Genetics, Punnett Squares, Pedigrees, Karotypes

What is a dominant gene?

A gene that is expressed when at least one dominant allele is present.

What are multiple alleles?

More than two possible alleles for a gene, such as blood type (A, B, O).

What is a recessive allele?

An allele that is only expressed when two copies are present (homozygous recessive).

What is a polygenic trait?

A trait controlled by multiple genes, such as skin color or height.

What is homozygous (purebred)?

An organism with two identical alleles for a trait (e.g., TT or tt).

What is heterozygous (hybrid)?

An organism with two different alleles for a trait (e.g., Tt).

What is the principle of independent assortment?

Genes for different traits assort independently during gamete formation.

What is a pedigree?

A diagram that traces the inheritance of a trait in a family.

What is a genotype? Give an example.

The genetic makeup of an organism (e.g., Bb or TT).

What is a phenotype? Give an example.

The physical expression of a trait (e.g., brown eyes, tall height).

What is incomplete dominance?

A situation where a heterozygous genotype results in a blended phenotype (e.g., red & white - pink flowers).

What is co-dominance?

A situation where both alleles are fully expressed (e.g., AB blood type).

What are autosomes?

The 22 pairs of non-sex chromosomes in humans.

What is a karyotype?

A picture of an organism’s chromosomes, used to detect genetic disorders.

What are sex chromosomes?

Chromosomes that determine biological sex (XX - female, XY - male).

What are some characteristics that can be inherited from parents?

Eye color, hair color, height, blood type, genetic disorders.

What does a Punnett square show? Does it guarantee results?

It predicts possible genotypes and phenotypes; it does not guarantee exact results.

Describe a polygenic trait.

A trait controlled by multiple genes, like skin color or height.

An organism with two different alleles for a trait is a

Heterozygous (hybrid.)

An organism with two identical alleles for a trait is a

Homozygous (purebred.)

In a Punnett square, where are the parent alleles placed?

Along the top and left sides of the square.

What is an example of multiple alleles and co-dominance in humans?

Blood type (A, B, O); AB shows co-dominance.

What is probability? How does it relate to Punnett squares?

Probability is the likelihood of an event occurring; Punnett squares predict genetic probability.

What is a purebred?

An organism that is homozygous for a trait.

What are the four human blood types? What must a person be to have type O blood?

A, B, AB, O; must have genotype OO.

Who is Gregor Mendel?

The father of genetics; discovered the basic principles of inheritance using pea plants.

What does a karyotype show?

The number and structure of chromosomes in an organism.

In sex-linked characteristics, a trait is determined by genes found only on the chromosome. What are some examples?

X chromosome; examples include color blindness and hemophilia.

Can males be carriers of an X-linked trait?

No, males only have one X chromosome, so they either have the trait or they don’t.

What is trisomy?

A genetic disorder caused by having an extra chromosome (e.g., Down syndrome is trisomy 21).

A normal karyotype contains pairs of autosomes and pair(s) of sex chromosomes.

22 pairs of autosomes, 1 pair of sex chromosomes.

What do circles and squares represent in a pedigree?

Circles - females, squares - males.

What does it mean if a circle or square is half-shaded in a pedigree?

The individual is a carrier of the trait.

What is epistasis?

A genetic interaction where one gene masks or modifies the expression of another.

If a homozygous short pea plant (tt) is crossed with a heterozygous tall pea plant (Tt), what are the expected phenotypic results?

50% tall, 50% short.

In mice, black fur (B) is dominant over white (b), and rough coat (R) is dominant over smooth (r). If a heterozygous black, rough coat mouse (BbRr) is crossed with a white, smooth coat mouse (bbrr), what are the possible offspring?

25% black/rough, 25% black/smooth, 25% white/rough, 25% white/smooth.

If a pink snapdragon (RW) is crossed with a red snapdragon (RR), what are the probable genotypic and phenotypic frequencies?

50% red (RR), 50% pink (RW).

If two pink snapdragons (RW x RW) are crossed, what percentage of offspring will have red flowers?

25% red (RR), 50% pink (RW), 25% white (WW).

If a Type A (IAi) person marries a Type B (IBi) person, what are the possible blood types of their children and their probabilities?

25% Type A, 25% Type B, 25% Type AB, 25% Type O.

If a pea plant with a homozygous dominant round seed shape (RR) is crossed with a heterozygous round seed plant (Rr), and 400 seeds are produced, how many are expected to be homozygous dominant?

200 seeds (50%).