Sexual Life Cycles

Question 0

Outline the haploid and diploid stages of the plant sexual cycle.

Answer 0

1) a multicellular adult plant (diploid) undergoes meiosis to form spores.
2) haploid spores undergo mitosis to form multi-cellular gametes.
3) fusion of gametes creates a diploid zygote.
4) diploid zygote continues to undergo mitosis until it grows to maturity.

Question 1

Outline the haploid and diploid phases of the animal sexual cycle.

Answer 1

1) a multicellular adult animal (diploid) undergoes meiosis to form gametes (haploid).
2) haploid gametes fuse during sexual reproduction to form a diploid zygote.
3) the diploid zygote grows by repeated cell division by mitosis until it becomes an adult.

Question 2

Outline the haploid and diploid stages of the fungal sexual cycle.

Answer 2

1) a diploid zygote immediately undergoes meiosis to create haploid spores.
2) haploid spores undergo mitosis to form a unicellular or multicellular organism (main life stage)
3) haploid fungal organisms undergo mitosis to form gametes.
4) gametes fuse to form a diploid zygote.

Unlike plants and animals fungus spend most of their life cycle haploid.

Question 3

Who was Gregor Mendel?

Answer 3

Modern Science of genetics has it’s roots in the pioneering work of Gregor Mendel. He made the observation that many of the physical characteristics observed in individuals are inherited in predictable ways.

Question 4

What is a homozygous organism?

Answer 4

When both alleles of a gene in a diploid organism are identical, the organism is said to be homozygous for that gene.

Question 5

What is a heterozygous organism?

Answer 5

When two alleles of a particular gene are different, the organism is said to be heterozygous for that gene.

Question 6

What are pure-breeding plants?

Answer 6

Those which when self-crossed, always yield progeny of the same phenotype as the parents.

Question 7

If inheritance occurred by a ‘blending’ of genes (which it doesn’t) what would you expect from crossing a white flowered pea plant with a violet flowered pea plant?

Answer 7

You’d expect pale violet flowers. This doesn’t happen.

Question 8

What is discontinuous variation?

Answer 8

Phenotypes which fall into distinct classes with nothing in between.

For example the white and violet flowered pea plants studied by Mendel.

Question 9

What is a dominant gene?

Answer 9

Where an organism is heterozygous the dominant gene is the one which appears in the phenotype.

Question 10

What term is used to describe the genotype of a plant that posses two copies of the same allele of the gene for petal colour?

Answer 10

The plant is homozygous.

Question 11

What is genetic linkage?

Answer 11

Two genes that are located on the same chromosome are linked; that is they are unable to assort independently.

Question 12

What is a recombination frequency?

Answer 12

The percentage of the different Phenotypes can be used to estimate the frequency at which recombination has occurred between the two gene loci - this is the recombination frequency.

Question 13

How do you work out the recombination frequency in crossbred offspring?

Answer 13

Total number of recombinant Phenotypes (variants not seen in parental generation) divided by total progeny, multiplied by 100.

Question 14

What is a heterogametic sex?

Answer 14

The sex which has different sex chromosomes in human beings males are the heterogametic sex (XY).

In birds the sex genes are called W and Z and it is the females who are heterogametic.

Question 15

What is a sex-linked gene?

Answer 15

A gene which occurs on the sex-linked gene.

Question 16

In a human pedigree chart if an affected male and unaffected female have four offspring, 2 boys & 2 girls where one boy & one girl are effected… The the affected boy marries an unaffected female and the third generation has two affected children and one unaffected child… Is the trait dominant or recessive?

Answer 16

It shows a dominant disorder. A person need only inherit one copy of a dominant disease-causing allele from their affected parent to develop the disease.

Question 17

Describe roughly what a pedigree chart showing a recessive disorder looks like.

Answer 17

Few fully affected individuals as parents can be unaffected genetic carriers.

Question 18

What is non-nuclear inheritance?

Answer 18

Inheritance in the DNA of sub cellular components (such as mitochondria).

Question 19

What are the implications of a pedigree where ALL of the offspring of any affected female are also affected.

Answer 19

It is non-nuclear inheritance caused by mitochondrial mutation, mitochondrial traits can only be passed on from a mother to her offspring. Males can be affected but they can’t pass the trait on.

Question 20

What is continuous variation? (In inheritance)

Answer 20

Phenotypes controlled by multiple genes which don’t fall into distinct categories but vary over a broad range.

Examples are height, weight, skin colour, intelligence.

Question 21

What is monogenic inheritance?

Answer 21

Phenotype affected by a single gene, falling into distinct classifications.