HOMOLOGUS CHROMOSOMES
BIOLOGY
Humans have 46 chromosomes, comprising 23
UNIT 2 inherited from their mother and 23 inherited from
their father .
OUTCOME 1 Matching pairs of chromosomes are called
Homologues chromosomes or Homologues
Chromosomes: A chromosome is a structure containing The two chromatids of chromosomes contain
a single DNA molecule and associated proteins. matching DNA molecules.
Eukaryotic organisms have sets of linear The sex chromosomes for all females are also
chromosomes located in the nucleus. homologues because they have a matching pair of X
Chromosomes in Eukaryotic consists of two strands chromosomes.
called chromatides, that are held together by a The sex chromosomes for males are not
region called the centromere. homologues because they have an X and a Y
Joined chromatides are known as sister chromatids. chromosome, which contain different gene sets.
The size and the number of chromosomes can vary Chromosomes replication occurs during the S
widely between organisms. phase (DNA synthesis) in mitosis
Chromosomes range in size from about 50 million to Non-dividing cells have two copies of each gene, so
300 million base pairs, with every chromosome they have two copies of alleles (which may be
carrying a different number of genes. identical or different) for each gene.
Each gene has a particular position, called a locus, on a During active cell division there is a period during
specific chromosomes the cell cycle, after chromosomes replication and
Chromosomes differ in size because of differences in before cytokinesis, when the diploid cells contain
the number of genes and the amount of spacer DNA four copies of each gene.
between the genes There can be no more than two alleles in total (one
from each parent)
DIAGRAMS
DIAGRAMS
CHROMOSOME NUMBER
The number of sets chromosomes in a cell is called
the ploidy level.
Haploid cells have one set, Diploid cells have two
sets, and Polypoid cells have three or more sets.
In human the diploid number is 46. , some ferns
have more than a thousand chromosomes in each
somatic cells.
, SEX CHROMOSOMES DIAGRAMS
Sex chromosomes (also called allosomes) are
chromosomes in sex determination.
An autosome is any chromosome that is not a sex
chromosome. Autosomes are represented by
numbers (e.g. chromosomes 12)
Individuals with two sex chromosomes that are the
same are the homogametic sex. (XX)
Individuals with two different sex chromosmes are
the heterogametic sex. (XY)
In humans and all other mammals, a pair of
chromosomes know as X and Y chromosomes
determine the biological sex of an individual.
Some organisms (such as fungi and algae) do not
have sex-determining chromosomes and therefore
do not have sexes; instead they having mating MEIOSIS
types.
The process of meiosis is essential to sexual
Sex is determined by the presence or absence of the
reproduction and the creation of new genetic
Y chromosomes.
variations .
GAMETES
Somatic cells are the cells in the body of an
organisms apart from the sex cells (gametes)
Germ cells are the cells that given rise to gametes,
which are specialized cells that combine in sexual
reproduction.
In meiosis two successive cell divisions produce
four daughter cells, each with half the number of
chromosomes of the parent cell.
Identical (monozygotic) twins develop from one
fertilized egg, so they have identical genes. but
because of non- genetic factors that affect the way
the embryos develop, identical twins are actually
are made not exactly identical.
The process of fertilization involves two haploid
gametes fusing to form a diploid zygote.
BIOLOGY
Humans have 46 chromosomes, comprising 23
UNIT 2 inherited from their mother and 23 inherited from
their father .
OUTCOME 1 Matching pairs of chromosomes are called
Homologues chromosomes or Homologues
Chromosomes: A chromosome is a structure containing The two chromatids of chromosomes contain
a single DNA molecule and associated proteins. matching DNA molecules.
Eukaryotic organisms have sets of linear The sex chromosomes for all females are also
chromosomes located in the nucleus. homologues because they have a matching pair of X
Chromosomes in Eukaryotic consists of two strands chromosomes.
called chromatides, that are held together by a The sex chromosomes for males are not
region called the centromere. homologues because they have an X and a Y
Joined chromatides are known as sister chromatids. chromosome, which contain different gene sets.
The size and the number of chromosomes can vary Chromosomes replication occurs during the S
widely between organisms. phase (DNA synthesis) in mitosis
Chromosomes range in size from about 50 million to Non-dividing cells have two copies of each gene, so
300 million base pairs, with every chromosome they have two copies of alleles (which may be
carrying a different number of genes. identical or different) for each gene.
Each gene has a particular position, called a locus, on a During active cell division there is a period during
specific chromosomes the cell cycle, after chromosomes replication and
Chromosomes differ in size because of differences in before cytokinesis, when the diploid cells contain
the number of genes and the amount of spacer DNA four copies of each gene.
between the genes There can be no more than two alleles in total (one
from each parent)
DIAGRAMS
DIAGRAMS
CHROMOSOME NUMBER
The number of sets chromosomes in a cell is called
the ploidy level.
Haploid cells have one set, Diploid cells have two
sets, and Polypoid cells have three or more sets.
In human the diploid number is 46. , some ferns
have more than a thousand chromosomes in each
somatic cells.
, SEX CHROMOSOMES DIAGRAMS
Sex chromosomes (also called allosomes) are
chromosomes in sex determination.
An autosome is any chromosome that is not a sex
chromosome. Autosomes are represented by
numbers (e.g. chromosomes 12)
Individuals with two sex chromosomes that are the
same are the homogametic sex. (XX)
Individuals with two different sex chromosmes are
the heterogametic sex. (XY)
In humans and all other mammals, a pair of
chromosomes know as X and Y chromosomes
determine the biological sex of an individual.
Some organisms (such as fungi and algae) do not
have sex-determining chromosomes and therefore
do not have sexes; instead they having mating MEIOSIS
types.
The process of meiosis is essential to sexual
Sex is determined by the presence or absence of the
reproduction and the creation of new genetic
Y chromosomes.
variations .
GAMETES
Somatic cells are the cells in the body of an
organisms apart from the sex cells (gametes)
Germ cells are the cells that given rise to gametes,
which are specialized cells that combine in sexual
reproduction.
In meiosis two successive cell divisions produce
four daughter cells, each with half the number of
chromosomes of the parent cell.
Identical (monozygotic) twins develop from one
fertilized egg, so they have identical genes. but
because of non- genetic factors that affect the way
the embryos develop, identical twins are actually
are made not exactly identical.
The process of fertilization involves two haploid
gametes fusing to form a diploid zygote.
