MCG - (Worksheet) Gene Inheritance, Human Pedigrees and DNA

Question 1

In an organism with a haploid chromosome number of 7, how many sister chromatids are presentin its mitotic metaphase nucleus?

Answer 1

28

haploid number = 7, each cell is diploid so has 14 chromosomes

replication takes place in prophase, in metaphase the sister chromatids are not yet separated therefore there are 14 x 2 = 28 chromatids.

Question 2

In an organism with a haploid chromosome number of 7, how many sister chromatids are present in its meiotic metaphase I nucleus?

Answer 2

28

The number of chromatids are the same as in mitotic metaphase but now aligned as homologous pairs.

Question 3

In an organism with a haploid chromosome number of 7, how many sister chromatids are present in its meiotic metaphase II nucleus?

Answer 3

14

At the end of meiosis I homologous chromosomes segregate into separate daughter cells. In metaphase II, each chromosome consists of 2 sister chromatids.

Question 4

An organism has five homologous pairs of chromosomes. In the absence of recombination, how many genetically different types of gametes can this organism produce?

Answer 4

Homologous chromosomes assort randomly at meiosis and a gamete has two choices for each chromosome (maternal or paternal).

Thus, there are 2^5 possible combinations, two choices for each of the five chromosomes.

Question 5

How many genetically different gametes can a human produce with 23 pairs of chromosomes (without recombination)?

Answer 5

In humans, 2^23 genetically different gametes (8 x10^6) can be produced without recombination.

Question 6

What are the features of Turner syndrome?

Answer 6

• short stature, lack of growth spurt at puberty, and non-functioning ovaries which causes infertility and incomplete sexual development
• some women may have swelling of the neck (webbed neck),
• puffiness or swelling (lymphedema) of the hands and feet,
• skeletal abnormalities, heart defects, kidney abnormalities
• eye problems

Question 7

A colour-blind man marries a homozygous normal woman and after four joyful years of marriage they have two children. Unfortunately, both children have Turner syndrome (one X chromosome), though one has normal vision and one is colour-blind. The type of colour-blindness involved is a sex-linked recessive trait.

For the colour-blind child with Turner syndrome, did nondisjunction occur in the mother or the father?

Explain your answer.

Answer 7

Turner syndrome is XO (only 1 sex chromosome).

The child is colour blind so must have inherited her X chromosome from her father.

So nondisjunction in the mother must have produced the gamete with no X chromosome.

Question 8

Phenylketonuria is caused by the alteration of what enzyme?

Answer 8

phenylalanine hydroxylase

Question 9

What are the untreated consequences of phenylketonuria?

Answer 9

• can be fatal
• mental retardation
• fair skin
• eczema
• epilepsy

Question 10

Describe the current method for treating phenylketonuria.

Answer 10

Restrict phenylalanine consumption in the diet.

Question 11

Human ABO blood groups are determined by three alleles (i, IA and IB ) of the same gene called ABO, that codes for an alpha 1-3-galactosyltransferase.

How would you describe the interaction between alleles IA and IB ?

Answer 11

Both A and B antigens are on the surfaces of red blood cells.

Therefore IA and IB are codominant, so you can see the activity of each allele in the cellular characteristics.

Question 12

Which of the three alleles (IA, IB, i) are dominant and which recessive?

Answer 12

IA = IB (= means codominant)

IA results in expression of antigen A
Therefore IA is dominant to i

IB results in expression of antigen B
Therefore IB is dominant to i

Question 13

What does pleiotropy indicate?

Answer 13

Pleiotropy indicates the gene product is required for a number of different tissues or organs. When the gene is mutant all tissues needing the gene product are affected.

Variable expressivity of a phenotype for a given genotype indicates the phenotype is affected by the different alleles of other genes in an individual’s genotype or environmental effects.

Question 14

From this list:

• the transcription start site
• exons
• introns
• the TATA box
• enhancer elements
• transcription factor binding sites in the promoter

Which of the sequence elements named above are transcribed as pre-mRNA?

Answer 14

The exons and the introns are transcribed in the pre-mRNA.

Question 15

From this list:

• the transcription start site
• exons
• introns
• the TATA box
• enhancer elements
• transcription factor binding sites in the promoter

Which of the sequence elements named above can encode the protein product of this gene?

Answer 15

The exons are spliced (joined) together in the mature mRNA to form a single open reading frame (ORF).

Question 16

From this list:

• the transcription start site
• exons
• introns
• the TATA box
• enhancer elements
• transcription factor binding sites in the promoter

Which of the sequence elements named above are involved in regulating transcription of the gene?

Answer 16

The TATA box.

The transcription factor binding sites in the promoter.

The enhancer elements.

Question 17

If a DNA molecule is found to be composed of 40% thymine, what percentage of guanine would be expected?

Answer 17

10%

(T=A, G=C)
so
T+A = 80%
C+G = 20%

so C = 10%

Question 18

During replication, what enzyme adds complementary bases?

Answer 18

Polymerase.

Question 19

What does transcription result in?

Answer 19

messenger RNA

Question 20

How many different amino acids are commonly found in proteins?

Answer 20

20