Answer the following questions:
1.What does it mean to say that DNA is the genetic material?
2.What is the difference between a 'gene" and an allele? Give an example of multiple alleles for a gene.
3.What is the principle of segregation and how is this principle demonstrated in the results of Mendel's dihybrid crosses?
brid crosses?
4.What is the “principle of independent assorment'and how is this principle demonstrated in the results of Mendel's dihybrid crosses?
5. Explain why random union of male and female gametes is necessary for Mendelian
segregation and independent assortment to occur.
6. What is the difference between inbreeding depression and heterosis?
7.Which of the following genotype frequencies of AA, Aa, and aa, respectively, satisfy the
Hardy-Weinberg principle?
(a) 0.25, 0.50, 0.25
(b) 0.36, 0.55, 0.09
(c) 0.49, 0.42, 0.09
(d) 0.64, 0.27, 0.09
(e) 0.29, 0.42, 0.29
8. The following blood-type data were collected in a sample of 700 Native Americans from South Dakota:
Blood Type
A
B
AB
O
Number of Individuals
326
20
16
338
* Estimate the frequencies of the A, B, and O alleles from the sample data.
9. Why animal breeders Estimate Heritability?
10. What are the three methods of selection that have been generally used and discovered by
Hazel and Lush.? Explain
1. Saying that DNA is the genetic material means that DNA carries the instructions for the development, functioning, and reproduction of living organisms. It contains the genetic code that determines the traits and characteristics of an organism.
2. A gene is a specific segment of DNA that contains the instructions for a particular trait. An allele, on the other hand, is a variant form of a gene. Each gene can have multiple alleles, which are different versions of the same gene. For example, the gene for eye color may have alleles for blue, brown, and green eyes.
3. The principle of segregation states that during the formation of gametes, the two alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene. This principle is demonstrated in Mendel's dihybrid crosses by observing the inheritance patterns of two different characteristics. For example, if Mendel crossed plants with yellow round seeds (YYRR) with plants with green wrinkled seeds (yyrr), the offspring (F1 generation) would all have yellow round seeds (YyRr). When these F1 individuals are crossed with each other (F1 x F1), the F2 generation would show a ratio of 9:3:3:1 for the different combinations of traits (Yellow Round: Yellow Wrinkled: Green Round: Green Wrinkled).
4. The principle of independent assortment states that the alleles of different genes segregate independently of one another during the formation of gametes. This principle is demonstrated in Mendel's dihybrid crosses by observing the inheritance patterns of two different characteristics. Using the same example as above, if Mendel crossed plants with yellow round seeds (YYRR) with plants with green wrinkled seeds (yyrr), the F1 generation would all have yellow round seeds (YyRr). When these F1 individuals are crossed with each other (F1 x F1), the F2 generation would show a 9:3:3:1 ratio for the different combinations of traits, indicating that the alleles for seed color and seed shape are assorting independently.
5. The random union of male and female gametes is necessary for Mendelian segregation and independent assortment to occur because it introduces variation into the offspring. If the union of gametes was not random and there was bias towards certain combinations, it would disrupt the principles of segregation and independent assortment, leading to non-Mendelian patterns of inheritance.
6. Inbreeding depression refers to the reduced fitness or viability of offspring that occurs when closely related individuals (usually within the same family) reproduce. It can lead to increased susceptibility to diseases, reduced fertility, and overall lower fitness. Heterosis, also known as hybrid vigor, refers to the increased fitness and performance of offspring resulting from the mating of two genetically diverse individuals. It often leads to improved growth, reproduction, and resistance to diseases.
7. The genotype frequencies that satisfy the Hardy-Weinberg principle are (c) 0.49, 0.42, 0.09. The Hardy-Weinberg principle describes a mathematical relationship between allele frequencies and genotype frequencies in a population under certain conditions. It states that if the population is large, mating is random, no migration or mutation occurs, and there is no selection, then the relative frequencies of genotypes will remain constant from one generation to the next.
8. To estimate the frequencies of the A, B, and O alleles, we can use the Hardy-Weinberg equation. Let p represent the frequency of the A allele, q represent the frequency of the B allele, and r represent the frequency of the O allele. The equation is p^2 + 2pq + q^2 + 2pr + 2qr + r^2 = 1. Using the given data, we can estimate the frequencies as follows: p^2 = 326/700, q^2 = 20/700, and r^2 = 338/700. Solving the equation, we can determine the approximate frequencies of the A, B, and O alleles.
9. Animal breeders estimate heritability to understand the genetic basis of traits and to make informed breeding decisions. Heritability estimates help determine the proportion of phenotypic variation that is attributed to genetic factors, which can inform breeding strategies and selection programs. By estimating heritability, breeders can select individuals that are more likely to pass on desirable traits to their offspring, leading to genetic improvement within a population.
10. The three methods of selection discovered by Hazel and Lush are mass selection, individual selection, and progeny testing. Mass selection involves selecting the best individuals from a population based on their phenotype and allowing them to reproduce. Individual selection focuses on selecting superior individuals based on estimated breeding values (EBVs), which take into account both the individual's phenotype and the phenotypes of their relatives. Progeny testing involves evaluating the performance of an individual's offspring to determine their genetic merit and potential for breeding. These methods are used to improve the genetic quality of livestock populations through selective breeding.