week 6 review questions Flashcards
- What is the difference between the ‘blending’ and ‘particulate’ models of inheritance? [see the relevant slide in the power-point to help answer this question] Which of these two models was in favor during the time Gregor Mendel was carrying out his research?
Blending: The idea that genetic material from the two parents blend together. Particulate: is the idea that the parents pass on discrete heritable units (genes).
During Mendel’s time blending was in favor although today that is not the case.
- Multiple Choice: Which of the following is true of Gregor Mendel?
A. He is known as the Father of Genetics B. His work with Pisum sativum demonstrated that the ‘blending’ model of inheritance is not correct C. His work involved crosses of true-breeding plants in which traits were controlled by a single gene D. His work with monohybrid crosses led to his Law of Independent Assortment E. His work with dihybrid crosses led to his Law of Segregation F. More than one of these is correct (which ones?)
A. He is known as the Father of Genetics B. His work with Pisum sativum demonstrated that the ‘blending’ model of inheritance is not correct C. His work involved crosses of true-breeding plants in which traits were controlled by a single gene
- Speaking of Mendel’s Laws…the Law of Segregation states that members of each pair of genes on homologous chromosomes end up in different gametes during meiosis (from the textbook)…what does this mean in terms of alleles? What are genes? What are chromosomes? What are homologous chromosomes? What are alleles? Mendel’s Law of Independent Assortment states that members of a pair of genes on homologous chromosomes are distributed into gametes independently of other gene pairs…what does this mean? Is this because the genes are on different chromosomes? A little tougher–what if the genes are on the same chromosome, could Cross-Over have anything to do with this? [when is Cross-Over more likely—when genes are located close together or widely separated on the chromosome?]
Each pair of alleles is sorted into gametes independently of other pairs during meiosis. Genes: a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring. Chromosomes: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Homologous Chromosomes: are similar but not identical. Each carries the same genes in the same order, but the alleles for each trait may not be the same. Alleles: one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
This means that each carries the same gene in the same order but alleles for each trait may not be the same (because genes are located on different pairs of homologous chromosomes)
Cross-over is more likely to happen when the genes are closer together on the chromosome.
- What is a locus (plural loci)? What is the difference between a character and a trait? What is the difference between genotype and phenotype? What is meant by the term ‘true-breeding’? What is meant by the term ‘hybrid’? What is the difference between homozygous and heterozygous? What is the difference between dominant and recessive alleles?
Locus (plural loci): is the specific location of a gene, DNA sequence, or position on a chromosome.
Character: a heritable feature that varies among individuals, such as flower color. Trait: each variant for a character, such as purple or white color for flowers. A genotype reflects which alleles are present and . a phenotype refer to an individuals’ observable traits. Homozygous: An individual with two identical alleles of a gene, Heterozygous: An individual with non-identical alleles of a gene. True breeding: individual that is homozygous for a particular trait; the same trait is produced over many generations.
A hybrid is the heterozygote offspring of a cross between two individuals that breed true for different forms of a trait. Dominant Allele: an allele that is fully expressed in the phenotype of a heterozygote.
Recessive Allele: an allele that is not expressed in the phenotype of a heterozygote.
True or False: AA and aa are both genotypes indicating a homozygous condition (both true-breeding, with the difference being that A is dominant over a). True or False: Aa is a genotype indicating a heterozygous condition (a hybrid) True or False: A true-breeding AA parent can only produce A gametes. True or False: A true-breeding aa parent can only produce a gametes. True or False: A hybrid Aa parent can produce both A and a gametes.
All True
True or False: The expected genotypic ratio of the F1 offspring of a Monohybrid Cross is 3:1
True or False: The expected genotypic ratio of the F2 offspring of a Monohybrid Cross is 3:1
True or False: The expected phenotypic ratio of the F1 offspring of a Monohybrid Cross is 3:1
True or False: The expected phenotypic ratio of the F2 offspring of a Monohybrid Cross is 3:1
False for first three: The monohybrid cross happens in F2 The genotypic ratio is 1:2:1 The Phenotypic ratio: 1:1 (all would be pink polka dot) True
True or False: If the color purple is dominant over the color blue—can someone determine the genotype of an individual by observing the phenotype?
False. Could be HH or Hh
What does P, F1, and F2 stand for? Is this used in both Monohybrid and Dihybrid Crosses?
P: parental generation F1: First Offspring Generation F2: Second Offspring Generation
True or False: A Monohybrid Cross involves a single gene whereas a Dihybrid Cross involves two genes (typically located on different chromosomes)*
true.
Multiple Choice: Which of the following is true for the Dihybrid Cross shown in the power-point? Mendel’s height and flower color in pea plants (tall purple X dwarf white plants)
A. In the P generation, true-breeding double dominant parents produce only ab gametes B. In the P generation, true-breeding double recessive parents produce only ab gametes C. In the F1 generation, all offspring are double heterozygotes AaBb D. F1 individuals produce the following gametes: AA, aa, BB and bb E. F2 offspring exhibit four genotypes and a 9:3:3:1 genotypic ratio F. F2 offspring exhibit 9 phenotypes and a 1:2:1:2:4:2:1:2:1 phenotypic ratio
C. In the F1 generation, all offspring are double heterozygotes AaBb
Refer to the slide showing Mendel’s Dihybrid Cross for plant height/flower color. What would the Punnett Square for a Dihybrid Cross look like? How many squares (indicating all combinations of alleles from parental gametes)? How many genotypes result? (hint: not the same as the number of squares…why?) Refer to the slide showing the breakdown of the genotypes obtained in the F2 generation of the Dihybrid Cross. Did you assign a phenotype to all of the genotypes listed? Talk your way through the set-up (cross of two parents that are true-breeding for two traits) and the actual Dihybrid Cross (cross of F1 double heterozygotes)—what is the result of each cross? Which phenotypes result? What is the ratio? How many genotypes result?
The Punnett square if a dihybrid cross would be 4 x 4 16 squares total. 9 genotypes, 4 phenotypes geno ratio: 1:2:1:2:4:2:1:2:1 Flower color (3:1 phenotypic ratio) Height (3:1 phenotypic ratio) And together (9:3:3:1 phenotypic ratio)
What if the results of a Monohybrid or Dihybrid Cross do not produce the predicted phenotypes and ratios? Mendelian Genetics involves traits controlled by a single gene (we might be looking at more than one gene at a time, as in the Dihybrid Cross) but there is a simple dominance relationship (known as complete dominance) operating between the alleles…one allele masks the expression of the other (this is why all of the F1 offspring in a Monohybrid Cross demonstrate the dominant trait, but when these hybrids are crossed (they are not true-breeding) we see the reappearance of the recessive trait in the F2 offspring). If we do not obtain a 3:1 phenotypic ratio in the F2 generation of Monohybrid Cross, co-dominance or incomplete dominance is likely operating—what is the difference between these two relationships between alleles?
Only possible if characters areOnly possible if characters are transmitted independently if one character affected another, ratios would be very different.
Mendel’s Law of Independent Assortment: During gamete formation, members of one pair of ‘genetic factors’ are distributed into gametes independently of other pair. What happens when to one gene does not affect the other.
Multiple Choice: A Monohybrid Cross involving a true breeding blue frog crossed with a true-breeding red from results in all purple frogs in the F1 generation… a. this is complete dominance b. this is incomplete dominance c. this is co-dominance d. this is baloney, there is no such thing as purple frogs
this is incomplete dominance
True or False: In incomplete dominance, both of the original parental phenotypes occur and the phenotypic and genotypic ratios are both 1:2:1 in the F2 generation.
False
True or False: In the case of co-dominance, a mixture of the original parental phenotypes occurs and the phenotypic and genotypic ratios are both 1:2:1 in the F2 generation.
true
