1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel The study of how characteristics are transmitted from parents to offspring is called genetics.

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued Mendel’s Methods –Mendel used cross-pollination - pollen is transferred between flowers of two different plants.

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions Recessive and Dominant Traits –Inherited characteristics are controlled by pairs of genes. –One factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heterozygous and Homozygous Homozygous - the individual has two of the same alleles. –Can have two dominant traits (YY) or two recessive traits (yy) Heterozygous – the individual has one dominant and one recessive allele.

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Support for Mendel’s Conclusions Alleles - alternative forms of a gene. One allele for each trait is passed from each parent to the offspring.

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued The Law of Segregation –The law of segregation states that a pair of factors is separated during the formation of gametes. Each sex cell has half of the genes that control a trait.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued The Law of Independent Assortment –The law of independent assortment states that genes are distributed to gametes independent of one another. Only for genes on separate chromosomes. Ex: hair color and eye color aren’t “partnered up”

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Genotype and Phenotype The genotype is the genetic makeup of an organism. The phenotype is the appearance of an organism.

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Probability Probability is the likelihood that a specific event will occur. A probability may be expressed as a decimal, a percentage, or a fraction.

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses A Punnett square can be used to predict the outcome of genetic crosses. A cross in which one characteristic is tracked is a monohybrid cross.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued A testcross can be used when the phenotype expresses the dominant trait. The tested organism could be YY or Yy It is crossed with a known recessive, yy If all offspring show the dominant trait, the tested organism is YY. If a few offspring show recessive traits, the tested organism is Yy

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Complete dominance occurs when heterozygous and dominant homozygous look the same. YY and Yy look alike. Eye color

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Incomplete dominance occurs when two or more alleles influence the phenotype and results are between the dominant trait and the recessive trait. A white rose and a red rose make a pink rose.

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring. Blood type; a person with type AB has an A allele and a B allele.

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Genetic Crosses Chapter 9 Predicting Results of Dihybrid Crosses A cross in which two characteristics are tracked is a dihybrid cross.