What did Mendel conclude determines biological inheritance?
Mendel concluded that traits were passed on to the next generation by genes, and that some alleles are dominant, while others are recessive
Describe how Mendel cross-pollinated pea plants.
Mendel cut away the pollen-bearing male parts and then dusted the pollen from another plant onto the flower. He called this cross-pollination, producing seeds that had two different plants as parents.
Why did only about one fourth of Mendel's F2 plants exhibit the recessive trait?
Because at some point the allele for shortness had been separated from the allele for tallness, in a process called segregation. Mendel suggested that the alleles for tallness and shortness in the F1 plants separated from each other to form gametes.
Why were true-breeding pea plants important for Mendel's experiment?
Because these peas were true-breedings, meaning that if they were allowed to self-pollinate, they would produce offspring identical to themselves.
How are the principles of probability used to predict the outcomes of genetic crosses?
The way in which the alleles segregate is random, and probability allows the calculation of the likelihood that a particular allele com- bination will occur in offspring.
An F1 plant that is homozygous for shortness is crossed with a heterozygous F1 plant. What is the probability that a seed from the cross will produce a tall plant. Use a Punnett square to explain your answer and to compare the probable genetic variations
50% tall (heterozygous) 50% short (homozygous)
t t
T Tt Tt
t tt tt
How are Punnett squares used?
To predict and compare the genetic variations that will result from a cross
A geneticist studying coat color in animals crosses a male rabbit having the genotype CC with a female having genotype Ccch. The genticist then crosses a ccch male with a Ccc female. In which of the two crosses are the offspring more likely to show greate
The offspring in the first row will show a smaller variation because all of the offspring from the first cross will be full color.
Why are fruit flies an ideal organism for genetic research?
They are able to produce a large amount of offspring in a small amount of times and are easy to maintain in a laboratory.
If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are?
The two genes are located very far apart from each other.
Difference between meiosis and mitosis.
Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells.
How does the principle of independent assortment apply to chromosomes?
It is the chromosomes that assort independ- ently, not individual genes.
How does crossing-over make gene mapping possible?
The farther apart two genes are, the more likely they are to be separated during a crossover in meiosis. Therefore, the frequency of crossing-over is equal to the distance between two genes.
How are gene maps produced?
The frequency of crossing-over between genes is used to produce a map of distances between genes.
List the four basic principles of genetics that Mendel discovered in his experiments. Briefly describe each of these principles.
The inheritance of biological characteristics is determined by genes. Where there are two or more alleles of the gene, some are dominant, some are recessive. In most sexually reproducing organisms, each adult has two copies of each gene, from each parent,
Why can multiple alleles provide many different phenotypes for a trait?
With two alleles for a trait, up to three phenotypes are possible. With three alleles, up to six phenotypes are possible.
Are an organisms characteristics determined only by its genes? Explain.
No, genes provide a plan for development depending on the environment that they are in.
Suppose that for an organism, 2N = 8. How many chromosomes do the organism's gametes contain?
4
In rabbits, B is an allele for black coat and b is an allele for brown coat. Write the genotypes for a rabbit that is homozygous for black coat and another rabbit that is heterozygous for black coat.
Homozygous black coat: BB; heterozygous black coat: Bb
Compare the phases of meiosis I with the phases of meiosis II in terms of the number and arrangement of the chromosomes.
During meiosis I, all of the chromosomes are doubled and consist of duplicate chromosomes. During meiosis II, the sister chromatids separate to produce four haploid daughter cells.
Explain why it is chromosomes, not individual genes, that assort independently.
The genes are linked to the chromosomes.
Suppose you found out that a mating between a black animal and a brown animal produced all black offspring. Propose a hypothesis to explain the color of the offspring.
The allele for black color is dominant, and the allele for brown color is recessive. The black parent is homozygous, and the brown parent is heterozygous.