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Not-so-Simple Inheritance Patterns. Remember… Genes are sections of a chromosome that have coded instructions for making proteins. Alleles are different.

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Presentation on theme: "Not-so-Simple Inheritance Patterns. Remember… Genes are sections of a chromosome that have coded instructions for making proteins. Alleles are different."— Presentation transcript:

1 Not-so-Simple Inheritance Patterns

2 Remember… Genes are sections of a chromosome that have coded instructions for making proteins. Alleles are different forms of a gene.

3 Simple Inheritance 2 alleles 2 phenotypes One allele is dominant The other allele is recessive The DOMINANT allele completely masks the recessive allele

4 Mendel Got Lucky In many ways Gregor Mendel was quite lucky in discovering his 4 genetic laws. He happened to use pea plants. Things in nature arent always so simple.

5 Not-so-Simple Inheritance 4 Main Types –Codominance –Incomplete Dominance –Multiple Alleles –Polygenic Traits

6 Codominance Co means together! Codominance = two alleles are dominant together. This produces a third heterozygous phenotype where BOTH traits are expressed TOGETHER Ex: Human Blood Type –A–A –B–B –O–O –AB Red Cow x White Cow Roan Cow Roan cattle have both red and white hairs mixed in together!

7 Codominance red x white red & white spotted

8 8 Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals.Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood typeExample: blood type 1.type A= I A I A or I A i 2.type B= I B I B or I B i 3.type AB= I A I B 4.type O= ii copyright cmassengale

9 9 Codominance Problem Example: homozygous male Type B (I B I B ) x heterozygous female Type A (I A i) IAIBIAIB IBiIBi IAIBIAIB IBiIBi 1/2 = I A I B 1/2 = I B i IBIB IAIA i IBIB copyright cmassengale

10 10 Another Codominance Problem Example:Example: male Type O (ii) x female type AB (I A I B ) IAiIAiIBiIBi IAiIAiIBiIBi 1/2 = I A i 1/2 = I B i i IAIA IBIB i copyright cmassengale

11 11 Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (I A I B ) copyright cmassengale

12 12 Codominance Answer:Answer: IAIBIAIB ii Parents: genotypes genotypes = I A i and I B i phenotypes phenotypes = A and B IBIB IAIA i i copyright cmassengale

13 Incomplete Dominance Incomplete Dominance = neither of the two alleles is completely dominant This produces a third heterozygous phenotype where the traits are BLENDED. Amel & Ultra are incompletely dominant to each other. Amel x Ultra Ultramel

14 Incomplete Dominance red flower x white flower PINK flower

15 Multiple Alleles Any of a set of three or more alleles. Only two of alleles can be present in a diploid organism. Examples: –Human Blood Type –Human skin, hair, and eye colors

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17 Polygenic Traits Result of the interaction of several genes Human skin, hair, and eye color –Influenced by more than one gene at different locations on the chromosomes Human Blood Pressure –Not just 1 blood pressure gene with several alleles –Caused by several genes that control other traits such as weight, cholesterol level, kidney function, etc… Human Height –The combined size of all of the body parts from head to foot determines the height of an individual.

18 Role of Environment Our environment also plays a key role in how traits are expressed. Genes can be turned on/off due to external environmental factors. Examples: –Stress –Nutrition –Chemical exposure –Light –Temperature

19 Example of Environmental Influence Human Height is heavily influenced by hormones produced in the pituitary gland and our diet during childhood and puberty. Usually, about 10% of an individual's height is due to the environment.

20 Sample Questions 1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. 2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

21 Sample Questions 3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritance does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

22 Sample Questions 1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver. The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

23 Sample Questions 2. The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?


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