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BTEC Applied Science biology Unit 11 learning aim B
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BTEC Applied Science biology Unit 11 learning aim B
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Unit 11: genetics and genetic engineeringLearning aim B: explore how the process of cell division in eukaryotic cells contributes to genetic
variation
Assignment title: Cell Division
Human chromosomes
The ability to pass on genetic information to the next generation of offspring is what defines living
beings. Chromosomes exist to convey genetic information, which is subsequently transcribed and copied
for daughter cells or offspring for inheritance.
Because the child inherits both parents’ DNA, the chromosomes are in charge of transporting and
storing the instructions that make up the child unique. To ensure that the offspring have qualities from
both parents, one chromosome is inherited from the mother and the other from the father. Certain
cells, such as productive cells, require the proper number of chromosomes in order to operate
effectively.
Chromosomes are threadlike structures that transmit genetic data in the form of genes. Proteins (known
as histones) and DNA make up chromosomes (Deoxyribonucleic acid). They can be seen under a
microscope. Chromosomes are present in the nucleus of cells in plants and animals (including humans).
Chromosome Number
The number of chromosomes in any species is constant for all the cells. And each species of plant and
animal has a set number of chromosomes. For example, a protozoan species contains as many as 1600
chromosomes in the cell while a rice plant has 12 and a fruit fly has 4 pairs of chromosomes.
Each cell in the human body has 23 pairs of chromosomes, for a total of 46 chromosomes. Each pair of
chromosomes contain two, one from each parent, meaning that half of a child's chromosomes come
from their mother and the other half from their father.
22 of these pairs, or 44 chromosomes that are non-sex chromosomes are called autosomes, which are
the numbered chromosomes that contain genes for anything and control the inheritance of all an
organisms' characteristics expect the sex-linked ones, which are controlled by the sex chromosomes.
The 23rd pair, are known as sex chromosomes (XX= female chromosome or XY= male chromosome). This
is the chromosomes that decide whether the baby will be born female or male. In females the sex
chromosome is made up two X sequence, on the other hand, male sex chromosome is made up of one X
and one Y sequence.
As you can see in the image below there are 46 chromosomes and 2 of them are sex chromosomes that
involve on sex determination. The image only shows male sex chromosomes (XY) the female sex
chromosomes are 2 XX.
,Homologous and non-homologous chromosomes
The genetic material of a particular or specific cell is structured by the chromosomes in the nucleus. The
two types of chromosomes determined based on the paring pattern of chromosomes during metaphase
1 of meiosis are homologous and non-homologous chromosomes.
Homologous chromosomes are those with the same pair of chromosomes, whereas non-homologous
chromosomes are those with separate pairings of chromosomes. The main difference between
homologous and nonhomologous chromosomes is that homologous chromosomes are made up of a
pair of chromosomes with the same gene sequence, or two copies of each chromosome.
Nonhomologous chromosomes, on the other hand, are made up of chromosomes that do not belong to
the same pair.
Homologous chromosomes include alleles of the same genes in the same loci, whereas nonhomologous
chromosomes contain alleles of different genes in distinct loci. Non-homologous chromosomes, on the
other hand, have alleles for separate genes. Non homologous chromosomes couple during metaphase 1,
but homologous chromosomes pair during meiosis 1.
For example, 22 autosomal chromosomes are homologous chromosomes and X & Y chromosomes are
nonhomologous chromosomes.
Structure
In general, viruses, prokaryotic, eukaryotic cells, and live beings have diverse chromosome structures
and locations. Furthermore, chromosomes range in size, with the X chromosome (in humans) being
significantly larger than the Y chromosome. It has about 900 genes, while the Y chromosome only has
about 55.
A chromosome is a thread-like structure made up of a DNA (deoxyribonucleic acid) molecule tightly
wrapped with proteins called histones that help to support its structure. The DNA is tightly twisted
around spool-like proteins called histones (a protein that provides structural support for chromosomes)
in this unique arrangement of chromosomes; otherwise, the chromosomes would be too huge to fit
within the cells.
, The length of chromosomes is determined by the length and number of genes on the chromosomes
themselves. In addition, the length of the cells varies with their age. A single human chromosome is
around 2 inches long on average.
Because prokaryotes (cells without a nucleus), such as bacteria, lack a nucleus, their chromosomes are
circular in shape. Instead, they employ a nucleoid to store their chromosomes, which contain the DNA.
The chromosomes in eukaryotes (cells with a nucleus) have a linear structure.
Chromosomes can exist in duplicated and unduplicated stages. In unduplicated stages it appears as a
single strand, however in duplicated stages chromosomes consist of two strands, which are joined
together by a centromere (a specific part of chromosome that connects a pair of sister chromatids
together during cell division). Each of the two strands made up the sister chromatids.
Duplicated chromosomes have a typical structure, likened to an asymmetrical version of the letter X,
with the two chromatids intersecting at the centromere. To be very specific, one arm is longer than the
other.
Commonly a chromosome has 8 different parts, this includes:
1) Centromere (primary constriction or kinetochore)
2) Telomere
3) Chromatid
4) Chromatin
5) Secondary constriction
6) Chromonema
7) Chromomeres
8) Matrix
Types of chromosomes: there are 4 types of chromosomes.
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