Classic Mendelian Genetics 1

Question 1

What are genetics?

Answer 1

Is the science of inheritance
The understanding of the mechanism by which blueprints of life are passed through the generations. Variations in these blueprints are essential for evolution and can also cause various diseases.

Question 2

What was Gregor Johann Mendel experiment and what did he propose?

Answer 2

He experimented with pea plants to explain heredity.
In 1866 he proposed his 4 postulates of heredity

Question 3

Character

Answer 3

A heritable factor that varies between individuals (ie seed colour seed shape etc)

Question 4

Trait

Answer 4

The variations in a character (ie The character of seed colour has the traits of yellow or green)

Question 5

True-breeding

Answer 5

Self-fertilisation has produced identical offspring to the parent
True-breeding parents are called P generation
True-breeding parent MUST be homozygous (ie true-breeding for round seeds RR)

Question 6

Hybrid

Answer 6

Offspring of 2 different varieties
Offspring from 2 different parents are called the F1 generation (ie yellow seed from true-breeding yellow seed generation and 1 green seed from true-breeding green seed generation. 1 trait is taken from each and you have a hybrid)

Question 7

Cross

Answer 7

Fertilisation between 2 different individuals (cross between 2 F1 individuals produces an F2 generation)

Question 8

What are Mendel’s 4 postulates

Answer 8

1) Unit of genetic inheritance
2) Dominance/Recessiveness
3) Segregation
4) Independent Assortment

Question 9

1) Unit of genetic inheritance

Answer 9

Alleles are alternative versions of genes that account for variations in inherited characters. An individual inherits 1 allele from each parent (may be the same or different)
Homozygous - identical alleles (RR or rr)
Heterozygous - different alleles (Rr)

Question 10

2) Dominance/Recessiveness

Answer 10

If alleles are different, then only one trait is visible (ie 1 trait is dominant and 1 is recessive)
The dominant allele is expressed and determines the phenotype
Recessive is NOT expressed

Question 11

3) Segregation

Answer 11

Alleles are separated or segregated randomly during gamete formation. So, each parent passes on 1 allele (Also called Mendel’s Law of segregation OR Mendel’s first law of inheritance)

Question 12

4) Independent Assortment

Answer 12

Segregating pairs of alleles assort independently of each other (also called Mendel’s second law of inheritance)

Question 13

What is the phenotype ratio and the genotype ratio of the F2 generation?

Answer 13

Phenotype ratio - 3:1
Genotype ratio - 1:2:1

Question 14

Alleles

Answer 14

Are alternative versions of genes that account for variations in inherited characters

Question 15

Gene

Answer 15

Section of DNA that contains regulatory and coding sequences for appropriate expression of the gene product

Question 16

Locus

Answer 16

The position on a chromosome where a particular allele is found

Question 17

The most common allele is called …….. and the less common allele is called …….

Answer 17

Major and Minor
The major allele is often referred to as ‘wildtype’

Question 18

All cells except for ………. are diploid

Answer 18

Gametes are haploid

Question 19

Heritability

Answer 19

The proportion of the variation in a population that is attributable to genetic differences

Question 20

How do you calculate heritability

Answer 20

Genetic variance / Genetic variance + Phenotypic variance

Question 21

Phenotype

Answer 21

Is the physical expression of the genes an individual has

Question 22

Genotype

Answer 22

Is the assortment of alleles

Question 23

Complete dominance

Answer 23

When phenotypes of the heterozygote and dominant homozygote are IDENTICAL

Question 24

Incomplete dominance

Answer 24

When the phenotype of F1 hybrids is somewhere between the phenotypes of the 2 parental varieties (an intermediate phenotype)

Question 25

Codominance

Answer 25

When 2 dominant alleles affect the phenotype in seperate ways

Question 26

What is it called when a gene has multiple phenotypic effects

Answer 26

Pleiotropy
(ie coat colour pattern & crossed eyes of Siamese cats are both caused by the same allele)

Question 27

Epistasis

Answer 27

When a gene at 1 locus influences the phenotypic expression of a gene at a 2nd locus (ie in labs coat colour depends on 2 genes - one gene determines pigment colour, the other gene determines whether pigment is deposited in the hair)