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Ch 11 Complex Patterns of Inheritance. 11.1 Basic Patterns of Human Inheritance Main Idea – The inheritance of a trait over several generations can be shown in a pedigree. Recessive Disorders. Simple recessive heredity is the cause of most genetic disorders.
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Ch 11 Complex Patterns of Inheritance 11.1 Basic Patterns of Human Inheritance Main Idea – The inheritance of a trait over several generations can be shown in a pedigree.
Recessive Disorders • Simple recessive heredity is the cause of most genetic disorders.
A recessive trait is expressed when the individual is homozygousrecessive for the trait. Therefore, those individuals with at least one dominant allele will NOT express the recessive trait. An individual who is heterozygous for a recessive disorder is called a carrier.
The following chart shows simple recessive human disorders. • Remember an individual must inherit a recessive allele from each parent in order to have this disease.
Recessive disorders are more common because carriers (heterozygous alleles) do not display the disorder so they don’t realize they could pass it on to offspring.
Dominant Traits/Disorders • These disorders are caused by the presence of a single dominant allele to be expressed in an individual. (fewer in number because if the trait interferes with survival, that individual is less likely to pass the gene to the next generation.)
5. Examples of simple dominant traits. hitchhiker’s thumb, tongue rolling, free earlobes
Dominant Traits • Six fingers or six toes - polydactyly
Girl in Burma with many digits Total fingers and toes = 26 6 fingers on each hand = 12 7 toes on each foot = 14
Tongue rolling and Ear lobes Free vs. attached
Widow’s Peak Hitchhiker’s thumb
6. Huntington’s Disease is a dominant inherited disorder that affects the CNS (central nervous system) and is fatal/lethal. It does not occur until between the ages of 30-50. A person with this disease has a 50%chance of passing it on to his/her children.
Achondroplasia (dwarfism) – 75% of individuals are born to parents of normal size. Therefore, the condition occurred because of a newmutationor genetic change.
Dominant disorders are caused by the presence of a single dominant allele.Therefore, those that do not have the disorder are homozygous recessive for the trait.
8. Apedigree is a family tree of inheritance used to predict disorders in future offspring. 9. In a pedigree, a circlerepresents a female and a square represents a male. 10. Horizontal connecting lines indicate parents. Vertical lines that drop down between the parents represent offspring. 11. Roman numerals (I, II, III, IV) indicate the generations.
12. Arabic numbers (1, 2, 3, 4) indicate individuals. 13. The trait being studied is represented by ashaded circle or square. 14. Acarrier is a heterozygous individual that carries the trait but does not show the trait phenotypically. 15. In a pedigree, a carrier is represented by a ½ shaded circle or square.
Achondroplasia pedigree Dominant Disorder
Generation I Generation II Generation III Generation IV White = Tall Dominant Black = Short Recessive Male Female
Generation I Generation II Generation III White = Tall Dominant Black = Short Recessive Male Generation IV Female 1. How many generations are shown in the pedigree?
Generation I Generation II Generation III White = Tall Dominant Black = Short Recessive Male Generation IV Female 2. How many offspring did the parents in the first generation have?
Generation I Generation II Generation III White = Tall Dominant Black = Short Recessive Male Generation IV Female 3. What does the square in generation I stand for? Why is it half shaded?
Generation I Generation II Generation III White = Tall Dominant Black = Short Recessive Male Generation IV Female 4. Which dog was the first in the family to be short?
Generation I Generation II Generation III White = Tall Dominant Black = Short Recessive Male Generation IV Female 5. A female dog from generation III has four puppies. How many of these offspring carry (are carriers for) the short trait? How many of the offspring are short?
6. How many roosters (males) lacked the trait being studied?
Inbreeding • May result in a far higher phenotypic expression of harmful recessive genes • increases the chances of passing harmful recessive traits to the next generation. • Selective breeding is a process to produce organisms with desired/favorable traits.
10. If your answer to question 9 is “yes” can you explain the results of the inbreeding? How does this relate to selective breeding?
Making A Pedigree Draw a pedigree that traces eye color for three generations. Assume that green eye is dominant and the blue-eye trait is recessive. The mother in generation I is homozygous recessive, and the father is homozygous dominant. Indicate the generation number and individual number.
John Jones, a green-eyed man, marries Jill Smith, a blue-eyed woman. John and Jill have four green-eyed children: John Jr., Alice, Lisa, and Sean. John Jr. later marries blue-eyed Pamela, and they have four children: Jessica, Shari, Mary, and John III. Shari and Mary both have green eyes, Jessica and John III have blue eyes. Sean marries Robin, a blue-eyed woman. Both of Robin’s parents have blue eyes also. Sean and Robin have four children: Nicholas, Harry, Donna, and Sean Jr. Nicholas, Harry, and Donna all have green eyes. Sean Jr. has blue eyes.
G = green eyes g = blue eyes GG gg gg gg I II III Robin’s mother John Robin’s father Jill gg Gg Gg Gg Gg gg Pamela John Jr. Alice Lisa Robin Sean gg Gg Gg gg Gg Gg Gg gg Mary Jessica Shari Nicholas Harry Donna Sean Jr. John III
Draw a pedigree that traces the trait for green eyes for three generations. GG gg gg gg I II III gg Gg Gg Gg Gg gg gg Gg Gg gg Gg Gg Gg gg
Draw a pedigree that traces the trait for blue eyes for three generations. GG gg gg gg I II III gg Gg Gg Gg Gg gg gg Gg Gg gg Gg Gg Gg gg
