Chapter 11

11-1 What is genetics? The scientific study of heredity

Gregor Mendel Born in 1822 in Czechoslovakia. Became a monk at a monastery in Taught biology and had interests in statistics. Also studied at the University of Vienna

continued Between 1856 and 1863 he grew and tested over 28,000 pea plants

Mendel’s Peas Easy to grow. Easily identifiable traits Can work with large numbers of samples

Mendel’s experiments The first thing Mendel did was create a “pure” generation or true-breeding generation. He made sure that certain pea plants were only able to self pollinate, eliminating unwanted traits. He did this by cutting away the stamen, or male part of each flower

Genes and dominance Trait : a characteristic Mendel studied seven of these traits After Mendel ensured that his true- breeding generation was pure, he then crossed plants showing contrasting traits. He called the offspring the F1F1 generation or first filial.

What will happen when pure yellow peas are crossed with pure green peas? All of the offspring were yellow. Hybrids = the offspring of crosses between parents with contrasting traits

What did Mendel conclude? Inheritance is determined by factors passed on from one generation to another. Mendel knew nothing about chromosomes, genes, or DNA. Why? These terms hadn’t yet been defined.

What were Mendel’s “factors” The ‘factors” that Mendel mentioned were the genes. Each gene has different forms called alleles Mendel’s second principle stated that some alleles are dominant and some are recessive.

Mendel’s second cross He allowed the F 1 generation to self- pollinate thus producing the F 2 generation. Did the recessive allele completely disappear? What happened when he crossed two yellow pea hybrid (F 1 ) plants?

Results: ¾ of the peas were yellow, ¼ of the peas were green. During the formation of the sex cells or gametes, the alleles separated or segregated to different gametes. (pollen and egg)

11-2 Probability The likelihood of a particular event occurring. Chance Can be expressed as a fraction or a percent. Example: coin flip.

Punnett Square Developed by Reginald Punnett. A diagram used to show the probability or chances of a certain trait being passed from one generation to another.

Reading Punnett squares Gametes are placed above and to the left of the square Offspring are placed in the square. Capital letters (Y) represent dominant alleles. Lower case letters (y) represent recessive alleles.

Punnett square example

Homozygous = when an organism possesses two identical alleles. ex. YY or yy Heterozygous = when an organism possesses different alleles. ex. Yy

Phenotype vs genotype Genotype  The genetic makeup  Symbolized with letters  Tt or TT Phenotype Physical appearance of the organism Expression of the trait Short, tall, yellow, smooth, etc.

Probability and statistics No one event has a greater chance of occurring than another. You cannot predict the precise outcome of an individual event. The more trials performed, the closer the actual results to the expected outcomes.

Punnett square review:

11-3 Independent Assortment The two factor cross. Example: color and shape of peas. F 1 cross to produce the F 2 generation Ex RRYY x rryy Round yellow mated with wrinkled green Offspring would all be hybrid for both traits (RrYy)

What is independent assortment? Alleles separate independently during the formation of gametes.

The dihybrid cross Punnett square on board:

Some exceptions to Mendel’s principles: Some alleles are neither dominant nor recessive. Many traits are controlled by more than one gene (polygenic traits)

Incomplete dominance A situation in which neither allele is dominant. When both alleles are present a “new” phenotype appears that is a blend of each allele. Alleles will be represented by capital letters only.

Japanese four-o-clock flowers Red flower plant genotype = RR White flower plant genotype = WW Pink flower plant genotype = RW

What happens when a red flower is crossed with a white flower? According to Mendel either some white and some red or all offspring either red or white. All are pink

Codominance When two alleles both appear in the phenotype. Usually signified using superscripts. example: color of hair coat in cattle. c r c r = red hairs c w c w = white hairs c r c w = roan coat (mixture of both colors)

Roan cattle inheritance

Multiple allele inheritance – Blood Types When two or more alleles contribute to the phenotype. Human blood types: A,B,O and AB A and B are codominant to each other. Both A and B are dominant over O.

Human Blood types: Type A TYPE A Allele = I A Blood cells have small antigens on the surface.

Human Blood types: Type B TYPE B Allele = IBIB Cells coated with type B antigens

Human Blood types: Type AB TYPE AB genotype = IAIBIAIB Blood cells contain both types of antigens Known as universal recipient

Human Blood types: Type O TYPE O Allele = i No antigens on the surface of the blood cells Known as universal donor

6 different genotypes IAIAIAIA IAIBIAIB IBIBIBIB IBiIBi IAiIAi i i Type A AB Type B B A O

How common are the different blood types?

Sample Problem: A man with type AB blood marries a woman with type B blood whose father has type O blood. What are the chances that they have a child with type A blood? Type AB?

Polygenic traits Traits controlled by two or more genes. Examples: Human height, eye and skin color

11-4 Meiosis A method of cell division similar to mitosis. 2 main differences: 1. There are two divisions to produce 4 daughter cells 2. The cells produce contain ½ the chromosomes as the original cell

Chromosome number All cells of an organism contain a specific number of chromosomes. Most cells are diploid (2n) meaning they have two copies of each chromosome

Events of Meiosis I During prophase I, each chromosome pairs with its homologous chromosome to form a tetrad

Crossing-Over Crossing-over: an exchange of genetic material between sister chromatids Results in greater variation

Meiosis II Neither cell replicates its chromosomes. Each cell splits (similar to mitosis) Produces four daughter cells. Animation

Gametogenesis Literally means “creation of gametes” Egg and sperm

2 types: Spermatogeneis & Oogenesis

Net result: Spermatogensis 4 mature sperm Each sperm has exactly half the number of chromosomes as the father. Oogensis 1 mature ova or egg. Each egg has exactly half the number of chromosomes as the mother.

11-5 Gene Linkage Are genes “linked” to each other on chromosomes? Morgan found that many genes are linked together. It was determined that chromosomes, not genes, assort independently during meiosis.

Gene Maps First developed by Sturtevant in The farther apart two genes are, the more likely they will be separated in meiosis.

Transcription – Translation to Protein Synthesis

Transcription – overview

Genetic Code = triplets in DNA=the amino acids in proteins

There are twenty different amino acids that build proteins There are 64 different triplets/codons Each amino acid is coded for by more than one triplet/codon

Translation-Overview

The Players mRNA:messenger RNA - carries protein recipe from the nucleus tRNA: transfer RNA -brings amino acids to the ribosome Ribosome: the site of protein synthesis - made of rRNA (ribosomal RNA ) and Protein

The Process of Translation mRNA takes recipe to the ribosome in cytoplasm ribosome attaches to the mRNA

Translation The ribosome moves along the mRNA until it reaches the “Start” codon Start codon = AUG signals the start of the recipe AUG also codes for the amino acid methionine

The process of Translation A molecule of transfer RNA brings the amino acid called for by the mRNA to the ribosome transfer RNA = tRNA

The process of Translation A second tRNA brings the second amino acid to the ribosome The amino acids are joined together to begin the protein

THE PROCESS OF TRANSLATION CONCLUDED The ribosome moves over 1 codon and another tRNA molecule brings another amino acid The process continues until the stop codon on the mRNA is reached -the stop codon = the end of the protein recipe

Meet tRNA each molecule of tRNA carries a specific type of amino acid - each tRNA molecule can only carry one type of amino acid The tRNA has a group of 3 nucleotides at the base called the anticodon

How does tRNA know which amino acid goes where? The anticodon on tRNA is complementary to a mRNA codon the amino acid that a tRNA molecule carries is the amino acid that the complementary mRNA codon codes for Example: mRNA codon = GAC = aspartic acid tRNA anticodon = CUG carries only aspartic acid

What’s What?

Making the building(protein)