Genetics and Heredity Ms. Edwards

Mendel’s Work Heredity- the passing of physical characteristics from parent to offspring. Trait- each different form of a characteristic. Genetics- the scientific study of heredity.

Pea plants are self-pollinating Pollen from a flower lands on the pistil (female part) of the same flower. Mendel “crossed” pea plants by removing pollen from one plant and brushing it onto another. Mendel crossed pea plants with opposite traits (ex: tall and short)

Crossing Pea Plants Purebred- the offspring of many generations that have the same trait (ex: all plants in the “family” are short). P generation = the parents The F1 offspring- first “filial” generation, come from crossing 2 P plants. The F2 offspring- second “filial” generation, come from crossing 2 F1 plants.

Crossing Pea Plants

Crossing Pea Plants In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. In the F2 generation, the “hidden” form of the trait always reappeared in about ¼ of the plants. Mendel’s Conclusions: 1. Individual factors must control the inheritance of traits in pea plants. 2. Those factors exist in pairs (one from male parent, one from female). 3. One factor in a pair can “hide” the other one.

Gene- the factor that controls a trait. Alleles- the different forms of a gene. (ex: tall and short alleles for the “height” gene) One allele for each gene comes from each parent. An organism’s traits are controlled by the alleles it inherits from its parents.

Dominant vs. Recessive Dominant Allele- the one whose trait always shows up in the organism when the allele is present (represented by a capital letter). Recessive Allele- is hidden when the dominant allele is present (represented by a lower case letter). Recessive traits will only show up if two copies of the allele are present.

Probability Probability- a number that describes the likelihood of an event happening. The laws of probability predict what is likely to occur, not what will actually happen. Each event occurs independently of the previous. Punnett Square- chart that shows the possible outcomes of a genetic cross.

Punnett Squares

Phenotypes and Genotypes Phenotype- an organisms’ visible traits. Genotype- an organism’s genetic traits. Homozygous- when organisms have two of the same alleles for a trait (ex: SS or ss). Heterozygous- when organisms have two different alleles for a trait (ex: Ss). Also called hybrids.

Codominance In codominance, the alleles are neither dominant nor recessive. Both alleles are expressed in the offspring.

Meiosis The process by which sperm and eggs are made (the chromosome number is reduced by half). During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting cells have only half as many chromosomes as every other cell in the organisms. Remember PMAT! (from mitosis)

Meiosis - The Cell and Inheritance During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.

Meiosis Important facts: During meiosis I, homologous chromosomes separate. During meiosis II, sister chromatids separate. Crossing over occurs during meiosis I. Creates genetic variability. Click here for a cool meiosis animation!

Punnett Square - The Cell and Inheritance A Punnett square is actually a way to show the events that occur at meiosis.

- The Cell and Inheritance A Lineup of Genes Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

The DNA Code - The DNA Connection Chromosomes are made of DNA. Each chromosome contains thousands of genes. The sequence of bases in a gene forms a code that tells the cell what protein to produce.

The Genetic Code The order of bases on a gene form a genetic code that determines what type of protein will be made. A group of 3 DNA bases is called a codon, and codes for a specific amino acid. Proteins are made of chains of amino acids (chains of proteins).

Making Proteins During protein synthesis, the cell uses information from a gene on a chromosome to make a specific protein. Takes place on the ribosome in the cytoplasm of the cell. Cytoplasm is outside the nucleus, and DNA can’t go outside the nucleus… the cell has a problem!

Mutations - The DNA Connection Mutations can cause a cell to produce a incorrect protein, which can change the organism’s phenotype.

Mutations Mutations can be helpful or harmful. Harmful= reduces organism’s chance for survival and reproduction. Whether a mutation is harmful or helpful depends partly on the organism’s environment. 2 types of mutations 1. single base 2. improper chromosome separation

Patterns of Inheritance Some traits are controlled by single genes with 2 alleles Other traits are controlled by single genes with multiple alleles Some traits are controlled by many genes that act together.

Single Genes with 2 Alleles Controlled by a single gene with one dominant and one recessive allele. Have 2 distinct phenotypes (for example, tall or short) Represented by the typical Punnett Square crosses that we used last chapter.

Single Genes with Multiple Alleles Multiple Alleles- 3 or more forms of a gene that code for a single trait. Even though a gene may have multiple alleles, a person can carry only 2 of those alleles because chromosomes exist in pairs. Example: Human blood types (A, B, AB, O) 3 alleles control blood type (IA, IB, i) - The alleles for A and B are codominant

Inheritance of Blood Type - Human Inheritance Blood type is determined by a single gene with three alleles. This chart shows which combinations of alleles result in each blood type.

Traits Controlled by Many Genes Height is controlled by many genes, which is why there are so many phenotypes for height. At least 4 genes control height in humans. Skin color is also controlled by many genes.

The Sex Chromosomes The sex chromosomes are one of the 23 pairs in each body cell. Sex chromosomes carry genes that determine gender and other traits. The sex chromosomes are the only pair of the 23 that do not always match. - Boys- X Y - Girls- X X All eggs carry X. Half of sperm carry X, the other half carry Y.

The Sex Chromosomes - Human Inheritance The sex chromosomes carry genes that determine whether a person is male or female. They also carry genes that determine other traits.

Sex-Linked Genes Sex-linked genes- those that are on the X and Y chromosomes. Traits controlled by sex-linked genes are called sex-linked traits. Color blindness is a sex-linked trait (carried on the X chromosome, recessive)

Inheritance of Colorblindness Carrier- person who has one recessive allele for a trait and one dominant allele. Carrier of a trait controlled by recessive allele does not show the trait. Carrier can pass trait to offspring. With sex-linked traits, only females are carriers.

Colorblindness Punnett Square - Human Inheritance Red-green colorblindness is a sex-linked trait. A girl who receives only one recessive allele (written Xc) for red-green colorblindness will not have the trait. However, a boy who receives one recessive allele will be colorblind.

Colorblind= yellow circle Color Normal= yellow circle and light brown square

The Effect of the Environment Many characteristics are controlled by interactions between genes and the environment. Environmental factors: diet, practice, exercise.

Human Genetic Disorders Genetic Disorder- abnormal condition that a person inherits through genes. Causes - Mutations in the DNA of genes - Changes in the structure or number of chromosomes. Karyotype- picture of all 23 pairs of chromosomes.

Genetic Disorders Cystic Fibrosis- body produces abnormally thick mucus in lungs and intestines. Makes breathing difficult. Caused by recessive allele on 1 chromosome (3 bases are removed from a DNA strand).

Genetic Disorders Sickle Cell Disease- Affects hemoglobin in RBCs. Causes sickle shape in RBCs Sickled RBCs clog arteries Allele for sickle cell trait is codominant with normal allele Must have 2 sickle cell alleles to have the disease

Genetic Disorders Hemophilia- person’s blood cannot clot properly. Danger of internal bleeding is increased. Caused by recessive allele on X chromosome. Sex-linked, so it occurs more in males than females.

Hemophilia - The Cell and Inheritance Earliest records documenting this disorder date back 2,300 years. Known as the “Royal Disease”. Queen Victoria of England (1819-1901) was an obligatory carrier of the defective gene, consequently passing the gene to the royal houses of Spain, Germany and Russia.

Genetic Disorders Down Syndrome- person has an extra copy of chromosome 21. Most often occurs when chromosomes fail to separate properly during meiosis.

A Pedigree - Human Genetic Disorders A pedigree is a chart or “family tree” that tracks which members of a family have a particular trait.

A Hemophilia Pedigree - Human Genetic Disorders The pedigree shows the inheritance of hemophilia, a sex-linked disorder in a family.

Managing Genetic Disorders Karyotype- picture of the chromosomes; shows if a person has the correct number of chromosomes. Genetic Counseling

Advances in Genetics Selective Breeding- selecting organisms with desired traits to be the parents of the next generation. - Used in food production 2 types of selective breeding: - Inbreeding - Hybridization

Inbreeding Crossing 2 individuals that have similar characteristics. Produces genetically similar individuals. Increases the probability that organisms will inherit alleles that lead to genetic disorders. Example: hip problems in many dog breeds

Hybridization Breeders cross 2 genetically different individuals. Hybrid organism contains the best traits from both parents. Red Delicious + Ralls Genet = Fuji

Cloning Clone- organism that has exactly the same genes as the organism from which it was produced. Dolly was the first cloned mammal (1997).

Genetic Engineering Genes from one organism are transferred into the DNA of another organism. Used in bacteria to produce insulin that is used for diabetic patients’ injections. Also used to create freeze and insect resistant plants

Genetic Engineering - Advances in Genetics Scientists use genetic engineering to create bacterial cells that produce important human proteins such as insulin.

Gene Therapy The use of genetic engineering to correct genetic disorders in humans. Concerns - Long-term effects? - Is it safe? - How does it affect the environment?

Human Genome Project Human genome is 6 BILLION letters long! Genome- all of the DNA in one cell of an organism. Goal of human genome project is to identify the DNA sequence of every gene in the human genome. Took 13 years, completed in 2003. Started by James Watson (he’s 80 now)