Evolution:
The phenotype of an individual is the external appearance of the individual.
The genotype refers to the genetic makeup of the individual which cannot be seen from the exterior.
Homozygous and heterozygous individuals:
Diploid human cells contain 23 pairs of homologous chromosomes. There will be two genes for each
trait in every cell, one borne on the maternal chromosome and one on the paternal chromosome. If
these two genes are the same (both for blue eyes) then the person is homozygous blue eyed.
If the person is heterozygous if the two genes are different (one for blue eyes and one for brown
eyes).
Dominant and recessive genes:
Some genes are dominate and they always show and mask the recessive gene, so the phenotype of
an individual will always show the dominant gene. When brown is dominate over blue, a
heterozygous brown eyed pig will have one gene for brown eyes and one for blue eyes, but brown
will show as it is dominate.
Gametes are haploid, carrying only one set of chromosomes and hence they contain one gene for
each characteristic. Gametes are produced during meiosis during which increased variety I
introduced into the species because:
Crossing over allows exchange of genes between the maternal and paternal chromosomes.
The chromosomes line up randomly at the equator during metaphase 1 and 2.
Genes are independently assorted (Mendel’s law of independent assortment). The gene for tall is not
affected by the gene for brown eyes and is sorted independently.
A gene is a part of the DNA. An allele is a form of a gene (blue eyes).
Monohybrid and dihybrid crosses:
If one trait is crossed (blue with brown eyes) this is termed monohybrid cross. If two factors (eye
colour and height) are crossed then this is termed dihybrid cross.
Sex determination of the individual:
In each diploid set of 46 chromosome there 22 pairs of autosomes and one pair of sex-determining
chromosomes, called gonosomes which can be either XX or XY. The sex of the individual is
determined by the presence of a Y chromosome, if the individual gets a Y chromosome he will be a
boy.
Gregor Mendel’s Laws:
The Law of Segregation: It states that factors occur in pairs in the parent, but segregate when
gametes are produced. This is supported by our knowledge of meiosis where haploid gametes are
produced.
The Law of Independent Assortment: It states that factors are passed from parent to offspring
independently and not attached to any other factor like wrinkled pods ad serrated leaves always
occurring together.
The Law of Dominance: It stated that there are dominant genes which mask the recessive ones.
The phenotype of an individual is the external appearance of the individual.
The genotype refers to the genetic makeup of the individual which cannot be seen from the exterior.
Homozygous and heterozygous individuals:
Diploid human cells contain 23 pairs of homologous chromosomes. There will be two genes for each
trait in every cell, one borne on the maternal chromosome and one on the paternal chromosome. If
these two genes are the same (both for blue eyes) then the person is homozygous blue eyed.
If the person is heterozygous if the two genes are different (one for blue eyes and one for brown
eyes).
Dominant and recessive genes:
Some genes are dominate and they always show and mask the recessive gene, so the phenotype of
an individual will always show the dominant gene. When brown is dominate over blue, a
heterozygous brown eyed pig will have one gene for brown eyes and one for blue eyes, but brown
will show as it is dominate.
Gametes are haploid, carrying only one set of chromosomes and hence they contain one gene for
each characteristic. Gametes are produced during meiosis during which increased variety I
introduced into the species because:
Crossing over allows exchange of genes between the maternal and paternal chromosomes.
The chromosomes line up randomly at the equator during metaphase 1 and 2.
Genes are independently assorted (Mendel’s law of independent assortment). The gene for tall is not
affected by the gene for brown eyes and is sorted independently.
A gene is a part of the DNA. An allele is a form of a gene (blue eyes).
Monohybrid and dihybrid crosses:
If one trait is crossed (blue with brown eyes) this is termed monohybrid cross. If two factors (eye
colour and height) are crossed then this is termed dihybrid cross.
Sex determination of the individual:
In each diploid set of 46 chromosome there 22 pairs of autosomes and one pair of sex-determining
chromosomes, called gonosomes which can be either XX or XY. The sex of the individual is
determined by the presence of a Y chromosome, if the individual gets a Y chromosome he will be a
boy.
Gregor Mendel’s Laws:
The Law of Segregation: It states that factors occur in pairs in the parent, but segregate when
gametes are produced. This is supported by our knowledge of meiosis where haploid gametes are
produced.
The Law of Independent Assortment: It states that factors are passed from parent to offspring
independently and not attached to any other factor like wrinkled pods ad serrated leaves always
occurring together.
The Law of Dominance: It stated that there are dominant genes which mask the recessive ones.
