Genetics

History Charles Darwin wrote The Origin of Species in 1859. Gregor Mendel – Basic laws of heredity in 1866 Miesher – Nucleic Acids in 1869 Watson and Crick – DNA in 1944 Human genome mapped in 2000

History Charles Darwin wrote The Origin of Species in 1859. Gregor Mendel – Basic laws of heredity in 1866 Miesher – Nucleic Acids in 1869 Watson and Crick – DNA in 1944 Human genome mapped in 2000

Terms Locus (plural – loci): Place on a chromosome where a gene is located. Alleles – genes of the same trait that occupy corresponding loci on homologous chromosomes.

Chromosome – DNA molecule wrapped around proteins. DNA – Deoxyribonucleic acid. Genetic material that organisms inherit from their parents. Gene – Made up of two alleles. Codes for a trait (or a protein). Dominant allele – one that expresses itself Recessive allele – is not expressed. Homozygous – Genotype where the 2 alleles that look exactly alike

Heterozygous – (hybrid) – Genotype where the 2 alleles are different. Genotype – organisms genetic constitution. (exp: Tt) Phenotype – appearance of an individual with respect to inherited trait. Test Cross – way to determine genotypes through mating.

Mendel’s Laws Law of Segregation Genes exist in allelic pairs, but gametes (sex cells) have only one of each kind of gene (allele). The two alleles for each gene separate during gamete production (meiosis). An egg and a sperm each get only one of the two alleles that are present in the body cells of the organism. A punnett square is very useful in demonstrating this segregation.

Mendel’s Laws Law of Independent Assortment During meiosis each pair of genes separates independently from each other (unless they are on the same chromosome).

More Terms Incomplete Dominance When the heterozygous has a phenotype that is intermediate between those of its two parents. When a red flower is crossed with a white flower, all of its offspring are pink. What will be the phenotypic ratio of a pink flower crossed with a red flower?

Co–Dominance both alleles of the heterozygous genotype are expressed. When a white horse is mated with a red horse all of the offspring are roan (both red and white hairs are produced) If two roan horses are mated what are the possible phenotypes of their offspring?

Epistasis Presence of a particular allele of one gene pair determines whether alleles of another gene pair will be expressed. (One gene masks the other.) Example: Labs

Labs 2 genes: The E locus and the B locus. E determines if the dog will be light or dark. Dark is dominant over light. If the dog is ee s/he will have a light coat regardless of what the B locus is. The B locus determines black versus chocolate. Black is dominant over chocolate.

Example Problem If a chocolate lab is mated with a yellow lab and all of their offspring are chocolate labs what is the genotype of both parents in regards to the E and B loci? If a yellow lab (whose mother was a chocolate lab and father was a homozygous black lab) is mated with a chocolate lab (whose mother was a yellow lab) what is the phenotypic ratio for their puppies?

Polygenic Inheritance Two or more independent pairs of genes have similar and additive effects on the same characteristic. Example: skin color (7 genes) and height (more then 10 genes)

Multiple Alleles 3 or more alternative forms of a gene that can occupy a single locus. But, a diploid individual has only two of the alleles. Example: Blood type has 3 possible antigens: A, B and no antigen. Blood type also exhibits co-dominance: AB blood type – both the A and B antigens are produced.

Blood Type (phenotype) Genotype Antigens A IA IA or IAi Antigen A B IB IB or IBi Antigen B AB IA IB Antigens A and B O ii NO antigens

Rh Factor of Blood Types Rh system – 8 different antigens Antigen D is the most important. Rh+ means that you have the antigen Rh- you don’t have the antigen. Rh+ is dominant over Rh-

Example Problems If the mother is heterozygous for blood type A and the father has blood type O, what are the possibilities for their children (include probabilities)? Who can be a donor for a person with blood type A+? B-? O+? AB+? O-? If the mother is heterozygous for blood type A and the Rh factor and the father is AB-, what are the possibilities for their children (include probabilities)?

Pedigree

Chromosomes Humans have 22 pairs of autosomes (non sex chromosomes) One pair of Sex chromosomes Females are XX Males are XY Show using a punnett square why there is always a 50% chance of having a boy and 50% chance of having a girl.

X-linked traits Also called sex-linked traits These are traits that are on the X chromosome. Recessive traits are more common in males then females because males only inherit one X chromosome – which always comes from their mother. Example: colorblindness, hemophilia, Duchenne’s muscular dystrophy

Example Problem What is the probability that a couple will have a colorblind child if the mother’s father was colorblind but the mother and father have both normal vision?