Biology unit 1


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  • Created by: Leah
  • Created on: 08-01-11 17:45

Differences between people

Differences between humans are caused by:

  • Genes
  • Environment
  • Mixture of both
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Members of a family may look like each other because they inherit their parents genes.

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A feature caused by one gene would be blood type because it is specific, you could put people into a specific group. This is called Discontinuous Variation.

A feature caused by two genes would be height because peoples height can range. You cant put height into specific groups. This is called Continuous Variation.

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Clones are Organisms which are genetically identical to one another.

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Forming Clones

Things which produce asexually to form clones would be:

  • Hydra
  • Bacteria
  • Some Fish
  • Plant Stems
  • Jellyfish
  • Corals
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Natural Cloning

Sperm and egg join together

Sperm fertilizes the egg

Cells start to grow

Cells split to create clones

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Artificial Cloning

Nucleus is thrown out from donor egg

Nucleus is taken mother clone egg

New nucleus is placed into donor egg

That now makes a clone of the mother.

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Male or Female

Human beings have 23 pairs of chromosomes in a normal body cell.

One of these pairs is called the sex chromosomes.

This pair controls whether the person is male or female.

In a man the chromosomes in this pair are different sizes.

There is one X and one Y chromosome. This Pair is called XY.

In a woman the chromosomes in this pair are both the same size.

There are two X chromosomes. The pair is called **.

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Having Children

"A couple have two girls. They think it is more likely that their next child will be a boy."

This is not the case as there is a 50% chance it could be either sex.

When a sperm cell fertilizes an egg cell the chances are 50% that it will be an X or a Y sperm. This means that there is a 50% chance that the baby will be a boy or a girl.

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Creating a Male

A male embryo's testes develop when it is 6 weeks old.

This is caused by a gene on the Y chromosome.

SRY stands for 'sex-determining region of the Y chromosome'

Testes produce the male sex hormone called androgen.

If there is no male sex hormone present, the sex organs develop into ovaries, ********, and vagina of a female.


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1. Chromosomes in one of the mother's cells are copied.
2. Chromosomes in one of the Father's cells are copied.
3. Just one of the copies from each pair of chromosomes goes into the egg cell.
Each egg cell nucleus has 23 single chromosomes.
5. Just one of the copies from each pair of chromosomes goes into a sperm cell. 
6. Each sperm cell nucleus has 23 single chromosomes.
7. The sperm cell nucleus enters the egg cell.
8. The egg cell is fertilized.
9. The fertilized egg cell nucleus has 23 pairs of chromosomes.
. The fertilized egg cell grows and divides many of times
11. The cell specialize into different types.
12. A new human baby develops. 

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Dominant allele:

You only need to have one copy of a dominant allele to have the feature it produces.

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Recessive allele:

You must have two copies of a recessive allele to have the feature it produces.

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Dominant allele for dimples= D

Recessive allele for no dimples= d

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Huntington's Disorder

Inherited condition.

Symptoms don't happen until middle age.

First the person has problems controlling their muscles.
This shows up as twitching.

Gradually becomes forgetful.

They find it hard to understand things.

The condition is fatal.


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Cystic Fibrosis

It is a genetic disorder.

Causes problems for breathing and digestion.

Cells which make mucus don't work properly.

The mucus is much thicker than it should be.

They get lots of chest infections.

Person can be short of nutrients.

Most can't have children.

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Genetic crosses

Sex cells in humans are X and Y.

Every sex cell carries a copy of half the parents' chromosomes.

Each sex cell has only one of each chromosome.

It is not possible to predict which sex cells will join together at fertilization.

Genetic cross diagrams show all the different possible ways that they could join up.

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Genetic crosses

Brothers and sister with the same biological parents do not look exactly the same because they inherit different genes.

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An ethical decision is when a person has to make a decision about what is the right or wrong way to behave.

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Genetic testing

A false-positive result:

A wrong test result.

The test results are unclear, but the baby is born clear of any disorder.

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Genetic testing

A false-negative result:

A wrong text result.

The test result says that a person does not have a medical condition when he/she does.


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Embryo Selelction

PGD= Pre-implantation genetic diagnosis.

-Female takes a 'fertility drug' so that she releases several ova.
Fertility drugs contain hormones.--->  In a small operation the doctor collects the ova. ---> Male's sperm fertilizes the ova in a Petri dish. This is in vitro fertilization.---> When the embryos reach the 8-cell stage, one cell is removed from each.---> The cells are tested for the disorder.


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Stem Cells

Stem Cells are unspesilized cells. They can grow into any type of cell in the human body.

Scientists want to grow stem cells to make new cells to treat patients with some diseases.

But these new cells would need to have the same genes as the person getting them as a treatment.

When someone Else's cells are used in a transplant they are rejected.


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Genetic screaning

When 2 people decide to have children, they could find out if their child would be at risk of inheriting the disorder.

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