Q1) Diploid organisms contain how many copies of each gene in each of their cells?

Q2) What sort of cells are gametes?

Q3) A zygote has how many copies of each gene?

A1) Diploid organisms contain 2 copies of each gene in each of their cells. i.e. each cell contains 2 complete sets of chromosomes (2n)

A2) Gametes are haploid cells (n). They contain half the normal number of chromosomes.

A3) A zygote has 2 copies of each gene, one from each parent.

Q1)By what type of cell division are gametes formed from diploid cells?

Q2) What happens during meiosis I?

Q3) What happens during meiosis II?

Q4) How many cells are produced in meitotic division?

A1) Gametes are formed from diploid cells by meiosis.

A2) Meiosis I is the first division. During prophase crossing over occurs. During metaphase bilvalents are arranged on the spindle. During anaphase homologous chromosomes are pulled to opposite poles. Teolphase does not always occur as meiosis II begins.

A3) Meiosis II is the second division. During prophase the centrioles move to poles (at right angles to in meiosis II). During anaphase, the chromatids are pulled apart to opposite poles.

A4) Four haploid cells are produced in meitotic division.

1. Crossing over in prophase I
2. Random arrangement of bivalents on the equator during metaphase I.

Q1) What is an allele?

Q2) What is a dominant allele?

Q3) What are codominant alleles? 

Q4) What does heterozygous mean?

Q5) What does homozygous mean?

Q6) What is a multiple allele? Give an example

A1) An allele is a variety of a gene.

A2) An allele which is dominant, has the same effect on phenotype on a heterozygote and a homozygote.

A3) Codominant alleles both have an effect on the phenotype of a heterozygous organism

A4) Heterozygous means having 2 different alleles of a gene.

A5) Homozygous means having two identical alleles of a gene.

A6) When 3 or more alleles of a gene exist e.g. human blood group.

What is a sex-linked gene?

Are men therefore homozygous or heterozygous for sex-linked genes.

Q1) What does a monohybrid cross consider?

Q2) What does a dihybrid cross consider?

Q3) What is independant assortment?

A1) A monohybrid cross considers the inheritance of one gene.

A2) A dihybrid cross considers the inheritance of two different genes

A3) Independant assortment occurs if many cells are undergoing meiosis. It means that roughly half the chromosomes will line up one way, and the other half will line up the other way. 

Q1) Define mutation

Q2) How do new alleles arise?

Q3) Name 3 types of gene mutation.

Q4) How did the sickle cell allele arise?

A1) A mutation is an unpredictable change in the base sequence in a DNA molecule (gene mutation) or the structure or number of chromosomes (chromosome mutation).

A2) New alleles arise by gene mutation

A3)

1. base substitution
2. base deletion
3. base addition

A4) The sickle cell allele arose by base substitution.

Q1) What gives an organism the potential to show a particular characteristic?

Q2) In some cases, what else affects the degree to which a characteristic is shown?

A1) Its genotype

A) The organisms environment

Q1) What is an operon?

Q2) What does the lac operon in Escherichia coli control?

A1) An operon is an operational unit of DNA molecule containing genes which code for the production of a polypeptide, plus other genes that control whether or not this gene is expressed.

A2) The lac operon controls the production of proteins that allow the bacterium to metabolise lactose, and ensures that these proteins are only syntesised when lactose is present in the environment.