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Transcript
Chapter 11 – Section 1 Heredity Open your book to page 306 Please take notes on your graphic organizer. Notes will be on the yellow slides. Heredity Who do you look like? Mom, dad, grandma? You could have your dad’s eyes and your mom’s cheekbones. As an organism, we are nothing more than a collection of traits. These traits are passed down from our parents. Heredity – the passing of traits from parent to offspring. Genetics Genetics has to do with our chromosomes and the genes that exist on our chromosomes. Because you come from two parents (each provides you with 23 chromosomes for a total of 46), each parent will provide one half of your genes for any trait. That is called an "allele.“ So you have two alleles for each gene, one from each parent. Allele – the different forms of a trait that a gene may have Genetics – the study of how traits are inherited through the interactions of alleles Gregor Mendel Father of Genetics Gregor Mendel was an Austrian monk who studied math and science, but became a gardener in a monastery. In 1856, Mendel experimented with pea pod plants because he was curious about the connection between the color of a pea flower and the type of seed that same plant produced. Mendel worked over eight years with pea plants before he was able to share his results with other scientists. Mendel was the first to trace one trait through several generations. He was the first to use probability to explain heredity. The use of math in science was not widely accepted in this time period. In 1900, three other scientists solidified Mendel’s work as they performed their own experiments and came up with the same conclusion. Since then, Mendel is known as the Father of Genetics Each time Mendel performed an experiment in his garden, he crossed two plants with different expressions of the trait and found that the new plants all looked like one of the two parents. He started out experimenting with tall and short pea pod plants. Mendel took pollen from tall plant and hand pollinated this pollen onto a short plant. He wanted to know what the offspring would look like…Tall, short, or would they be a medium height. The first generation of plants (the offspring) were tall. He performed the experiment again with the offspring and got three tall plants and one short plant. Mendel called the “Tall” trait the dominant allele, because it dominated, or covered up the “short” trait. Mendel called the “short” trait the recessive allele because the trait seemed to disappear. Dominate traits are always represented with a capital letter. So a tall plant would be represented with a capital T. =T Recessive traits are always represented with a lowercase letter. So a short plant would be represented with a small t. =t Since Mendel’s death, other scientists have performed many of Mendel’s experiments coming up with the same results. Let’s Take Some Notes… Heredity – the passing of traits from parent to offspring. You get 23 chromosomes from your mom and 23 from your dad. Each chromosome contains genes, and on each gene are two alleles. Alleles contain your traits. Let’s Take Some Notes… Alleles - the different forms of a trait that a gene may have – they determine the traits you receive Mendel – called the Father of Genetics He worked with pea plants to investigate how traits were passed from one plant to another Let’s Take Some Notes… Dominate Alleles – Covers up and dominates the other trait (always a capital letter) Recessive Alleles – the trait that seems to disappear (always a lower case letter) Probability Probability helps you to predict the chances of something happening. Mendel used probability to make predictions of his pea plants. In order to make accurate predictions, Mendel used over 30,000 plants over an eight-year period to gather enough data to draw a conclusion. Punnett Squares Punnett squares are used to predict what traits an offspring of two parents may look like. Letters represent the dominant and recessive alleles. An uppercase letter represents the dominant allele. A lowercase letter represents the recessive allele. Making a Punnett Square Each parent will have two Mom goes on top T alleles for each trait. The two alleles for your mom would run across the top of the square, and dad’s traits would run along the side. Let’s say mom carries two dominant traits for tall (T) and dad carries two recessive traits for short (t). t t T Mom is top, Dad is down the side! Now we just fill in the square. Follow the white lines first for the top two squares, then follow the green lines to get the two bottom squares Since T is dominate for being tall, all four offspring will be tall. The dominate T covers up the recessive t allele. T T Tt Tt t t Tt Tt Let’s practice again.. Mom goes on top Mom is dominate for brown eyes (B) Dad is recessive for blue eyes (b) Notice I use the same letter for the alleles. The only difference is one is capital and the other is lowercase B b b B Let’s practice again.. Mom goes on top Mom is dominate for red feathers (A) Dad is recessive for blue feathers (a) What will there four offspring look like? What percent chance do we have that the kids will have red feathers? A a a A A Let’s practice again… Mom carries a dominant trait for curly hair (C) AND a recessive trait for straight hair (c). Dad carries two recessive traits for straight hair (c). What will their offspring look like? What percentage will have curly hair? What percentage will have straight hair? Mom goes on top C c c c Mom is recessive for brown fur (b) Dad is dominant for gray fur (B) Notice Dad is on top of the square. It doesn’t really matter which parent goes on top and which goes on the side. It will work out the same. For this class, we will always put the mother on top Dad is on top Genotype The two letter code for each T T t Tt Tt t Tt Tt offspring is called a genotype. For example, Tt is the genotype for all four offspring. This is a genotype Phenotype The description for each two T T t Tt Tt t Tt Tt letter code for each offspring is called a phenotype. For example, if I were to describe each offspring I would say that all of the offspring will be tall. Describing an offspring as being tall is stating its phenotype. Let’s put it together! Mom goes on top Mom carries two recessive alleles for blonde hair (b). Dad carries a dominate allele for black hair (B) and a recessive allele for blonde hair (b). What percentage of their offspring will have blonde hair? What percentage of their offspring will have black hair? b B b b There is a 50% chance the babies will have blonde hair and a 50% chance the babies will have black hair. Mom goes on top b b B Bb Bb b b b b b What are the possible genotypes? Bb, bb What are the possible phenotypes? Black hair, blonde hair Let’s Take Some Notes… Punnett Squares Punnett squares are used to predict what traits an offspring of two parents may look like. Letters represent the dominant and recessive alleles. An uppercase letter represents the dominate allele. A lowercase letter represents the recessive allele. Let’s Take Some Notes… The letters form a code of the genotype, or the genetic makeup of an organism. Phenotype – the way an organism looks and behaves as a result of its phenotype (the way an organism looks) Homozygous When the two letter code (the genotype) is the same, we say that the pair is homozygous. “Homo” means the same Examples – BB, bb It doesn’t matter if the code is two dominant alleles (BB) or two recessive alleles (bb) as long as they are the same. Purebred A purebred is the same thing as a homozygous pair. For example – if you have a black lab and you breed the dog with another black lab, the dog would be a purebred because both parents have the same alleles. Heterozygous When the two letter code (the genotype) is different, we say that the pair is heterozygous. “Hetero” means different Examples – Bb Hybrid A hybrid is the same thing as a heterozygous pair. For example – if you have a poodle and breed it with a golden retriever, the dog would be a mix of the two. The alleles from each parent are different. Hybrid You may have heard of hybrid cars. These cars run on both gasoline AND a battery. They are called hybrids because they run on both. One could assume that an all gasoline car could be called a purebred (this is a joke of course!) Let’s Take Some Notes… Homozygous – an organism that has two alleles that are the same (BB or bb) Heterozygous – an organism that has two different alleles for a trait (Bb) Hybrids – when an organism receives different alleles from each parent (Example - Bb) Purebred - An organism that always produces the same traits generation after generation. (Example – BB or bb)