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