Question

Chapters 11-12 Practice your Knowledge Activity separate daring or crossitig over C Mciosis n. D Mitosis E. B and D 2. Cienetic recombination (crossing o ver) oocurs during A. Zygote development B. After Meiosis 1 C. Middle of Meiosis II D. Beginning of Mciosis 1 E. End of Meiosis II 3. Which of the following increases genetic diversity A. Random fertilization B. Independent assortment of chromosomes C. Genetic recombination D. All of the above E. None of the above Isabella breeds and sells chocolate labs, which are homozygous recessive. Isabella conducts a cross which produces the following results: 1 black lab: 1 chocolate lab. What are the parental genotypes? 4. Ar BB x bb B. Bbx Bb C. Bb x bb D. BB x Bb The tt genotype produces a serious disease. Ben and his wife both have genotype Tt. What is their chance of having an affected child 5. a. b. e. d. 100% 75% 50% 25%

Answer 1

1) The correct answer is option (E).

During the anaphase stage of meiosis I and mitosis, homologous chromosomes separate and move towards the spindle poles so that one chromosome of homologous pair reach to each gamete.
During the anaphase stage of meiosis II, sister chromatids separate. Hence, option (C) is incorrect.

2) The correct answer is option (D).

Crossing over is defined as the exchange of genetic material between the homologous chromosomes of non-sister chromatids to form genetic recombinants. This occurs during the diakinesis stage of prophase I of meiosis I.

3) The correct answer is option (D).

Random fertilization, independent assortment, and genetic recombination are the primary ways that increase the genetic diversity.
Each gamete contains a unique set of genes. The fertilization between a male and female occurs randomly. As a result, a zygote receives a unique combination of genes and hence variation occurs which leads to genetic diversity.
Genetic recombination is the exchange of genetic material between the homologous chromosomes of non-sister chromatids to form genetic recombinants. This allows a novel combination of maternal and paternal genetic material and causes genetic diversity.
Independent assortment occurs during metaphase I of meiosis I. Here, during the formation of gametes, the allele pairs (homologous chromosomes) segregate randomly and independently of each other. It results in the formation of gametes with unique combinations of chromosomes which also leads to the genetic diversity.

4) The correct answer is option (C).
Let us suppose that chocolate color is represented by a recessive allele b and black color is represented by a dominant allele B.
According to the question, chocolate labs are homozygous recessive. This means that the genotype of chocolate lab is bb.
Parents:    Bb X bb
Gametes: B, b           b
Offsprings: 1 Bb    : 1 bb
           (Black lab)   (Chocolate lab)

If we consider option (1), all the offsprings will be Bb. Hence, this option is incorrect.
If we consider option (2), 3 types of offsprings will produce, i.e., BB, Bb and bb in the ratio of 1:2:1. Hence, this option is incorrect.
If we consider option (4), 2 types of offsprings will produce, i.e., BB and Bb in the ratio of 1:1. But as given in the question, bb represents chocolate lab. Therefore, this option is also incorrect.

5) The correct answer is option (d).

Both parents have the same genotype, i.e., Tt.
The cross between them follows as
Parents:      Tt       X      Tt
Gametes:    T,t          T,t
Offsprings:

Gametes	T	t
T	TT (Normal offspring)	Tt (Normal offspring)
t	Tt (Normal offspring)	tt (Diseased offspring)

From the Punnett square, it is clear that 1/4, i.e., 25% offsprings are affected and produce a serious disease.