DOMINANT AND RECESSIVE TRAITS

ATTACHED / UNATTACHED EARLOBES UNATTACHEDATTACHED DOMINANTRECESSIVE

ROLLING YOUR TONGUE ROLLER NONROLLER DOMINANTRECESSIVE

WIDOW’S PEAK STRAIGHT HAIRLINE DOMINANTRECESSIVE

HITCHHIKER’S THUMB STRAIGHT THUMB HITCHHIKER’S THUMB DOMINANTRECESSIVE

PINKIES BENT PINKIES STRAIGHT PINKIES DOMINANTRECESSIVE

CLEFT CHIN NO CLEFT CLEFT DOMINANTRECESSIVE

SECOND TOES LONGER SECOND TOE SHORTER SECOND TOE DOMINANTRECESSIVE

NUMBER OF FINGERS SIX FINGERS: POLYDACTYLY FIVE FINGERS DOMINANT!!!!RECESSIVE

12.1 Section Objectives – page 309 Interpret a pedigree. Section Objectives: Identify human genetic disorders caused by inherited recessive alleles. Predict how a human trait can be determined by a simple dominant allele.

Section 12.1 Summary – pages A family tree traces a family name and various family members through successive generations. Through a family tree, you can identify the relationships among your cousins, aunts, uncles, grandparents, and great-grandparents.

Section 12.1 Summary – pages A pedigree is a graphic representation of genetic inheritance. It is a diagram made up of a set of symbols that identify males and females, individuals affected by the trait being studied, and family relationships. Basically, a family tree that traces an inherited trait.

Section 12.1 Summary – pages Some pedigree symbols Male Female Affected male Affected female Mating Parents Siblings Known heterozygotes for recessive allele Death

Section 12.1 Summary – pages Highlighted circles and squares represent individuals showing the trait being studied. ? I II III IV

Section 12.1 Summary – pages Circles and squares that are not highlighted designate individuals that do not show the trait. ? I II III IV

Section 12.1 Summary – pages A half-shaded circle or square represents a carrier, a heterozygous individual.

? I II III IV Section 12.1 Summary – pages A horizontal line connecting a circle and a square indicates that the individuals are parents, and a vertical line connects parents with their offspring.

Section 12.1 Summary – pages Each horizontal row of circles and squares in a pedigree designates a generation, with the most recent generation shown at the bottom ? I II III IV

? Section 12.1 Summary – pages The generations are identified in sequence by Roman numerals, and each individual is given an Arabic number. I II III IV

Section 12.1 Summary – pages Simple Recessive Heredity Most genetic disorders are caused by recessive alleles. Bb x Bb bb Bb x bb bb

Section 12.1 Summary – pages Cystic fibrosis (CF) is one of the most common fatal genetic disorders among mostly white Americans. Cystic Fibrosis Due to a defective protein in the plasma membrane, cystic fibrosis results in the formation and accumulation of thick mucus in the lungs and digestive tract.

Approximately one in 28 white Americans carries the recessive allele, and 1 in 3000 children born to white Americans inherits the disorder. (1 in every 15,000 black babies are born with the disease every year)

Section 12.1 Summary – pages Tay-Sachs (tay saks) disease is a fatal recessive disorder of the central nervous system. In this disorder, a recessive allele results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system. Because this lipid fails to break down properly, it accumulates in the cells. Tay-Sachs

A baby born with Tay-Sachs usually seems healthy for the first few months, but as nerve cells become packed down with fatty material a relentless deterioration of mental and physical abilities begins to occur. Tay-Sachs Tay-Sachs is very rare, and more commonly found in families with Jewish heritage and Cajun-French families.

Section 12.1 Summary – pages I II III IV What’s wrong with this Tay-sachs pedigree?

Section 12.1 Summary – pages Phenylketonuria (fenal key ton Your ree uh), also called (PKU), is a recessive disorder that results from the absence of an enzyme that breaks down the amino acid, phenylalanine. Because phenylalanine cannot be broken down, it and its by-products accumulate in the body and result in severe damage to the central nervous system. Phenylketonuria

Section 12.1 Summary – pages Affects around 1 in every 15,000 births. Usually found mostly in Caucasian and Asian families Phenylketonuria Infants affected by PKU are given a diet that is low in phenylalanine until their brains are fully developed.

Section 12.1 Summary – pages Phenylketonuria Contains Phenylalanine

Section 12.1 Summary – pages Simple Dominant Heredity Remember that in Mendelian inheritance, a single dominant allele inherited from one parent is all that is needed for a person to show the dominant trait. Many traits are inherited just as the rule of dominance predicts.

Section 12.1 Summary – pages Simple dominant traits A cleft chin, widow’s peak hairline, almond shaped eyes, thick lips, and the presence of hair on the middle section of your fingers all are examples of dominant traits.

Section 12.1 Summary – pages Huntington’s disease is a lethal genetic disorder caused by a rare dominant allele. It results in a breakdown of certain areas of the brain. Causing gradual involuntary muscle movements and eventually dementia. Huntington’s Disease

Section 12.1 Summary – pages Ordinarily, a dominant allele with such severe effects would result in death before the affected individual could have children and pass the allele on to the next generation. But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may already have had children before knowing whether he or she is affected. Huntington’s Disease

Section 12.1 Summary – pages Typical Pedigree of Huntington’s Disease I 1 II III

I II III IV Section 1 Check Question 1 What does this pedigree tell you about those who show the recessive phenotype for the disease?

I II III IV Section 1 Check The pedigree indicates that showing the recessive phenotype for the disease is fatal.

Section 1 Check Question 2 What must happen for a person to show a recessive phenotype? Answer The person must inherit a recessive allele for the trait from both parents.

Section 1 Check Question 3 Which of the following diseases is the result of a dominant allele? D. phenylketonuria C. cystic fibrosis B. Tay-Sachs disease A. Huntington’s disease The answer is A.

Question 2 If T is the allele for tall plants and t is the allele for short plants, the phenotype of individual 4 is _______. T t Tt

The answer is short. Recall that phenotype describes the way an organism looks. T t Tt

Question 3 The genotype of individual 1 is _______. T t Tt

The answer is TT. The allele combination that an organism contains is its genotype. T t Tt