Genetics Since Mendel

1. Genetics Since Mendel GLE 0707.4.4 Predict the probable appearance of offspring based on the genetic characteristics of the parents.

2. What You’ll Learn • Explain how traits are inherited by incomplete dominance • Compare multiple alleles and polygenic inheritance, and give examples of each. • Describe two human genetics disorders and how they are inherited. • Explain how sex-linked traits are passed to offspring.

3. Why it’s important! • Most of your inherited traits involve more complex patterns of inheritance than Mendel discovered.

4. I. Incomplete Dominance Chestnut horse • When a pure-bred organism is crossed with another pure bred organism, an intermediate phenotype is created. • The offspring of two homozygous parents – incomplete dominance • examples of this dominance include flower color of some plant breeds and the coat color of some horse breeds. • Figure 5 Cremello horse Palomino horse

5. A. Multiple Alleles Example of Multiple alleles. Blood type example https://www.youtube.com/watch?v=ZU0uiuqUYng 3.33 minutes • Many traits are controlled by more than two alleles. • This trait is said to be controlled by multiple alleles. • And, produce more than three phenotypes of that trait.

6. II. Polygenic Inheritance • Polygenic inheritance – when a group of gene pairs acts together to produce a trait • It produces a wide variety of phenotypes • Example – eye color (lots of genes),skin (3 to 6 genes), height and hair. • The environment – plays a role in expression of traits controlled by polygenic inheritance. • It is common in grain color in wheat, milk production in cows, and egg production in chickens. • https://www.youtube.com/watch?v=gouqTq5p168- 3 minutes

7. A. Impact of the environment • Environmental influence can be internal or external. • Ex. Male birds are colorful, not the females. • A chemical in their body determines the expression of color. • Some people have genes that make them at risk for developing certain cancers • Skin cancer genes • – limit exposure to sun and take care of skin. A person may never get skin cancer. • Figure 6 – • Himalayan rabbits have alleles for dark-colored hair. • This allele is able to be express in low temperatures • only the ears, nose, feet and tail have dark-colored hair.

8. III. Human Genes and Mutations • Sometimes a gene undergoes a change-trait is expressed differently. • Errors occurs in DNA when copied causing mutations. • Certain chemicals can produce mutation in plants or animals, including humans; X-rays and radioactive also causes it. • Chromosomes Disorders Problems can occur in incorrect number of chromosomes In humans, it is usually fatal to unborn embryo or baby after birth. • Ex. Down syndrome (three copies of chromosome 21 are in fertilized egg) • Individual with DS – short, exhibit learning disabilities and heart problems.

9. IV. Recessive Genetic Disorders • Some recessive genes result in mutations within the gene. • Both parents carry the recessive gene (heterozygous); therefore no symptom show. • They can pass on the recessive allele to the childand he or she will have a recessive genetic disorder. • Reading Check: How is cystic fibrosis inherited? • Cystic Fibrosis (production of extremely thick mucus) – homozygous recessive disorder commonly found in Caucasian Americans. • Results in repeated bacterial respiratory infections • Physical therapy, special diets, and new drug therapies increase life span of patients.

10. V. Gender Determination • Genetics used labels when studying organism- • X – female egg ; X or Y – male sperm • Fertilization of both sex cells - causes offspring • Female XX and males offspring XY Sometimes chromosomes don’t separate during meiosis, and the individual can inherit an abnormal number of sex chromosomes. https://www.youtube.com/watch?v=Nrv5yqEMQ4Q 3 min. Figure 8 How do the X (left) and Y (right) chromosomes differ from one another in shape and size?

11. VI. Sex-linked Disorders • A sex-linked gene is an allele on a sex chromosome. • Some conditions from inheriting this gene is called a sex-linked disorder. • Ex. Red-green color blindness-are found on X chromosomes • People have trouble seeing difference between red and green and sometimes yellow. (It is a recessive sex-linked disorder) • Dominant sex-linked disorders are rare and result when a person inherits at least one dominant sex-linked allele. • Vitamin D resistant Rickets – X linked dominant disorder • https://www.youtube.com/watch?v=8OGA4rGDk3M 6:52 min

12. VII. Pedigrees Trace Traits • A pedigree is a visual too for following a trait through generations of a family. • Males = squares & females = circles • Filled circles/squares represent trait seen in person • Half colored circles/squares represent carriers (heterozygous for the trait and it is not seen) • Empty circles or squares do not have the trait nor carriers it.

13. A. Using Pedigrees • A pedigree is a useful tool for a geneticist. • Geneticist need to understand: • Who had a trait through several generations. • If a trait is recessive, dominant, sex-linked or has some other pattern of inheritance. • How a trait is inherited – to predict the probability that a baby will born with a specific trait. • Pedigrees also are import in breeding animals or plants • Use for source of food (increase their yield and nutritional value. • For desired physical and ability traits