Biology GCSE - AQA Edexcel

  • Created by: Ellie
  • Created on: 21-09-17 16:25

What is Mitosis?

Mitosis is the name for making new cells. The new cells are genetically identical to the orginial cell.

  • Step One: Chromosomes in nucleus are copied.
  • Step Two: Chromotids pulled apart and moved towards poles.
  • Step Three: Chromosomes seperate.
  • Step Four: Cell Divides.

Mitosis is also diploid which means there is 23 pairs instead of Haploid which is 23 chromosomes (half).

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What is Meiosis?

'a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores' - Google.

Meoisis produces cells which have half the normal number of chromosomes (Haploid).

Step One: Before the cells start to divide, it duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.

Step Two: In the first division in meiosis the chromosome pairs line up in the centre of the cell.

Step Three: The pairs are then pulled apart so each new cellonly has one copy of each chromsomes and some of the mothers chromosomes go into each new cell.

Step Four: In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.

You get four gametes (sex cells), each with only a single set of chromosomes in it. Each of the gametes is genetically different from the others because the chromosome all get shuffled up during meiosis and each gamete only gets half of them, at random.

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What is Asexual Reproduction?

'asexual reproduction occurs when a single organism reproduces without the genetic input of another' - Google.

  • Only one parent.
  • Exactly the same.

Doesn't need a partner to reproduce, it is also alot quicker.

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What is sexual reproduction?

'the production of new living organisms by combining genetic information from two individuals of different types (sexes). In most higher organisms, one sex (male) produces a small motile gamete which travels to fuse with a larger stationary gamete produced by the other (female).' - Google.

  • Has two parents.
  • Not the same.

Needs a partner to reproduce, therefor takes alot longer.

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What does Heterozygous mean?

This word refers to a pair of chromosomes being made of two different alleles of a gene.

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What does Homozygous mean?

This word refers to a pair of chromosomes being made of two of the same alleles of a gene.

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What is a gamete?

A gamete is another word for an egg or sperm cell; they are able to unit with a cell of the opposite sex to form a zygote.

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What's the difference between Haploid and Diploid?

Haploid = 23 Chromosomes (1/2 amount of pairs)

Diploid = 23 pairs (46 chromomes A.K.A the full amount of chromosomes)

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What is a Zygote?

A zygote is what is formed when an egg is fertilised by the sperm (When one gamete meets with another cell of the opposite sex).

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What is an Allele?

'each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.' - Google.

An alternative form of a gene.

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What does dominant mean?

The dominant allele determines the development of a characteristic. For example, if the mother has blue eyes and the dad has brown eyes..then the child produced will more than likely have brown eyes because brown is the most dominant colour.

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What does recessive mean?

This allele will determine a characteristic only if there are no dominant ones.

E.g If the mother and father of a baby both have blue eyes, then the baby will have blue eyes.

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How is the sex of a baby determined?

  • The sex of a baby is completely determined by the man.
  • The last chromosome out of the 46 determines the gender.

**- Girl.

XY - Boy.

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What is Polydactly?

Polidactly is a genetic disorder where a baby is born with extra fingers or toes.

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What doees Homozygote mean?

Homozygote is an individual with two identical alleles for a characteristic, for example, BB or bb.

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What does Heterozygote mean?

An individual with different alleles for a characteristic, for example, Bb.

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What is a genotype?

This describes the alleles present or genetic makeup of an individual regarding a particular characteristic, Bb or bb.

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What is a phenotype?

This describes the physical appearance of an individual regarding a particular characteristic.

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What is pre-implantation genetic screening?

  • Alternatively, if there is a known inherited disorder in the family, embreyos produced by IVF can be tested before being implanted into the mother.
  • This means that only babies without the disorder are born.
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