Topic F: Simple Inheritance

Question 1

What are the two categories of inheritance?

Answer 1

• simple inheritance
• complex inheritance

Question 2

What is simple inheritance?

Answer 2

• inheritance of traits that are determined by one (or very few) genes
• qualitative traits, like eye colour in drosophila
• show discontinuous variation on bar graphs, easily able to put them into separate groups or categories.
• relatively easy to study

Question 3

What is complex inheritance?

Answer 3

• traits determined by many genes
• can also be affected by then environment
• quantitative traits
• continuous variation, so they can not be easily put into separate groups, ex like height.
• challenging to study

Question 4

Most phenotypes in multicellular eukaryotes are not determined by _________ inheritance, but ______ inheritance

Answer 4

Most phenotypes in multicellular eukaryotes are not determined by SIMPLE inheritance, but COMPLEX inheritance

Question 5

most human medical conditions and diseases are the result of ______ ______

Answer 5

complex genetics

Question 6

complex traits often also have _______ influences, meaning that factors such as _____ or ________ can influence whether or not a trait develops.

Answer 6

complex traits often also have ENVIRONMENTAL influences, meaning that factors such as DIET or EXPOSURE TO VIRAL INFECTION can influence whether or not a trait develops.

Question 7

genes that determine simply inherited traits can be located on the ____________ or _______

Answer 7

sex chromosomes or on the autosomes

Question 8

Simply inherited single gene traits exhibit one of four inheritance patterns:

Answer 8

1. Autosomal Dominant
2. Autosomal Recessive
3. Sex-Linked Dominant
4. Sex-Linked Recessive

Question 9

the 2 types of inherited genes on autosomes

Answer 9

• Autosomal Dominant
• Autosomal Recessive

Question 10

the 2 types of inherited genes on the sex chromosomes

Answer 10

• Sex-Linked Dominant
• Sex-Linked Recessive

Question 11

What are autosomes?

Answer 11

• chromosomes that are NOT sex chromosomes
• in humans, we have 23 pairs of chromosomes total. 22 pairs are autosomal, 1 pair is sex chromosomes.

Question 12

Seeing the same phenotypes and frequencies in the F1 and F2 generation of a OG cross and reciprocal cross, means that this is evidence of …..

Answer 12

Autosomal inheritance

Question 13

If inherited traits are autosomal, and we perform a reciprocal cross, what happens?

Answer 13

nothing changes. F1 and F2 generations would be the same, as the trait is not sex-linked, and so swapping the genes of the parents would not change the subsequent generations.

Question 14

2 importance characteristics of sex-linked inheritance;

Answer 14

1. we do NOT observe the same phenotypes and ratios in the F1 and F2 generations of reciprocal crosses
2. We observe different patterns of inheritance (phenotypes) in males vs. females

Question 15

Homogametic sex is ______, while heterogametic sex is ______

Answer 15

Homogametic sex is female (XX), while heterogametic sex is Male (XY)

Question 16

4 reasons why studying inheritance in humans is so challenging?

Answer 16

1. no control crosses
2. small sample size
3. long generation time
4. lack of family histories

Question 17

What is a pedigree?

Answer 17

a family tree is which a particular phenotype/trait is being tracked in order to try to determine how it is inherited. The emphasis in a pedigree is to represent the inheritance of a particular trait between blood relatives

Question 18

5 KEY traits to remember when analyzing a pedigree?

Answer 18

1. Genetic disorders are rare
2. mendelian ratios are rarely seen in a pedigree
3. non-family members are assumed to be homozygous unaffected for the disease (Unless there is compelling evidence for the contrary)
4. recessive disorders are more common than dominant ones
5. most human traits do NOT demonstrate simple inheritance

Question 19

To carry out a pedigree analysis, and figure out if the disorder is autosomal/sex-linked or dominant/recessive, what are the questions you need to ask?

Answer 19

1. Do two unaffected individuals ever produce an affected child? (or do affected children always have an affected adult?)
2. is there any clear sex bias (are mainly females affected? males?)

Question 20

What is the evidence that suggests an autosomal dominant disorder?

Answer 20

• we do not see UNAFFECTED parents produce affected child (so dominant)
• additionally we do not see any instance where two unaffected individuals produce an affected child (so again dominant)
• no sex bias, males and female children are both affected (so autosomal)

Question 21

If we know a trait is autosomal dominant, we know that individuals that are affected will have then genotype ____, and unaffected will have _____

Answer 21

affected: Aa or AA

unaffected: aa

Question 22

What is the evidence that suggests an autosomal recessive disorder?

Answer 22

• when two unaffected individuals produce an affected child, so the trait is recessive.
• no sex bias, males and female children are both affected (so autosomal)

Question 23

If we know a trait is autosomal recessive, we know that individuals that are affected will have then genotype ____, and unaffected will have _____

Answer 23

affected: aa

unaffected: Aa and AA

Question 24

What is the evidence that suggests an X-linked dominant disorder?

Answer 24

• affected individuals always have an affected parent (two unaffected individuals will never have an affected child) so this is a dominant trait
• the affected male parent passes the trait on to all of his daughters, and none of his sons, Whereas the affected female passes the trait on to daughters and sons equally. this indicates X-linkage

Question 25

If we know a trait is X-linked dominant, we know that individuals that are affected will have then genotype ____, and unaffected will have _____ (for both females and males)

Answer 25

Female:
(XX) A_ = Affected
(XX) aa = Unaffected

Male:
(XY) A = affected
(XY) a = unaffected

Question 26

What is the evidence that suggests an X-linked recessive disorder?

Answer 26

• we see two unaffected individuals have an affected child. This suggests the trait is recessive
• we see only males are effected. this suggests the trait is X-linked

Question 27

If we know a trait is X-linked recessive, we know that individuals that are affected will have then genotype ____, and unaffected will have _____ (for both females and males)

Answer 27

Female:
(XX) A_ = unaffected
(XX) aa = affected

Male:
(XY) A = unaffected
(XY) a =affected

Question 28

at what phase of meiosis do alleles of a locus segregate?

Answer 28

• Anaphase 1
• or Anaphase 2 for sister chromatids