Genetics Chapter 4

What is Chapter 4 about?

The chromosome theory of inheritance.

What chromosome abnormality causes Down syndrome?

Trisomy 21.

What is trisomy 21?

Three copies of chromosome 21 instead of two.

What does Down syndrome show about chromosomes?

Chromosomes transmit genetic information, and type/amount of genetic material matters for normal development.

What does diploid, 2n, mean?

Two chromosome sets; each pair has one maternal and one paternal copy.

What does haploid, n, mean?

One chromosome set.

What produces haploid gametes?

Meiosis.

What are 2n and n in Drosophila?

2n = 8; n = 4.

What are 2n and n in humans?

2n = 46; n = 23.

What is fertilization?

Union of haploid gametes to form a diploid zygote.

What are sister chromatids?

Identical copies of a replicated chromosome.

What are homologs?

Chromosomes with the same genes that may have different alleles.

What are nonhomologs?

Chromosomes carrying completely unrelated sets of genes.

What is a karyotype?

A micrograph of stained chromosomes arranged in homologous pairs.

How are homologous chromosomes alike in a karyotype?

Same size, shape, and banding.

What are autosomes?

All chromosomes except X and Y.

What determines sex in humans according to the slides?

Presence or absence of the Y chromosome.

What chromosome does a child receive from the mother?

X.

What chromosome does a child receive from the father?

X or Y.

What sex ratio results from X- and Y-bearing sperm?

1:1 female to male.

What is SRY?

Sex-determining region of Y, the primary determinant of maleness.

What does sex reversal show about SRY?

SRY is present in XX males and nonfunctional in XY females.

What are the main cell-cycle phases?

Interphase and mitosis.

What occurs in G1?

Chromosomes are not duplicating or dividing.

What occurs in S phase?

Chromosomes duplicate into sister chromatids.

What occurs in G2?

Proteins required for mitosis are synthesized.

What is G0?

A resting/nondividing stage.

List mitosis stages in order.

Prophase, prometaphase, metaphase, anaphase, telophase.

What happens in prophase?

Chromosomes condense and become visible.

What happens in prometaphase?

The spindle forms and sister chromatids attach to microtubules from opposite centrosomes.

What happens in metaphase?

Chromosomes align at the cell equator.

What happens in anaphase?

Sister chromatids separate and move to opposite poles.

What happens in telophase?

Chromosomes are enclosed in two nuclei.

What are somatic cells?

The vast majority of cells in the organism; they may be in G0 or undergoing mitosis.

What are germ cells?

Cells set aside during embryogenesis that become incorporated into reproductive organs and are precursors to gametes.

How many divisions occur in meiosis?

Two.

How many times do chromosomes duplicate in meiosis?

Once.

What happens in meiosis I?

Homologs pair, cross over, and segregate; sister chromatids remain intact.

What happens in prophase I?

Homologs pair through the synaptonemal complex, and crossing over occurs.

What are the first three substages of prophase I?

Leptotene, zygotene, pachytene.

When does crossing over start and finish according to the notes?

It starts in zygotene and finishes in pachytene.

What is a tetrad?

The paired homolog structure formed in prophase I.

Why is meiosis I reductional?

Homologs separate, reducing 2n to n.

What happens in meiosis II?

Sister chromatids separate and move to opposite poles.

Why is meiosis II equational?

It separates sister chromatids.

What is nondisjunction?

A mistake in chromosome segregation during meiosis I or II.

What can nondisjunction cause?

Nonviable gametes/embryos or abnormal chromosome numbers in viable individuals.

What conditions are listed as nondisjunction examples?

Trisomy 21/Down syndrome, XXY/Klinefelter syndrome, and _X/Turner syndrome.

How does meiosis create genetic diversity?

Independent assortment of nonhomologs and crossing over between homologs.

What is the X-linked recessive pedigree pattern?

No father-to-son transmission; daughters of affected males are carriers; half of carrier sons inherit the trait.

What is the X-linked dominant pedigree pattern?

The trait occurs in every generation; affected males have affected daughters and unaffected sons.

What is the Y-linked pedigree pattern?

Only males are affected.

What is dosage compensation?

Females have two X chromosomes but one X is inactivated in female cells.

What is a Barr body?

The condensed inactive X chromosome.

Why are females a patchwork for X-linked expression?

Early in development, each cell independently inactivates one X chromosome.