HBHD II Chapter 25

In the example of albinism, a person with the gene combination of Aa is said to be a genetic ________.

Answer explanation

A person with the gene combination Aa has one dominant and one recessive allele. They do not express albinism but can pass the recessive allele to offspring, making them a genetic carrier.

If two different dominant genes occur together, a form of dominance called ________ ________ exists.

Answer explanation

When two different dominant genes occur together, they can exhibit a form of dominance known as incomplete dominance, where neither gene completely masks the other, resulting in a blend of traits.

________ ________ chromosomes do not have matching structures.

Answer explanation

Sex-linked chromosomes, such as X and Y in humans, do not have matching structures, as they differ in size and gene content. This is why the correct answer is 'sex linked'.

If an individual has the sex chromosomes XX, that person will have the sexual characteristics of a ________.

Answer explanation

Individuals with the sex chromosomes XX typically develop female sexual characteristics due to the presence of two X chromosomes, which are associated with female biological traits.

Caused by recessive genes in chromosome pair 7

• Monosomy

• Nondisjunction

• Leber hereditary optic neuropathy

• Single-gene disease

• Cystic fibrosis

Answer explanation

Cystic fibrosis is caused by recessive genes located on chromosome pair 7. It is a single-gene disease that affects the respiratory and digestive systems, making it the correct answer among the options provided.

Results in total blindness by age 30

• Nondisjunction

• Monosomy

• Leber hereditary optic neuropathy

• Single-gene disease

• Cystic fibrosis

Answer explanation

Leber hereditary optic neuropathy is a genetic condition that typically leads to vision loss and can result in total blindness by age 30, making it the correct choice among the options provided.

Disease conditions that result from the combined effects of inheritance and environmental factors

• Single-gene disease

• Monosomy

• Nondisjunction

• Leber hereditary optic neuropathy

• Genetic predisposition

Answer explanation

Genetic predisposition refers to disease conditions influenced by both genetic inheritance and environmental factors, making it the correct choice. Other options focus on specific genetic disorders or mechanisms, not the combined effects.

Results from a failure to produce the enzyme phenylalanine hydroxylase

• Phenylketonuria

• Single-gene disease

• Nondisjunction

• Monosomy

• Leber hereditary optic neuropathy

Answer explanation

Phenylketonuria results from a deficiency in the enzyme phenylalanine hydroxylase, leading to the accumulation of phenylalanine, which can cause intellectual disability and other health issues if not managed.

Presence of only one autosome instead of a pair

• Leber hereditary optic neuropathy

• Cystic fibrosis

• Single-gene disease

• Monosomy

• Nondisjunction

Answer explanation

Monosomy refers to the presence of only one autosome instead of a pair, which is a chromosomal abnormality. This distinguishes it from other options like single-gene diseases or conditions caused by nondisjunction.

Usually caused by trisomy of chromosome 21

• Down syndrome

• Nondisjunction

• Leber hereditary optic neuropathy

• Monosomy

• Single-gene disease

Answer explanation

Down syndrome is usually caused by trisomy of chromosome 21, where an individual has three copies of this chromosome instead of the usual two. This genetic condition leads to various developmental and physical characteristics.