AP Bio Ch 12 Chromosome & Genes

Down syndrome is caused by the presence of an extra chromosome 21. Normally, individuals have two copies of chromosome 21, but individuals with Down syndrome have three copies. This extra genetic material disrupts the normal development and functioning of the body, leading to the characteristic physical and intellectual disabilities associated with the condition.

The hereditary cause of type AB blood is the presence of two different codominant alleles. This means that an individual with type AB blood has inherited one A allele and one B allele from their parents. These alleles are codominant, meaning that neither one is dominant over the other, resulting in the expression of both A and B antigens on the surface of red blood cells. This is why individuals with type AB blood have both A and B antigens and do not produce antibodies against either type.

A human male has 46 chromosomes, with 2 sex chromosomes represented as XY. The number 46 refers to the total number of chromosomes present in a human cell, while XY indicates the specific combination of sex chromosomes found in males.

Crossing over is a process that occurs during meiosis where genetic material is exchanged between homologous chromosomes. This process can lead to the formation of recombinant chromosomes, which contain a combination of genes from both parents. When genes are linked, meaning they are close together on the same chromosome, crossing over between them is less likely to occur. Therefore, a small number of recombinants will occur due to crossing over between linked genes on homologous chromosomes. Hence, the statement is true.

Trisomy actually occurs when there is an extra copy of a chromosome, rather than a lost chromosome. It is a condition where an individual has three copies of a particular chromosome instead of the usual two. This can result in various genetic disorders and developmental abnormalities. Therefore, the statement that trisomy occurs when a chromosome is lost during meiosis is incorrect.

Different pairs of recessive alleles can interfere with a biochemical pathway and disrupt the production of melanin, resulting in albinism. Albinism is a genetic condition characterized by the absence or reduction of pigment in the skin, hair, and eyes. Inheritance of two copies of the recessive allele from both parents is necessary for albinism to occur. This interference with the biochemical pathway prevents the normal synthesis of melanin, leading to the characteristic features of albinism. Therefore, the statement "Different pairs of recessive alleles can interfere with a biochemical pathway and thus produce albinism" is true.

Pleiotropy refers to a situation where a single gene has multiple effects on an organism. Marfan's disease is a genetic disorder that affects multiple systems in the body, including the skeletal, cardiovascular, and ocular systems. This demonstrates pleiotropy because a single gene mutation leads to a wide range of symptoms and effects in different parts of the body.

Coat color in rabbits is a classical example of multiple alleles. This means that there are more than two possible alleles that can determine the coat color in rabbits. Different combinations of these alleles can result in a variety of coat colors, such as black, brown, white, or spotted. This is in contrast to traits like height in garden peas or pink flowers in heterozygous snapdragons, which are determined by only two alleles. Albinism in humans and animals is also determined by a single allele, making it different from the example of coat color in rabbits.