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All organisms share a common coding system for their genomic information. The common features of heredity imply all of the following EXCEPT:

All organisms will have the same number of genes.

Recent discoveries in genetic engineering allowed humans to alter the genome of plants (crops) for the first time.

False. Humans have altered plant genomes for thousands of years through selective breeding.

Why is Gregor Mendel considered the father of genetics?

He discovered the principles of heredity by crossing different varieties of pea plants and analyzing traits in subsequent generations.

Which features of heredity explain Mendel's results?

Traits are transmitted via discrete units, units can be hidden but not lost, and offspring receive one unit from each parent (1, 2, and 4).

What do you call a trait produced by a set of alleles?

Phenotype.

What characteristics make an organism useful as a model organism?

Short generation time, many offspring, and easy maintenance in the laboratory.

What did the zebrafish pigmentation study find?

Scientists discovered a gene that contributes to pigmentation in both zebrafish and humans.

Are Bacteria and Archaea interchangeable names for the same organisms?

No. They are separate domains of life.

What does it mean for a cell to be diploid?

It contains two sets of chromosomes.

What best distinguishes meiosis from mitosis?

Meiosis involves two divisions and produces genetically variable cells with half the chromosome number.

What characteristic distinguishes bacteria from both archaea and eukaryotes?

Bacteria generally lack histones associated with their chromosomes.

What is true about homologous chromosomes?

They usually have the same genes in the same order.

A diploid cell has 4 chromosomes during G1. After S phase, what does it contain?

4 chromosomes, each with two sister chromatids, for a total of 8 DNA molecules.

Meiosis produces ________, which contain ________ the genetic material of the original diploid cell.

Haploid gametes; half

Meiosis I separates ________, while Meiosis II separates ________.

Homologous chromosomes; sister chromatids.

The haploid amount of DNA in a human cell is 1.91 × 10¹² Daltons. How much DNA is present after Meiosis I?

3.82 × 10¹² Daltons.

What are the overall consequences of meiosis?

Chromosome number is reduced and daughter cells are genetically different (Only B and C).

: Which meiosis-specific process is NOT responsible for introducing genetic variation?

Random separation of sister chromatids.

Sex is determined in organisms

In many different ways in different organisms

Sex determination without sex chromosomes

Genic sex determination

Active X chromosomes in a somatic cell

1

Tortoiseshell cat pattern is caused by

Random X-inactivation

Dosage compensation in mammals

X-inactivation

Female AB / male BB sex system example

Female AB and male BB

Males are haploid for X-linked genes

True

Red eye female × white male (X-linked cross outcome)

All progeny red-eyed

X-linked dominant vitamin D disorder inheritance

Half females and half males affected

Z-linked feathering cross genotype (fast male × slow female)

Females Z+W, males ZsZs

Fast-feather male × slow-feather female: fast female percentage

None

Barr bodies in XXXX female

3

X-inactivation process

Random process in individual cells

Dosage compensation meaning

Equalizing X-linked gene expression via X-inactivation

Tan seed dominance relationship

Tan is dominant over cream

Possible genotypes for dominant phenotype

SS and Ss

Probability 3/4 × 1/4

3/16

Purpose of a test cross

Determine genotype of an individual

9:3:3:1 ratio represents

Dihybrid cross

F2 generation definition

Offspring of F1 × F1 cross

White offspring probability (Ww × ww)

1/2

Alkaptonuria case (father affected, daughter healthy)

Aa

Black × long-haired guinea pig genotype

WWhh or Wwhh

Gametes from WwHh

WH, Wh, wH, wh

Round and yellow from RrYy × RrYy

9/16

Recessive phenotype genotype (dull, orange, nonbitter)

ddrrbb

Trihybrid recessive probability

1/64

Probability rule for independent traits

Multiply probabilities

Epistasis definition

One gene masks another gene at a different locus

Labrador BBEE × bbee offspring

All BbEe (black)

Yellow Labrador genotype

bb ee

Yellow Labrador probability in BbEe × BbEe

4/16 (1/4)

Epistatic allele in Labradors

e (recessive ee masks B gene)

Mitochondrial DNA inheritance

Separate genome; only from mother

Human colorblindness inheritance type

Sex-linked

Snail shell coiling inheritance type

Maternal effect

Precocious puberty inheritance type

Sex-limited

Male baldness inheritance type

Sex-influenced trait

Goat horn sex-influenced cross

H−H− male × H+H+ female

Maternal RNA/protein in egg effect

Genetic maternal effect

Maternal effect embryo outcome

100% same phenotype as mother

Penetrance definition example (OI 70%)

Penetrance

Variable severity in cystic fibrosis

Variable expressivity

Same genotype, different phenotypes (white fur patches)

Variable expressivity

Epistasis definition (formal)

Gene at one locus affects gene at another locus

Sex-limited traits definition

Expressed in only one sex

Sex-influenced traits definition

Expression depends on sex (dominance differs)

Genetic maternal effect vs cytoplasmic inheritance

Not the same (false equivalence)

Prenatal testing of placental tissue

Chorionic villus sampling (CVS)
Placental tissue sampled early in pregnancy

NIPS differs from maternal blood screening because it

B. Directly analyzes fetal DNA fragments found in maternal blood

Next step after positive NIPS

Amniocentesis or Chorionic villus sampling (CVS)
✔ NIPS is screening, not diagnostic

Dihybrid ratio not 9:3:3:1

B. The two genes are close to each other and linked

5) Testcross of dihybrid tomato plant

D. DdPp x ddpp

6) NOT responsible for genetic variation in meiosis

A. Random separation of sister chromatids
✔ sister chromatids are identical (normally no variation source)

One crossover per meiosis gametes

2 recombinant and 2 nonrecombinant

Crossing over every meiosis → recombinant proportion

50%

Fully linked genes, no crossing over

Correct statements: 1 and 2
A. 1 and 2

Gametes if genes far apart (recombination possible)

MD, md, Md, and mD

Completely linked genes gametes

MD and md

Why testcrosses are useful

Offspring phenotypes reveal gametes from heterozygous parent

13) Gene linkage data (8,56,53,7)

The genes are unlinked and assort independently
✔ ~1:1:1:1 ratio

Recombination frequency

Recombinants = 8 + 7 = 15
Total = 124
15/124 ≈ 12%
A. 12%

Gene arrangement (TtPp)

TP/tp

12% map distance

12 map units (m.u.)

D–E = 35%, D–F = 19%

D and F are closer to each other than D and E

Farthest apart genes

Max RF = 40%→ q and o
C. Q and O

Gene order Correct order: q – t – s – p – o (closest consistent chain)
Best match:

A. p-o-t-s-q (same sequence reversed orientation allowed)

Gene r (50% with all)

Gene r is likely on a different chromosome

Identify nonrecombinant progeny

Two most abundant phenotypes

Double crossover → middle gene

From pattern:
B. e locus

Gene order from that trihybrid

ss st e (same as e st ss)

Correct trihybrid testcross

e⁺e t⁺t b⁺b x eettbb

Middle locus (frequency table)

The t locus

Gene order

e t b (same as b t e)

An organism with three functional copies of a gene will produce ____ of the protein encoded by that gene as an individual with two copies.

More

DE•FGHIJ → DE•FIJ represents what rearrangement?

Chromosome deletion

Diploid organism gains an extra chromosome (karyotype change)

Aneuploidy

Down syndrome (Trisomy 21) is the most common autosomal ____ in humans.

Aneuploidy

Nullisomy is the loss of ____

A pair of homologous chromosomes

Philadelphia chromosome results from what rearrangement?

Translocation

Chromosome duplication statement (image question)

False

Rearrangement represented by a reversed chromosome segment

Inversion