An individual can be a heterozygote for one trait and a homozygote for another A

Question

An individual can be a heterozygote for one trait and a homozygote for another A. True B. False Humans have 22 pairs of autosomes plus one sex chromosome pair. How many autosomes are present in a normal human primary spermatocyte? A. 22 B. 23 C. 44 D, 45 In the dihybrid cross AaBb and aabb, what proportion of individuals are expected to be homozygotic for both genes in the Fl generation? A. 1/4 B. 1/2 C. 3/4 D. All are homozygotes. E. None are homozygotes. An allele that expresses its phenotype even when heterozygous with a recessive allele is termed A. recessive B. recombinant C. dominant D. parental E. independent Mitosis results in _____ chromosome number, whereas meiosis results in _____ chromosome number A. a doubling of. no change in B no change in, no change in C. a reduction by half in, no change in D. no change in, a doubling of E. no change in, a reduction by half in Which of the following is not a property of homologous chromosomes? A. They pair physically during prophase of meiosis I. B. They exchange genes by crossing over during meiosis, C. They carry alleles for the same genes at the same chromosomal position D. They are attached to the same centromere during G2 of the cell cycle. E. They segregate to opposite poles at anaphase I. In some genetically engineered corn plants, the dominant gene Bt produces a protein that is lethal to certain flying insect pests that eat the com plants. If the com plant is heterozygous for Bt, what proportion of the pollen would carry the dominant gene? A. all pollen B. 1/2 C. 1/3 D. 1/4 E. 1/8 In a monohybrid cross between AA and aa, what proportion of homozygotes is expected among the F2 offspring? A. 1/4 B. 1/2 C. 3/4 D. All are homozygotes. E. None are homozygotes.

Explanation / Answer

Answer 29) The correct answer is option (A).
An individual can be heterozygous for one trait and homozygous for another trait. The alternative forms of a gene are known as alleles and each trait is defined by two alleles. When both the alleles of a gene (responsible for the expression of the trait) are identical, the individual is homozygous for the trait and when both alleles are different, the individual is heterozygous for the trait.
For example, suppose that a garden pea plant has yellow wrinkled seeds. So, the yellow color and wrinkled shape are the two traits of a pea seed but yellow trait can be homozygous dominant (YY) or heterozygous dominant (Yy) and the wrinkled trait is always homozygous recessive (rr).

Answer 30) The correct answer is option (C).

According to the information given in the question, human has 22 pairs of autosomes and 1 pair of sex chromosome.
In a normal human primary spermatocyte, there are total 46 chromosomes, out of which 44 are the autosomes and 2 are the sex chromosomes.

Answer 31) The correct answer is option (A).

In the given cross,
Parents:   AaBb X aabb
Gametes: AB,Ab,aB,ab ab
Offsprings: AaBb (heterozygous for both genes)
   Aabb (heterozygous for first gene and homozygous for second gene)
aaBb (homozygous for the first gene and heterozygous for the second gene)
aabb (homozygous for both genes)
So, out of 4 offsprings, only one offspring has homozygous dominant alleles. Therefore, the ratio is 1/4.

Answer 32) The correct answer is option (C).
In heterozygous recessive condition, one allele is dominant and another allele is recessive. The dominant allele expresses its phenotype and hides the effect of the recessive allele.

Answer 33) The correct answer is option (E).

Mitosis causes no change in chromosome number. The chromosomes replicate during S phase get distributed equally in two daughter cells such that the number of chromosomes remains same as of parent cell. Hence, it is called as an equational division.
Meiosis causes reduction by half in chromosome number. The chromosomes replicated during S phase get distributed equally in four daughter cells such that each daughter cell receives half the number of chromosomes as of parent cell. Hence, it is called a reductional division.

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