4-2 Notes – Understanding Inheritance Chapter 4, Lesson 2

Punnett Squares A Punnett square is a model used to predict possible genotypes and phenotypes of offspring. If the genotypes of the parents are known, the genotypes and phenotypes of the offspring can be predicted.

Punnett Squares B = black fur b = brown fur

Punnett Squares B = black fur b = brown fur Female = BB Male = bb

Punnett Squares B = black fur b = brown fur Female = BB Male = bb

Punnett Squares B = black fur b = brown fur Female = BB Male = bb B

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b Bb

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b Bb Bb

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b Bb Bb bB

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b Bb Bb bB Bb

Punnett Squares B = black fur b = brown fur Female = BB Male = bb BB b b Bb Bb bB Bb black

Punnett Squares (5:00)

One-Trait Model A cross between two homozygous pea plants: one with yellow seeds (YY) and one with green seeds (yy).

One-Trait Model All offspring have the heterozygous genotype (Yy). All offspring have the yellow phenotype because Y is dominant to y. We call these offspring hybrid because they have one of each type of allele.

Two-Trait Model

A cross between two heterozygous genotypes (Yy and Yy)

Two-Trait Model The offspring would have three different genotypes and two phenotypes.

Two-Trait Model FFFf ff F = freckles f = no freckles freckles no freckles Cross a freckled Dad (Ff) with a freckled Mom (Ff).

Two-Trait Model Genotypes: ___% are FF ___% are Ff ___% are ff FFFf ff F = freckles f = no freckles freckles no freckles

Two-Trait Model Phenotypes: ___% have freckles ___% have no freckles F = freckles f = no freckles FFFf ff freckles no freckles 75 25

Pedigrees All the genetically related members of a family are part of a family tree. A pedigree shows genetic traits that were inherited by members of a family tree. Pedigrees are important tools for tracking complex patterns of inheritance and genetic disorders in families.

Pedigrees This pedigree chart shows three generations of a family.

Pedigrees Fill in the key!

Incomplete Dominance This is a blend of the parents’ phenotypes.

Codominance This is when both alleles can be observed in the phenotype because both are dominant. The human blood type AB is an example of codominance.

Codominance

Multiple Alleles Some genes have more than two alleles, or multiple alleles. The human ABO blood group is determined by multiple alleles as well as codominance. There are three different alleles for blood types: I A, I B, and i.

Multiple Alleles

Sex-Linked Inheritance Chromosomes X and Y are the sex chromosomes - they contain the genes that determine sex (male or female).

Sex-Linked Inheritance Except for sperm and eggs, each cell in a male has an X and a Y chromosome, and each cell in a female has two X chromosomes.

Sex-Linked Inheritance A recessive phenotype is observed in a male when a one-allele gene on his X chromosome has a recessive allele. There is no allele on his Y chromosome to “mask” the recessive allele.

Sex-Linked Inheritance

In this family, the grandmother’s genome included the color blindness allele.

Sex-Linked Inheritance Example: red-green colorblindness A carrier has one recessive allele and one dominant allele for a trait. They don’t have the trait but can pass it on to offspring.

Polygenic Inheritance This is when more than one gene determines the phenotype of a trait. Many phenotypes are possible when possible when polygenic inheritance determines a trait. Examples: hair color, height, skin color

Human Genetic Disorders If a change occurs in a gene, the organism with the mutation may not be able to function as it should. An inherited mutation can result in a phenotype called a genetic disorder.

Chris Sutter

Genes and the Environment An organism’s environment can affect its phenotype. –Genes affect heart disease, but so do diet and exercise. –Genes affect skin color, but so does exposure to sunlight.

Genes and the Environment Siamese cats have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder (ears, feet, tail) will develop the darker pigmentation of the Siamese cats.

Punnett squares model the ____ of offspring. Agenotypes Bphenotypes Cgenotypes and phenotypes Dgenes 4.2 Understanding Inheritance

What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes? Aincomplete dominance Bcodominance Cmultiple alleles Dpolygenic inheritance 4.2 Understanding Inheritance

How many Y chromosomes do females have? A0A0 B1B1 C2C2 D4D4 4.2 Understanding Inheritance

What is a good example of a trait that is determined by multiple alleles? Acolor of camellia flowers Bhuman AB blood type Ccolor blindness Dhuman ABO blood group

Why are male humans more likely to be color-blind than females? Amaternal inheritance Bsex-linked inheritance Cpolygenic inheritance Dincomplete dominance

If two plants with genotypes Mm are crossed, what percent of the offspring will have phenotype M? A0% B25% C75% D100% SCI 2.d

What is the term for when more than one gene determine a trait? Aincomplete dominance Bmultiple alleles Cpolygenic inheritance Dsex-linked inheritance SCI 2.c, 2.d

What type of genetic disorder is hemophilia? Adominant BX-linked recessive Ccodominant Drecessive SCI 2.d

4-2 Vocab – Understanding Inheritance text p Punnett square 2.pedigree 3.incomplete dominance 4.codominance 5.multiple alleles 6.sex chromosome 7.polygenic inheritance 8.genetic disorder

1. Cross a tall plant (Tt) with a tall plant (Tt). T = tall, t = short _____ % tall _____ % short Under each genotype, write the correct phenotype.

2. Tall plant (TT) with short plant (tt). _____ % tall _____ % short

3. Short plant (tt) with tall plant (Tt). _____ % tall _____ % short

4. Tall plant (TT) with tall plant (Tt). _____ % tall _____ % short

1. Cross a tall plant (Tt) with a tall plant (Tt). T = tall, t = short _75__ % tall _25__ % short T t T t TT tall Tt tall Tt tall tt short

2. Tall plant (TT) with short plant (tt). _100__ % tall _0__ % short T T t t Tt tall Tt tall Tt tall Tt tall

3. Short plant (tt) with tall plant (Tt). _50__ % tall _50__ % short t t T t Tt tall Tt tall tt short tt short

4. Tall plant (TT) with tall plant (Tt). _100__ % tall _0__ % short T T T t TT tall TT tall Tt tall Tt tall