Heredity: Determining genotypes, multiple alleles

Question 1

Define heredity

Answer 1

• characteristic
• passed on from generation to another
• e.g. hair type, earlobe shape

Question 2

Define genetics

Answer 2

• study of inheritance of characteristics

- by transmission of genetic materials

Question 3

Define chromosome

Answer 3

• rod-like structure visible in nucleus during cell division
• made up of deoxyribonucleic acid (DNA) and histone proteins

Question 4

Define gene

Answer 4

• unit of inheritance
• on a particular gene locus of chromosome
• controls particular characteristic/protein in an organism

Question 5

Define alleles

Answer 5

• pairs/homologous chromosomes
• diff forms of the same gene
• same gene loci

Question 6

Define homologous chromosomes

Answer 6

• pair
• one maternal, paternal
• same sequence on gene loci

Question 7

Define phenotype

Answer 7

• observable traits
• influenced by genotype (genes) and environment (e.g. skin colour -sun)
• not all phenotypes influenced by environment e.g. ability to roll tongue

Question 8

Define genotype

Answer 8

• genetic make-up of organism

- inherited frm parents

Question 9

Homozygous

Answer 9

• 2 alleles controlling trait are the same

- homozygous dominant (TT)/recessive (tt)

Question 10

Heterozygous

Answer 10

• 2 alleles controlling trait are diff

- e.g Tt

Question 11

Define monohybrid inheritance

Answer 11

• inheritance of one characteristic that has 2 contrasting forms
• each characteristic controlled by single gene
• each gene consist of pair of alleles
• alleles can be dominant/recessive

Question 12

Mendel’s model of heredity

Answer 12

• hereditary factors (genes) responsible for transmission of characteristics
• each characteristic controlled by 2 factors (dominant and recessive)
• only dominant factor shows characteristic

Question 13

Law of Segregation

Answer 13

• 2 factors (alleles) segregate during gamete formation (anaphase I)
• each gamete contains one factor (allele)
• random fusion of gametes ensures zygote contain 2 factors/alleles (fertilisation)

Question 14

Modelling genetic crosses

Answer 14

• explains how alleles are passed down to offspring
• predict traits that will be displayed by an offspring
• Genetic Diagram
• Punnett Square

Question 15

Determining genotypes

Answer 15

Displays:
Recessive trait: Homozygous recessive (e.g tt)
Dominant trait: Homozygous dominant (e.g. TT), heterozygous (e.g. Tt)

Question 16

What can be used to identify genotypes?

Answer 16

Breeding experiments

Question 17

Test cross

Answer 17

• used to determine genotype of an organism with dominant trait
• cross it with homozygous recessive organism
• if homozygous dominant, all offspring show dominant trait
• if heterozygous, 1:1 shows dominant and recessive trait

Question 18

Co-dominance

Answer 18

• both alleles equally expressed in heterozygous condition
• more than 2 different phenotypes
• e.g. short-horned cattle hair colour, ABO blood group

Question 19

Sex chromosomes (Sex-determination)

Answer 19

• chromosomes that determine sex of organism
• X and Y chromosome
• humans have 1 pair of sex chromosomes
• sex cells produce gametes by meiosis
• Male gametes (sperms) contain either X or Y chromosomes
• Female gametes contain only X

Question 20

Autosomes

Answer 20

• non-sex chromosomes

- human have 22 pairs

Question 21

Somatic cells

Answer 21

• other cells in body other than sex cells

Question 22

Sex determination

Answer 22

• 1:1 chance

- when male and female gametes fuse

Question 23

Multiple alleles

Answer 23

• when particular trait exists in more than 2 alleles

- e.g coat colour in rabbits

Question 24

Multiple alleles: Human blood group

Answer 24

• determined by 3 alleles (IO, IA, IB)
• IA and IB are co-dominant (both phenotypes expressed)
• IO recessive to IA and IB