QUESTION 14 Sex-linked traits affect only sexual characteristics. True or False?

Question

QUESTION 14 Sex-linked traits affect only sexual characteristics. True or False? O True False QUESTION 15 Which disorder is more common among the babies of older mothers? O Turner syndrome O Klinefelter syndrome O Trisomy X XYY syndrome O Down syndrome QUESTION 16 In humans, the sex of the offspring is determined by the O sex chromosome carried by the sperm cell. O autosomes carried by the egg cell. O sex chromosome carried by the egg cell. O autosomes carried by the sperm cel O cytoplasm carried by the egg cell. QUESTION 17 A type of muscular dystrophy shows sex-linked recessive inheritance. Affected persons usually die by the age of 20. Suppose that a boy with the disease lives long enough to marry a woman heterozygous for the trait. If they have a son, what is the probablity that he will have the disease? ? 75% 00% 25% 050% 10% QUESTION 18 What type of allele produces its effects in only homozygous individuals? O Dominant O Haploid O Recessive O Diploid QUESTION 19 The blood types of humans are an example of Arial 3 (12pt)

Explanation / Answer

Question 14

Genetic characteristics determined by genes located on sex chromosomes are referred to as sex-linked traits. Sex chromosomes are present on the gametes and determine the sex of an individual. Sex-linked traits not only affects the sexual characteristics but other features as well. For example color blindness (males are more likely to be color blind than females since the gene for color blindness is found on the X chromosome), hemophilia (is an X linked inheritance, hence males are more likely no develop the disease), baldness in males (gene is present on the X chromosome), etc. are sex-linked traits.

Hence, the statement ‘sex-linked traits affect only sexual characteristics’ is false.

Question 15

Babies born to older mothers are at a risk of many diseases.

Turner syndrome is a condition in which a female is missing an X chromosome – XO condition. It arises as a result of chromosomal abnormality and mother’s age does not play a role.

Hence, first option is incorrect.

Klienfelter syndrome is a condition in which a male will have an extra X chromosome – XXY. It results as a result of random genetic error during the formation of egg or sperm. Mother’s age is not a reason for this condition.

Hence, second option is incorrect.

A condition in which a person has an additional chromosome is referred to as trisomy. It may be autosomal (trisomy 21 – Down’s syndrome; trisomy 17 – Edward’s syndrome) or trisomy of sex chromosomes (XXY - Klienfelter syndrome; XXX – triple X syndrome).

Hence, third option is incorrect.

XXY syndrome is Klienfelter syndrome.

Hence, fourth option is incorrect.

Down syndrome is also called trisomy 21. It occurs due to the presence of a third copy of chromosome 21. Older mothers above the age of 35 tend to have an extra copy of chromosome 21. Hence, they are more likely to have baby with Down syndrome than younger mothers.

Therefore, the correct answer is fifth option.

Question 16

X and Y are the sex chromosomes of the humans. The combination of these determines the sex of a person. Females possess two X chromosomes, while males have an X and Y chromosome. Since the sperm cell carries the Y chromosome, sex of the offspring is determined by the sex chromosome carried by the sperm cell.

Therefore, the correct answer is first option.

Question 17

Sex-linked recessive inheritance is a mutation in the gene on the X chromosome causing the phenotype be expressed in males (in hemizygous form) and in females who are homozygous for the trait, heterozygous females will thus be carriers of the trait.

Here, let us represent muscular dystrophy in male as XMY and heterozygous female as XMX. On crossing

XMY x XMX

XM

X

XM

XMXM

Distrophic female

XMX

Carrier female

Y

XM Y

Distrophic male

XY

Normal

male

Hence, proportion of male offsprings having the disease and not having it is 1:1.

Hence, the probability that the son will have the disease is 50%.

Therefore, the correct answer is fourth option.

Question 18

Dominant alleles are expressed in both homozygous and heterozygous individuals (HH and Hh), whereas recessive alleles are expressed only in homozygous individuals (hh).

Therefore, the correct answer is third option.

Question 19

Humans have four different types of blood types: A, B, AB, and O determined by A, B, and O alleles. The condition in which two or more alleles existing for the same gene is called multiple allelism.

Hence, the blood types of humans are example of multiple alleles.

XM

X

XM

XMXM

Distrophic female

XMX

Carrier female

Y

XM Y

Distrophic male

XY

Normal

male

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