Genetics Clifton L. Hamilton Biology

Concepts  Instructions for specifying characteristics are carried in nucleic acids.  Mulitcellular organisms, including humans, form from cells that contain two copies of each chromosome. This explains many features of heredity.

History  Genetics: Study of inherited traits  Heredity: Passing of traits from parents to offspring.  Gregor Mendel: Given credit for what we know about genetics/heredity.  Mendel studied garden peas and came up with a model for inheritance.

How does the environment influence traits we have? Students will…  Construct Punnett squares in order to determine phenotype of offspring.  Predict what genes individuals carry based on traits they have.  Identify mechanisms of change that influence evolution  Distinguish between mechanisms of change influencing traits of organisms.  Compare conditions necessary for populations to be in Hardy-Weinberg equilibrium.  Design animal with adaptations to help them survive.

Who was Gregor Mendel? An Austrian monk: he was known as the “FATHER OF GENETICS” He discovered how traits were inherited GENETICS –is the scientific study of heredity. HEREDITY – the passing of traits from parents to offspring (This is what makes each species unique)

Mendel’s Peas Mendel did his study on pea plants Pea plants have many traits (tall/short, purple flowers/white flowers) Pea plants can be self-fertilized (self- pollinated) or cross-fertilized.

Mendel’s Work Mendel used true-breeding plants which means if they were left to breed with themselves they would produce offspring identical to themselves. Mendel studied 7 different traits in pea plants (Pod Shape, Pod Color, Seed Coat, Flower Color, Plant Height, etc.) Trait: is a specific characteristic that varies from one individual to another.

Types of Plants He Used… 1.True-Breeding - these plants always create plants that look like themselves 2.Hybrids – offspring of two different “true-breeding” plants Tall x Short = Hybrid (TT) (tt) (Tt)

Dominance Some traits are dominant over others. Tall x Short = all tall offspring (hybrids) *Tall is the dominant trait (T_) *Short is recessive (tt)

Mendel’s Model  For each trait, we have two copies of the gene— one from the mother and one from the father.  There are alternative forms of genes. These are called alleles. For example, we possess two alleles for freckles. Their combination determines whether we will have freckles or not.  These alleles can be dominant or recessive. Dominant alleles, when present, will be expressed. Recessive alleles can be masked by dominant alleles. In order for recessive alleles to be expressed both must be recessive.

 Gametes carry only one allele for each inherited trait. At fertilization each gamete contributes one allele.  If a person is carrying two alleles for a trait that are the same—they are homozygous for that trait. If the alleles are different they are heterozygous.  The genes we are carrying for traits is our genotype (Ex. AA, Aa, aa, BB, Bb, bb, etc.) The outward expression of those genes is our phenotype (Tall, Short, Hair Color, Eye Color, etc.).

If Tall is dominant in pea plants and short is recessive. Which would represent the genotype of a heterozygous plant A.TT B.Tt C.tt D.ST Response Grid Countdown 20

Which would represent the genotype of a short pea plant? A.TT B.Tt C.tt D.ST Response Grid Countdown 20

How many plants would be tall if you cross a heterozygous parent with a short parent? A.¼ B.½ C.¾ D.All would be tall Response Grid Countdown 20

Monohybrid vs. Dihybrid Crosses  Monohybrid cross: – Looks at only one trait at a time. – Ex. AA X aa  All Aa  Dihybrid cross: – Looks at two traits at one time (Ex. Eye Color and Height) – Each trait gets a different letter (A: Eye & B:Height) – Letters on Punnett Square are determined from all possible combinations of parent alleles. AA aAa a

 Example: If black fur and long whiskers are dominant in rabbits.  First, a rabbit would need two letters to represent each trait.  Homozygous Dominant for color and Homozygous Recessive for whisker length would be [BBll]  this means the rabbit would be black with short whiskers.  Question: What would a rabbit look like if it were heterozygous for both traits? [BbLl]

What would the following rabbits look like?  BbLl – Black with long whiskers  bbLL – Grey with long whiskers  BBll – Black with short whiskers  Bbll – Black with short whiskers

Example: Dihybrid Cross *When crossing parents that are both heterozygous for two traits, you will ALWAYS end up with a 9:3:3:1 ratio. (R & Y) (rr & Y) (R & yy) (rr & yy)

Predicting offspring  In your notes, Cross two parents heterozygous for both traits.  Remember: Black is dominant to Grey and Long Whiskers is Dominant to Short Whiskers. BbLl X BbLl

If Black is dominant and Long whiskers is dominant. What would the genotype of a rabbit that is grey and heterozygous for whisker length be? A.BBLL B.Bbll C.bbll D.bbLl Response Grid Countdown 20

What would the rabbits look like if you crossed one that is homozygous dominant for color and whisker length with a rabbit who is grey with short whiskers? A.¼ black long, ¼ black short, ½ grey short. B.¼ black long, ¼ black short, ¼ grey long, ¼ grey short C.All grey short D.All black long Response Grid Countdown 20

In pea plants being tall is dominant over short and green is dominant over yellow (T-Tall, G-Green). 1.Cross two pea plants heterozygous for both traits. [TtGg X TtGg] 2.Cross a pea plant heterozygous for both traits with one that is short and yellow.[TtGg X ttgg] 3.Cross a homozygous dominant pea plant with one heterozygous for both traits. [TTGG X TtGg] 4.Cross a plant homozygous recessive for height and heterozygous for color with one heterozygous for height and homozygous dominant for color. [ttGg X TtGG] Additional Practice w/ Dihybrid Crosses: Complete All Problems in Your Notes!

Other Traits  Multiple Allele: Determines blood type. A & B are dominant—O is recessive.  Codominance: When two dominant alleles are expressed together. (Ex: Black Fur X White Fur  Black and White Fur).  Incomplete dominance: Intermediate trait is expressed in heterozygous individuals. Ex: In snapdragons a red (RR) and white (rr) cross makes pink flowers (Rr).

What color would the flowers be if you cross a red flower with a pink flower? A.Red & Pink B.Red, Pink & White C.All Red D.All White Response Grid Countdown 20

If a woman has type O blood, and a man has type A blood, what could the children have? A.Only Type O B.Only Type A C.Type A or Type B D.Type A or Type O Response Grid Countdown 20

Inherited diseases  Genetic predisposition: Having an increased chance of a disease due to inheritance. Ex: Heart disease & Diabetes  Genetic disorder: If you have the genes for the disorder, you will definitely have the disease. Ex: Colorblindness & albinism

Autosomal Disorders  Autosomal traits mean that the genes are carried on one of the 22 autosomes. – BOTH male and females can be carriers of autosomal disorders. – A carrier can pass on the genes but does not have the disorder. – Some include: albinism, cystic fibrosis, and sickle cell anemia

Sex-linked Traits  Sex-linked traits are carried on the X chromosome. – ONLY females can be carriers of sex-linked disorders. – Some of these include: Colorblindness, Muscular Dystrophy & Hemophilia. – Because males only have one X, they are more likely to have sex-linked diseases than females.

If a man with MD marries a carrier, could they have a child with MD? A.Yes, but only a girl B.Yes, but only a boy C.Yes, could be a boy or girl D.No Response Grid Countdown 20

Pedigrees  Chart showing how a trait is inherited over several generations.  Males are squares—females are circles.  Children are listed in order of birth.  Shapes are colored completely if they express the trait. Only half shaded if they are heterozygous for trait.