Meiosis Flashcards
A person normally inherits ___ pairs of autosomal chromosomes.
22
Sometimes a person inherits too many or too few ___ chromosomes.
autosomal
The most common autosomal abnormality is called ___ 21, or ___ ___.
trisomy / Down syndrome
A child with trisomy 21 has ___ copies of chromosome 21 instead of ___ copies.
3 / 2
Autosomal abnormalities are usually caused by ___.
nondisjunction
The failure of the chromosomes to separate during meiosis, thereby causing the formation of eggs or sperm with too many or too few chromosomes.
Nondisjunction
If nondisjunction eggs and sperm lead to pregnancy, the embryo may have one too ___ or too ___ chromosomes.
many / few
Most pregnancies with an unbalanced number of chromosomes ___ in the first trimester.
miscarry
Down syndrome is the most common chromosomal abnormality because the condition is least likely to cause the pregnancy to ___. Even so, an estimated ___% of pregnancies with Down syndrome spontaneously ___, usually in the first trimester.
miscarry / 70 / miscarry
Determines what the offspring looks like.
Genetic expression
Influenced by a number of factors, including the person’s gender, the influence of other genes, and environmental conditions. For example, certain types of baldness and color blindness may be inherited by males and females, but these traits are more apt to appear in the male. A child may also have the genetic capability of growing very tall. If the child is deprived of adequate nutrition and exercise, however, that child may not grow as tall as the genetic makeup has predicted.
Genetic expression
Normally, DNA replicates all information with ___ mistakes. Because of this precision, information is passed along reliably and efficiently to the next ___. Sometimes, however, a change occurs in a gene or a chromosome breaks in some unexpected way. The result may be a unique feature or a birth defect. This change in the genetic code is called a ___.
few / generation / mutation
Some mutations occur ___; others are caused by mutagenic agents, such as chemicals, ___, and radiation.
spontaneously / drugs
Can be beneficial or harmful and may even cause the death of the offspring. For example, a ___ in the cells of the immune system may render a child resistant to a particular disease, thereby enhancing health. Another ___, however, may weaken the immune system, making it more susceptible to pathogens.
Mutations
mutation x2