Basics of Genetic Inheritance (Embryology)

Question 1

Describe the human karyotype:

Answer 1

23 pairs of chromosome:

• 22 autosomal pairs
• 1 Sex pair
• XY = Female
• XY = Male

Question 2

Define ‘gene’

Answer 2

Section of DNA that codes for characteristic

Question 3

Define ‘allele’

Answer 3

Versions of a gene

Question 4

Define ‘genotype’

Answer 4

Actual state of genes in an organism (e.g. AA, aa or Aa)

Question 5

Define ‘phenotype’

Answer 5

Physical manifestation of the genes

Question 6

List the two principles of Mendelian Inheritance

Answer 6

• Law of segregation

- Law of independent assortment

Question 7

Define ‘law of segregation’

Answer 7

Alleles that are together in one generation, will be separated in next.

Question 8

Define ‘law of independent assortment

Answer 8

Alleles will mix independently in the offspring.

Question 9

List the exceptions of Mendelian Inheritance

Answer 9

• Incomplete dominance
• Quantitative inheritance
• Co-dominant expression
• Gene linkage
• Sex chromosome

Question 10

Define ‘incomplete dominance’

Answer 10

Heterogenous alleles lead to intermediate characteristic (e.g. Red rose + white rose -> Pink rose)

Question 11

Define ‘Quantitative inheritance’

Answer 11

Multiple genes have minor effects on trait, with sum of gene leading to phenotype (e.g. Skin colour is reguulated by >4 genes)

Question 12

Define ‘co-dominant expression’

Answer 12

Each allele is fully expressed (e.g. Blood type)

Question 13

Define ‘gene linkage’

Answer 13

Genes located closely on the same chromosome are often inherited together (i.e. linked gene)

Question 14

Define ‘sex chromosome’

Answer 14

Females get XX with 50% inactivated; Males get XY

Question 15

List the patterns of genetic inheritance

Answer 15

• Autosomal dominant
• Autosomal recessive
• X-linked recessive
• X-linked dominant
• Maternal inheritance

Question 16

Describe ‘autosomal dominant’

Answer 16

Need only one copy of gene for phenotype:

• Male and female equally probable
• If parents don’t have phenotype, 0% of offspring having phenotype
• If one parent has phenotype, 50-100% of offspring will (statistically)

Question 17

Describe ‘autosomal recessive’

Answer 17

Need two copies of gene for phenotype

• Male or female equally probable
• Two/both parents need to be at least carriers

Question 18

Describe ‘X-linked recessive’

Answer 18

Only manifests in men, unless females get two copies of gene.
No father to son transmission.

Question 19

Describe ‘X-linked Dominant’

Answer 19

Only one copy needed in females and males.

• Passed from mothers to sons and daughters
• No father to son transmission
• Fathers always pass to daughters.

Question 20

Describe ‘Maternal inheritance’

Answer 20

Mitochondrial genes are only passed from mother.

• Passed from mother only to sons and daughter equally
• No transmission from father

Question 21

Describe gene imprinting

Answer 21

• One allele has an epigenetic mark that makes it silent, but it reappears in next generation
• All offspring inherit a silent gene for one generation
• Paternal imprinting = Through fathers
• Maternal Imprinting - through mothers