4.6.1.6 Genetic Inheritance

Question 1

Gamete:

Answer 1

• an organism’s reproductive cell (egg cells in females and sperm in males)
• has half the number of chromosomes (23 chromosomes, 23 chromatids)

Question 2

Chromsome:

Answer 2

• a structure found in the nucleus consists of a long, coiled molecule of DNA
• carries genetic information in the form of genes

Question 3

Gene:

Answer 3

• a short section of DNA found on chromosomes that codes for a protein, and therefore contributes to a characteristic
• some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans
• however, most characteristics are the result of many different genes interacting

Question 4

Alleles:

Answer 4

• different forms of a gene
• humans have 2 alleles for each gene as they inherit one from each parent

Question 5

Dominant allele:

Answer 5

• only 1 out of the 2 alleles is needed for it to be expressed and for the corresponding phenotype to be observed
• represented by an upper case letter

Question 6

Recessive allele:

Answer 6

• 2 copies are needed it for it to be expressed in an individual and for the phenotype to be observed
• represented by a lower case letter

Question 7

Homozygous:

Answer 7

• when both inherited alleles are the same (2 dominant alleles or 2 recessive alleles)
• can be homozygous dominant or homozygous recessive

Question 8

Heterozygous:

Answer 8

• the inherited forms of an allele are different
• when one of the inherited alleles is dominant and the other is recessive

Question 9

Genotype:

Answer 9

• the combination of alleles an individual has e.g. Aa
• the genetic make-up of an individual

Question 10

Phenotype:

Answer 10

physical characteristics that are observed in an individual e.g. eye colour

Question 11

Inbreeding:

Answer 11

the formation of offspring from the breeding of closely related individuals

Question 12

Punnett square:

Answer 12

a grid used to predict the potential outcomes of a genetic cross

Question 13

What are some characteristics controlled by?

Answer 13

some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans

Question 14

What are different characteristics controlled by?

Answer 14

different characteristics are controlled by different genes

Question 15

How can the chromosomes of a cell be ordered?

Answer 15

• chromosomes in each cell can be put into pairs which means there are 2 genes for every characteristic
• sometimes these genes are the same and sometimes they are different
• if they are different, the allele which is expressed is said to be dominant and the allele which is not expressed is said to be recessive

Question 16

What may each gene have?

Answer 16

each gene may have different forms called alleles

Question 17

What do the alleles present / genotype do?

Answer 17

the alleles present or genotype operate at a molecular level to develop characteristics that can be expressed as a phenotype

Question 18

What is the difference between a dominant and a recessive allele?

Answer 18

• a dominant allele is always expressed, even if only 1 copy is present
• a recessive allele is only expressed if 2 copies are present (therefore no dominant allele present)

Question 19

What are most characteristics as a result of?

Answer 19

most characteristics are as a result of multiple genes interacting, rather than a single gene