Heredity and Evolution Test - 19

Human cells are having two types of chromosomes: autosomes and sex chromosomes. Sex chromosomes in a male are XY and in females they are XX. There are no differences in the cytoplasm or membrane. The chromosome is present inside a nucleus. 

Human females have XX chromosomes and males have XY chromosomes. The sperm may contain either X or Y chromosome. The sperm is the factor in deciding the sex of the child. If the sperm carries an X chromosome, it will fuse with the egg’s X chromosome to form a female. If the sperm carries a Y chromosome, it will result in a male child. Hence the probability of getting a boy or girl is 50%. Thus the correct answer is option  A.

Human females have two XX chromosomes and males have XY chromosomes. The sperm may contain either the X or Y chromosome.

• A human female produces only one type of ovum having half the number of autosomes and one X chromosome. However, a male produces two types of sperms having half the number of autosomes and either an X or a Y chromosome. 
• In case, the sperm with X type of chromosome fertilizes ovum then a female child is produced and if the sperm with a Y chromosome fertilizes the ovum a male child is produced. 
• Hence, the type of sperm that actually fertilizes the ovum determines the sex of the baby. 

• Acquired characters are characteristics that are gained by an organism after birth as a result of external influences or its own activities, that change its structure or function. These characters cannot be inherited. 
• For example, If we breed a group of mice whose tails are removed by surgery, then these tailless mice will not have tailless progeny because removal of the tail cannot change the genes of the germ cells of the mice.
• So, the correct answer is option A.

• The trait is a distinguishable feature of a character and its detectable variant. For example, tallness and dwarfness. 
• The hybrid plant possesses a heterozygous condition in which genotype have both contrasting alleles such as Tt in the hybrid plant. T represents tallness and t represents dwarfness.
•  Dominant character tallness (T) can be expressed in both conditions such as homozygous (TT) and heterozygous condition (Tt) but recessive character dwarfness (t) can be expressed only in homozygous (tt) condition and thus unable to express in hybrid plants.

A) Correct option (A)
B) Explanation of the correct option

• Genetics is the branch of biology, that refers to the study of genes, genetic variations, and heredity in organisms.
• Gregor Mendel discovered the fundamental laws of inheritance by working on pea plants. Hence he is called the father of genetics. 

Anatomically, the human arm, the flippers of seals, and the wings of the birds are the forelimbs containing similar bones. These forelimbs have a common origin and similar anatomical features but have been modified to perform different functions. Flippers allow the seal to swim, birds fly using their wings and humans perform a variety of functions using the arms. Such structures are homologous to each other. The wings of insects are anatomically different.