Classic Mendelian Genetics

Question 1

What were Mendel’s observations?

Answer 1

• a heritable factor (now called a gene)
• the heritable factor is not diluted or destroyed
• 3:1 inheritance pattern in F2 offspring

Question 2

What were Mendel’s postulates? (4)

Answer 2

1) Units of genetic inheritance
2) Dominance/Recessiveness
3) Segregation
4) Independent assortment

Question 3

MENDEL’S POSTULATES: Units of genetic inheritance

Answer 3

Alleles as alternate versions of genes that cause variation in inherited characters.

Question 4

MENDEL’S POSTULATES: Dominance/Recessiveness

Answer 4

Where there are different alleles the only one is expressed so one is dominant (expressed) other is recessive.

Question 5

MENDEL’S POSTULATES: Segregation

Answer 5

alleles are separated randomly during gamete formation

Question 6

MENDEL’S POSTULATES: Independent assortment

Answer 6

Segregating pairs of alleles assort independently of each other.

Question 7

Genetic recombination during meiosis

Answer 7

• During prophase 1= crossing over between homologous chromosomes

Question 8

Types of genetic dominance

Answer 8

-COMPLETE DOMINANCE: when phenotypes of homozygote and heterozygote are identical
-INCOMPLETE DOMINANCE: when phenotype of F1 hybrids is halfway between the two parental varieties
-CODOMINANCE: when two dominant alleles affect the phenotype in separate ways.

Question 9

Epistasis

Answer 9

When a gene at one locus influences the phenotypic expression of a gene at a second locus.

Question 10

Sex determination in mammals

Answer 10

• the gonad has the potential to develop into either a testis or an ovary
• female has homomorphic XX male has heteromorphic XY
• X chromosome is larger than Y
• no paired genes between the chromosomes
  -Sry expression; masculine phenotype

Question 11

X chromosome inactivation

Answer 11

-occurs in female mammals
- each female carries 2 X chromosomes, one from each parent- males only have one
- in females one of each X is inactivated in each cell, dosage compensation
- inactive X chromosome is called Barr body

Question 12

Autosomal Dominant Inheritance

Answer 12

• have at leat one affected parent
• at least a 50% chance of passing on trait
• males and females equally affected
• 2 affected individuals may have unaffected offspring

Question 13

Autosomal Recessive Inheritance

Answer 13

• two affected individuals have an 100% chance of having an affected offspring
• males and females equally affected
• two unaffected heterozygotes resulting in one or more homozygotes

Question 14

X-linked recessive inheritance

Answer 14

• hemizygous males and homozygous females are affected
• Daughters of affected males are heterozygous so unaffected
  -Sons of affected males are unaffected
• Sons of heterozygous females have 50% chance of receiving recessive gene therefore being affected

Question 15

X-linked dominant inheritance

Answer 15

• heterozygous females are affected males are usually not viable
• because males aren’t viable homozygous females don’t exist
• affected offspring have an affected mother

Question 16

Loss-of-function mutation

Answer 16

Inactivating mutation: the gene has reduced or lost function
Most commonly seen in recessive alleles

Question 17

Gain-of-function mutation

Answer 17

Activating mutation: the gene product has an abnormal function
Could be positive or negative, as in dominant disease alleles

Question 18

Heterosis

Answer 18

When two homozygous strains are crossed, offspring are generally phenotypically stronger and larger than either parent.

Question 19

Overdominance

Answer 19

Heterozygotes in certain genes are superior to homozygotes eg. sickle cell anemia
Heterozygotes are affected to a lesser degree

Question 20

Polygenic inheritance

Answer 20

Quantitative variation indicates polygenic inheritance, two or more genes affects a single characteristic.

Question 21

Define penetrance

Answer 21

the proportion of individuals in a population with a given genotype that express the correct phenotype

Question 22

Define expressivity

Answer 22

the degree to which a characteristic is expressed in a given individual

Question 23

4 processes in population genetics

Answer 23

1) Selection
2) Mutation
3) Genetic drift
4) Gene flow