Heredity is the

transmission of traits from one generation to the next

Variation is demonstrated by

the differences in appearance that offspring show from parents and siblings

Genetics is the

scientific study of heredity and variation

Offspring acquire genes from parents

by inheriting chromosomes

In a literal sense, children do not inherit particular physical traits from their parents

It is genes that are actually inherited

Genes are the units of

heredity and are made up of segments of DNA

Genes are passed to the next generation via reproductive cells called

gametes (sperm and eggs)

Most DNA is packaged into

chromosomes

Humans have

46 chromosomes in the nuclei of their somatic cells, all cells of the body except gametes and their precursors

A gene’s specific position along a chromosome is called its

locus

In asexual reproduction,

a single individual passes all of its genes to its offspring without the fusion of gametes

A clone is a group of

genetically identical individuals from the same parent

In sexual reproduction,

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

A life cycle is the

generation-to-generation sequence of stages in the reproductive history of an organism

Human somatic cells have

23 pairs of chromosomes

A karyotype is an

ordered display of the pairs of chromosomes from a cell

The two chromosomes in each pair are called homologous chromosomes, or homologs

homologous chromosomes, or homologs

Chromosomes in a homologous pair

are the same length and shape and carry genes controlling the same inherited characters

The sex chromosomes, which determine the sex of the individual, are called X and Y

Human females have a homologous pair of X chromosomes (XX)

Human males have one X and one Y chromosome

The remaining 22 pairs of chromosomes are called autosomes

are called X and Y

Human females have a

homologous pair of X chromosomes (XX)

Human males have

one X and one Y chromosome

he remaining 22 pairs of chromosomes are called

autosomes

Each pair of homologous chromosomes includes one chromosome from each parent

The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father

A diploid cell (2n) has two sets of chromosomes

For humans, the diploid number is 46 (2n = 46)

one chromosome from each parent

The 46 chromosomes in a human somatic cell are

two sets of 23: one from the mother and one from the father

A diploid cell (2n) has

two sets of chromosomes

For humans, the diploid number is

46 (2n = 46)

In a cell in which DNA synthesis has occurred,

each chromosome is replicated

Each replicated chromosome consists of

two identical sister chromatids

A gamete (sperm or egg) contains

For humans, the haploid number is 23 (n = 23)

Each set of 23 consists of 22 autosomes and a single sex chromosome

In an unfertilized egg (ovum), the sex chromosome is X

In a sperm cell, the sex chromosome may be either X or Y

a single set of chromosomes and is thus a haploid cell (n)

For humans, the haploid number

is 23 (n = 23)

Each set of 23 consists of

22 autosomes and a single sex chromosome

In an unfertilized egg (ovum),

the sex chromosome is X

In a sperm cell, the sex chromosome may

be either X or Y

Fertilization is the

The fertilized egg is called a zygote and has one set of chromosomes from each parent

The zygote produces somatic cells by mitosis and develops into an adult

union of gametes (the sperm and the egg)

The fertilized egg is called a

zygote and has one set of chromosomes from each parent

The zygote produces somatic cells by

mitosis and develops into an adult

At sexual maturity, the ovaries and testes produce haploid gametes

Gametes are the only types of human cells produced by meiosis, rather than mitosis

Meiosis results in one set of chromosomes in each gamete

Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number

the ovaries and testes produce haploid gametes

Gametes are the only types of human cells produced by

meiosis, rather than mitosis

Meiosis results in

one set of chromosomes in each gamete

Fertilization and meiosis

alternate in sexual life cycles to maintain chromosome number