Midterm 2 (2.3)

Question 1

Stamens

Answer 1

Produce pollen

Male parts

Question 2

Carpels

Answer 2

Bears eggs

Female part

Question 3

True-breeding plants

Answer 3

Plants self-pollinated over many generations

Produced only the same variety as the parent plant

Question 4

Hybridization

Answer 4

Crossing of two true-breeding varieties

Question 5

Dominant allele

Answer 5

Determines organism’s appearance

Question 6

Recessive allele

Answer 6

Has no noticeable effect on organism’s appearance

Question 7

Law of segregation

Answer 7

2 alleles for a character segregate during gamete formation
- End up in different gametes

Egg or sperm gets only ONE of two alleles present in somatic cells

If individual is true-breeding
– All gametes have identical alleles for particular character

If different alleles present
– 50% gametes get dominant allele
– 50% gametes get recessive allele

Question 8

Homozygous

Answer 8

2 identical alleles for a gene

All gametes contain same allele

Question 9

Heterozygous

Answer 9

2 different allele for a gene

1/2 gametes will have ones allele, 1/2 gametes will have the other

Question 10

Phenotype

Answer 10

Appearance, observable traits

Question 11

Genotype

Answer 11

Genetic makeup

Question 12

Monohybrid

Answer 12

Heterozygous for one character followed in a cross

All F1 progeny from crosses of true-breeding parents are monohybrids

Question 13

Monohybrid cross

Answer 13

Cross between heterozygous for one character

Question 14

Dihybrids

Answer 14

Individuals heterozygous for two characters followed in a cross

YyRr

F1 plants formed by crossing two true-breeding pea varieties that differ in both of these characters

Question 15

Dihybrid cross

Answer 15

Cross between F1 dihybrids

Are two characters transmitted as a package or independently?

Question 16

Law of independent assortment

Answer 16

Each pair of alleles segregates independently of each other pair of alleles during gamete formation

Applies only to genes on different homologous chromosomes

Or far apart on same chromosome

Question 17

Complete dominance

Answer 17

Phenotype of heterozygote and dominant homozygote indistinguishable

Question 18

Incomplete dominance

Answer 18

Phenotype of heterozygote is intermediate between phenotypes of individuals homozygous for either allele

Question 19

Codominance

Answer 19

2 alleles each affect phenotype in separate ways

Phenotypes of both alleles exhibited in heterozygote

Question 20

Pleiotropy

Answer 20

Ability of a single gene to have multiple phenotypic effects

Example: gene that determines flower color in garden pea also affects colour of coating on outer surface of seed

Question 21

Epistasis

Answer 21

Phenotypic expression of gene at one locus alters that of gene at second locus

Example: Labrador retrievers
– Black coat (B) dominant to brown coat (b)
– Separate gene determines whether pigment will be deposited in hair or not
– Dominant allele (E) results in black or brown coat

Question 22

Polygenic inheritance

Answer 22

Additive effect of ≥2 genes on single phenotypic character

Converse of pleiotropy

Question 23

Pedigree

Answer 23

Diagram of family tree showing occurrence of heritable characters in parents and offspring over multiple generations

Question 24

Wildtype

Answer 24

Phenotype most commonly observed in natural populations

Question 25

Cystic fibrosis

Answer 25

Normal (wildtype) allele gene codes for membrane protein involved in Cl- transport in and out of cells

Homozygous recessive
- Ultimate result is thicker mucus coating certain cells, builds up in pancreas, lungs, digestive tract

Question 26

Tay-Sachs disease

Answer 26

Neurodegenerative disease

Question 27

Sickle-cell anemia

Answer 27

Affects 1/400 African-Americans

1 amino acid substituted for another in hemoglobin

Change in amino acid caused by point mutation

Heterozygotes may have some symptoms
– Wild-type allele not completely dominant

May persist in population because it reduces risk of malaria
– Advantage to heterozygotes

Question 28

Dominantly inherited disorders

Answer 28

Achondroplasia
- From of dwarfism
- Heterozygous individuals have dwarf phenotype

Most of the population is homozygous recessive
- Recessive allele more prevalent in population

Dominant alleles causing lethal diseases much rarer than recessive alleles with lethal effects
– If it causes death before person can reproduce -> Allele not passed on

Timing of disease onset affects inheritance: Huntington’s disease
-Degenerative disease of nervous system
- Lethal dominant allele
- No obvious effect until individual is 35-40

Question 29

Hemizygous

Answer 29

Male receiving gene from recessive X-linked trait

Question 30

Sex-linked crosses: X-linked disorders

Answer 30

Color blindness

Duchenne muscular dystrophy

Hemophilia

Question 31

X inactivation in female mammals

Answer 31

Most of one X chromosome in each female’s cells INACTIVATED
– Occurs during early embryonic development
– Barr body

Result
– Females and males, effectively, have one copy of X-
linked genes

Which X chromosome inactivates in each cell is random
– Females are mosaics of 2 cell types

Ex:
Tortoiseshell cats, inactivation of sweat glands

Question 32

Recessively inherited disorders

Answer 32

Cystic fibrosis

Tay-Sachs disease

Sickle-cell anemia