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04/17/2017 Bill Nye Genes video – Complete the handout as the video plays. What are traits? – A trait is a characteristic that an organism exhibits, such as the shape of your ears or the color of your eyes. – The traits we exhibit are determined by our DNA (an organism’s genetic material) Genetics and Inheritance How does DNA determine what we look like? – All of the DNA in your cells exists as chromosomes. – Chromosomes are tightly coiled strands of DNA that carry genetic information. Ch 12 Genetics Goals – SC.7.L.16.1: Understand and explain that every organism requires a set of instructions that specifies its traits, that this hereditary information (DNA) contains genes located in the chromosomes of each cell, and that heredity is the passage of these instructions from one generation to another. – SC.7.L.16.2: Determine the probabilities for genotype and phenotype combinations using Punnett Squares and pedigrees. – SC.7.L.16.4: Recognize and explore the impact of biotechnology (cloning, genetic engineering, artificial selection) on the individual, society and the environment.. – Every human has 46 individual chromosomes, 23 pairs. 1 04/17/2017 Asexual Reproduction – Each chromosome is made of multiple genes. - In asexual reproduction, one organism makes a copy of itself. - The “daughters” are exact copies of the “parent”. – A gene is a section on a chromosome that has genetic information for one trait. Where do Genes Come From? – All living organisms inherit their genes from their parents through reproduction. Reproduction - There are two ways that organisms can reproduce: - Sexually, with two parents or - Asexually, with one parent - In both forms of reproduction, the parent’s genes are passed from parent(s) to child. Asexual Reproduction - Both multicellular organisms like us, and unicellular organisms like bacteria use mitosis to make new cells. - Mitosis is the process by which one cell divides to make two identical cells. Mitosis: - During mitosis, one cell makes a copy of each chromosome (its DNA ), then it split into two cells. 2 04/17/2017 Mitosis: - Mitosis produces genetic copies of the parent cells. - The “daughter cells” have the same DNA as the “parent cells”. Mitosis: - Unicellular organisms use mitosis to reproduce asexually. - Multicellular organisms use mitosis to grow (by making more cells) and replace old or damaged cells. Mitosis: - Because all new cells are copies of old cells, mitosis DOES NOT increase genetic diversity in a species that uses it to reproduce. Sexual Reproduction - In sexual reproduction, two parents donate half of their DNA to make offspring that are different than themselves. - Child receives ½ of their chromosomes from each parent. - Chromosomes are passed on through sex cells – eggs and sperm known as gametes. How are sex cells (eggs and sperm) made? - Gametes (sex cells) for sexual reproduction are made through a process called meiosis. - Meiosis is the process by which one cell divides to create 4 cells, each with half of the DNA of the original parent. How are sex cells (eggs and sperm) made? - During meiosis, one sex cell doubles its number of chromosomes (DNA) and divides twice so it only has half of the DNA of the original cell. - This makes 4 gametes (eggs or sperm) 3 04/17/2017 Fertilization Inheritance - In order for offspring to form, the gametes of male and female must join and combine their DNA. This process is called fertilization. 1. Traits are passed on from parent to child. 2. Cell nucleus controls inheritance. 3. Genes for traits are on chromosomes and are located inside the nucleus How it Works - The offspring then has a full compliment of DNA and can grow. - Sexual reproduction in this manner is only used by multicellular organisms, like humans. - - - Because the parents donate a mix of their DNA, sexual reproductions increases genetic diversity in a species. Recall that each human has 46 chromosomes. Each chromosome has one other chromosome that carries the same genes as it does. These are homologous chromosomes: pairs of chromosomes (one inherited from each parent) that have genes for the same traits arranged in the same order Humans have 23 pairs of homologous chromosomes. - Homologous chromosomes carry the same genes, but may have different alleles. - An allele is a different form of a gene. 4 04/17/2017 Example: - Chromosome 1 came from the father. - Chromosome 2 came from the mother. - Each chromosome carries the gene for ear shape. - Chromosome 1 has the allele for attached ear lobes. - Chromosome 2 has the allele for free-hanging ear lobes. Gregor Mendel •Austrian Monk that lives in the1800s •He is known as the Father of Modern Genetics •Observed inherited traits. •He asked: Why did some traits found in the parent plants show up in offspring while others did not? •experimented with pea plants ie. Height, color, covering type •Experiments lead to development of the Principals of Genetics WHICH STILL HOLDS TRUE Mendel’s Work - When this child is grown and is ready to pass on their genetic traits, they will pass on either chromosome 1 OR chromosome 2. • In his experiments, Mendel took pollen from the flowers of purebred pea plants to pollinate the flowers of other purebred pea plants by using a paint brush to transfer the pollen. • This process is called crosspollination. How did we discover genes and how they are passed on? https://www.youtube.com/watch?v=Mehz7tCxjSE Why Peas? Mendel’s Work Pea flowers are constructed in such a way that they typically self fertilize. Because of this, it is relatively easy to control crosses in peas. 5 04/17/2017 Crossing Pea Plants Mendel’s Work Gregor Mendel crossed pea plants that had different traits. Crossing Pea Plants Mendel’s Work Mendel’s Work In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants. Mendel’s Experiments Mendel’s Work • F1 generation was a cross between a pea plant with purple flowers and a pea plant with white flowers. • All plants of the F2 generation had purple flowers. • He bred the F2 generation plants together and found that ¼ of the plants had white flowers. The illustrations show how he did this. Mendel’s Experiments Mendel’s Experiments Mendel’s Work - Mendel called the original purebred parent plants the P1 generation. - The offspring were called the F1 generation. - He then crossed (bred) the F1 generation together. This produced the F2 generation. Dominant and Recessive Factors • Mendel called the purple flower form the dominant (DAH muh nunt) factor because it dominated, or covered up, the white flower form. • He called the form that seemed to disappear the recessive (rih SE sihv) factor. Click image to view movie. 6 04/17/2017 Dominant and Recessive Alleles - Mendel’s Work Mendel studied several traits in pea plants. Mendel's observations from these experiments can be summarized in two principles: 1. the principle of segregation - for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance. 2. the principle of independent assortment - different pairs of alleles are passed to offspring independently of each other. The result is that new combinations of genes present in neither parent are possible. Law of Independent Assortment • When Mendel crossed peas and looked at two different traits, he discovered that the traits assorted independently • In other words, if he was looking at the height of the plants and the color of the flowers, all four possible combinations of height and flower color were produced: • Tall Purple • Tall white • dwarf Purple • dwarf white Other things •Pure trait – inherits 2 of same gene = homozygous •Hybrid – inherits 1 dominant and one recessive = heterozygous •No organism is pure in every trait. An individual is a mix of pure and hybrid. Genotype - what the 2 alleles are Phenotype – what the organism looks like Menedel’s Law of Dominance: 1. An organism receives 2 genes for each trait. One from each parent. 2. One of the genes may be stronger than the other. The trait of the stronger is expressed. 7