Patterns of Inheritance Chapter 10 Patterns of Inheritance

10.1 Genetics trait: a variation of a particular character Ex yellow or red flowers gene: a unit of inherited information

Blending Hypothesis 1800 Explains how offspring inherit traits from both parents Ex. yellow flower + red flower = orange flower Discarded because it could not explain traits disappearing and reappearing in another generation

Gregor Mendel 19th century Austrian Monk First to apply an experimental approach to the question of inheritance genetics: the study of heredity Used pea plant breeding

Particulate Hypothesis Parents pass on to their offspring separate and distinct factors (genes) that are responsible for inherited traits Heritable factors retain their identity through generations

Mendel’s Pea Plants

Mendel’s Experiment Identify pea plants that were true-breeding When self-fertilized, only produces identical offspring To insure self-fertilization, Mendel tied cloth bags around each plant’s flowers to prevent cross pollination Mendel crossed true-breeding plants with two distinct traits (color and roundness) cross-fertilization: sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant The fertilized eggs developed into embryos within seeds (peas) that were planted These then grew to produce flowers Purple crossed with white flowers

10.2 Mendel’s Principle of Segregation hybrids: the offspring of two different true-breeding varieties P generation= parental F1 generation = the hybrid offspring F2 generation = offspring when F1 self-fertilize each other

Monohybrid Cross monohybrid cross: a pairing in which parent plants differ in only one character Mendel found that F1 produced all purple flowers but F2 3/4 purple and 1/4 white He repeated this for other traits (seed color, shape, pod shape & color, flower position, and stem length) Same result

Mendel’s 4 Hypotheses There are alternate forms of genes alleles: the alternate forms of genes Ex. Purple and white For each inherited character, an organism has 2 alleles for the gene controlling that character, one from each parent homozygous: 2 alleles are the same for that character heterozygous: the 2 alleles are different

3. dominant: only one allele appears to affect the trait recessive: the allele that does not appear to affect the trait Pp; P = dominant, p = recessive 4. Principle of Segregation Two alleles for a character separate during formation of gametes (meiosis) so that each gamete carries only one allele for each character

Punnett Square Diagram that shows all possible outcomes of a genetic cross

Phenotype and Genotype phenotype: an observable trait Hair color, height, tongue rolling The dominant trait shows up Bb and BB = dominant; brown bb = recessive; blond genotype: the genetic makeup (combination of alleles) 1/2 Bb; 1/2 bb = 2:2

Test Cross test cross: breeds an individual of unknown genotype but dominant phenotype with a homozygous recessive individual

Principle of Independent Assortment During gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another

Dihybrid Cross dihybrid cross: crossing organisms differing in 2 characters

10.3 Variations of Inheritance Patterns

Intermediate Inheritance (Incomplete Dominance) intermediate inheritance: the heterozygotes have a phenotype that is intermediate between the two homozygotes Ex. Red + white flowers = pink, red & white

Codominance codominance: a heterozygote expresses both traits Ex. Blood Type A, B, AB, O A & B refer to 2 carbohydrates that are found on the surface of red blood cells O = ii = neither carbohydrates Universal donor A= IAIA or IAi = A carb (A) B= IBIB or IBi = B carb AB= IAIA or IAi = both A & B Universal receiver

Polygenic Inheritance polygenic inheritance: two or more genes affect a single character Ex. Eye color, skin, height Eye color = tone of pigment , amount, and position pleiotropy: a single gene affects more than one trait Ex sickle cell anemia

Importance in the Environment Temperature can have an effect on animal coloring Ex siamese cats, rabbits Height can be affected by nutrition and exercise Ex. Dancers Nature vs Nurture

10.4 Meiosis Explains Mendel’s Principles Chromosome Theory of Inheritance States that genes are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

Genes gene locus: the alleles of a gene reside at the same location on homologous chromosomes The homologous chromosomes may bear the same or different alleles

Genetic Linkage genetic linkage: the tendency for the alleles on one chromosome to be inherited together The closer the genes are on a chromosome, the greater the genetic linkage and crossing over will not separate them The probability of genetic linkage is measured in centiMorgans (cM) Represents 1% of the probability of crossing over 1 cM apart = 1% chance of separation 20 cM = 20% chance

10.5 Sex-Linked Genes sex-linked gene: any gene located on a sex chromosome Most are found on the X chromosome Thomas Hunt Morgan Discovered sex-linked genes while studying fruit flies Normal fruit flies have red eyes which is carried on the X, but sometimes males have white (recessive)

Sex-linked Traits in Humans Colorblindness X-linked recessive Lack of red receptors in the retina 8% males 0.4% females