Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
24 Cards in this Set
- Front
- Back
|
What is a chromosome? |
A very long molecule of tightly coiled DNA. |
|
|
What is a gene? |
A small section of DNA that determines a particular feature. |
|
|
What determines the gender of a human? |
Women have two X chromosomes whilst men have an X and a Y chromosome (the Y chromosome is much shorter than the X chromsome) |
|
|
Describe the structure of DNA. Make references to bases and nucleotides. |
-double helix (spiral shape) -strands are made up of riboses and phosphates -two strands are connected by two bases, that are connected by hydrogen bonds -the bases are thymine, cytosine, adenine and guanine -A and T pair with two hydrogen bonds -C and G pair up with three hydrogen bonds -A nucleotide consists of the sugar, a base and a phosphate -A codon is a sequence of three adjacent nucleotides that corresponds with a specific amino acid |
|
|
What are alleles? |
Different forms of the same gene. |
|
|
What is a phenotype? |
The physical appearance of an organism. |
|
|
What is a genotype? |
The set of genes an organism possesses. |
|
|
What is heterozygous? |
When the two alleles are different. |
|
|
What is homozygous? |
When the two alleles are the same. |
|
|
What is a dominant allele? |
An allele that is expressed in the phenotype whenever it is present in the genotype. |
|
|
What is a recessive allele? |
An allele that is only expressed in the phenotype when both the alleles are recessive. |
|
|
What is meant by codominance? Give an example of codominance in humans. |
Both alleles are expressed in the phenotype. E.g. sickle cell anaemia or blood type. |
|
|
What are diploid cells? |
Cells with the full number of chromosomes. |
|
|
What are haploid cells? |
Cells with half the number of chromosomes, e.g. gametes.
|
|
|
In humans, how many chromosomes do diploid and haploid cells contain? |
46 chromosomes in diploid (23 pairs) and 23 chromosomes in haploid cells |
|
|
What is the difference between mitosis and meiosis? |
Mitosis is the cell division of diploid cells whilst meiosis is the cell division of haploid cells. |
|
|
Explain the process of mitosis. |
-DNA replicates itself- each chromosome has an identical copy of itself -Copies of the chromosomes are pulled to opposite sides of the nucleus -The nucleus splits in half -The cell splits in half -There are now two daughter cells, each with 23 pairs of chromosomes |
|
|
Explain what is meant by asexual reproduction. |
When organisms can reproduce by mitosis. |
|
|
Explain the process of meiosis. |
-Each chromosome makes a copy of itself -The membrane around the nucleus disappears -The pairs of chromosomes split up- there are four of them -The cell splits into four, producing four daughter cells each with 23 chromosomes only |
|
|
What is the difference between the daughter cells of mitosis and meiosis? |
The daughter cells of mitosis are exactly the same as the parent cells, whereas the daughter cells of meiosis are different. |
|
|
What are mutations, how do they form and what do they lead to? |
Mutations are changes to structure of genes/DNA sequences They are formed when DNA is not copied properly in cell division They lead to faulty genes |
|
|
What are the different types of mutation? Explain them. |
Insertion- an extra nucleotide is added Deletion- a nucleotide is taken away Translation- DNA sequence is moved to somewhere else in the genome Substitution- one nucleotide is swapped for another Inversion- sequence of DNA is turned around |
|
|
What is natural selection? |
The better adapted individuals survive and reproduce, passing their alleles onto the next generation survival of the fittest leads to evolution |
|
|
What causes variation? |
Environment (e.g. accent) Genotype New alleles arise in a population through mutations |
