chromosome crossover: Homologous recombination of twochromatids during meiosis caused the alleles to shuffle, resultingin a breakdown of the independent assortment of the alleles forthose genes. |
Random variation: No two situations are alike. In finitepopulations, you are going to get some variation across a mean. |
When determining the relative genetic distance between twogenes, why is dihybrid back-cross preferable over traditionaldihybrid cross?
9:3:3:1 phenotypic ratio is easier to work with than 1:1:1:1ratio. |
Genotypes of the offspring can be determined based on theirphenotype. |
If the genes are independently assorted, the dihybrid back-crosswould result in only 2 genotypes in the F1 generation. |
B and C |
Why do we map genes?
To understand how genes interact with each other |
Comparative genomics analysis |
To determine the genotype of an organism |
All of the above |
These all relate to exceptions to the inheritance patterns encountered by Mendel.â
Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?
Select the four correct statements.
-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios. |
-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance. |
-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance. |
-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios. |
-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios. |
-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios. |
-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon. |
-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon. |
In what phases is the genetic material in the cell correctly referred to as chromatids?
A. | metaphase and telophase | |
B. | anaphase and metaphase | |
C. | interphase and telophase | |
D. | interphase and prophase | |
E. | metaphase and prophase |
Consider two traits for an organism, determined by two genes, each of which is governed by at least two alleles. In the case of a dihybrid individual, the gametes formed will be of either the parental type or the recombinant type. Recombinant type gametes are formed because of
A. | the principle of dihybrids. | |
B. | multiple alleles. | |
C. | heterozygosity. | |
D. | incomplete dominance. | |
E. | independent assortment. |
An allele is
A. | an alternate form of a gene. | |
B. | always recessive. | |
C. | the main factor determining a trait. | |
D. | always one of a pair. | |
E. | the dominant form of a gene. |
After the DNA is replicated, and it condenses in prophase, two identical rods of DNA are seen. These are
A. | spindle fibers. | |
B. | kinetochores. | |
C. | chromatids. | |
D. | chromatin. | |
E. | centromeres. |
Special cells found in the gonads that give rise to gametes upon division are called
A. | egg cells. | |
B. | somatic cells. | |
C. | germ cells. | |
D. | stem cells. | |
E. | basal cells. |