Observable Patterns of Inheritance Genetics Observable Patterns of Inheritance

Gregor Mendel Mendel’s Insight Into Patterns of Inheritance

Pisum sativum The pea plant has seven major traits that Mendel studied that are true dominant and recessive characteristics. The pea was an excellent plant to study because… 1. it is self-fertilizing 2. many samples can be grown at one time 3. the traits were easy to see

Seven Major Traits of the Pea Dominant Recessive Seed Shape Round Wrinkled Seed Color Yellow Green Pod Shape Inflated deflated Pod Color Flower Color Purple White Flower Position Along stem At the tip Stem Length Tall Dwarf

Genetic Terminology Genes Units of information about specific traits. These are passed from parent to offspring. Each gene has a specific location (GENE LOCUS) on a chromosome.

Diploid Cells (2N) ~ have a pair of genes on a pair of homologous chromosomes. (human diploid cells have 46 chromosomes) Haploid Cells (N) ~ have ½ the number of chromosomes as a diploid cell with no homologous pairs. (human haploid cells only have 23 chromosomes)

Alleles ~ the different forms of a gene. Ex Alleles ~ the different forms of a gene. Ex. “T” is used for tall and “t” is used for short (T and t are alleles) Homozygous alleles ~ 2 alleles in a pair are the same. Ex. TT or tt Heterozygous alleles ~ 2 alleles in a pair are different. Ex. Tt

Genotype ~ refers to the actual genes present in the individual. Phenotype ~ refers to the individual’s observable traits, “physical appearance”

Eyes are blue. Blue is the phenotype and the alleles that make them blue (bb) is the genotype.

Parental Generation (P)~ represents the parents in the first cross F1 Generation ~ first generation offspring (the babies of the P generation) F2 Generation ~ second generation offspring (the babies of the F1 generation)

Mendel’s Theory of Segregation Mendel believed that a plant inherited 2 genes of information for a trait, one from each parent. To test this idea, he performed thousands of monohybrid crossings.

Monohybrid cross a cross between 2 individuals where only one trait is being studied

Probability Being a mathematics major, Mendel was fascinated with the idea of probability (the chance of each outcome occurring is proportional to the number of ways that it can be reached). Mendel created a visual solution to the probable outcome for each of his monohybrid crossings. This was called the “Punnett-Square Method”

Punnett~Square Method Setting up a Punnett square 1. Set up a 2 x 2 Punnett square.

2. Write the alleles for parent 1 on the left side of the Punnett square. Each gamete will have one of the two alleles of the parent. In this particular cross, half of the gametes will have the dominant (S) allele, and half will have the recessive (s) allele. We will use blue and brown to keep track of the alleles of each parent. S s

s S S s 3. Write the alleles from parent 2 above the Punnett square. For this heterozygous parent (Ss), half of the gametes will have the dominant (S) allele, and half will have the recessive (s) allele. S s S s

4. Fill the squares for parent 1. Fill each square with the allele from Parent 1 that lines up with the row. Capital letters go in the first position, lower case go in the second position. S s S S S s s s

5. Fill the squares for parent 2. Fill each square with the allele from Parent 2 that lines up with the column. S s S S S S s s S s s s

Mendel’s Theory of Segregation Theory of Segregation was the first in Mendel’s research. It states… ~Diploid cells have pairs of genes that segregate during meiosis and as a result, each half ends up segregated in different gametes.

Dihybrid Crosses Experimental crosses where two pairs of genes are observed instead of one.

Theory of Independent Assortment From his work with dihybrid crosses, Mendel created his theory of independent assortment which states… At meiosis, gene pairs on homologous chromosomes are sorted randomly of each other.

Human Traits Most traits in humans are controlled by multiple alleles. That means that more than one type of letter could be received from a parent. Example… Blood Type you could inherit an A, B or o allelle from a parent. This creates many different varieties in one trait (A blood, B blood, AB blood and o blood)

Sex-Linked Traits Some traits in humans are linked to an X or a Y Chromosome These are called Sex-Linked Traits Examples of sex linked traits are… COLOR BLINDNESS and HEMOPHILIA

How might a biologist determine whether a mutation has occurred and, if so, what type of a mutation it is?

Frameshift mutation A frameshift mutation changes the amino acid sequence from the site of the mutation.

                                                                                                                                               In this example, one nucleotide (adenine) is added in the DNA code, changing the amino acid sequence that follows.

                                                                                                                                               In this example, one nucleotide (adenine) is deleted from the DNA code, changing the amino acid sequence that follows.

Tranlocation/Inversion Translocation ~ switch the genes from one chromosome to another Inversion ~ flip the genes upsidedown!

                                                                                                               A section of DNA is accidentally duplicated when a chromosome is copied.

Pair Share A’s tell B’s how a mutation affects proteins B’s tell A’s three different ways mutations can occur.

Point Mutations An alteration in DNA sequence caused by a single nucleotide base change, insertion, or deletion.

The Operon Model of gene regulation was proposed by Francois Jacob and Jacques Monod. Groups of genes coding for related proteins are in units known as operons. An operon consists of an operator, promoter, regulator, and structural genes. The regulator gene codes for a repressor protein that binds to the operator, obstructing the promoter (thus, transcription) of the structural genes.                                

Now its your turn! What kind of mutations occurred? DNA ~ ATTCGGATAACG RNA ~ UAAGCCAUUGC RNA ~ UAAGCCGCCUAUUGC RNA ~ UAACCGUAUUGC RNA ~ CUAAGCCUAUUG

Try it with your partner. Do you really get this? Try it with your partner.

How else can your genes mutate? What if your whole chromosome is deleted? What if you ended up with an extra one? How does this happen?

Nondisjunction Occurs when homologous chromosomes do not separate during meiosis.

Individuals that receive nondisjunctive gametes are often sterile There are two possible results from nondisjunction in chromosomes Monosomy – resulting when one chromosome is missing (often lethal) 2. Trisomy – resulting when there is one EXTRA chromosome. Individuals that receive nondisjunctive gametes are often sterile

Disorders caused by Nondisjunction Down Syndrome – the most common chromosomal disorder. Called trisomy 21 because of the extra chromosome on the 21st pair. Mental retardation, abnormal eyelids, thick lips deformed hearts, short stature

Klinefelter’s Syndrome Caused by nondisjunction of the sex chromosome and results in a man with an extra X chromosome. Appearance Enlarged breasts, high pitched voice Abnormally long arms Bad skin condition on feet and legs

Turner’s Syndrome Due to nondisjunction of the sex chromosomes resulting in monosomy. Appearance: short, stocky girl, immature sex organs and breasts as an adult.