B2.7 Inheritance

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  • Created by: Fiona S
  • Created on: 08-04-15 11:30


  • Your body is made up of cells.
  • Each cell contains a nucleas which contains the genetic material and controls the cell.
  • Each nucleas contains lots of little threads called chromosomes.
  • Chromosomes carry the genetic information which controls how your body works and what you look like (controls your characteristics).
  • There are 46 chromosomes in a human body cell.
  • Each chromosome is made up of tangled thread. The threads are made up of a very long molecule called DNA.
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A type of cell division which produces genetically identical cells or clones. It used for growth, repair and asexual reproduction.

The chromosomes replicate into sister chromotids so now there are too many chromosomes.

The cell uses a special structure called a spindle cell

The sister chromatids separate to opposite poles

The cell then separates into two cells each with a full set of chromosomes

Now we have two genetically identical cells

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Differentiation is ... when a stem cell becomes specialised

Some examples are:

Animal cells: Ciliated, Red and White Blood Cells, Sperm Cell

Plant cells: Root hair cell, Palisade cells, Stomata cells, Guard Cells

Differentiation in animals: Occurs very early in life, in the lining of embryo. It is permanent and it difficult to clone.

Differentiation in plants: Occurs all through life, at the growing points e.g. the roots and shoot tips. It is not permanent and it is easy clone, with cuttings. 

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Stem Cells

A stem cell is the cell that has the potential/ability to differentiate into any cell type.

In adults they are found in bone marrow - produces red blood cells constantly

In an embryo they are found in the inner lining of the embryo

Stem cells can be made to differentiate into many different types of cells. Treatment with these cells has the potential to treat conditions such as paralysis

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Stem Cell Research


  • Can be used for medical reasons - improve quality of life, can save lives
  • Have to be destroyed after 14 days so arguably not murder
  • Only a few embryos used in ratio in potential lives saved
  • Can be used to produce be genetically identical recipient = no rejection
  • Removes need to test on existing life
  • Make use of discarded embryo - abortion, IVF donation (better than throwing away)
  • Used to help cure diseases like Parkinsons


  • Religious objection: seen as abortion, killing a child, life at fertilisation
  • Can lead to cloning - disagreed with
  • Embryos being destroyed upsetting for infertile couples
  • Violation of human rights
  • Still no real successful outcome
  • Don't know long term effects
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Using Stem Cells

  • Could be used to replace/repair damaged tissues/organs that can't repair themselves naturally
     - Paralysis(Nerve spinal tissue)
     - Diabetes(Grow areas of pancreas)
     - Transplant Organs
     - Dementia
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Cell division to form the gametes is called meiosis.

The chromosomes in the parent cell clone to form sister chromatids

They swap over genes - genetic exchange, increase variation of offspring

The cell then divides into daughter cells

They then split again so you e up with 4 cells, all genetically unique

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Mitosis vs. Meiosis


  • 2 daughter cells, 1 division
  • Starts with diploid parent cells and ends with diploid daughter cells
  • No genetic swapping
  • Daughter cells genetically identical/clones
  • All body cells (not R.B.C) undergo this
  • Used for growth and repair of cells and asexual reproduction
  • Spindle used


  • 4 daughter cells, 2 divisions
  • Starts with diploid parent cells and ends with haploid daughter cells
  • 'Cross over' of genetic information takes place
  • Daughter cells show genetic variety
  • Takes place only in the GONADS(ovaries/testes)
  • To make gametes
  • Spindle used
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Genes and Proteins

Chromosomes are long molecules of DNA which have a double helix structure. DNA has two main functions:

  • It is the permanent store of genetic information and needs to be copied or replicated
  • The genetic information is used to make proteins such as enzymes and hormones. The proteins determine how the cell develops and functions

Chromosomes in the nucleus are made of DNA. This is a double helix. DNA contains coded information. A gene is a small section of DNA that codes for a specific protein.

The proteins determine the cells and hence the organisms characteristics. For example - our blood group, eye colour etc.

DNA contains coded information that determines inherited characteristics.

DNA is made of very long chains which have four different compounds called protein.

These bases are given the letter A, T, C, G.

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A codon of three bases is the code for a particular amino acid.

The order of the bases in the genes of the DNA controls the order in which amino acids are assembled to produce a particular protein.

If the order of the bases is wrong, the wrong amino acid will be used to make the protein which may then not function properly.

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DNA changing

  • DNA is a sequence of bases
  • If the sequence is changed then it has mutated
  • So the sequence of amino acids is different
  • So the protein is different
  • Which could probably change the active site
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Protein Synthesis

  • DNA is found in the nucleus
  • It is not possible to remove the DNA from the Nucleus
  • So you make an mRNA gene 
  • You take the mRNA out of the nucleus to the ribosome where you turn the gene into a protein

The DNA has a code for a protein. This code is called a GENE. It can't leave the nucleus so it doesn't mutate as easily, it has to be able to transfer code from the nucleus to the ribosomes.

The mRNA copies the code that goes to the ribosomes.

The ribosomes have all the right ingredients to form the protein. It uses the mRNA to assemble amino aids in correct sequences for particular proteins.

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From Mendel to DNA

1. Pea plants grow quickly

2. Pea plants are available in pure-breeding (homozygous) strains

3. Many pea plant characteristics show discontinuous variation; either one form or another, with no intermediates. This means their phenotypes are easily distinguishable.

4. Mendels First Law - the law of segregation: alternate versions of genes (alleles) causes variation in inherited characteristics

5. An organism inherits two alleles for each characteristics - one from each parent

6. Dominant alleles always masks recessive alleles

7. The two alleles for each characteristic separate during gamete production

8. Mendels Second Law: Law of Independant assortment - genes for different characteristics are sorted independently during gamete production.

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Genetics - Key Words

Allele One of a number of alternative forms of a gene.

Recessive An allele of a gene that does not normally effect how an organism develops because it is dominated by the dominant allele.

Dominant The allele of a gene that's more strongly expressed than any other allele. It determines which characteristic appears.

Haploid A cell which contains only half the number of chromosomes within its nucleus. Occurs in cells such as sperm, eggs or pollen involved in sexual reproduction.

Heterozygous Having a different allele of a gene on each chromosome of a chromosome pair. E.g. having allele B and b.

Homologous Pair Two chromosomes that contain the same genetic information. Although the genes are the same the may not have the same alleles at each gene.

Nucleus The membrane-bound region in a cell which contains the chromosomes.

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Genetics - Key Words

Diploid A cell which has its correct, full number of pairs of chromosomes in its nucleus.

Homozygous Having the same allele of a gene on each chromosome of a chromosome pair. E.g. alleles B and B.

Mitosis The cell division process producing identical, clone cells of the parent cell.

Chromatid One arm (or leg?) of a chromosome.

Chromosome An X-shaped piece of tightly wound DNA. One of a pair found in the nucleus of a cell.

Phenotype An organism's outward appearance.

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Punit Square

These are used to show the combinations of gametes and determine a ratio to decide what the dominant allele will be. In this case the pea plant will 100% be green.

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Cystic Fibrosis

The Cystic Fibrosis gene is a recessive allele, you have to be homozygous recessive to have this allele. Since the disease is caused by a recessive gene, it must be inherited by both parents. Parents who have the recessive allele are carriers of the disorder. Carriers have no ill effects themselves.

It affects the cell membrane of respiratory and digestive system by producing abnormally thick mucus.

The affect on the lungs is: Breathlessness and coughs. Repeated chest infections - bacteria are trapped and thrive in the thick mucus.

The affect on the digestive system is: the pancreatic duct clogs and block enzyme secretion. This results in poor digestion, causing low weight gain and low energy levels.


Inhaler - widen airway and break down excess mucus while antibiotics treat chest infections. Oxygen gas helps improve breathing. Physiotherapy loosens mucus , making it easier to cough up.

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Polydactyly is a genetic disorder and it is the development of too many fingers or toes. On average 1 baby in a thousand is affected. The treatment for this is simply surgery to remove the extra fingers or toes.

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Genetic Screening and Genetic Fingerprinting

Genetic Screening is checking for genetic abnormalities of a foetus or of individuals before they reproduce.

Amniocentesis - fetal cells are collected from the amniotic fluid via a hollow needle.

Chrionic Villus Sampling - fetal cells are collected from the chrionic villi in the placenta with a suction tube.

Pro's: - If embryos carrying are detected they can be discarded, reduces the number of CF alleles in gene pool
           reduction in health costs
           - if a baby is known early to have CF = early treatment = emotional preparation

Con's: - Screening increases risk of miscarriage
            - May pose risk to mother (invasive treatment)
            - Why screen for diseases/disorders that aren't life threatening?
            ethical decisions are often difficult to make - best not to know

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Genetic Fingerprinting

Scientists use a small number of sequences of DNA that are known to vary among individuals a great deal, and analyze those to get a certain probability of a match.

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