Theoretical Genetics

Genetic Terms: P = parental generation of a cross F1 = the first generation after the parental (the results of the first cross) F2 = a cross between F1 individuals yields F2

Genotype – the alleles of an organism as inherited from the parents Phenotype – the characteristics of the organism due to the interaction of the genotype and the environment

Homozygous – having two identical alleles of a gene Heterozygous – having two different alleles of a gene AA aa are homozygous Aa are heterozygous

Dominant allele – expressed phenotypically whether it is homozygous or heterozygous Recessive allele – expressed phenotypically only in the homozygous state Capital letters are used to represent the dominant allele Lower case for the recessive Dominant allele always listed first

Codominant alleles – pairs of alleles that both affect the phenotype when present in the heterozygous state

Locus – the particular position of a gene on homologous chromosomes

Carrier – an individual that has one copy of a recessive gene that causes a genetic disease in individuals that are homozygous for the gene Test cross – checking the genotype of an individual by crossing it with a known homozygous recessive B? X bb The percentage phenotype give answer

Determine genotypes and phenotypes using a punnett square.

The possible gametes of each individual are determined. Each gamete will have one of the two alleles of the parent. Generate a punnett square and write the alleles for parent 1 on the left side of the Punnett square. Place the alleles for parent 2 above the square Fill the squares for each parent

The odds of 2 or more independent events occurring together is the product of each independent event. In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability that the offspring will be homozygous recessive? ½ x ½ = ¼

Probability that events that can occur in 2 or more different ways will occur, is the sum of the separate problems. In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability of the offspring being heterozygous? ¼ + ¼ = ½

The odds of two different traits occurring together in the same offspring is the product of each independent trait occurring in the offspring. In which phase of meiosis does this event occur? What assumption did Mendel make for this law to work?

Some traits have more than two alleles Coat color in rabbits and cats Drosophila wings Human blood types

Women – homozygous XX Men – heterozygous XY 23 rd pair chromosomes Dimorphic SRY gene on Y determines Presence of male features

Mothers can only contribute X chromosome Fathers can contribute either X or Y thus determine gender of child 50% chance boy, 50% chance girl for each fertilization event

Nile crocodiles sand temperature around the eggs during incubation affects gender - higher temperatures favor males Turtles and lizards high temperatures favor females Many fish are hermaphrodites and under certain environmental conditions will switch gender

oser.shtml oser.shtml X chromosome much larger than Y Many genes found on X that are not present on Y

Genes on X with no counterpart on Y are called sex linked genes Often affect one gender more than another Color Blindness and Hemophilia

Caused by mutant gene recessive Encodes either clotting factor Vlll = h-A Or clotting factor lX = h-B Carried on X chromosome Heterozygous will clot normally as their good copy of gene produces enough clotting factor If only mutant gene copy present will suffer from excessive bleeding

Red-green color blindness carried on X Blue color sensitivity is carried on chromosome 7 and inherited as any autosomal gene

4 Sex-Linked Traits: 1. Normal Color Vision: A: 29, B: 45, C: --, D: Red-Green Color- Blind: A: 70, B: --, C: 5, D: Red Color-blind: A: 70, B: --, C: 5, D: 6 4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

Females can be homozygous or heterozygous for sex- linked traits Females with one or two dominant alleles for a sex linked trait will not exhibit the trait Females that are heterozygous for sex-linked traits are called carriers Only females can pass on sex-linked traits to their sons

The calico cat is the result of multiple alleles on the X chromosome combines with X inactivation. One allele causes orange fur and the other causes black fur. The male cat will be either orange or black. Only a heterozygous female will be calico with regions that are orange and regions that are black based on the X inactivation

Predict genotype and phenotype using Punnett Squares for all of the inheritance patterns mentioned above

Deduce the genotype and phenotype of individuals in a pedigree chart