Homework #24 (130222): Chapter 14 (due Friday 130222)
Total points: 20 for Attempt on all questions
ONE Concept Map: 10 points
Gregor Mendel’s Discoveries
1. Explain how Mendel’s particulate mechanism differed from the blending theory of inheritance. • Blending: parents genes mixed
• Particulate: parents genes still retain identity\
The blending theory was that genetic material contributed by the two parents mixes in a manner analogous to the way blue and yellow make green. It predicts that over generations, freely mating populations will eventually becoming a uniform population of individuals. According to Mendel’s particulate hypothesis of inheritance, the gene idea was that parents pass on discrete heritable units that retain their separate identities in offspring. 2. Define the following terms: true-breeding, hybridization, monohybrid cross, P generation, F1 generation, and F2 generation. True breeding: When true-breeding plants self-pollinate, all their offspring are of the same variety. For example, purple flowers give rise to plants with purple flowers. Hybridization: The crossing of two true-breeding varieties is hybridization. Monohybrid cross: A monohybrid cross is a genetic cross using a single trait with two alleles. P generation: The true-breeding parents are referred to as the P generation, or parental generation. F1 generation: The hybrid of the P generation is the F1 generation, or the first filial generation. F2 generation: The offspring of the self-fertilizing F1 generation is the F2 generation, or second filial generation. 3. List and explain the four components of Mendel’s hypothesis that led him to deduce the law of segregation. • Alleles make different characters
• Two alleles inherited
• Dominance and recessive
• Alleles segregate in gamete formation
First, alternative versions of genes account for variations in inherited characters. A gene exists in different versions. Second, for each character, an organism inherits two alleles, one from each parent. An organism inherits one set of chromosomes from each parent, giving two representations for a gene. Third, if the two alleles at a locus differ, then the dominant allele determines the organisms, while the recessive allele has no noticeable effect on the organism’s appearance. Fourth, the law of segregation, states that the two alleles for a heritable character separate, or segregate, during gamete formation and end up in different gametes. 4. Use a Punnett square to predict the results of a monohybrid cross, stating the phenotypic and genotypic ratios of the F2 generation.
Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype.
• Dominant masks recessive
• Heterozygous is two alleles, homozygous is one
• Phenotype = appearance, genotype = alleles in gene
A dominant allele determines an organism’s appearance, or phenotype, and masks the recessive allele. However, the recessive allele is still present in the genotype, or genetic makeup. A homozygous gene has a pair of identical alleles for that character. An organism that has two different alleles for a gene is said to be heterozygous for that gene.
Explain how a testcross can be used to determine if an individual with the dominant phenotype is homozygous or heterozygous.
• Determined to cross allele to find phenotype
• Based on genotype
A testcross, which is the breeding of a recessive homozygote with an organism of dominant phenotype is a method used to determine the genotype. They cross the two plants and observe their offspring and based on that can determine the genotype of the dominant organism with the unknown genotype of the P generation.
Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic ratios of the F2 generation.
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