Chapter 9

Question 1

blending hypothesis

Answer 1

• the idea that the heredity materials contributed by the male and female parents mix in forming the offspring (ex: blue + yellow = green)
• rejected because it doesn’t explain how traits that disappear in one generation can reappear in later ones

Question 2

true-breeding

Answer 2

• varieties result when self-fertilization produces all identical to the parent
• P generation

Question 3

hybrids

Answer 3

• the offspring of two different varieties

* F1 generation

Question 4

cross-fertilization

Answer 4

• a hybridization, or genetic cross.

* cross of F1 plant produces an F2 generation

Question 5

homo- vs. hetero-

zygous

Answer 5

• homozygous: genotype has identical alleles

* heterozygous: genotype has two different alleles

Question 6

allele

Answer 6

• alternative versions of genes that account for variations in inherited characters
• dominant: determines the organism’s appearance
• recessive: has no noticeable affect on the organism

Question 7

phenotype

Answer 7

• appearance or expression of a trait (ex: blonde hair, blue eyes)

Question 8

genotype

Answer 8

• the genetic makeup of a trait

ex: blue eyes=bb ; brown eyes=BB

Question 9

monohybrid cross

Answer 9

• a cross between two individuals differing in a single character

Question 10

dihybrid cross

Answer 10

• mating of parental varieties that differ in two characteristics (9:3:3:1 phenotypic ratio)

Question 11

punnett square

Answer 11

• shows the possible combinations of alleles that could occur when gametes combine

Question 12

law of segregation

Answer 12

• a sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other in gamete production

Question 13

law of independent assortment

Answer 13

mendel suggested that…

• the inheritance of one character has no effect on the inheritance of another
• the dihybrid cross is equivalent to 2 monohybrid crosses

Question 14

genetic relationship between homologous chromosomes

Answer 14

• for a pair of homo. chrom., alleles of a gene reside at the same locus (specific location of a gene along a chromosome)
• homozygous individuals have same allele on both homologues; while heterozygous individuals have different alleles on each homologue

Question 15

pedigree

Answer 15

• shows inheritance of a trait in a family through multiple generations
• demonstrates dominant or recessive inheritance
• also be used to predict genotypes of family members

Question 16

wild type traits

Answer 16

• those prevailing in nature, are not necessarily specified by dominant alleles
ex: freckles (D), albinism (r)
• recessive disorders:
- albinism
- sickle-cell disease
• dominant disorders:
- achondroplasia
- huntington's disease

Question 17

incomplete dominance

Answer 17

• results in intermediate phenotypes–heterozygous genotype (ex: red + white = pink)

Question 18

codominance

Answer 18

• more that 2 different alleles for one particular gene exist in the wider population
• neither allele is dominant over the other
(ex: ABO blood group–A and B alleles are both expressed in heterozygous individuals = AB blood type)

Question 19

environmental effects

Answer 19

• skin color affected by sunlight exposer
• diseases, i.e. cancer, has hereditary and environmental components
• nutrition
• pollution

Question 20

pleiotropy

Answer 20

• when one gene influences many phenotypic characteristics
• often seen in human disease, leading to syndromes, or groups of symptoms related to a genetic mutation
(ex: sick cell disease, mar fan syndrome)

Question 21

polygenic inheritance

Answer 21

• results from the additive affects of two or more genes
• controlled by at least 3 separately inherited genes
(ex: skin color)

Question 22

sex-linked genes

Answer 22

• most found on X chromosome
• mostly affect males due to recessive alleles
• a male receiving a single X-linked recessive allele from his mother will have the disorder; a female must receive the allele from both parents to be affected
(ex: red-green color blindness)

Question 23

chromosome theory of inheritance

Answer 23

• genes occupy specific loci (positions) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment during meiosis–its behavior accounts for inheritance patterns