2: Genetics

Geneticsand Heredity

Genetics and Evolution

Evolution = change in gene frequencies within populations over time.

Cell Diagram

DNA (deoxyriboneucleic acid)

Protein Synthesis

• DNA is a molecule that provides the cell instructions on how to create proteins.

• Protein Synthesis refers to the construction of proteins from the DNA sequence

Proteins

• Proteins are large organic compounds composed of amino acids.

• Most enzymes are proteins. Many hormones are also proteins.

The DNA Code

• Four Bases: Adenine Thymine Guanine Cytosine

• A T C G A T T A T C G C G

• T A G C T A A T A G C G C

Protein Synthesis (simplified)

• The DNA molecule “unzips” itself.

• One side of the DNA molecule is “read” and a complementary strand is made by messenger RNA (mRNA).

• Transfer RNA (tRNA) transports amino acids to the ribosome in order to make protein based on the messenger RNA sequence.

DNA and Genes

• A gene is a unit of DNA that codes for one protein.

• A gene is located at particular region or locus of a particular chromosome.

DNA, Genes and Chromosomes

Long strands of DNA (containing many genes) are wound up into structures called chromosomes.

Chromosomes

• Humans have 23 pairs of chromosomes (46 total).

• 22 pairs of autosomes.

• 1 pair of sex chromosomes.

Sex Chromosomes

XX = Female (two copies of the same chromosome)

XY= Male (two different chromosomes)

Chromosomes

Meiosis and Mitosis

• Mitosis = cellular division resulting in new cells with the same number of chromosomes as their “parents.”

• Meiosis = cellular division resulting in cells with HALF the number of chromosomes as our body cells (sperm & ova).

Mutation

• Random changes in genetic material occur all the time. We refer to these as mutations.

• Mutations are responsible for the genetic variation we see within a population of organisms.

Alleles

• Allele: a variation of a particular gene.

Genes and Inheritance

In most circumstances, we inherit two copies of each gene (allele): one from each parent.

Genotype vs. Phenotype

• Genotype = the genes you’ve inherited from your parents

• Phenotype = a particular observable trait (blood type, hair color…etc.).

Genes and Inheritance

• Alleles (gene variants) can be said to be dominant or recessive in relationship to each other.

• Dominant alleles can “hide” or “cover up” the expression of recessive alleles.

Heterozygous vs. Homozygous

• Heterozygous: having two different alleles. (A and a)

• Homozygous: having two of the same alleles (A and A)

Eye Color: an Exercise

• The Eye-Color gene has two alleles:

• B (brown) is dominant

• b (blue) is recessive


Genotype:

BB

Phenotype


Genotype:

Bb

Phenotype


Genotype:

bb

Phenotype

Eye Color Exercise

Mother Father

Bb X bb

Child

B b

Bb

Punnett Square

Incomplete Domination

• The Petal color gene has two alleles: R (red) and W (white)

Genotype Phenotype

RR Red

WW White

RW Pink

Blood Groups

Blood Type

• Three alleles: A, B & O

• A is dominant to O

• B is dominant to O

• A and B are co-dominant

Possible Genotypes: AO, AA, BO, BB, OO, AB

Monogenic vs. Polygenic

• Monogenic = one gene

• Polygenic = multiple genes

Gene to Trait

Genotype

+

Environmental Influences

=

Phenotype

Education

2: Genetics