Genetics

Question 1

Model Organisms

Answer 1

• Genetic discoveries made in a model organism are often true of related species and may even apply to all forms of
  life.
• Small size, small genome, large numbers of offspring, and short generation time are the common features
• Geneticists working with the same model organism share
  stocks and information.

Question 2

Genetics

Answer 2

study of heredity (transmission of properties from generation
to generation)

Question 3

Continuous trait (Quantitative)

Answer 3

a trait that can take on a potentially infinite number of states over a continuous range (e.g. height)

Question 4

Discontinuous (qualitative)

Answer 4

a trait that has a limited number of states with clearly defined differences (e.g. smooth vs wrinkled peas)

Question 5

Gene discovery

Answer 5

1) collect mutants affecting the trait of interest
2) cross (mate) mutant individuals to wild-type individuals to see if their offspring show
ratios of wild-type-to-mutant phenotypes that are characteristic of single-gene inheritance.
3) Identify the function of the gene at the molecular level
4) Identify how the gene interacts with other genes to produce the trait in question

Question 6

Variant

Answer 6

individual who inherits a trait that expresses differently from some
standard form

Question 7

allele

Answer 7

variant form of a specific gene

Question 8

Wild type

Answer 8

normal/most common form of a property/trait of an organism

Question 9

Mutant

Answer 9

individual having an altered form of a property/trait (differs from the
normal form of the property/trait)

Question 10

Phenotype

Answer 10

form taken by a trait (or group of traits) in a specific individual; detectable outward appearance of a specific genotype

Question 11

Genotype

Answer 11

the allelic composition of an individual, commonly of a certain gene or set of genes

Question 12

Mendel’s Law of Equal Segregation

Answer 12

• During meiosis, members of a gene pair segregate equally into gametes (pollen/sperm or eggs)
• Single gamete contains only one member of the gene pair
• At fertilization gametes fuse randomly to create zygote

Question 13

Zygote

Answer 13

diploid cell formed by union of two haploid gametes (egg and sperm)

Question 14

Monohybrid

Answer 14

heterozygote for one gene

Question 15

Monohybrid cross

Answer 15

cross of 2 heterozygotes

Question 16

Test cross

Answer 16

• cross individual of unknown genotype with homozygous recessive tester strain (a/a)
• If A/? x a/a → 1:1 (½ A/a and ½ a/a); then individual is heterozygous (A/a)
• If A/? x a/a → all progeny has dominant phenotype; then individual is homozygous (A/A)
• If tester strain not available: selfing A/? → 3:1 ratio, then individual is heterozygous (A/a)

Question 17

True breeding

Answer 17

always produce the same phenotype with each
generation when interbred/selfed

Question 18

mitosis

Answer 18

somatic cell division

Question 19

meiosis

Answer 19

sexual cell division

Question 20

meiocyte

Answer 20

• specialized diploid cell set aside to produce gametes by meiosis

Diploid Meiocyte: 2n -> n + n + n + n

Question 21

haploid number

Answer 21

• The number of chromosomes in the basic genomic set of a species

Diploid: 2n -> 2n + 2n
Haploid: n -> n + n

Question 22

Early S phase

Answer 22

• One DNA double helix per chromosome
• chromosomes = 2n
• DNA = 2C (one each from mom and dad with an allele of a gene)

Question 23

Late S Phase

Answer 23

• DNA Replication
• Two DNA double helices per chromosome
• chromosomes = 2n (2 sister chromatids)
• DNA = 4C (since DNA got replicated)

Question 24

M Phase

Answer 24

• sister chromatids separate to give two chromosomes that are distributed into two daughter cells
• chromosomes = 2n (2 sister chromatids)
• DNA = 4C
• Chromosomes = 4n (sister chromatids split apart)
  -DNA = 4C
• Chromosomes = 2n (2 chromosomes in each daughter cell)
  -DNA = 2C

Question 25

Mitosis in a diploid heterozygote

Answer 25

Aa→Aa+Aa

Question 26

Meiosis in a diploid heterozygote

Answer 26

Aa→A+A+a+a
Aa→1/2 A and 1/2 a
ratio=1 A : 1 a

Question 27

Single Nucleotide Changes

Answer 27

• Synonymous: same AA
• Nonsynonymous:
  missense: different AA
  nonsense: stop codon

Question 28

Single Nucleotide Polymorphisms (SNPs)

Answer 28

• The “swap” of a single nucleotide with another is referred to either as a mutation, if present in <1% of the general population, or as SNP, if present at a frequency >1%.
• Most single-nucleotide changes are found outside
  coding regions (noncoding) and have no impact on the
  biological function of a protein (silent), though they may affect gene expression or splicing.
• Variants found within the coding region may code for
  functional changes in amino acid structure (missense) or predict premature protein (nonsense).

Question 29

haplosufficient gene

Answer 29

• one wild-type allele (+) has enough function to produce a wild-type phenotype
• Recessiveness: heterozygote with a recessive and wild-type allele expressing wild-type phenotype

Question 30

haploinsufficient gene

Answer 30

• a single wild-type allele (+) is not enough to promote
  wild-type function
• Dominance: heterozygote with a dominant allele and wild type allele expressing mutant phenotype

Question 31

Gametes

Answer 31

• A haploid reproductive cell that can fuse with another haploid cell to form a zygote.
• Egg cells (ova) and sperm of multicellular eukaryotes.

Question 32

Zygote

Answer 32

Diploid cell formed by union of two haploid gametes (egg and sperm)

Question 33

Haploid

Answer 33

• Having one set of chromosomes (1n)

Question 34

Diploid

Answer 34

• Having two sets of chromosomes (2n)

Question 35

Sexual dimorphism

Answer 35

individuals are either male or female

Question 36

Human sex chromosomes

Answer 36

• 46 chromosomes: 22 homologous pairs of autosomes (A) plus 2 sex chromosomes:
• females: 44A + XX
• males: 44A + XY
• X and Y sex chromosomes contain different sets of genes

Question 37

homogametic sex

Answer 37

gametes of one type (females since XX)

Question 38

heterogametic sex

Answer 38

gametes of two types (males since XY)

Question 39

X and Y Chromosome divided into 2 regions