GeneticsChapters 6 and 7

Introduction to Mendel’s Law of Independent Assortment:

1. Use coins to represent 2 animals– Heads = Dominant Allele (H)

– Tails = Recessive Allele (h)

2. Flip coins simultaneously to represent a pairing of alleles. (Perform 100 tests)

3. Record Results as Homozygous dominant (HH), Heterozygous (Hh), or homozygous recessive (hh)

Recorded Genotypes

Amount of Offspring

Homozygous Dominant (HH)

Heterozygous (Hh)

Homozygous Recessive (hh)

Genotypic Percentage

Investigation Questions1. Create a hypothesis of which scenario will

be the most common. Explain your reasoning.

2. Which scenario ended up occurring the most often? Why do you think that was?

3. What did the coins represent?

4. Why did we use 2 coins? Why not 1 or 3, 4, 5…?

5. How does this lab relate to real life?

Mendel’s 3 Theories

• Principle of Dominance and Recessive• Principle of Segregation• Principle of Independent Assortment

The law of segregation

• Each parent would contribute one factor to the new individual.

• Random Segregation would occur during the formation of the sex cells.

The law of independent assortment

• Factors for different characteristics are distributed to reproductive cells independently.

• Example: seed shape and seed color are inherited independently of each other.

Incomplete Dominance/ Co-Dominance

• Some traits do not have one clear dominant gene or one clear recessive trait

• Traits appear to blend together

• Ex: Red flower with white flower makes a pink flower

• Ex: Blood Types A, B, O

Patterns of Inheritance

• Polygenetic Inheritance:

• genes that are controlled by multiple genes that are located on different chromosomes

–Examples: eye color, skin color, height, and facial features.

Multiple Alleles

• Control Several Traits

• Human Blood: Blood Typing

• Possible Alleles: A, B, and O

• Rhesus Factor (RH): Antigen in Red Blood Cells

– factor has cell markers that make you positive (antigens present) or negative (no antigens present)

• A and B are both dominant over O

• A and B presence is never masked

• O is a universal donor• AB is a universal recipient

Blood Types

Genotype Phenotype

• AA A

• BB B

• OO O

• AO A

• BO B

• AB AB

Punnet Square Practice:• Round Seeds are dominant over wrinkled

seeds. Cross: Pure round seeds with Pure wrinkled seeds.

• Green pods are dominant over yellow pods. Cross: Hybrid green pods with Hybrid Green pods.

• Axial flowers are dominant over terminal flowers. Cross: Hybrid axial flowers with Pure axial flowers.

• Colored seed coats are dominant over white seed coats. Cross: Hybrid colored seeds with Hybrid colored seeds.

• Horned cattle is dominant over the hornless condition. Cross: Pure hornless with Hybrid Horned.

• Black fur is dominant over white fur in guinea pigs. Cross: Hybrid black with Hybrid Black.

• Long wings aer dominant over curly wing in fruit flies. Show all the idfferent crosses that can produce hybrid long wing individuals.

In Sheep, black wool is recessive to white wool. What happens when you mate a black ram to a heterozygous ewe? Use W to represent dominant white, w for the recessive black allele.

• What is the genotype of the ram?

• What is the genotype of the ewe?

• What are the genotypes of the offspring?

• What is the genotypic ratio of the offspring?

• What are the phenotypes of the offspring?

Cross a heterozygous black female angus to a heterozygous bull (B = black; b = red)

• What is the genotype of the female angus?• What is the genotype of the bull?• What are the genotypes of the offspring?• What is the genotypic ratio of the offspring?• What are the phenotypes of the offspring?

In cattle, the polled gene (P) is dominant over the horned gene (p). A polled cow with genotype (Pp) is mated to a horned bull. ½ of the offspring were polled and ½ were horned?

• What is the genotype of the bull?• Whare the genotypes of the offspring?

Cross a heterozygous polled black angus bull (BbPp) to a heterozygous polled black angus cow (BbPp).

• Use a punnet square to determine genotype and phenotype of offspring.

Sex Linked Inheritance/Sex Limited

• Males have XY sex chromosomes

• Females have XX sex chromosomes

• Humans have 23 pairs of chromosomes

–22 pairs are called autosomes

• Pairs of matching homologous chromosomes

–1 pair is known as sex chromosomes

• Many genetic disorders are linked to the X Chromosome

• Much more common phenotypically in males

• Females are typically carriers

• These traits become evident after puberty due to the chemical production in the body

Sex-linked Traits

Common Sex Linked/Sex Limited Disorders

• Color Blindness–People with this disorder are unable to

see the full color spectrum• Hemophilia

– Inability for blood to clot• Muscular Dystrophy

–Deterioration of the muscles, early death in males

Sex Influenced

• Traits controlled by hormones or chemical in the body of one particular sex

–Ex: Baldness

Disorders by Mutations of Chromosomes

• Sickle Cell Anemia– Occurs among people of African descent– Red Blood Cells are sickle shaped rather than

circular– Causes anemia, clogged blood vessels, and

restricted blood flow

• Cystic Fibrosis– One in 20 males are carriers– Causes respiratory infections due to fluid in the

lungs.

Continued…

• Huntington’s Disease–Lethal disease which does not occur

until age 40–Breakdown of areas of the brain,

caused by dominant allele–Causes loss of muscle control

Disorders by Non-Disjunction• Chromosomes fail to separate

during meiosis

• Down Syndrome: non-disjunction of the 21st chromosome (extra chromosome)

• Multiple traits are effected

• Klinefelters Syndrome

–Non-disjunction of the sex chromosome

–Extra X chromosome, XXY instead of XY

–Male is sterile

• Turners Syndrome

–Female’s X Chromosome is missing

–Female is sterile

Twins

• Identical Twins

–Produced from a single zygote that splits after fertilization

–Babies will have exact same genotypes

• Fraternal Twins

–Two eggs are fertilized by different sperm cells

–Genotypes are not exactly the same