Introduction to Genetics Biology 30

What is GENETICS? The science of heredity and variation in living organisms A modern science that seeks to trace the patterns of inheritance

Genetic Terminology Genetics – study of the inheritance of biological traits Heredity – passing of traits from parents to offspring, through the use of genes. Acquired Characteristics – developed based on the environment you live in. (Environmental dependent)

Genetic Terminology Chromosomes Genes Alleles Produced from long strands of DNA Long string of genes Ex. Chromosomes 1-22 and the X,Y Genes Sections of a chromosome Represented by a pair of letters designating a particular spot (loci) on a homologous pair of chromosomes Units of instruction Ex. Eye color Alleles Alternate forms of a particular gene Have the same position of a pair of homologous chromosomes Ex. Blue, Brown, or Green eye color

Genetic Terminology

Dominant – the allele that is expressed when present with another Recessive – the allele that is masked when present with a dominant gene; is expressed when individuals are homozygous for 2 recessive genes. Genotype – the genetic make-up of an individual; TT, Tt, or tt Phenotype – the physical expression or appearance of an individual; TT tall, Tt tall, tt short

Homozygous – offspring inheriting identical alleles (TT – tall or tt – short) Heterozygous – offspring inheriting different alleles (Tt – tall) Hybrid – an individual which is heterozygous for one or more alleles Monohybrid – studying a cross involving only one characteristic or allele Dihybrid – studying a cross involving two characteristics or alleles

Parent generation (P1) – the parents involved in a cross 1st Filial Generation (F1) – the offspring from the P1 2nd Filial Generation (F2) – the second set of offspring extending from the P1 (ie, the children of F1)

Gregor Mendel Was a monk in the 1800’s who studied pea plants. He crossed different types of peas to see what kind of offspring they yielded.

Review of Mendel’s Theories Factors occur in pairs (genes) As humans we have two “versions/alleles” of every gene Dominant vs. Recessive – dominant gene masks recessive gene Law of segregation – during sex cell formation these paired factors (genes) separate/segregate into separate sex cells

Pure Breeding vs. Hybrids – pure breeding contains two genes that are identical (homozygous TT or tt) hybrids are heterozygous (Tt) Law of Independent Assortment – chromosomes separate independently of each other

Gamete Formation Represent traits using the same letter i.e., earlobes Free = E; attached = e Gametes only contain one of each kind of gene i.e., Ee parent makes gametes with either E or e

Single Trait Inheritance (monohybrid Crosses) Comparing a single trait in two reproducing organisms Use a Punnett square – a chart that shows potential gametes and offspring frequencies (ratios, probabilities)

Problem: A homozygous round seed is crossed with a homozygous wrinkled seed. What are the genotype and phenotype frequencies in the F1? b) cross 2 F1’s