Topic 8: Classical Genetics

Question 1

Genotype

Answer 1

All of an organism’s genes/alleles (i.e., the DNA/genome)

Question 2

Phenotype

Answer 2

The physical manifestation of the genotype (i.e., anything above the gene level, so proteins, physical features, what the gene is coded to make)

Question 3

Discrete (Mendelian) Traits

Answer 3

Some traits can be controlled by the action of a single genetic locus (gene)
- it’s one or the other
- often controlled by one gene
- easy to work with genetically
- Genome-wide association mapping

Question 4

Quantitative (Continuous) Traits

Answer 4

Other traits require the influence of multiple genes to result in the phenotype
- Often ends up as a normal distribution
- Often highly influence by the environment
- E.g., height, weight, etc.

Question 5

Homozygous

Answer 5

A cell/organism with identical alleles of a gene of interest

Question 6

Heterozygous

Answer 6

A cell/organism with different alleles of a gene of interest

Question 7

Hemizygous

Answer 7

A cell/organism that naturally only has one copy of a gene normally raising on a sex chromosome

Question 8

Gene

Answer 8

A region of a chromosome that is transcribed and influences phenotype

Question 9

Alleles

Answer 9

A variant of a gene

Question 10

Homologous Pairs of Chromosomes

Answer 10

Same genes and in the same order.
- One homolog comes from the mother, one homolog comes from the father

Question 11

Haplosufficient

Answer 11

refers to a situation where having only one functional copy of a particular gene is sufficient to produce a normal phenotype (observable characteristics). In other words, the gene is able to perform its function with only one copy present in the genome
- Dominant allele is fully expressed when only one copy is present
- The alternative allele will be fully recessive (not observed at the phenotypic level)
- Most WT are haploinsufficient

R Allele = WT allele is dominant and haploinsufficient
(Rr, RR = R phenotype)

Question 12

Haploinsufficient

Answer 12

Having only one functional copy is not sufficient to produce a normal phenotype. In such cases, a loss-of-function mutation in one copy of the gene can cause disease or abnormal development.
- If a mutant allele is dominant

r allele = mutant allele, enzyme is broken
(rr = r phenotype)

Question 13

Mendel’s research led him to discover the basic principles of heredity (FIVE POINTS):

Answer 13

1. Existence of genes
2. Genes are occurring in pairs (i.e., diploid)
3. 1st Law: segregation (separation of alleles in equal proportions in gametes - separation of sister chromatids)
4. 3rd Law: dominance
5. 2nd Law: independent assortment

Points 1-4: monohybrid cross
Point 5: dihybrid cross

Question 14

Complete Dominance

Answer 14

Complete dominance is a term used in genetics to describe the relationship between two alleles of a gene, where one allele completely masks or overrides the expression of the other allele in the heterozygous genotype. In other words, when a dominant allele is present, it will always be expressed in the phenotype, regardless of whether the individual is homozygous (has two copies of the same allele) or heterozygous (has one copy of each allele).

Question 15

Characteristics of Peas

Answer 15

• Studied discrete traits
• Used traits that showed complete dominance
• Self-fertilization

Question 16

Truebredding

Answer 16

• Individuals that are homozygous for a trait
• When crossed they will give back the same phenotype generation after generation.

Question 17

monohybrid cross

Answer 17

• An individual is heterozygous with respect to a specific gene.
• They are generated by crossing two true- breds with different phenotypes