Unit 4 - Ch 11 - Mendelian Genetics

Question 1

Alleles definition

Answer 1

Alternate forms of a gene found on gene loci of homologous chromosomes

There are usually two alleles per trait (diploid)

Question 2

Dominant alleles vs. Recessive alleles

Answer 2

Dominant

• expressed if present
• represented with capitol letters

Recessive

• expressed only if there’s no dominant alleles present
• represented with lower case letters

Question 3

Genotype

Answer 3

Genetic makeup of an organism. Formed at conception, spread throughout cells of the body by mitotic cell division

Question 4

Homozygous Dominant

Answer 4

Genotype where both alleles are dominant at gene locus (TT)

Example of pure breeding

Question 5

Homozygous Recessive

Answer 5

Genotype where both alleles are recessive at a locus (tt)

Example of pure breeding

Question 6

Heterozygous

Answer 6

Genotype where there is one dominant and one recessive at a gene locus (Tt)

= hybrid

Carrier of recessive traits

Question 7

Phenotype

Answer 7

The expression of the genotype in an organism - often outwardly visible

Question 8

Dominant phenotype

Answer 8

Expressed in homozygous dominant and heterzygous genotypes

Question 9

Recessive phenotype

Answer 9

Expressed only in homozygous recessive genotypes

Question 10

Mendel’s findings when breeding pea plants multiple generations ( P, F1, F2 )

Answer 10

1. P - Parental
   - crossed pure breeding pea plants with different expressions of the same trait
2. F1 - First filial
   - showed all dominant phenotypes
3. F2 - Second filial
   - produced by inbreeding F1 plants
   - dominant and recessive phenotypes present, dominant was more common

Question 11

Law of Segregation

Answer 11

Traits are determined by 2 factors (alleles) separating during gamete formation

• Mendel’s First Law

Question 12

Formula for gamete formation

Answer 12

2(nth power) = # of different kinds of gametes

where n = # of heterozygous loci

Examples
TT = 2(0 power) = 1 unique gamete (T)
tt = 2(0 power) = 1 unique gamete (t)
Tt = 2(1st power) = 2 unique gametes (1/2 T and 1/2 t)

Question 13

Phenotypic Ratio

Answer 13

(# dom. phenotypes) : (# rec. phenotypes)

= 3:1, 0:1, 1:0

Question 14

Genotypic Ratio

Answer 14

HD : # Het. : #HR

= TtxTt = 3:1 phenotypic ratio, 1:2:1 genotypic ratio

Question 15

Monohybrid Cross

Answer 15

The inheritance of two different alleles of a single locus

P gen: black f (BB) x brown m (bb)

F1 gen: will all be heterozygous (Bb), all black

F2 gen: Bb x Bb = 1//4 BB, 2/4 Bb, 1/4 bb
phenotypic ratio= 3:1
genotypic ratio= 1:2:1

Question 16

Test Cross

Answer 16

Used to identify the genotype of an organism with the dominant phenotype by crossing with an organism with the recessive phenotype

recessive pheno. = homozygous recessive
dominant pheno. = homozygous dominant or heterozygous

Question 17

Law of Independent Assortment

Answer 17

Alleles for traits separate independently of alleles for other traits
(only if traits are not linked)
- Mendel’s second law

Question 18

Dihybrid Cross

Answer 18

P gen: A mating of individuals with different alleles at two loci.
Black, short hair (BBSS) and Brown, long hair (bbss)

F1 gen: all heterozygous for two traits

F2 gen: genotypic ratio 9:3:3:1 
9/16 black short
3/16 black long
3/16 brown short
1/16 brown long

Question 19

Fork Line Method

Answer 19

based on product rule of probability

Question 20

Locus

Answer 20

(pl. loci)

Designates the location where a gene is located on a chromosome