Section 6.5
description
Transcript of Section 6.5
![Page 1: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/1.jpg)
1
Section 6.5
Traits and Probability
![Page 2: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/2.jpg)
2
Objectives
• SWBAT describe what a monohybrid and dihybrid crosses are.
• SWBAT explain how heredity can be illustrated mathematically
![Page 3: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/3.jpg)
3
Vocabulary
• Punnett square• Monohybrid cross• Dihybrid cross• Testcross • Law of independent assortment• Probability
![Page 4: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/4.jpg)
4
Punnett Squares• Punnett squares illustrate genetic crosses.
• The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.– The axes represent
the possible gametesof each parent.
– The boxes show thepossible genotypesof the offspring.
• The Punnett square yields the ratio of possible genotypes and phenotypes.
![Page 5: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/5.jpg)
5
Punnett SquaresA monohybrid cross involves one trait.
• Monohybrid crosses examine the inheritance of only one specific trait.– homozygous dominant-
homozygous recessive: all heterozygous, all dominant
![Page 6: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/6.jpg)
6
Punnett Squares
Heterozygous X heterozygous cross results in 1:2:1 genotypic ratio.
Phenotypic ratio is 3:1 dominant to recessive
![Page 7: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/7.jpg)
7
Punnett Squares
• Heterozygous X homozygous recessive results in a genotypic ratio of 1:1
• Heterozygous X homozygous recessive results in a phenotypic ratio of 1:1 dominant to recessive
![Page 8: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/8.jpg)
8
Dihybrid Cross: 2 Traits
• Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio.
• Mendel’s dihybrid crosses led to his second law,the law of independent assortment.
• The law of independent assortment states that allele pairs separate independently of each other during meiosis.
![Page 9: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/9.jpg)
9
Heredity patterns calculated with probability.
• Probability is the likelihood that something will happen.
• Probability predicts an average number of occurrences, not an exact number of occurrences.
• Probability = number of ways a specific event can occurnumber of total possible outcomes
• Probability applies to random events such as meiosis and fertilization.
![Page 10: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/10.jpg)
10
Probability
![Page 11: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/11.jpg)
11
Phenotype can depend on interactions of alleles.
• In incomplete dominance, neither allele is completely dominant nor completely recessive.– Heterozygous phenotype is intermediate between the two
homozygous phenotypes– Homozygous parental phenotypes not seen in F1 offspring
![Page 12: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/12.jpg)
12
Many genes have more than two alleles.
![Page 13: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/13.jpg)
13
Polygenic Traits
Polygenic traits are the result of two or more genes interacting. They are expressed as gradations.
Human height is a polygenic trait.
![Page 14: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/14.jpg)
14
Polygenic Traits
Skin color is a polygenic trait.
![Page 15: Section 6.5](https://reader035.fdocuments.us/reader035/viewer/2022062501/56816720550346895ddba22d/html5/thumbnails/15.jpg)
15