Variation and Inheritance 20.1

Question 1

Why does variation occur?

Answer 1

Mutations in the genetic code that happen randomly and constantly. It is necessary for natural selection and evolution.

Question 2

What is chlorosis?

Answer 2

A condition where the plants look pale and yellow as their plant cells are not producing enough chlorophyll and therefore they cannot photosynthesize properly.

Question 3

What causes chlorosis?

Answer 3

Usually, plants with chlorosis have all the correct genetic code to produce chlorophyll so it’s just the environmental factors that make it occur.

• Lack of light
• If iron and magnesium minerals are lacking. Iron is the cofactor for chlorophyll producing enzymes.
• Virus Infections will affect the metabolism of the plant

Question 4

What causes variation in an organisms body mass?

Answer 4

There are many environmental factors such as how much the organism eats, if it gets any exercise or if it has a disease. It could also be genetic and could have a mutation of chromosome 7 which affects how fat is deposited.

Question 5

What actually creates genetic variation?

Answer 5

The different versions of genes that you inherit from both your parents. Organisms in the same species have the same genes, however, they have different versions of the same gene called alleles and that’s what causes variation.

Question 6

How are genes inherited?

Answer 6

You inherit two alleles for most genes - one from each parent and they could be the same or different versions of the same gene.

Question 7

Genotype

Answer 7

The different combinations of alleles that is the genetic makeup of that organism and code for different characteristics

Question 8

Phenotype

Answer 8

Observable characteristics that the genotype code for. This can also be influenced by environmental factors and these are called modifications e.g hair dye.

Question 9

Why can’t you always determine an organisms allele from its phenotype?

Answer 9

Because there could be 2 different alleles and only the dominant one will be expressed.

Question 10

Dominant allele

Answer 10

The version of a gene that will always be expressed if present. A person could have one or two copies of the same allele.

Question 11

Recessive allele

Answer 11

The version of a gene that will not be expressed unless two of them are present so you can tell what their genotype is.

Question 12

Homozygous genotype

Answer 12

Have two identical alleles for a characteristic and can be homozygous dominant (AA) or homozygous recessive (aa)

Question 13

Heterozygous genotype

Answer 13

Have one dominant allele and one recessive (Aa), the dominant one will be expressed.

Question 14

Continuous variation

Answer 14

Where you have two extremes and every degree of variation is possible between them. E.g weight, height etc… This can be genetic or environmental and are controlled by many genes.

Question 15

Discontinuous variation

Answer 15

Each individual will fall into a distinct group e.g. blood group and it is mostly genetic and controlled by one or two genes

Question 16

What is a locus?

Answer 16

It’s a specific area on a chromosome where a gene is located

Question 17

List 3 sources of variation from meiosis

Answer 17

• Independent assortment where chromosomes line up along the metaphase plate during metaphase 1
• Independent assortment during metaphase 2
• Crossing over where chromosomes exchange DNA during prophase 1.