Genotype, Phenotype and Inheritance

• Variation encompasses the study of genotype and phenotype of organisms, and the analysis of sex-linked diseases and pedigrees.

DNA

• Complementary DNA strands must pair correctly:
  • CGTAAGCGCTAATTA pairs with GCATTCGCGATTAAT
  • TCTTAAATGATCGATC pairs with AGAATTTACTAGCTAG
  • AATGAATAGCTAGCTT pairs with TTACTTATCGATCGA

Chromosomes and Inheritance

• Humans have 46 chromosomes containing around 100,000 genes that code for traits and characteristics.
• A gene is a section of chromosomal DNA with a code for specific traits such as right or left-handedness.
• Alleles are different forms of a gene, represented by letters like "R" for right-handed and "r" for left-handed.

Dominant and Recessive Genes

• Alleles can be represented as (RR or rr) or (Rr or rR)
• Dominant alleles, such as RR or Rr, are stronger and more likely to express a trait.
• Recessive alleles need to be homozygous (rr) to express the trait.
• Darker colors in eye and hair color are often dominant, such as black hair over blonde hair.

Punnett Square

• The Punnett Square shows potential allele combinations.
• Genotype refers to the RR alleles of a chromosome.
• Phenotype is the physical expression, like right-handedness.

Genes and Variation

• Variation comes from sexual reproduction.
• Homozygous alleles are a pair of identical alleles (RR or rr).
• Heterozygous alleles are a pair of different alleles (Rr).

Genetic Crosses: Gregor Mendel (1822-1884)

• He researched how traits were passed from generation to generation.
• Mendel conducted breeding experiments using green pea plants.
• Observable characteristics include seed shape, seed color, seed coat color, pod shape, pod color, flower color, plant height, and position of flower.
• Mendel's garden pea experiment included pure breeding purple plants vs pure breeding white plants.
• The pure breeding purple plants crossed with pure breeding white plants resulted in F1 offspring being all purple.
• When F1 plants breed, the F2 generation produces both purple and white flowers.

Inheritance and Partial Dominance

• Blending of traits results from partial dominance or codominance.
• Incomplete dominance is where neither allele is completely dominant.
• Red flowering crossed with white flowering results in pink flowers.

Partial Dominance

• Both alleles are expressed in the phenotype because neither is dominant.

Human Blood Groups

• Human blood groups have three alleles: A, B, and O.
• Each individual has two of the three alleles.
• A and B alleles control the production of antigens that determine a person’s blood group and are codominant over the O allele.
• AB blood type means both A and B alleles are present.
• O blood type means neither A nor B is present.

Sex-Linked Inherited Conditions and Diseases

• Some genes are carried on the sex chromosome resulting in conditions.
• Colorblindness is linked to the X chromosome, where normal vision (C) is dominant over colorblindness (c).
• Colorblindness is more common in men than women.
• Females who are heterozygous will have varied vision.
• Haemophilia is a genetic condition in which blood does not clot properly after an injury due to an inability to produce factor 8.
• The allele responsible for hemophilia is recessive and located on the X chromosome.

Human Genetic Disease and Inherited Conditions

• These are caused by abnormalities in the number of chromosomes or by mutations.
• Albinism is an inherited condition where those affected have little or none of the melanin pigment that creates color in their eyes, skin, or hair.
• Genes responsible are located on several different chromosomes, including the X chromosome.
• The recessive allele for albinism is "a", and the genotype for albinism is "aa".

Sickle Cell Anemia

• Sickle cell anemia is an inherited blood disease that causes the red blood cells to develop an odd C-shape.
• Affected red blood cells contain abnormal hemoglobin (S) and cannot carry oxygen as well as normal cells.

Pedigrees

• Pedigrees chart the incidence of various conditions in families.
• Pedigrees show the pattern of inheritance of certain characteristics.

Variation and Change

• Continuous variation happens when variations are spread over a range of measurements.
• Discontinuous variation happens without any intermediate factors.

Sources of Variation

• Sources include genetic and environmental causes.
• Environmental factors can modify the outward appearance and characteristics.

Genetic vs Environmental Causes of Variation

• Genetic causes involve sexual reproduction, mutation, and meiosis.
• Environmental causes involve nutrition, drugs, and physical training.

Natural Selection

• Evolved species change over time and this is known as evolution.
• Charles Darwin is the "father of evolution".
• Organisms with structures and way of life that are well-suited (adapted) to make the best of limited resources survive long enough to reproduce.
• Natural selection is the process through which populations or living organisms adapt and change.

Resistance

• Insects become resistant to insecticides.
• Bacteria become resistant to antibiotics.
• Resistance is passed on to their offspring.

New Species Formation

• Environments change and affect the selection pressures on species.
• When populations adapt to new environmental conditions, new species may be formed through speciation.
• When organisms can no longer interbreed to produce healthy, fertile offspring, they are no longer members of the same species.
• Isolation and separation occurs by mountains or bodies of water.

Artificial Selection

• Selective breeding results in desired characteristics.
• It helps produce new varieties in a short time.
• It improves the productivity of farm animals and crops.

Hybridization

• Involves crossing two different varieties.