AP Biology Unit 5 Exam Review: 5.1-5.3

If an organism is diploid and a certain gene found in the organism has 18 known alleles (variants), then any given organism of that species can/must have how many alleles for a gene?

A) At most, 2 alleles for that gene

How many homologous chromosomes are there for a species that has a chromosome number of 2n = 16?

8 homologous sets

In humans, each of the 22 maternal autosomes has a ______________________________

homologous paternal pair

What does the human X and Y chromosomes contain?

Include genes that determine an individual's sex.

What are two ways that the sexual life cycle increases genetic variation in a species?

Crossing over & independent assortment of homologous chromosomes.

A given organism has 46 chromosomes in its karyotype. What are the number of chromosomes in the gametes?

23 chromosomes

If a cell has completed the first meiotic division and is just beginning meiosis II, describe the amount of DNA that is present.

It has half the amount of DNA as the cell that began meiosis.

What is the chromosomal makeup of each daughter cell after telophase I of meiosis?

haploid, and the chromosomes are each composed of two chromatids.

What of the following happens at the conclusion of meiosis I?

Homologous chromosomes of a pair are separated from each other.

What occurs in meiosis I but not in mitosis?

synapsis of chromosomes

In which process does mitosis and meiosis II have chromatids are separated from each other.

Mitosis and Meiosis II

A pair of homologous chromosomes includes how many sets of DNA?

four sister chromatids

When we see chiasmata under a microscope, that lets us know what phase of meiosis has occurred?

prophase I

Independent assortment of chromosomes occurs in which phase of meiosis I?

Metaphase I

A human cell containing 22 autosomes and a Y chromosome is

a sperm

Homologous chromosomes move toward opposite poles of a dividing cell during which phase?

Meiosis I

What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants?

Traits are inherited in discrete units, and are not the results of blending.

Why did Mendel continue some of his experiments to the F2 or F3 generation?

To observe whether or not a recessive trait would reappear

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. What does this suggest?

That the parents were both heterozygous for a single trait

When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

50%

Mendel accounted for the observation that traits which had disappeared in the F1 generation reappeared in the F2 generation by proposing that

Traits can be dominant or recessive and the recessive traits were obscured by the dominant ones in the F1.

Mendel's observation of the segregation of alleles in gamete formation has its basis in which of the phases of cell division?

anaphase I of meiosis

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of crosses BbTt × BBtt will be expected to have black fur and long tails?

1/2

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

0

In the cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?

1/64

Given the parents AABBCc × AabbCc, assume simple dominance for each trait and independent assortment. What proportion of the progeny will be expected to phenotypically resemble the first parent?

3/4

What are homologous chromosomes?

Two chromosomes with the same set of genes, sometimes with different alleles

What is a gene?

basic unit of heredity and a sequence of nucleotides in DNA or RNA

What is an allele?

Different forms of a gene

Purpose of meiosis

produce gametes

Why in meiosis the chromosome number is halved?

Halves the sex cells in half, so that in fertilization, it will result in a normal amount of chromosomes (46 -> 23)

What is the end product of meiosis?

4 haploid cells

What happens in meiosis I?

- Homologous chromosomes pair up
- Homologous chromosomes separates
- Two haploid cells are made with their sister chromatids still joined.

What happens in meiosis II?

- Sister chromatids separate
- 4 haploid daughter cells are formed

Significance of meiosis

Causes genetic variation

How is genetic variation achieved?

- crossing over
- independent assortment
- random fertilization

What is crossing over?

exchange of genetic material between homologous chromosomes

How does crossing over contribute to genetic variation?

Crossing over creates new combinations of genes in the gametes that are not found in either parent

What is independent assortment?

random separation of homologous chromosomes

How does independent assortment contribute to genetic variation?

each gamete ends up with a different set of DNA
- independent assortment affects which chromosomes end up in each cell

How does random fertilization contribute to genetic variation?

each parent to randomly contributes a unique set of genes to a zygote

What is a recessive allele?

A form of a gene that is not expressed when paired with a dominant allele

What is a dominant allele?

A form of a gene that is fully expressed, even when two different alleles are present

What is the law of segregation?

Parents pass on only one allele for each gene

What is the law of independent assortment?

during gamete formation, different pairs of alleles segregate independently of each other
- EX. which allele a gamete receives for gene A has no bearing of which allele a gamete receives for gene B
- ONLY DEALS WITH UNLINKED GENES

A cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?

1/64