Variation And Inheritance

Question 1

What are dominant alleles?

Answer 1

Alleles that will always be expressed in the phenotype if present.

Question 2

What are recessive alleles?

Answer 2

Alleles that will only be expressed in the phenotype if 2 copies of the allele are present.

Question 3

What does homozygous mean?

Answer 3

When an organism has 2 identical alleles for a particular gene.

Question 4

What does heterozygous mean?

Answer 4

When an organism has 2 different alleles for a particular gene.

Question 5

What are polymorphic genes?

Answer 5

Genes that have more than one possible allele.

Question 6

What are monomorphic genes?

Answer 6

Genes that have 1 possible gene.

Question 7

Why are most genes monomorphic? (2)?

Answer 7

1. Necessary for many proteins we need to make.
2. A useful characteristic as any mutations to other alleles can be fatal.

Question 8

What does a high proportion of polymorphic genes mean?

Answer 8

The individual will have an increased genetic variation.

Question 9

What is the equation for working out the proportion of polymorphic genes?

Answer 9

Number of polymorophic genes in population/the total number of genes in the population.

Question 10

What is continuous variation? Example?

Answer 10

When the individual in a population vary within a range and not distinct categories. For example, height or fur length.

Question 11

What is the gene locus in continuous variation and discontinuous variation?

Answer 11

C: many loci on different chromosomes.

D: usually only one or a very small number.

Question 12

What is discontinuous variation? Example?

Answer 12

When there are two or more distinct categories with no intermediates.

Question 13

What is the number of alleles in continuous variation and discontinuous variation?

Answer 13

C: many genes contribute to inheritance, each has alleles.

D: often just a pair of alleles, can be a very small number.

Question 14

What is the effect on the phenotype in continuous variation and discontinuous variation?

Answer 14

C: many intermediates between the extremes.

D: feature is either present or absent.

Question 15

What is the environmental influence in continuous variation and discontinuous variation?

Answer 15

C: significant effect.

D: environment has little effect.

Question 16

How can the environment affect variation? Example? (2)?

Answer 16

1. A person’s offspring will not inherit an accent through genes, only through hearing others speak.
2. For example, losing a limb/having a scar.

Question 17

How can variation in plants be caused by the environment interacting with genes?

Answer 17

Chlorotic plants don’t photosynthesise but have a gene for chlorophyll but the environment can prevent the expression of the gene.

Question 18

How can variation in animals be caused by the environment interacting with genes?

Answer 18

Obesity can be caused by the environment interacting with genes;
- Overfed.
- Reduced activity.
- Health conditions.
- Specific genes in obesity.

Question 19

What is an example of how variation in animals can be caused by the environment interacting with genes?

Answer 19

A mouse has a mutation of chromosome number 7 that causes the pattern of fat deposition to be altered.

Question 20

What is interspecific variation?

Answer 20

Variation between members of species.

Question 21

What is intraspecific variation?

Answer 21

Variation within members of the same species.

Question 22

What is a genotype?

Answer 22

The genetic material of an organisms (alleles present).

Question 23

What is a phenotype?

Answer 23

The physical characteristics of an organism (not always visible):
- the genotype and environmental effects.

Question 24

Where does genetic variation arise from?

Answer 24

Meiosis.

Question 25

What does meiosis produce?

Answer 25

Genetically different gametes.

Question 26

What may genetic variation result from in meiosis? (3)?

Answer 26

1. Alleles shuffling (swapping of alleles between non-sister chromatids) during crossing over in prophase 1.
2. Independent assortment of chromosomes during metaphase 1 and anaphase 1.
3. Independent assortment of chromatids during crossing over in metaphase 2 and anaphase 2.

Question 27

What are the gametes produced like in meiosis?

Answer 27

They are individual and genetically dissimilar and haploid (contain only one of each pair of homologous chromosomes and one allele for every gene).

Question 28

How does random fertilisation in meiosis cause genetic variation?

Answer 28

Any male gamete can potentially combine with any female gamete from an organism of the same species and so random fertilisation produces extensive genetic diversity among offspring.