Unit 5: Genetics

Gregor Mendel

Experimented with crossbreeding of pea plants to discover patterns of inheritance

Dominant

refers to the ability of one allele for a trait to mask the presence of another allele

Recessive

refers to an allele for a trait whose expression in the phenotype is masked by the presence of a dominant allele.

Genes

are the physical units of inheritance through which a number of traits are passed from generation to generation.

Alleles

Genes have two units (one from the mother and one from the father). In other words, alleles are the alternate forms of the same genes.

Homozygous

When the two alleles for a trait are of the same kind

Heterozygous

when an organism has two different alleles for a trait

Genotype

the genetic constitution of an organism

Phenotype

the observable, physical appearance of an organism

Mendel’s Law

Law of segregation

Law of independent assortment

Law of segregation

Demonstrated that genes do not blend. In fact, organisms inherit one allele from each parent.

Law of independent assortment

demonstrated that genes controlling different traits are inherited independently from one another.

Germ-plasm theory

according to Weismann, the germ-plasm was isolated from the somatoplasm and, for this reason, it could not incorporate the soma’s responses to the environment.

Deoxyribonucleic acid (DNA)

the nucleic acid that carries the individual’s genetic information.

Nucleotides

building blocks of nucleic acid made of three parts: a phosphate group, a sugar group (five-carbon sugar), and a nitrogen base.

How many chromosomes do humans have?

23 pairs of chromosomes, including 22 pairs of body chromosomes plus one pair of sex chromosomes

Homoplasmic

it is the same in each and every cell.

Heteroplasmic

It differs among different parts of an organism’s body.

Proteins

complex chemical substances that are present in all living things. They are of great nutritional value and they are involved in many chemical processes essential for life.

Amino acids

Are 20 different kinds of organic molecule that are combined in a specific sequence to constitute proteins.

Two main categories of proteins

Structural proteins

Regulatory or functional proteins

How is the DNA template converted into a protein?

Through a process called protein synthesis

Two steps of protein synthesis

Transcription and translation

Transcription

The first step of protein synthesis

The process starts out when a double strand of parental DNA unzips. In other words, because DNA cannot leave the cell’s nucleus, it makes a ‘copy’ of one of its strands. This copy is called RNA (ribonucleic acid) and is made up only from one of the two DNA parental strands. The strand of DNA now called messenger RNA (mRNA) leaves the cell’s nucleus and moves to specialized structures in the cell called ribosomes

Translation

Second step of protein synthesis

The main component of ribosomes is ribosomal ribonucleic acid (rRNA), which is essential for protein synthesis. The ribosome ‘reads’ the codons (a sequence of three bases) composing the mRNA and ‘translates’ them into actual proteins. In other words, a protein constituted as the ribosome reads the mRNA and the suitable amino acids are linked together.

Cell division

starts when the chromosome replicates, forming a second pair that duplicates the original pair of chromosomes in the nucleus.

Cells resulting from mitosis

Somatic cells

Meiosis

Production of gametes (or sex cells)

Haploid

this means that they contain only a single set of unpaired chromosomes (one chromosome for each pair).