Variation and inheritance

Question 1

What is the definition of a gene?

Answer 1

A region of DNA on a chromosome that codes for a characteristic.

Question 2

What is the definition of an allele?

Answer 2

Different forms of the same gene.

Question 3

What is the definition of homozygous/true breeding?

Answer 3

An individual with two copies of the same allele present.

Question 4

What is the definition of heterozygous?

Answer 4

An individual with two different alleles present.

Question 5

What is the definition of phenotype?

Answer 5

The physical characteristics of an organism.

Question 6

What is the definition of dominant?

Answer 6

An allele that always shows its effect as a phenotype and masks the presence of the other form.

Question 7

What is the definition of recessive?

Answer 7

An allele that is masked by the dominant allele i.e. it will only show its effect/show in the phenotype if both alleles are present.

Question 8

What is the definition of a genotype?

Answer 8

The set of genes (alleles) possessed by an individual.

Question 9

What does P stand for?

Answer 9

Parent generation

Question 10

What does F1 stand for?

Answer 10

First (filial) generation

Question 11

What does F2 stand for?

Answer 11

Second (filial) generation

Question 12

What is the definition of phenotypic ratio?

Answer 12

The ratio of the appearance of the offspring produced in a genetics cross.

Question 13

What is the ratio of genotypic ratio?

Answer 13

The ratio of genotypes of the offspring produced in a genetics cross.

Question 14

What is meant by variation?

Answer 14

Although members of the same species have similar characteristics, they are not identical to each other i.e their is variation (differences) between members of species.

Question 15

What contributes to variation within species?

Answer 15

Combing genes from two parents, through sexual reproduction, contributes to variation within species.

Question 16

What are the main two types of variation?

Answer 16

Discrete variation

Continuous variation

Question 17

What is discrete variation?

Answer 17

Single gene inheritance of characteristics shows discrete variation where measurements fall into distinct groups.

Question 18

Give an example of discrete variation.

Answer 18

tongue roller/non tongue roller, blood type or leaf shape.

Question 19

How can discrete variation be displayed?

Answer 19

This information can be displayed in a bar graph.

Question 20

What is meant by continuous variation?

Answer 20

Polygenic inheritance of characteristics shows continuous variation where there is a range of values between a minimum and maximum.

Question 21

Give an example of continuous variation.

Answer 21

e.g. human height and milk yield in dairy cows

Question 22

Why does continuous variation occur?

Answer 22

Continuous variation occurs because several different genes influence the same characteristic.

Question 23

How can continuous variation be displayed?

Answer 23

Continuous variation can be displayed as a histogram. When a curve is drawn, a bell shape normal distribution curve is produced.

Question 24

Why are alleles such as tallness in plants said to be tallness?

Answer 24

Alleles such as tallness in plants are said to be dominant because they always show up in the phenotype of the offspring even though both types of the alleles are present.

Question 25

Why are allele for dwarfness in plants said to be recessive?

Answer 25

Alleles for dwarfness in plants are said to be recessive because they only show up in the phenotype if the organism inherits both of them.

Question 26

What types of letters are dominant and recessive given?

Answer 26

Dominants are usually given the capital letter e.g. T while recessive alleles are given lower case of the same letter.

Question 27

Why do actual or observed ratios in offspring not always match the predicted ratios?

Answer 27

Fertilisation is a random process.

The numbers of organisms in the cross are too small.

Question 28

What are family tree diagrams used for?

Answer 28

Family tree diagrams can be used to show the inheritance of characteristics over generations.

Question 29

Give an example of a use of family trees?

Answer 29

For example, they are useful in studying human families, especially where genetic disorders such as cystic fibrosis or haemophilia are known to occur.