11/4 Lecture: Inheritance, Genes, and Chromosomes + PCV: Punnett Squares and Probability

Dihybrid Cross: What is a simpler way to calculate the probabilities of genotypes than creating a 4×4 Punnett squares?

create 2x2 punnett squares for each of the two genes and combine the probabilities for each genotype

How do you calculate the probability of A and B?

the probability of A multiplied by the probability of B

How do you calculate the probability of A or B?

the sum of the probability of A and the probability of B

What is the goal of Meiosis I vs Meiosis II?

In Meiosis I, the homologous chromosomes are separated.

In Meiosis II, the sister chromatids separate.

What happens in meiosis that increases genetic variation?

When do they happen?

(2 pts)

Crossing over: Maternal and paternal homologous chromosomes pair up, forming tetrads, and exchange genetic material

• During synapsis during prophase I

Independent assortment: homologous chromosomes are randomly separated to either pole of the cell

• during anaphase I

What is an error that can occur during meiosis? What is the result?

Include one example and a specific disease that can be caused.

Nondisjunction occurs when homologous chromosomes fail to separate during anaphase I or when sister chromatids fail to separate during anaphase II.

Nondisjunction causes aneuploidy, meaning the resulting cell has the wrong number of chromosomes (incorrect ploidy).

• Trisomy is an example of aneuploidy where the cell gets three copies of a chromosome instead of two. Trisomy 21 (where the cell has three copies of the 21 chromosome) causes down syndrome.

What are Polyploids?

Inculde an example.

organisms that have more than 2 complete sets of chromosomes

wheat plants

Why did Gregor Mendel use pea plants for his breeding experiments? (3 pts)

Pea plants can self-pollinate (with themselves) or cross-pollinate (with other pea plants).

They produce large numbers of offspring.

They have a fast generation time (the time it takes for a seed to grow into a plant and yield new seeds).

What is a hybrid cross?

What is the purpose of a hybrid cross?

a breeding experiment between two heterozygous organisms

in order to examine the inheritance patterns of traits

Describe two different types of hybrid crosses?

A monohybrid cross involves only one gene.

A dihybrid cross involves two genes.