Please answer 3, 4, and 5 and show ALL WORK EVEN FOR MULTIPLE CHOICE QUESTIONS 3

Question

Please answer 3, 4, and 5 and show ALL WORK EVEN FOR MULTIPLE CHOICE QUESTIONS

3) The autosomal gene for brachydactyly, short fingers, is dominant to normal finger length. Assume that a female with brachydactyly in the heterozygous condition is married to a man with normal fingers. What is the probability that: (1.5pts)

a. The first child will have brachydactyly?

b. The first two children will have brachydactyly?

c. Their first child will be a brachydactyly girl?

4) If a diploid cell replicates its DNA, so it contains an amount of DNA equal to 4n, how does a haploid gamete get a 1n number of chromosomes and a 1n amount of DNA?

(1.0pts)

a. There is only one meiotic division and two daughter cells produced in meiotic cell division.

b. There are two meiotic divisions and four daughter cells produced in meiotic cell division.

c. There is only one meiotic division and four daughter cell produced in meiotic cell division.

d. a & c.

5) If an organism has only three chromosomes, how many chromosomes are autosomes? (1.0 pts)

a. Two

b. Three

c. None

d. One

Explanation / Answer

1 Female heterozygous for brachydactyly XBXb is crossed with man of normal fingers. XBYb

Drawing punnet square we get the following result;

Male XbXb

XBYb (2child)

1a) The probability that the first child will have brachydactyly is 1/2

1b) The probability that the first two children will have brachydactyly is 1/2 x 1/2 = 1/4

1c) The probability that the first child will have brachydactyly girl is is 1/4

2.There are two meiotic divisions and four daughter cells produced in meiotic cell division.

Chromosome gets duplicated in interphase (actually chromatid number and DNA number doubles). . Therefore Chromosome after replication in Interphase finally contains 1 chromosome with 2n ploidy and 4 DNA in terms of genetic content.

In meiosis, during fist division: the chromosome number 2n is reduced to 1n. Here homologous chromosomes separate to daughter cells ( sister chromatids donot separate) forming haploid cells (1n). The separation of each pair of homologous chromosome occur independently, so in daughter cells all possible combinations of maternal and paternal chromosomes are possible ( but not both). Haploid (1n) with 2 Chromosomes with 4 chromatids 4 DNA.

NOTE: Here haploid (1n) represents 1 in terms of daughter cells having either maternal or paternal chromosome not both of them.

In second meiotic division sister chromatids separate forming four daughter cells, each cell having haploid (1n) chromosome. 1n chromosome with 1 DNA.

3.If an organism has only three chromosomes, Two chromosomes are autosomes, (one from maternal and one from paternal and another chromosome) will be sex chromosome.

XBYb (2child)

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