Mendelian Genetics and Inheritance

Question 1

what is tooth agenesis?

Answer 1

• failure of a tooth to form
• the most common heritable disorder in humans

Question 2

tooth agenesis affects ___% of the population worldwide, if ___ are excluded

Answer 2

• 4-7%
• 3rd molars

Question 3

of the population affected by tooth agenesis, ___% are missing 3 or more teeth

Answer 3

1%

Question 4

if 3rd molars are included in tooth agenesis stats, ___% of the population is considered to be affected by tooth agenesis

Answer 4

20%

Question 5

mendelian genetics is a model of ___ first described by gregor mendel

Answer 5

inheritance

Question 6

what is a phenotype?

Answer 6

a physical trait

Question 7

mendel cross bred plants with various phenotypes and recorded the ratio of offspring across generations. this led him to formulate his ___

Answer 7

3 laws of inheritance

Question 8

name the 3 laws of inheritance

Answer 8

1. the law of segregation
2. the law of independent assortment
3. the law of dominance

Question 9

what is the law of segregation?

Answer 9

• factors for each trait segregate, such that each gamete carries only one factor for each trait

Question 10

what is the law of independent assortment?

Answer 10

each factor that segregates does so independently

Question 11

what is the law of dominance?

Answer 11

some factors are dominant and some are recessive. the dominant trait will always be expressed when present

Question 12

what are mendel’s heritable factors referred to as?

Answer 12

alleles

Question 13

what are alleles?

Answer 13

• the different forms of a gene
• for example, flower color

Question 14

law of segregation

there are ___ copies of each allele, and further, they are ___

Answer 14

• two
• separated
• consider meiosis: diploid (2n) cells become haploid (1n)

Question 15

the law of segregation

one copy of a ___ comes from one parent, and the other copy comes from the second parent

Answer 15

gene (allele)

Question 16

law of independent assortment

mendel concluded that not only did copies of a single allele separate, but that alleles for different traits separated ___ of one another

Answer 16

• independently
• for example: flower color and seed color both have an allele with 2 copies. both of these alleles will be distributed according to the law of segregation, but will do so independently of one another.

Question 17

law of independent assortment

the number of ___ depends on the number of ___ we are considering

Answer 17

• combinations
• alleles

Question 18

law of dominance

mendel observed that each trait has a ___ and ___ form

Answer 18

dominant and recessive

Question 19

law of dominance

a ___ allele will always be expressed when present

Answer 19

dominant

Question 20

law of dominance

what must occur in order for a recessive allele to be expressed?

Answer 20

both copies of the allele must be recessive

in other words, the dominant allele must not be present

Question 21

describe the difference between homozygous and heterozygous

Answer 21

• homozygous: organisms can be either homozygous dominant or homozygous recessive, and therefore will only pass along the allele they express
  
  • ex. AA or aa
• heterozygous: organisms will always express the dominant allele, while carrying (and passing) the recessive allele
  
  • ex. Aa

Question 22

does dominance imply normality?

Answer 22

no; it is simply preferred expression

Question 23

dominance is not ___, but relative to an allele that is also present

Answer 23

inherent

Question 24

T or F:

dominant traits are always the most common in a population

Answer 24

false:

they can actually be rare

Question 25

what is a genotype?

Answer 25

alleles that are present vs. phenotype, which are the traits that are expressed

Question 26

in mendel's observations from his second generation crosses, he observed a phenotypic ratio of \_\_\_:\_\_\_

Answer 26

3 dominant : 1 recessive

Question 27

in the first generation, assuming a cross between two "true breeding" or homozygous organisms, we will always get what? what laws of inheritance do we see here?

Answer 27

* heterozygotes, expressing the dominant allele * 1st and 3rd laws

Question 28

once we start crossing the results of the F1 generation, are we dealing with true breeding parents?

Answer 28

no

Question 29

breeding of what generation yields mendel's 3:1 phenotypic ratio?

Answer 29

breeding of the F1 generation, so the F2 generation shows the 3:1 phenotypic ratio

Question 30

what is the phenotypic composition of the F2 generation when parents of the F1 generation are true breeders? which laws of inheritance are seen?

Answer 30

* 50% true breeding (homozygous) and 50% heterozygous organisms * 1st and 3rd laws * this will be the result regardless of the offspring chosen from the F1 generation

Question 31

the fact that recessive genes can be carried allows the ___ of certain genes, even if they aren't favored when expressed.

Answer 31

* preservation * it will eventually allow a recessive phenotype to resurface should environmental selection pressure change

Question 32

\_\_\_ and ___ allows a species to resist extinction

Answer 32

genetic variability and selection

Question 33

any patterns of inheritance which do not strictly follow the three laws of inheritance are said to be \_\_\_

Answer 33

non-mendelian

Question 34

what are two examples of co-dominance?

Answer 34

1. more than two possible alleles, even though each individual only carries two copies 2. situations where more than one of these possible alleles are dominant, and can be expressed as a distinct co-dominant phenotype

Question 35

blood groups are an example of what?

Answer 35

co-dominance \*non-mendelian genetics

Question 36

what is incomplete dominance?

Answer 36

snapdragon example * if the alleles for white flowers (recessive) and red flowers (dominant) are both present, you end up with a weaker expression of red, resulting in pink flowers * there is no allele for pink flowers, but it is a possible phenotype when both red and white alleles are present

Question 37

what is mosaicism?

Answer 37

* when different cells in the body have different genotypes, and thus express different phenotypes * calico cats are an exmaple

Question 38

sex-linked dominance a \_\_-linked trait would only be passed on to male offspring, and is relatively small so it contains ___ genes.

Answer 38

* Y * fewer

Question 39

sex-linked dominance for \_\_-linked dominant traits, inheritance depends on the relative genotypes of the parents

Answer 39

X

Question 40

sex-linked dominance a father with a dominant X trait will pass it to his ___ but not his \_\_\_. a mother would distribute \_\_\_% of all offspring depending on her genotype.

Answer 40

* daughters * sons * 50-100%

Question 41

sex-linked dominance which traits will predominate in males? which females will be affected?

Answer 41

* X-linked recessive * females who are homozygous are affected

Question 42

sex-linked dominance \_\_\_ in females can result in limited expression of an X-linked recessive trait

Answer 42

X-inactivation

Question 43

what is extranuclear inheritance? what is an example?

Answer 43

* factors passed form the cytoplasm * ex. mitochondrial DNA all comes from the ova

Question 44

\_\_\_ is a recombination event where DNA sequence from one homologous chromosome can replace a sequence on its counterpart.

Answer 44

gene conversion

Question 45

gene conversion can interfere with \_\_\_

Answer 45

mendelian ratios

Question 46

describe infectious heredity

Answer 46

when integrated traits introduced by a virus are passed along the germ line; this is typically passed directly along from one parent

Question 47

T or F: traits result as equal contributions from parent organisms

Answer 47

not always