Inheritance (Cell Divison)

Question 1

What are the two types of cell division?

Answer 1

• Mitosis
• Meiosis

Question 2

What cells are the result of mitosis?

Answer 2

Two genetically identical diploid cells

The cells are genetically identical to the parent cell and eachother

Question 3

What is the process of mitosis?

Answer 3

• Each chromosome in the nucleus of the diploid parent cell copies itself exactly (forms X-shaped chromosomes)
• The chromosomes line up in the centre of the cell, where cell fibres pull each half of the X-shaped chromosomes apart
• The cell divides, forming two exact copies of the original cell

Question 4

What is mitosis used for?

Answer 4

• Growth
• Repair
• Cloning
• Asexual reproduction

Question 5

What cells are the result of meiosis?

Answer 5

Four genetically different haploid cells

They are genetically different because they have a random one of the two alleles possesed by the individual for each gene

Question 6

What is the process of meiosis?

Answer 6

• Each chromosome in the nucleus of the diploid parent cell copies itself exactly (forms X-shaped chromosomes) and pairs up with its homologous chromosome
• Recombination of some genes between homologous chromosomes occurs
• The pairs line up along the centre of the cell and cell fibres pull the pairs apart
• The cell divides once, forming two cells with one recombinant chromosome from each pair
• The two cells each divide again without DNA replication in a process similar to mitosis, forming four haploid cells

Question 7

What is meiosis used for?

Answer 7

• It is used for the production of gametes (sperm, egg, pollen)
• It produces variation by forming new combinations of maternal and paternal chromosomes

Question 8

How does random fertilisation lead to genetic variation?

Answer 8

• In meiosis, every haploid cell (gamete) produced will be genetically unique as it will have a unique combination of maternal and paternal chromosomes (so a unique combination of alleles)
• Because of this, each gamete (egg, sperm) will be genetically different in an organism so the random fusion of any of these gametes will result in a genetically different zygote, leading to genetic variation

Question 9

What is the other way variation in organisms can occur other than genetic and what are examples?

Answer 9

• Environmental
• For example, diet causes you to gain weight, an accident can cause scarring, trees in the shade will grow taller than normal in order to reach the light

Variation is, of course, caused by a combination of genetic and environmental factors - continuous features like height are clearly affected by both

Question 10

What’s the difference between continuous and discontinuous features?

Answer 10

• Continuous feautres, like height, are when there are very small degrees of differences and variation is seen on a spectrum
• Discontinuous features, like blood group, are when there are no inbetweens

Question 11

In human cells, what is the diploid number of chromosomes?

Answer 11

46 chromosomes (23 pairs)

Question 12

In human cells, what is the haploid number of chromosomes?

Answer 12

23 chromosomes