How traits are passed from parents to offspring. Ch 5 Genetics How traits are passed from parents to offspring.

Lesson 1 Early Ideas about Heredity Gregor Mendel, the “father of genetics”

In the 1850’s Mendel studied genetics using controlled breeding in pea plants Peas reproduce quickly.(lots of data to study) Peas have many observable traits. Mendel could control which pairs of plants reproduced.

So how do peas reproduce anyway???

Mendel began his experiments with peas that were true-breeding for a trait. When a true-breeding plant self-pollinates, it always produces offspring with the same traits as the parent.

Then Mendel cross-pollinated plants with traits he selected….. Suppose you cross hundreds of true-breeding purple flowers with hundreds of true-breeding white flowers. Based on the results to the left, would any offspring produce white flowers? Explain.

PP pp Pp Genetics vocabulary: Dominant trait: is a genetic factor that blocks another genetic factor, ex: purple pea flowers Recessive trait: is a genetic factor that is blocked when in the presence of a dominant trait, ex: white pea flowers *Remember*, these traits are inherited as pairs. A pea plant can only have white flowers if it has BOTH factors for white flowers. PP pp Pp

Lesson 2: Understanding inheritance

Understanding Inheritance Based on his work, Mendel concluded that 2 factors (1 from each parent) controlled each trait. We know that these “factors” are genes that are found on a section of a chromosome. The different forms of a gene are called alleles. For ex: height is the gene, tall and short are the alleles.

Genotype and Phenotype Phenotype: the appearance of a trait (how we see it, tall or short) Genotype: the 2 alleles responsible for the phenotype (in this case Aa)

So how do we write a genotype??? Uppercase letters represent dominant alleles, ex: R for round seeds Lowercase letters represent recessive alleles, ex: r for wrinkled seeds

More vocabulary…… Homozygous: the 2 alleles of a gene are identical, RR or rr, for example. Sometimes this is called pure. Heterozygous: the 2 alleles of a gene are different, Rr, for example. Sometimes this is called hybrid.

Probability: the mathematical chance that an event will occur Probability is used to predict possible genotypes and phenotypes of offspring if the genetic makeup of the parents is known. Punnett Squares Offspring have a 50% chance of having Hybrid Unattached earlobes and 50% chance of pure Attached earlobes

Pedigrees Pedigrees show phenotypes of genetically related family members.

Complex Patterns of Inheritance Incomplete Dominance: the offspring’s phenotype is a combination of the parents’ phenotypes.

Complex Patterns of Inheritance, continued Codominance: is when both alleles from the parents can be observed in the offspring…

Complex Patterns of Inheritance, continued Multiple Alleles: some traits are controlled by more than two alleles (for example, human blood types- blood types A & B are codominant with each other but, dominant over recessive type O).

Complex Patterns of Inheritance, continued Polygenic Inheritance: is found often in humans. This is when a trait is determined by many genes. This explains why we have so many different eye colors, skin tones, and heights.

Genes and the Environment Environmental factors, such as temperature, pH, sunlight, diet can affect an organism’s phenotype The flowers below have different colors due to differences in pH of the soil.

Lesson 3

DNA and Genetics DNA is a complex molecule that makes up chromosomes along with proteins. DNA is tightly coiled like a spring so that it can allow many genes to fit in a small space. DNA is double stranded, each strand is a chain of nucleotides. The shape of DNA is called a double helix.

Four Nucleotides Shape DNA A nucleotide is a subunit of DNA consisting of a nitrogen base, a sugar, and a phosphate group.

The 4 different bases are: Adenine or A Cytosine or C Thymine or T Guanine or G A always bonds with T C always bonds with G

Replication: is how DNA makes a copy of itself This happens every time a cell divides and all the chromosomes are copied for the new cell.

RNA: the nucleic acid that carries the code for making proteins. RNA is single stranded, unlike DNA. RNA does not have the base, thymine. It has the base, uracil, instead. RNA has the sugar, ribose – not deoxyribose.

Transcription: the process of making RNA from DNA DNA unwinds and a single strand provides the code of bases for the RNA Complementary RNA nucleotides pair up with the DNA strand

Transcription: the process of making RNA from DNA The sequence (order) of bases in the DNA determines the sequence of bases in the RNA Once the RNA is made, it moves from the nucleus to the cytoplasm

Transcription: Notice how the RNA has U not T for its nucleotides.

Translation: how the RNA code is used to make proteins The order of the bases in the RNA determines the order of the subunits of proteins, amino acids, in the newly made protein

Mutations: changes in the nucleotide sequence of a gene Mistakes can happen during DNA replication. Some mutations are not harmful, many are. The rate of mutations occurring is increased by exposure to x-rays, UV light, radiation, and chemicals.

If a mutation occurs in a sex cell, it will be passed on to the next generation. Mutations are a source of variation that can help populations of a species survive changes in their environments.