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Heredity LN #18 California Content Standard Genetics 2g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup.

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Presentation on theme: "Heredity LN #18 California Content Standard Genetics 2g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup."— Presentation transcript:

1 Heredity LN #18 California Content Standard Genetics 2g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents.

2 What is Meiosis? Meiosis makes SEX CELLS. –Haploid cells –Gametes –Sperm & egg cells Diploid is 2n –All of our body cells are diploid. Haploid is n –ONLY gametes are haploid. += fertilization

3 What is a Phenotype? A phenotype describes what an organism looks like. In order to determine an organisms phenotype you need to look at it. Phenotype = widows peak Phenotype = free earlobes Phenotype = attached earlobes

4 What is a Genotype? A genotype is the combination of genes in an organism. Genes are section of DNA that codes for a trait. Genes are located on chromosomes. Alleles are different forms of a gene. Genes are labeled by using letters. Homologous chromosomes have genes for the same trait. Gene location for earlobes. F free f attached F and f are alleles. Genotype = Ff

5 Who was Gregor Mendel? Mendel carried out the first important studies in heredity. Mendel studied heredity using pea plants. Mendel was the first to develop laws and rules for heredity. One of Mendels rules is the rule of dominance. –Some traits are dominant and others are recessive. (1822 – 1884)

6 Punnett Squares Punnett squares are used to determine the chance of seeing a trait in the offspring. Remember every organism has two copies of a gene. Only one of the two is passed to the offspring. If the genotype of a father is Aa, then he can either pass down A or a.

7 Words to know Monohybrid cross involves studying a single trait. Homozygous means that both alleles are the same. We can have homozygous dominant, TT or homozygous recessive tt. Heterozygous means that the alleles are different from one another. We would have Tt. With the rule of dominance TT and Tt have the same phenotype. The only way to show a recessive trait is to be homozygous recessive, tt.

8 Monohybrid Cross problem Widows peak is a dominant trait (P). A woman homozygous dominant for widows peak marries a man without a widows peak. What are the chances that their children will have a widows peak? Parents genotypePP x pp P P pppp Pp 100% chance that the children will have a widows peak. Pp

9 Summary What is a genotype and phenotype? Who was Mendel? What are Punnett squares used for? What are alleles? How are homozygous and heterozygous different?


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