Question

-With respect to chromosome content, which of the following cells will be most similar to a cell that is about to enter S phase?

A cell that has just completed meiosis II.

A cell just after mitosis.

A cell just before mitosis.

A cell that has just completed meiosis I.

-State two ways meiosis generates genetic variability.

-If you cross a parent with attached earlobes (recessive trait) with one that has free earlobes (dominant trait), what are ALL of the possible offspring phenotypic ratios?

3 free earlobes: 1 attached earlobes only

1 free: 0 attached or 1 free: 1 attached

1 free: 0 attached only

1 free: 3 attached only

-If you cross a heterozygous tongue roller with another heterozygous tongue roller, what are all of the possible offspring phenotypic ratios. Note: The ability to tongue roll is dominant to lacking the ability.

3 roller: 1 non-roller

1 roller: 0 non-roller

1 roller: 3 non-roller

1 roller: 0 non-roller or 1 free: 1 non-roller

Answer 1

1) a cell entering into S phase has one unreplicated copy of each chromosome,

a cell that has completed meiosis II is haploid, there is only one set of chromosomes.

cell after mitosis has one unreplicated copy of each chromosome, during mitosis, the sister chromatids were separated and it ends up in two daughter cells, and the chromatids become chromosomes in the daughter cells.

cell before mitosis has chromosomes in duplicated state,

a cell that has completed meiosis I are haploid, homologous chromosomes are separated during meiosis I.

so the answer is b)A cell just after mitosis.

2) genetic variability is generated in meiosis via two processes

i) crossing over between non-sister chromatids

crossing over between non-sister chromatids changes the allele combination in a chromatid of a chromosome.

ii) independent assortment of chromosomes

the daughter cells can get one of the homologous chromosomes, so different combinations are possible.

if the diploid cell has 6 chromosomes, that is the haploid number is 3, for each chromosome, there are two chances so the number of different gametes due to independent assortment of chromosomes is 2^3=8

3) let the alleles be E-free earlobes e-attached earlobes

the genotype of the attached earlobe is ee, the genotype of the free earlobes can be EE or Ee

EE * ee

Ee ( free ear lobes)

all the progenies have free earlobes

if the genotype of the free earlobes is Ee

Ee * ee

	E	e
e	Ee (free-earlobes)	ee ( attached earlobes)

the phenotypic ratio is free earlobes: attached earlobes=1:1

so the answer is 1 free: 0 attached or 1 free: 1 attached

4) T- tongue rolling r- cannor roll tongue

Tt * Tt

	T	t
T	TT( tongue rolling)	Tt ( tongue rolling)
t	Tt( tongue rolling)	tt ( cannot roll tongue)

so phenotypic ratio is a) 3 roller: 1 non-roller