Part A (Summary) : Inheritance and Evolution: Chapter 14
INHERITANCE
CHROMOSOMES:
Chromosomes are long threads of DNA, made of strings of genes.
In the nucleus are the chromosomes chromosomes contain DNA DNA carries
genes.
Genes are a length of (piece of) DNA that is the unit of heredity, and they code for
protein. Genes can be copied and passed through generations.
Inheritance is the transmission of genetic information from generations to generation.
The genes in the chromosomes determine your characteristics and these come from
your parents.
The number and variety of genes of each species of an organism are what makes
each species different.
Cell division: mitosis and meiosis
There are two types of cells; somatic (body cells) and gamete (sex) cells.
Somatic cells are diploid: they have a nucleus containing two sets of chromosomes.
Gamete cells are haploid: they have a nucleus with a single set of unpaired
chromosomes.
Two chromosomes of a pair are called homologous chromosomes
So, chromosome pair 1,2,3... 46 in the body cells of a human have one part
from the mother and the other part from the father that were fused during
fertilisation.
Single cell zygote embryo fetus baby.
Mitosis is a nuclear division giving rise to genetically identical cells in which the
chromosome number is maintained because chromosomes are exactly copied.
Cells divide by mitosis for growth and repair.
1
, Growth is the permanent increase in size and dry mass by an increase in cell
number or cell size, or both.
Let’s unpack this definition:
Dry mass = mass of all biological material in the body, minus water mass.
This increase occurs by means of an increase of number of cells in the body
(happens via mitosis), or the cell size (cells become bigger) or both (more cells
and bigger cells).
Development is an increase in complexity of the body of an organism.
(like the way we start off as a single cell and become more and more complex and
we become a zygote, embryo, fetus… developing organs and limbs etc…)
The chromosome before mitosis: remember that just before splitting the
chromosome will become shorter and fatter, making it slightly more visible.
Position of a certain gene (allele)
Centromere
Two identical chromatids
The two chromatids are held together at the centromere.
Mitosis:
1. Chromosomes in the nucleus of one cell split into chromatids.
2. One chromatid from each chromosome goes to each daughter cell.
3. Growth occurs and each chromatid that is now in the daughter cells and an exact
copy is made of each chromosome.
4. Two daughter cells now exist that can divide in this same way again.
Meiosis:
Meiosis is a reduction division in which the chromosome number is halved from
diploid to haploid
(This takes place in the reproductive organs.)
Meiosis 1:
1. Homologous chromosomes come closer together.
2. Crossing over occurs and genes are exchanged.
2
INHERITANCE
CHROMOSOMES:
Chromosomes are long threads of DNA, made of strings of genes.
In the nucleus are the chromosomes chromosomes contain DNA DNA carries
genes.
Genes are a length of (piece of) DNA that is the unit of heredity, and they code for
protein. Genes can be copied and passed through generations.
Inheritance is the transmission of genetic information from generations to generation.
The genes in the chromosomes determine your characteristics and these come from
your parents.
The number and variety of genes of each species of an organism are what makes
each species different.
Cell division: mitosis and meiosis
There are two types of cells; somatic (body cells) and gamete (sex) cells.
Somatic cells are diploid: they have a nucleus containing two sets of chromosomes.
Gamete cells are haploid: they have a nucleus with a single set of unpaired
chromosomes.
Two chromosomes of a pair are called homologous chromosomes
So, chromosome pair 1,2,3... 46 in the body cells of a human have one part
from the mother and the other part from the father that were fused during
fertilisation.
Single cell zygote embryo fetus baby.
Mitosis is a nuclear division giving rise to genetically identical cells in which the
chromosome number is maintained because chromosomes are exactly copied.
Cells divide by mitosis for growth and repair.
1
, Growth is the permanent increase in size and dry mass by an increase in cell
number or cell size, or both.
Let’s unpack this definition:
Dry mass = mass of all biological material in the body, minus water mass.
This increase occurs by means of an increase of number of cells in the body
(happens via mitosis), or the cell size (cells become bigger) or both (more cells
and bigger cells).
Development is an increase in complexity of the body of an organism.
(like the way we start off as a single cell and become more and more complex and
we become a zygote, embryo, fetus… developing organs and limbs etc…)
The chromosome before mitosis: remember that just before splitting the
chromosome will become shorter and fatter, making it slightly more visible.
Position of a certain gene (allele)
Centromere
Two identical chromatids
The two chromatids are held together at the centromere.
Mitosis:
1. Chromosomes in the nucleus of one cell split into chromatids.
2. One chromatid from each chromosome goes to each daughter cell.
3. Growth occurs and each chromatid that is now in the daughter cells and an exact
copy is made of each chromosome.
4. Two daughter cells now exist that can divide in this same way again.
Meiosis:
Meiosis is a reduction division in which the chromosome number is halved from
diploid to haploid
(This takes place in the reproductive organs.)
Meiosis 1:
1. Homologous chromosomes come closer together.
2. Crossing over occurs and genes are exchanged.
2
