Ch. 23- Pattern of Gene Inheritance

1. Ch. 23- Pattern of Gene Inheritance Ch. 23.2- Pedigree Analysis & Genetic Disorders

2. Target #17- I can describe the layout & purpose of a pedigree • Many human disorders are genetic in origin • Genetic disorders are medical conditions caused by alleles inherited from the parents • Diagrammed in a pedigree • Pedigree: a chart of a family’s history with regard to a particular genetic trait • Males are designated as squares • Females are designated as circles • A line between a square and a circle represents a mating • A vertical line going downward leads to a child of the mating • Child are listed in age from left to right • Generations are identified with a roman numeral • Purpose of a pedigree is to follow the inheritance pattern of a particular trait • Affect individuals are usually shaded

5. Target #18- I can identify the genotypes of a pedigree

8. Autosomal recessive disorders • Can be carried by the parents, and expressed by the child • Parents are heterozygous for disorder • Examples • Cystic fibrosis • Tay-Sachs • Sickle-cell anemia • Autosomal dominant disorders • Can be expressed by parents if they are heterozygous and not passed to the child • Examples • Marfan Syndrome • Huntington disease Target #19- I can differentiate between autosomal recessive and autosomal dominant disorders

11. Ch. 23- Patterns of Gene Inheritance Ch. 23.3- Complex inheritance Patterns

12. Target #20- I can describe incomplete dominanceTarget #21- I can describe codominance • Incomplete Dominance • Occurs when the heterozygote is intermediate between the two homozygotes • Example • A straight haired parent and a curly haired parents will produce a wavy haired child • Codominance • Occurs when alleles are equally expressed in a heterozygote • Occurs when multiple alleles are present also • Example • Human blood type

13. Multiple Allele Inheritance • When a gene exists in more than two forms • Each person still has only two alleles • Blood types • Three alleles control the inheritance of blood type • IA, IB, i • IA and IB are dominant over I • 4 possible blood types • A, B, AB, and O Target #22- I can explain multiple allele inheritance

14. Sex-linked traits • Aka: X-linked traits

15. Target #23- I can describe polygenic traits • Polygenic traits • Characteristics that are influenced by several different genes • Show degrees of variation • Example: skin color • There are between 3 and 6 genes that control skin color • Controls the production of melanin • The more melanin produced, the darker the skin

16. Ch. 23- Patterns of Gene Inheritance Ch. 23.4- Environmental INfluences

17. An organism’s genotype is not the only thing responsible for the phenotype of the organism • Many phenotypes are influenced by the environment • Examples • Skin color • Can be both polygenic and complex • Exposure to sunlight generally causes the skin to become darker, no matter the genotype • Height • Controlled by an unknown number of genes that influence skeleton growth • Influenced by environmental factors like nutrition and disease Target #25- I can explain how the environment can cause changes in the phenotype and provide an example

18. Target #26- I can describe examples of how the environment affects phenotypes of organisms • The Arctic Fox • When the outside temperature is warm the hair is made with dark pigment • When it is cold the hair is made with no pigment

19. Target #26- cont. • Himalayan Rabbit • This rabbit has white fur with black fur on its ears, nose and tail • A scientist conducted an experiment to determine the effect of environment on the color of fur of a Himalayan rabbit. • The scientist shaved an area of hair on the back of each rabbit, then placed an ice pack over the shaved area on one rabbit

20. Target #26- cont. Black pigment is deposited in fur when the temperature falls below 330C When hair is shaved and an ice pack is placed in the area, the new fur will grow in black

21. Target #27- I can explain the conclusions made about the environmental influence on phenotype using twin studies • A twin study is a kind of genetic study done to determine heritability. • Some researchers believe that since identical twins have identical genotypes, any differences between them are solely due to environmental factors. • Basic info • Identical twins have identical genes • They share DNA but not fingerprints • Have identical brain-wave patterns • Occur once in every 254 births

22. Target #27- cont. • By examining the how twins (especially twins raised apart) are different, a study may determine the extent that a particular trait is influenced by genes or the environment. • Example • Jim Springer and Jim Lewis are identical twins that were separated four weeks after birth • They were reunited 39 years later!

24. Target #27- cont. • The “Jim Twins” shared many things: • They had first wives named Linda and second wives named Betty • They both named their sons “James Allen” • They drove the same model and color car • They both chewed their fingernails • They got headaches the same time of day • They enjoyed mechanical drawing and carpentry • They were good at math but failed spelling in school Other twin studies

25. Target #27- cont. • Conclusions • The environment molds your personality, but your genes determine what kind personality traits you have to start with • Since the early 1960s, several twin studies have reported that identical twins reared apart are actually more alike than those raised in the same home • By studying identical and fraternal twins and their families, we can estimate how genes and environment interact to influence character, strengths, vulnerabilities, and values.