3.2.3 Genetic Inheritance

Question 1

What is a gene

Answer 1

A gene is a short length of DNA found on a chromosome that codes for a particular characteristic

Question 2

What are Alleles

Answer 2

Alleles are variations of the same gene

• As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene
• One of the alleles is inherited from the mother and the other from the father
• This means that the alleles do not have to ‘say’ the same thing
• For example, an individual has two copies of the gene for eye colour but one allele could code for brown eyes and one allele could code for blue eyes

Question 3

The observable characteristics of an organism is called, what?

Answer 3

the phenotype

Question 4

The combination of alleles that control each characteristic is called, what?

Answer 4

the genotype

Question 5

Alleles can be dominant, or?

Answer 5

or recessive

Question 6

A dominant allele only needs to be inherited from one parent in order for, what?

Answer 6

the characteristic to show up in the phenotype

Question 7

A recessive allele needs to be inherited from both parents in order for, what?

Answer 7

the characteristic to show up in the phenotype

Question 8

If there is only one recessive allele, what happens?

Answer 8

it will remain hidden and the dominant characteristic will show

Question 9

If the two alleles of a gene are the same, we describe the individual as being, what?

Answer 9

homozygous (homo = same)

Question 10

Define homozygous dominant

Answer 10

having two copies of the dominant allele

Question 11

Define homozygous recessive

Answer 11

having two copies of the recessive allele

Question 12

An individual could be both, homozygous ____, or homozygous ___

Answer 12

homozygous dominant or homozygous recessive

Question 13

We describe the individual as being heterozygous if, what?

Answer 13

If the two alleles of a gene are different

Question 14

When completing genetic diagrams, alleles are abbreviated, to what?

Answer 14

to single letters

Question 15

Which allele is given a capital, or lower case

Answer 15

The dominant allele is given a capital letter

the recessive allele is given the same letter, but lower case

Question 16

We cannot always tell the genotype of an individual for a particular characteristic just by looking at the phenotype – a phenotype associated with a dominant allele will be seen in both, what?

Answer 16

a dominant homozygous and a dominant heterozygous genotype

Question 17

If two individuals who are both identically homozygous for a particular characteristic are bred together, what happens?

Answer 17

they will produce offspring with exactly the same genotype and phenotype as the parents

• we describe them as being ‘pure breeding’ as they will always produce offspring with the same characteristics

Question 18

A heterozygous individual can pass on different alleles for the same characteristic each time it is bred with any other individual and can therefore, what?

Answer 18

produce offspring with a different genotype and phenotype than the parents – as such, heterozygous individuals are not pure breeding

Question 19

Gamete Definition

Answer 19

Gametes are sex cells

Question 20

Chromosomes Definition

Answer 20

Chromosomes are threat-like structures of DNA, carrying genetic information in the form of genes. They are located in the nucleus of the cell.

Question 21

Gene Definintion

Answer 21

Genes are short lengths of DNA found on chromosomes. They code for specific proteins

Question 22

Allele Definiton

Answer 22

Alleles are different versions of a particular gene.

Question 23

Dominant Definition

Answer 23

A dominant allele is always expressed, even if only one copy is present.

Question 24

Recessive Definition

Answer 24

A recessive allele is only expressed if two copies are present

Question 25

Homozygous Definition

Answer 25

If the two alleles of a gene are the same, we describe the individual as being heterozygous

Question 26

Genetype Definition

Answer 26

The combination of alleles that control each characteristics is called the genotype

Question 27

Phenotype Definition

Answer 27

The observable characteristics of an organism (seen just by looking - like eye colour, or found through testing - like bood type) is called the phenotype.

Question 28

What is sex determined by?

Answer 28

an entire chromosome pair

Question 29

Females have the sex chromosomes:

Answer 29

XX

Question 30

Males have the sex chromosomes:

Answer 30

XY

Question 31

Who determines the sex of the child

Answer 31

As only a father can pass on a Y chromosome, he is responsible for determining the sex of the child

Question 32

The inheritance of sex can be shown using a genetic diagram, known as?

Answer 32

known as a Punnett square

• with the X and Y chromosomes taking the place of the alleles usually written in the boxes

Question 33

On occasion, both alleles within a genotype are expressed in the phenotype of an individual, what is this known as?

Answer 33

codominance

Question 34

Give an example of codominance

Answer 34

Inheritance of blood group

Question 35

There are three alleles of the gene governing this instead of the usual two, what are they?

Answer 35

I represents the gene and the superscript A, B and O represent the alleles

Question 36

Alleles IA and IB are, what?

Answer 36

codominant, but both are dominant to IO

Question 37

IA results in the production of, what?

Answer 37

antigen A in the blood

Question 38

IB results in the production of what?

Answer 38

antigen B in the blood

Question 39

IO results in, what?

Answer 39

no antigens being produced in the blood

Question 40

The parent with blood group A, has what genotype

Answer 40

IAIO

Question 41

The parent with the blood group B has the genotype

Answer 41

IBIO

Question 42

How do we know that these are their genotypes

Answer 42

as they are able to produce a child with blood group O and so the child must have inherited an allele for group O from each parent