The Genetics of Inheritance

The Science of Heredity The scientific study of heredity is called GENETICS

The study of heredity started with the work of Gregor Mendel and his pea plant garden The study of heredity started with the work of Gregor Mendel and his pea plant garden

Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.

Gregor Mendel Pea Plant Experiment Gregor Mendel chose pea plants to conduct genetic experiments because of their plant life special properties. For example: When pollen fertilizes an egg cell, a seed for a new plant is formed. Pea plants normally reproduce by self- pollination.

Gregor Mendel Pea Plant Experiment What does it mean when pea plants are described as being true-breeding (pure breed)? If the plants are allowed to self- pollinate, they would produce offspring identical to themselves.

Gregor Mendel Pea Plant Experiment To perform his experiments, how did Mendel prevent pea flowers from self-pollinating and control their cross-pollination? He cut away the pollen-bearing male parts of a flower and dusted that flower with pollen from another plant.

Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. X = x = X =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x =

Gregor Mendel Pea Plant Experiment Traits - Specific characteristics that vary from one individual to another Hybrids-The offspring of crosses between parents with different traits Genes - Chemical factors that determine traits Alleles - The different forms of a gene

Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. -Carrying the information are chromosomes. -Chromosomes are made up of sections called genes. -Genes are made up of DNA

Why do we look the way we do? All organisms are made of cells. Inside of these cells, a chemical called DNA contains the “instructions” that control the way we look. DNA

DNA: the instruction manual The segments in the DNA that carry the “instructions” are called GENES. Every individual has two of every gene. Blue Eyes Brown Eyes Brown Hair Black Hair Fair Skin Olive Skin There is more than one version of each gene. The different versions are called alleles.

Genetics There are three basic kinds of genes: – Dominant - A gene that is always expressed and hides others – Recessive - An organism with a recessive allele for a particular form of a trait will NOT always exhibit that form. – Codominant - Genes that work together to produce a third trait

Dominant Alleles State the principle of dominance: The trait will always be expressed mask the other gene. – Dominant -Expressed regardless of what paired with – Dominant -Expressed with a capital letter (T)

Recessive Alleles – Recessive Allele-A gene that is only expressed when a dominant gene isn’t present – Recessive-Physically expressed when paired with another recessive allele – Recessive-Expressed with a lower case letter (t)

Codominant Allele Codominant - Genes that work together to produce a third trait – In your genetic smiley baby it was the ears and nose color Red (RR) Orange (RY) Yellow (YY)

Incomplete Dominant Traits Blood types: Flower color: In incomplete dominance, the dominant allele does not cover up the expression of the recessive allele.

Characteristics of Traits What are gametes? They are the sex cells.

In the diagram above, the dominant allele is represented by ___and the recessive allele is represented by __.

Dominant & Recessive Human Traits Earlobes:Widow’s peak: # Students w/ free lobes # Students w/ attached lobes Free Attached # Students w/ a widow’s peak # Students w/out a Widow’s peak One allele is dominant and the other allele is recessive. The dominant allele covers the expression of the recessive allele.

Genotype & Phenotype # Students w/ free lobes# Students w/ attached lobes The observable traits of an organism is called the phenotype. The genotype is the combination of all of the different alleles that make up an individual

Allele Types Definitions Organisms that have two identical alleles of a particular trait (TT or tt) Homozygous Organisms that have two different alleles of a trait (Tt) Heterozygous Physical characteristic of an organism Phenotype Genetic makeup of an organism (Tt) Genotype

Allele Types Homo - Same Hetero - Opposite Pheno – Physical Geno - Genetic

Gene Expression Is the following sentence true or false? -Plants with the same phenotype always have the same genotype. False

Why do we look like our parents? AaAaa Aa AaAaa AaAa a AaAa a aa

The likelihood that a particular event will occur is called_______. Probability

Circle the letter of the probability that a single coin flip will come up heads. a. 100 percent b. 75 percent c. 50 percent d. 25 percent

Probability Why can the principles of probability be used to predict the outcomes of genetic crosses? The way in which the alleles segregate is completely random, like a coin flip.

Genetics Punnet Square - A tool we use for predicting the traits of an offspring – Letters are used as symbols to designate genes – Capital letters are used for dominant genes – Lower case letters are used for recessive genes – Genes always exist in pairs

Punnett Squares A diagram that is used to predict the genotype and phenotype of the offspring based on the genotype of the parents. Chart of possible combinations of the outcomes of alleles that may result from genetic cross pp PPp ppp Pp pp It’s a probability problem! ½ purple pea plants; ½ white pea plants

Punnett Squares Male parent goes across the top of the square Female parent goes across the left side of square

Practice Draw a Punnett square - 4 small squares in the shape of a window. Write the possible gene(s) of male parent across the top-Father is black fur (dominant) homozygous and the gene(s) of the female parent that is blond fur recessive homozygous along the left side of the Punnett square. Complete a Punnett square to show the possible gene combinations for the F1 offspring.

Punnett Square- practice Complete a Punnett square to show the possible gene combinations for the F2 offspring.

Probability and Segregation b. The F2 ratio of black fur to pink fur produced in a cross between two hybrid Black fur (Bb) is 3 black for every 1 pink. c. observe that about 3⁄4 of the F2 offspring showed the dominant trait.

Probability Is the following sentence true or false? Probabilities predict the precise outcome of an individual event. False

Punnett Squares 1.What is the probability that this couple will have a child with brown eyes? Bb 2. What is the probability that this couple will have 3 children with brown eyes? BB=bb=Bb=

More Punnett Squares There are 10 guinea pigs in a litter. Five of the guinea pigs have long hair, and five have short hair. Long hair is dominant and short hair is recessive. What are the genotypes of the parents? Genotype for long hair: Genotype for short hair:

Applications of math in genetics Selective breeding—The selection of certain seeds or animals for reproduction so that the next generation has the same desirable traits.