chapter 3

down syndrome

a condition in which a person has 3 rather than 2 chromosomes at the 21st site

X-linked

a gene carried on the X chromosome. If a male inherits an X-linked recessive trait from his mother, he expresses that trait because the y from his father has no counteracting gene. females are more likely to be carriers

assisted reproductive technology (ART)

a general term for the techniques designed to help infertile couples conceive and then sustain a pregnancy

gene

a small section of a chromosome; the basic unit for the transmission of heredity. A gene consists of a string of chemicals that provide instructions for the cell to manufacture certain proteins.

allele

a variation that makes a gene different in some way from other genes for the same characteristics. many genes never vary; others have several possible alleles

genotype

an organisms entire genetic inheritance, or genetic potential

uncertain sex

every now and then, a baby is born with "ambiguous genitals" meaning that childs sex is not abundantly clear

chromosome

one of the 46 molecules of DNA (in 23 pairs) that virtually each cell of the human body contains and that, together, contain all the genes. Other species have more or fewer of these.

deoxyribonucleic acid (DNA)

the chemical composition of the molecules that contain the genes, which are the chemical instructions for cells to manufacture various proteins

23rd pair

the chromosome pair that determines sex. The other 22 pairs are autosomes,inherited equally from the male and female

genome

the full set of genes that are the instructions to make an individual member of a certain species

dominant-recessive pattern

the interaction of a heterozygous pair of alleles in such a way that the phenotype reflects one allele(the dominant gene) more than the other(the recessive gene)

phenotype

the observable characteristics of a person, including appearance, personality, intelligence, and all other traits

zygote

the single cell formed from the union of two gametes, a sperm and an ovum

dizygotic (DZ) twins

twins that are formed with two separate sperm and two separate ova are fertilized at the same time. (Also called fraternal twins)

XX

23rd chromosome pair that determines that the fetus is a female

XY

23rd chromosome pair that determines that the fetus is a male

in vitro fertilization (IVF)

fertilization that take place outside of the women body. usually in a lab

copy number variations

genes with various repeats or delegations of base pairs

multifactorial

referring to a trait that is affected by many factors, both genetic and environmental, that enhance, halt, shape, or alter the expression of genes, resulting in a phenotype that may differ markedly from the genotype

polygenic

referring to a trait that is influenced by many genes

homozygous

referring to two genes of one pair that are exactly the same in every letter of their code. Most gene pairs are this.

heterozygous

referring to two genes of one pair that differ in some way, Typically one allele has only a few base pairs that differ from the other member of the pair

gamete

reproductive cell that is a sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote

carrier

A person whose genotype includes a gene that is not expressed in the phenotype. The carried gene occurs in half of the carriers gamete and thus is passed on to half of the carriers children

intra-cytoplasmic injection (ICSI)

An in vitro fertilization technique in which a single sperm cell is injected directly into an ovum

monozygotic (MZ) twins

Twins who originate from one zygote that splits apart very early in development. Also called identical twins