Genetics

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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.

Traits are controlled by genes

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

•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).

What is a trait?

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 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 vs. Recessive

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

The Punnett Square

•Reginald Punnett created the Punnett Square

•A tool used by scientists to predict the genotypes of offspring.

•Genotype – The two specific two alleles inherited for a particular gene (example TT, Ss, oo, Gg, etc.)

•Phenotype – The observable characteristic that appears such as blue eyes, two legs, tallness, etc.

Genotype & Phenotype

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 (%)

•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

Answers

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

Symbols in a Pedigree Chart

Examples of Pedigrees