Key Area 4 - Inheritance

Question 1

What is a gene?

Answer 1

Part of a chromosome controlling one characteristic

Question 2

What are alleles?

Answer 2

Different forms of a gene that control a characteristic

Question 3

What does dominant mean (in terms of genes)?

Answer 3

Allele that always shows itself in the phenotype

Question 4

What does recessive mean ( in terms of genes)?

Answer 4

Allele that is masked by a dominant one

Question 5

What does genotype mean?

Answer 5

The genetic makeup (complete set of genes possessed) of an organism (always written in letters e,g TT)

Question 6

What does phenotype mean?

Answer 6

The outward (physical) appearance of an organism (always written in words)

Question 7

What does diploid (2n) mean?

Answer 7

Having two sets of chromosomes in the cells - normal cells

Question 8

What does haploid (n) mean?

Answer 8

Having one set of chromosomes in the cells - sex cells/gametes

Question 9

What does True Breeding mean?

Answer 9

An organism that has either 2 dominant (e.g TT) or 2 recessive alleles (e.g tt)

Question 10

What does homozygous mean?

Answer 10

A condition in which an organism has two identical alleles of a gene e.g TT or tt

Question 11

What does heterozygous mean?

Answer 11

A condition in which an organism has two different alleles of a gene e.g Tt

Question 12

What is continuous variation?

Answer 12

Can be measured, large range of values (polygenic, determined by more than one gene)
e.g. Height, Mass, Foot Length

Question 13

What is discrete variation?

Answer 13

Can be put into categories (single-gene inheritance)

e.g. Gender, Blood group, Eye Colour

Question 14

What is variation?

Answer 14

Differences between individuals of the same species that aren’t caused by accident or disease

Question 15

Why is it that children resemble but aren’t identical to their parents?

Answer 15

• Each parent has two different sets of genes
• Each parents passes only half of their gene
• The half that gets passed down is random

Question 16

What are used to symbolise genes and alleles?

Answer 16

Letters

Question 17

With allele is given the capital letter?

Answer 17

The dominant allele

Question 18

Therefore, which allele is given the lower-case letter?

Answer 18

Recessive allele

Question 19

What can be used to help us work out the genotypes?

Answer 19

A Punnet square

Question 20

What are homozygous individuals also referred to?

Answer 20

True-breeding

Question 21

Why is there often a difference between the observed and the predicted numbers of different types of offspring?

Answer 21

As fertilisation is a random process.

Question 22

What does polygenic mean?

Answer 22

Determined by more than one gene, they show continuous variation

Question 23

How many alleles does every body cell have?

Answer 23

Two alleles

Question 24

What is the dominant phenotype?

Answer 24

The phenotype that appears most often

Question 25

What is the recessive phenotype?

Answer 25

The one that appears to skip generations

Question 26

Why did Mendel choose to study pea plants when investigating inheritance? (3 reasons)

Answer 26

• possess certain characteristics that always show discrete variation
• have a shirt life-cycle, therefore many generations can be studied
• produce large numbers of offspring therefore ratios are more reliable

Question 27

What is a somatic cell?

Answer 27

A body (diploid) cell

Question 28

What can be used to work out genotypes?

Answer 28

A punnet square

Question 29

Why is there often a difference between the observed and predicted numbers of different types of offspring?

Answer 29

As fertilisation is a random process