BIO 2311 CH 12/13

What causes sickle-cell anemia?

Inheriting 2 mutated copies of a hemoglobin gene, one from each parent.

How does sickle-cell hemoglobin differ from normal hemoglobin?

By just 1 amino acid in a polypeptide subunit.

Why do red blood cells become sickle-shaped?

Low oxygen causes altered hemoglobin to form crystals that distort the cells

What was the blending theory of inheritance?

The belief that parents' traits blend in offspring.

What did Mendel study in the 1860s?

how traits pass from parents to offspring through controlled breeding experiments.

What are self-pollination and cross-pollination?

Self: pollen fertilizes the same plant.

Cross: pollen comes from another plant.

What are the reproductive parts of a pea flower?

Male: Anther (produces pollen)
Female: Stigma (receives pollen), ovary (contains ovules)

What happens after pea plants are cross-fertilized?

The plant produces seeds (F1 generation), which grow into offspring with observable traits.

What is a reciprocal cross?

Repeating a cross with parental sexes switched (purple ♂ × white ♀ vs. white ♂ × purple ♀).

What are the P, F1, and F2 generations?

P: true-breeding parents;

F1: first offspring;

F2: offspring from F1 self-pollination.

What are Mendel's three conclusions?

1. Dominance: One allele can mask another.

2. Segregation: Alleles separate during gamete formation.

3. Independent assortment: Different genes are inherited independently.

What are dominant and recessive alleles?

Dominant: expressed with a different allele. Recessive: masked by the dominant allele.

What is the difference between homozygous and heterozygous?

Homozygous: 2 identical alleles, 1 gamete type. Heterozygous: 2 different alleles, 2 gamete types (50% each).

What is a monohybrid?

An F1 heterozygote from a cross involving one character.

What is a monohybrid cross?

A cross between two individuals heterozygous for the same gene (Aa × Aa).

What is the difference between genotype and phenotype?

Genotype: genetic makeup (alleles).

Phenotype: observable appearance or traits.

What happens when true-breeding purple (PP) and white (pp) peas are crossed?

All F1 offspring are purple (Pp) because purple is dominant over white.

What is probability?

The likelihood that an event will happen, expressed from 0 (impossible) to 1 (certain).

What is the product rule of probability?

Multiply probabilities of independent events.

What is the sum rule of probability?

Add probabilities of different ways to get an outcome.

What is a testcross how are results interpreted?

Cross dominant phenotype × homozygous recessive.

how are testcross results interpreted?

1:1 dominant/recessive = heterozygous

all dominant = likely homozygous dominant.

What is Sutton's Chromosome Theory of Inheritance?

that genes are carried on chromosomes because their behavior during meiosis matches Mendel's laws.

How do chromosomes parallel Mendel's alleles?

Both occur in pairs, separate into gametes during meiosis, and inherit one copy from each parent at fertilization.

What is a gene locus?

The specific location of a gene on a chromosome

its DNA sequence typically codes for a protein affecting phenotype.

How do alleles of the same gene differ?

They have different DNA sequences, which may produce proteins with different functions.

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What is incomplete dominance?

Neither allele is fully dominant; the heterozygote has an intermediate phenotype.

What is codominance?

Both alleles are equally and fully expressed in a heterozygote.

How does the human MN blood group show codominance?

Both M and N alleles are expressed equally, so a person with genotype LᴹLᴺ has both M and N antigens.

What are multiple alleles?

More than 2 versions of a gene exist in a population, but each individual carries only 2; alleles differ in DNA sequence (e.g., b₁, b₂, b₃).

How can multiple alleles affect a protein?

DNA base changes may alter amino acids and protein function

some changes have no effect.

How does the ABO blood group show multiple alleles and codominance?

Three alleles: Iᴬ, Iᴮ, i. Iᴬ and Iᴮ are codominant; both dominate i.

What causes blood agglutination during an incompatible transfusion?

Antibodies attack foreign red blood cell antigens, causing clumping that can be fatal.

What antigens, antibodies, and compatible donor types does type A blood have?

A: A antigen, anti-B, receives A/O. B: B antigen, anti-A, receives B/O. AB: A+B, no antibodies, receives all. O: no antigens, anti-A+B, receives O.

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delete

What is epistasis?

One gene masks or inhibits another gene at a different locus, altering expected phenotypes

epistasis can

affect disease risk (e.g., insulin resistance).

What is polygenic inheritance?

When several genes contribute to one trait, such as height.

What are quantitative traits and QTLs?

Quantitative traits show continuous variation, often a bell-shaped curve

contributing gene loci are QTLs.

What is continuous variation?

A range of phenotypes, like height, often forming a bell-shaped distribution.

How does the environment affect polygenic traits?

Environmental factors can modify how traits are expressed, not just genes.

How does nutrition affect human height?

Poor childhood nutrition limits growth; good nutrition promotes growth.

What is pleiotropy, and how does sickle-cell anemia demonstrate it?

One gene affects multiple traits; altered hemoglobin can damage many organs and body functions.

What are linked genes?

Genes close together on the same chromosome that tend to be inherited together.

How do linked and unlinked genes differ?

Linked genes tend to be inherited together; genes on different chromosomes assort independently.

What is genetic recombination?

Exchange of DNA segments between homologous chromosomes through crossing-over during meiosis.

How does distance between linked genes affect recombination?

Closer genes recombine less often and are more likely inherited together

__________ genes recombine more.

farther

What is recombination frequency, and how is it calculated?

(recombinant offspring ÷ total offspring) × 100.

What is chromosome mapping?

Using recombination frequencies to determine the relative locations of linked genes on a chromosome.

Why can widely separated genes on the same chromosome appear unlinked?

Frequent crossing-over makes them appear to assort independently.

How can linkage between widely separated genes be detected?

By testing their linkage to intermediate genes on the same chromosome.

How can chromosome maps show distances greater than 50 cM?

Add distances between intermediate genes.

Example: a–b = 23 cM, b–c = 34 cM, so a–c = 57 cM.

Sex-linked

on X or Y chromosomes, inherited differently by sex.

Autosomal:

on chromosomes 1–22, inherited similarly in both sexes.

What sex chromosomes do human males and females have?

Females: XX (homologous pair). Males: XY.

Homogametic

XX females make X eggs only.

Heterogametic

XY males make X or Y sperm (50% each).

How is biological sex determined at fertilization?

X sperm + X egg = XX female; Y sperm + X egg = XY male.

What are other sex chromosome systems in animals?

• XX = female, XO = male (some insects)

• ZZ = male, ZW = female (birds, butterflies, some reptiles)

How is sex determined in bees, wasps, and some microorganisms?

Bees/wasps: haploid or diploid.

Some microorganisms: specific alleles of a gene.

What is the role of the SRY gene?

A gene on the Y chromosome that triggers testes development in embryos.

How do testes influence reproductive development?

Testicular hormones promote male structures and cause female structures to degenerate.

What is crisscross inheritance?

Passing an X-linked allele from father → daughter → grandson.

What is a pedigree?

A family record showing genotypes and phenotypes across generations to trace inheritance.

Why are X-linked recessive traits more common in males?

Males need only 1 recessive X allele; females need 2 (one from each parent).

How was Queen Victoria connected to hemophilia?

She was an unaffected heterozygous carrier (XᴴXʰ) who passed the recessive allele to descendants.

Why can X-linked traits skip generations?

Fathers pass their X to daughters, not sons;

sons receive their X from their mother.

What is X-chromosome inactivation?

Dosage compensation: one X chromosome is silenced in most female mammalian cells.

What is a Barr body?

The tightly condensed, inactive X chromosome in a cell.

How does X-chromosome inactivation occur?

Early in development, one X is randomly silenced

the same X stays _ in descendant cells.

inactive

Why do calico cats have patches of different fur colors?

Different cells activate different X-linked color alleles; white patches lack pigment.

How does Xist lncRNA spread across the X chromosome?

It searches in 3D, changes chromosome structure, and coats newly accessible regions.

What antigens, antibodies, and compatible donor types does type A blood have?

A antigens, anti-B antibodies, receives A/O.

What antigens, antibodies, and compatible donor types does type B blood have?

B antigens, anti-A antibodies, receives B/O.

What antigens, antibodies, and compatible donor types does type AB blood have?

A+B antigens, no anti-A/anti-B antibodies, receives all ABO types.

What antigens, antibodies, and compatible donor types does type O blood have?

No A/B antigens, anti-A and anti-B antibodies, receives O only.

What are chromosomal mutations?

Changes in chromosome structure or number.

How do chromosome structure and number mutations occur?

Structure: DNA breaks, fragments are lost or reattached. Number: chromosomes or entire sets are gained or lost.

deletion

chromosome segment is lost

Duplication

an extra copy of a segment is added.

Translocation

segment moves to a nonhomologous chromosome.

Inversion

segment reattaches reversed.

What are the effects of chromosome deletion?

Loss of essential genes can disrupt development or cell function

How can chromosome duplications affect evolution?

Extra gene copies can mutate into new forms while the original gene keeps functioning.

What causes chromosome duplications during meiosis?

Uneven crossing-over: one homolog loses a segment while the other gains it.

What is a reciprocal translocation?

Two nonhomologous chromosomes exchange segments.

How are translocations linked to cancer?

They are common in cancers; in CML, the Philadelphia chromosome forms when ABL (9) fuses with BCR (22).

What are the effects of chromosome inversions?

Genes may break and lose function or move intact to a new location on the same chromosome.

How have inversions and translocations affected evolution?

They have contributed to the evolution of plants and animals, including humans.

What is nondisjunction?

Failure of homologous chromosomes or sister chromatids to separate during meiosis.

aneuploid

extra or missing chromosomes

Euploid

normal chromosome set.

What happens during nondisjunction in meiosis I?

Homologous chromosomes fail to separate → 2 gametes with an extra chromosome (n+1), 2 missing one (n−1).

What happens during nondisjunction in meiosis II?

Sister chromatids fail to separate → 2 normal gametes, 1 extra chromosome (n+1), 1 missing one (n−1).

What happens when an embryo gains or loses an autosomal chromosome?

It often causes severe abnormalities and spontaneous miscarriage.

What causes Down syndrome, and what are its characteristics?

Trisomy 21 (3 copies of chromosome 21); short stature and moderate to severe intellectual disability.

How does maternal age affect Down syndrome risk?

Risk increases with maternal age due to a higher chance of chromosome 21 nondisjunction in eggs.