AQA B2 2.7 Cell division and inheritance

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  • Created by: Rchilds
  • Created on: 30-05-17 14:35
What are chromosomes?
They contain genetic information, are usually found in pairs (one from your mother, one from your father) in the nucleus of a cell. Chromosomes are made up of large molecules of DNA (deoxyribonucleic acid) which has a double helix structure.
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How many chromosomes does a normal body cell in a human have?
46 as 23 pairs
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When does mitosis happen?
Most cells reproduce via mitosis for growth and repair/replacement cells
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What are the stages of mitosis?
(1) copies of the genetic material (chromosomes now have 2 strands) are made (2)then the cell divides once to form two genetically IDENTICAL body cells
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Why must chromosomes be copied as the first stage of mitosis?
one copy of each chromosome strand goes to each offspring cell so that each offspring cell receives a complete set / the same genetic material
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What is meiosis?
Cell division to produce gametes
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What are the stages of meiosis?
(1) copies of the genetic material (chromosomes now have 2 strands) are made (2) the cell divides TWICE to form 4 NON-IDENTICAL gamete cells, each with only 23 chromosomes
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What is a gamete?
The sex cells e.g. in a human they are the sperm and egg cells
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Where are gametes produced in the human body?
testes make sperm, ovaries make eggs
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How many chromosomes does a gamete in a human have?
Half the normal number - 23 unpaired chromosomes
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Why do gametes only need half the number of chromosomes of a normal cell?
When they join during fertilisation, new, complete sets of chromosomes pairs are formed
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What happens after fertilisation?
Normal cell division takes place via mitosis to produce an embryo
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What is differentiation in cells?
When a cell becomes specialised. Most cells do this by adulthood so can only divide to make the same type of cell - for growth or repair
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What are cells that can differentiate into any type of cell called?
Stem cells
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Where can stem cells be found in humans?
embryos and adult bone marrow
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Give an example of where stem cell technology may be useful
for paralysis victims - stem cells can differentiate into any cell including nerve cells (normal adult nerve cells cannot divide to make new cells once they are differentiated)
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What is asexual reproduction?
Offspring cells that are made through normal mitosis of adult cells, they therefore have identical chromosomes to the parent.
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What is sexual reproduction?
When gametes from two different parents fertilize to produce offspring. The offspring is not identical to the parents as it gives rise to variation. When gametes fuse, one of each pair of alleles comes from each parent.
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How is the sex of humans determined?
In females the sex chromosomes are the same (**); in males the sex chromosomes are different (XY)
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What is a gene?
A section of DNA that controls a characteristic in the organism. Each gene codes for a particular combination of amino acids which make a specific protein
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What is are alleles?
Different versions of the same gene. Humans have 2 alleles of every gene, one from their mother and one from their father. They may be the same allele or they may be different.
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What is the dominant allele?
An allele that will control the development of a characteristic when it is present, it is notated with a capital letter e.g. R
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What is the recessive allele?
An allele that will only control the development of a characteristic when the dominant allele is not present. It is notated with a lower case letter e.g. r
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What is your genotype?
The combination of alleles you have in your chromosome pair e.g. RR, Rr or rr
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What is your phenotype?
The physical characteristic your display based on your genotype. This will be the dominant allele if you have it (RR or Rr), if your genotype is two recessive alleles (rr) then you will display this
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What does homozygous dominant mean?
Both your alleles for a gene are the same and are the dominant ones (RR)
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What is DNA fingerprinting?
A technique used to identify people from their DNA. Everyone's DNA sequence is unique, except for identical twins
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What does homozygous recessive mean?
Both your alleles for a gene are the same and are the recessive ones (rr)
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What does hetrozygous mean?
Your alleles for a gene are different, one is dominant and one is recessive (Rr)
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What is embryo screening?
During embryo screening, a technician tests the genetic material of the embryo to find out which alleles are present
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What are some issues with embryo screening?
Technique may damage the embryo/ cause a miscarriage. If the embryo DNA shows it has a disability or genetic disease it may be aborted (embryo can't give consent, religious reasons, prejudice against disability, designer babies)
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What are some advantages of embryo screening?
Inherited disorders can be identified and parents can prepare, can prevent future suffering and spread of disease, embryos with disorders can be used for stem cell research instead
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What is polydactyly?
Having extra fingers or toes – is caused by a dominant allele of a gene and can therefore be passed on by only one parent who has the disorder.
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What cystic fibrosis?
a genetic disease that causes a defect in cell membranes so it produces too much mucus (in respiratory system and digestive system). It is a recessive allele
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How can two parents without cystic fibrosis have a child who does have the disorder?
Because it is a recessive allele, the parents might be carriers of it (be hetrozygous Cc) but not actually show it. If they both pass on the recessive allele to the child then the child will have the disorder. There is a 25% chance of this happening.
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How did Gregor Mendel study inheritance?
He looked at different characteristics in pea plants. He found that if he bred red-flower plants with white-flower plants, all offspring had red flowers. If he bred these plants with each other, most offspring had red but some had white flowers
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What did Mendel conclude from his pea experiments?
Characteristics in plants are passed on from parents in 'hereditary units', some traits are dominant some are recessive. Mendel showed that red flowers in pea plants is a dominant characteristic, and white flowers in pea plants is a recessive trait.
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Why did Mendel's ideas take some time to be accepted?
Mendel was a monk, not a scientist so many people didn't look at his research for many years. Scientists also hadn't discovered DNA, genes and chromosomes yet. Mendel's mathematical approach was new and went against other theories
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What is a hybrid and what is one reason why it may not be able to breed sexually?
When two closely related species mate but their offspring is not fertile, you call it a hybrid. The hybrid cannot go through meiosis successfully as it often has unpaired chromosomes so some of the gametes will have missing chromosomes
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What are the similarities between mitosis and meiosis?
Both start by the chromosomes doubling (producing duplicate strands), both are types of cell division to produce new cells
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What are the differences between mitosis and meiosis?
mitosis happens in all cells, cells divide once to produce 2 genetically identical cells with 46 chromosomes. Meiosis only happens in sex cells, cell division happens twice to produce 4 genetically difference gametes with 23 chromosomes in them.
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Card 2

Front

How many chromosomes does a normal body cell in a human have?

Back

46 as 23 pairs

Card 3

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When does mitosis happen?

Back

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Card 4

Front

What are the stages of mitosis?

Back

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Card 5

Front

Why must chromosomes be copied as the first stage of mitosis?

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