IG2 - Inheritance (Online Lesson 5)

Inheritance

Chapter 12, Online Lesson 5

Multiple Choice

Which of the following definitions best describes a chromosome?

• A structure composed of nucleic acids

• A structure composed of protein

• A structure composed of nucleic acids and protein

• A structure composed of nucleic acids and carbohydrates

Multiple Choice

What is a gene?

• A length of DNA that codes for a carbohydrate

• A length of DNA that codes for a protein

• A length of DNA that codes for a lipid

• A length of DNA that codes for a nucleic acid

Every chromosome contains a different number of genes. There are roughly 20 000 genes in the human genome.

Multiple Choice

How many chromosomes does a human have in 1 somatic (body) cell?

• 46

• 23

• 21

• 92

A diagram displaying all the chromosomes in a cell is called a karyotype

Multiple Choice

What do we call the two chromosomes in each pair?

• paired chromosomes

• karyotypes

• genes

• homologous chromosomes

Inheritance

• A gene is a blueprint for a trait (example: eye colour)

• These genes may have several different versions (example: brown/blue)

• A version of a gene is called an allele

Example: Chinchilla

• Chinchillas are rodents native to South America (Andes mountains)

• Genes determine the colour of a chinchilla's fur

• These genes are instructions for producing proteins that cause different fur colours

Genes & Alleles

• In this example, chinchillas can have 2 different fur colours: grey or charcoal

• Therefore, there are 2 alleles for the fur colour gene

Genes & Alleles

• When looking at the inheritance of gene alleles, we simplify each allele to a single letter

• Tip: Always choose a letter that looks distinctly different when capital and lowercase

• A/a and B/b are good

• C/c and S/s are bad

Genes & Alleles

• In each cell of the chinchilla, there are 2 copies of the fur colour gene (1 from mother, 1 from father)

• Let's say that the gene for fur colour is represented by the letter G or g

• Grey fur is G

• Charcoal fur is g

Genes & Alleles

• There are 3 possible combinations of this gene for any chinchilla to have in their cells:

• GG

• Gg

• gg

Genes & Alleles

• If the 2 alleles are the same (GG or gg), we say that the chinchilla is homozygous

• If the 2 alleles are different (Gg), we say that the chinchilla is heterozygous

Multiple Choice

Labradors have 2 different fur colours: blonde and black. The gene is represented by the letter B (B for blonde fur, b for black fur).

Which of the following represents a heterozygous individual?

• BB

• black fur

• Bb

• blonde fur

Genotype & Phenotype

• The genetic makeup of an organism in terms of the alleles present is called its genotype

• The observable features/traits an organism has is called its phenotype

• Example: GG/Gg/gg = genotype Grey/charcoal fur = phenotype

Genotype & Phenotype

• The chinchilla has 3 possible genotypes (GG, Gg, gg) but only 2 possible phenotypes (grey and charcoal)

• GG = grey

• gg = charcoal

Dominant & Recessive

• Genotype Gg corresponds with the phenotype Grey

• This is because the G allele is dominant over the g allele (it will silence g)

• A dominant allele is an allele that is expressed when it is present

Dominant & Recessive

• A heterozygous chinchilla (Gg) is also called a carrier because it has the allele for charcoal fur but doesn't express it

• The allele g is called recessive because it is only expressed when there is no dominant allele present