Classical Genetics

Question 1

Law of Dominance

Answer 1

When 2 organisms, each homozygous (pure) for 2 opposing traits are crossed, the offspring will be hybrid (carry out 2 different alleles) but will exhibit only the dominant trait
Trait that remains hidden = recessive trait

Question 2

Law of Segregation

Answer 2

When an organism makes gametes, each gamete receives just 1 copy, which is selected randomly

Question 3

Monohybrid cross

Answer 3

A cross between 2 organisms that are each hybrid for a single trait
(Tt x Tt)

Question 4

Genotype

Answer 4

Type of gene
The set of genes in DNA which is responsible for a particular trait
Genes responsible for: eye colour, height, shoe size

Question 5

Phenotype

Answer 5

What an organism looks like
The visible expression/characteristics of that trait
Visible characteristics for; eye colour, height, shoe size

Question 6

Backcross (Testcross)

Answer 6

A technique to determine whether an individual plant or animal showing the dominant trait is homozygous dominant (BB) or heterozygous (Bb)

Question 7

Incomplete Dominanc

Answer 7

An inheritance pattern characterised by blending of traits

Black animal cross with white animal = grey offspring

Question 8

Law of Independent Assortment

Answer 8

A cross that is carried out between 2 individuals hybrid for 2 or more traits that are not on the same chromosome
Resulting phenotype ratio: 9:3:3:1

Question 9

Codominance

Answer 9

When the alleles of a gene are expressed equally & neither is dominant or recessive
Blood type; A & B -> AB

Question 10

Multiple Alleles

Answer 10

When there are more than 2 allelic forms of a gene

Humans, more than 2 alleles for blood type

Question 11

Polygenic

Answer 11

More than 2 allelic forms of a gene, like height or colour, the trait exhibits a multitude of variation
Two short parents -> tall offspring

Question 12

Sex-Linked

Answer 12

Traits that are carried on the X chromosome

Recessive traits: colour blindness, haemophilia

Question 13

Sex-Influenced Trait

Answer 13

Inheritance is influenced by sex of individual carrying the traits
Baldness

Question 14

Karyotype

Answer 14

Procedure that analyses the size, shape, & number of chromosomes
During metaphase of mitosis

Question 15

Pedigree

Answer 15

Family tree that indicates the phenotype of 1 trait being studied for every member of a family
Used to determine how a particular trait is inherited

Question 16

Mutation

Answer 16

Any change in a gene or chromosome, when/where mutations occur is random

Question 17

Gene Mutations

Answer 17

Caused by a change in the DNA sequence

Question 18

Chromosome Mutations

Answer 18

Chromosome may sustain a deletion/addition, or cell may have an entirely extra chromosome which results from nondisjunction

Question 19

Nondisjunction

Answer 19

An error that sometimes happens during meiosis in which homologous chromosomes fail to separate as they should

Question 20

Aneuploidy

Answer 20

Any abnormal condition of the chromosomes

Question 21

Deletion

Answer 21

A fragment lacking a centromere is lost during cell division

Question 22

Inversion

Answer 22

A chromosomal fragment reattaches to its original chromosome but in the reverse orientation

Question 23

Translocation

Answer 23

A fragment of a chromosome becomes attached to a non-homologous chromosome

Question 24

Polyploidy

Answer 24

A cell/organism that has extra sets of chromosomes

Often plants or flowers

Question 25

Gene

Answer 25

Heritable factor that controls a specific characteristic

Question 26

Allele

Answer 26

1 specific form of a gene, occupying the same gene locus as other alleles of the gene

Question 27

Genome

Answer 27

The whole of the genetic information of an organism

Question 28

Homologous Chromosomes

Answer 28

Chromosomes that have the same structural features & the same genes

Question 29

Dominant Allele

Answer 29

An allele that is expressed in the phenotype in a homozygous or heterozygous state

Question 30

Recessive allele

Answer 30

An allele that is only expressed in the phenotype in a homozygous state

Question 31

Codominant Alleles

Answer 31

A pair of alleles which both affect the phenotype in a heterozygous

Question 32

Homozygous

Answer 32

Having 2 identical alleles of a gene

Question 33

Heterozygous

Answer 33

Having 2 different alleles of a gene

Question 34

Carrier

Answer 34

A heterozygote who has 1 copy of a recessive allele that causes a genetic disease

Question 35

Autosome

Answer 35

Any chromosome that is not a sex linked chromosome