Modes of Inheritance

The probability that a certain trait will occur in the offspring of two individuals can be determined by knowing how genes are distributed in meiosis and the combinations in which they can come together at fertilization.

Chromosomes and Genes Come in Pairs

From the moment of conception, a human cell is diploid, containing two copies of each of the 23 different chromosomes. Chromosome charts called karyotypes are used to display the 23 chromosome pairs in size order (fig. 24.4). Pairs 1 through 22 are autosomes (aw'to-somz), which are chromosomes that do not carry genes that determine sex. The other two chromosomes, the X and the Y, determine sex and are called sex chromosomes. They are discussed later in the chapter in the section titled "Matters of Sex."

Brain 67,679 Smooth muscle 297

Blood cells 23,505 Skeletal muscle 4,693 Breast 4,001

Liver 37,807

Pancreas 5,534 Gallbladder 3,754 Small intestine 1,009 Ovary (women) 3,848

Uterus (women) 6,392

Eye 1,932

Salivary gland 186 Parathyroid glands 197 Thyroid gland 2,381 Esophagus 194

Heart 9,400

Eye 1,932

Heart 9,400

How Bones Maintain Homeostasis

Bone 5,736

Predicted Distribution of Human Genes' Cellular Roles

Skin 3,043 Kidney 3,213

-Colon 4,832

Prostate gland (men) 7,971

Testis (men) 7,117

Bone 5,736

Cell division/ DNA synthesis

Cell signaling/ communication

Cell structure/

motility Cell/organism defense/ homeostasis

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