16.2 The roles of genes in determining the phenotype

Question 1

Gene

Answer 1

a length of DNA that codes for the production of a polypeptide molecule.

Question 2

Alleles

Answer 2

Different varieties of the same gene

Question 3

Genotype

Answer 3

The alleles possessed by an organism

Question 4

Heterozygous

Answer 4

having two different alleles of a particular gene (e.g. Tt or Gg), not pure-breeding.

Question 5

Homozygous

Answer 5

having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding.

Question 6

Phenotype

Answer 6

An organism’s characteristics, often resulting from an interaction between its genotype and its environment

Question 7

Dominant

Answer 7

an allele that is expressed if it is present (e.g. T or G)

Question 8

Recessive

Answer 8

an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g)

Question 9

Genetic Diagrams

Answer 9

A genetic diagram is the standard way of showing the
genotypes of ofspring that might be expected from two
parents.

Question 10

Test Cross

Answer 10

A genetic cross in which an organism showing a characteristic caused by a dominant allele is crossed with an organism that is homozygous recessive; the phenotypes of the offspring can be a guide to whether the first organism is homozygous or heterozygous

Question 11

F1 Generation

Answer 11

The offspring resulting from a cross between an organism with a homozygous dominant genotype, and one with a homozygous recessive genotype

Question 12

F2 Generation

Answer 12

The offspring resulting from a cross between two two F1 (heterozygous) organisms

Question 13

Sex Chromosomes

Answer 13

One of the 23 pairs of chromosomes

Question 14

Monohybrid Crosses

Answer 14

the inheritance of just one gene.

Question 15

Autosomes

Answer 15

22 Pairs of chromosomes (without the pair of sex chromosomes)

Question 16

How do Sex Chromosomes differ from Autosomes

Answer 16

• The two sex chromosomes in a cell are not always alike.
• They do not always have the same genes in the same
  position, and so they are not always homologous.
• This is because there are two types of sex chromosome, known as the X and Y chromosomes because of their shapes.
• The Y chromosome is much shorter than the X, and carries fewer genes.
• A person with two X chromosomes is female, whereas a person with one X and one Y chromosome is male.

Question 17

Multiple Alleles

Answer 17

Most genes have more than two alleles.
- Etc. the various blood groups: 3 alleles of the blood gene exist, IA, IB, IO. IA and IB are codominant. IO is recessive

Question 18

Sex Linked Gene

Answer 18

A gene that is carried on an X chromosome but not on a Y chromosome

Question 19

Dihybrid Crosses

Answer 19

A genetic cross in which two different genes are considered

Question 20

Offspring Ratio 1:1:1:1

Answer 20

Dihybrid cross between a heterozygous organism (AaDd) and a homozygous organism (aadd)

Question 21

Offspring Ratio 9:3:3:1

Answer 21

Dihybrid cross between two heterozygous organisms (AaDd)

Question 22

Linkage (Autosomal)

Answer 22

The presence of two genes on the same chromosome, so they tend to be inherited together and do not assort independently

Question 23

Chi-squared (x^2) test

Answer 23

a statistical test that can be used to determine whether any diference between observed results and expected results is signifcant or is due to chance