Genetics and Heredity

Deoxyribonucleic Acid (DNA) DNA is an organism’s genetic material. Large molecule with a shape similar to a twisted ladder (double helix).

Chromosomes – made of coiled DNA. Gene – a section (pair) of a chromosome that has genetic information for 1 trait. Allele – 1 copy of a gene. Each characteristic (trait) has two alleles, one from each parent.

Topic: Traits EQ: why are genes important?

Traits are controlled by genes Genes are located on your chromosomes Individuals inherit genes from their parents Your cells contain 23 chromosome pairs

What is a trait? Trait – a physical characteristic that can be seen. Example of traits – eye color, freckles, number of legs, thumb on top, rolling tongue. Each trait is represented by two letters (ex: Tt).

Heredity and Genetics Heredity – passing of traits from parents to offspring. Genetics – the study of how traits are passed from parent to offspring.

The Father of Genetics Gregor Mendel Austrian Monk Gardener, bee keeper, scientist Experimented on plants, especially known for his work on pea plants.

Mendel studied 30,000 common pea plants over 8 years and many generations. Mendel found that traits show up without any blending.

Dominant vs. Recessive Dominant trait – the allele that masks the appearance of another allele. Represented by a capital letter. Recessive trait – the allele that is blocked by a Dominant allele. Represented by a lower case letter.

Dominant Traits Recessive Traits Broad lips Hazel or green eyes Second toe longest Widow’s peak hairline Crossing thumbs – left on top Unattached earlobe Rolling tongue Dimples Freckles Straight thumb when extended Curly hair Thin lips Blue or grey eyes Big toe longest Straight hairline Crossing thumbs – right on top Attached earlobe Non-rolling tongue No dimples No freckles Bent thumb when extended Straight hair

Genotype & Phenotype Genotype – The specific two alleles inherited for a particular trait (example TT, Ss, oo, Gg, etc.) Phenotype – The physical characteristic that appears.

The Punnett Square Reginald Punnett created the Punnett Square A tool used by scientists to predict the genotypes of offspring.

Using the Punnett Square Draw the square

Using the Punnett Square Write the genotypes of the parents on the outside of the box. T t T t

Using the Punnett Square Fill in the boxes with the alleles down and across T t T t T T T t t T t t

Using the Punnett Square Each box represents 1 offspring. In the above Punnett Square, how many different genotypes are there? How many different phenotypes are there? How can you represent those number in a percent (%)

Answers The genotypes are 1 or 25% BB , 2 or 50% Bb, and or 25% bb The phenotypes are 3 or 75% purple and or 25% white

Different types of Genotypes Heterozygous genotype – a genotype in which the two alleles are different. (example Tt) Homozygous genotype – a genotype in which the two alleles are the same. (example TT or tt)

Different types of Genotypes Hybrid – a heterozygous genotype and is the result of 2 genetically different parents. Example: TT + tt = Tt Pure Bred – a homozygous genotype and is the result of 2 genetically same parents Example: TT + TT = TT or tt + tt = tt

What is a pedigree? A pedigree is a chart of the genetic history of family over several generations. Show the phenotypes of genetically related family members. http://www.schooltube.com/video/c188ce8266b54a18992b/tions

Constructing a Pedigree Female Male You must learn the symbols of the pedigree charts before you can start to learn how to interpret it. These are the symbols that represent a male and a female.

Connecting Pedigree Symbols Married Couple Children These symbols also represent relationships between people. some may have to each other.

A heterozygous genotype such as Hh or Bb What is a carrier? A heterozygous genotype such as Hh or Bb

Example What does a pedigree chart look like? This is just an example of a pedigree and there can be many more different types.

Symbols in a Pedigree Chart