Mendelian VS. Non-Mendelian Genetics GENETICS UNIT 2015 Mendelian VS. Non-Mendelian Genetics

GENE Gene = section of DNA that codes for a particular protein. Locus = specific position on a pair of homologous chromosomes.

ALLELE Allele = alternative form of a gene. Each parent donates one for every gene Homozygous = two alleles are that are the same Heterozygous = two alleles that are different.

TRAIT Trait = genetically determined characteristic of a person.

Genotype = makeup of a specific set of genes. Phenotype = physical expression of a trait.

Dominant vs. Recessive Dominant = expressed when at least one allele is dominant. Represented by uppercase letters Recessive = expressed only when two copies are present. Represented by lowercase letters

PUNNETT SQUARES Punnett square = grid system for predicting possible genotypes from a cross. Axes = possible gametes from each parent Boxes = possible genotypes of offspring.

Mendel Gregor Mendel was born in 1822. Called the “Father of Genetics” & worked on Pea Plants. Late 1800 chromosomes and the process of meiosis were unknown. Mendel’s work was considered obscure and unimportant until 1900.

Gregor Mendel’s Findings Principle of Dominance When contrasting traits are crossed, the offspring will express the dominant trait. Principle of Segregation The pair of homologous chromosomes separate during meiosis so that only one chromosome is in each gamete. Principle of Independent Assortment Genes separate independently of one another in meiosis.

MONOHYBRID CROSS Monohybrid = examines a specific trait.

PROBABILITY Probability = likelihood that something will happen.

TESTCROSS Testcross = cross between an organism with the unknown genotype and an organism with the recessive phenotype.

DIHYBRID CROSS Dihybrid = cross that involves two traits. Cross with two heterozygous traits will always yield a 9:3:3:1 phenotypic ratio.

Non-Mendelian Inheritance Exception to the Rules

Let’s Review Mendelian Genetics B b Blue(B) is dominant to green(b). Alien Body Color BB bb Bb

INCOMPLETE DOMINANCE Incomplete dominance = neither allele is completely dominant nor completely recessive. Result = The phenotype of the heterozygous is a blend of the two homozygous phenotypes. R r R r RR Rr rr RR Rr rr

CODOMINANCE Codominance = alleles are neither dominant or recessive. Result = both alleles will be completely expressed. Ex: Blood types of humans. Type B is dominant to Type O Type O is recessive Type AB is co-dominant Type A is dominant to Type O

Codominance W w Ww W w WW Ww Ww ww Both alleles are expressed equally

POLYGENIC Polygenic traits = produced by two or more genes Genes may be located on the same chromosome or on different chromosomes Order of dominance: brown > green > blue.

SEX-LINKED GENES Sex-linked genes = genes on sex chromosomes.. Y chromosome genes in mammals are responsible for male characteristics. X chromosome genes in mammals affect many traits.

SEX-LINKED GENES Male mammals have XY genotype All sex-linked genes are expressed Have no second copies of the genes XX XY

SEX-LINKED GENES Genes found only on the X chromosomes Female mammals have XX genotype Expression similar to autosomal genes One X chromosome is randomly turned off Colorblindness and Baldness are examples of sex-linked traits.

SEX-LINKED GENETIC DISORDERS Females can be carriers of sex-linked disorders Males express all of their sex-linked genes.

PEDIGREE Pedigree = chart for tracing genes in a family

PEDIGREES