11 - Single Gene Inheritance

Question 1

What is Mendelian Inheritance?

Answer 1

• each parent has 2 alleles for each character
• There are dominant and recessive alleles
• combination of dominant and recessive alleles makes the phenotype

Question 2

Explain Mendel’s pea experiment

Answer 2

• crossed pure yellow and pure green peas
• the crossed the F1 generation
• F2 generation 3/4 yellow, 1/4 green - 1:2:1ratio
• yellow is dominant

Question 3

How would you determine an unknown genotype?

Answer 3

test cross

Question 4

How would you carry out a test cross?

Answer 4

• unknown genotype crossed with a homozygous recessive genotype
• if F1 is 1:1 then unknown must be heterozygous
• if F1 is all one trait, unknown must be homozygous dominant

Question 5

what organisms can mendelian inheritance occur in?

Answer 5

diploid organisms with 2 copies of a gene

Question 6

Name 4 different modes of single gene inheritance

Answer 6

• autosomal dominant
• autosomal recessive
• sex-linked dominant
• sex-linked recessive

Question 7

What are pedigrees?

Answer 7

family trees that have information about disease

Question 8

How do you identify a male on a pedigree?

Answer 8

a square

Question 9

How do you identify a female on a pedigree?

Answer 9

a circle

Question 10

How do you determine affected individuals in a pedigree?

Answer 10

filled in shapes

Question 11

how do you determine individuals heterozygous in autosomal recessive?

Answer 11

half filled in

Question 12

How do you determine a carrier of sex linked recessive?

Answer 12

a dot in the shape

Question 13

How can you tell if someone is dead in a pedigree?

Answer 13

line through the shape

Question 14

What are signs of autosomal dominant?

Answer 14

• all generations affected
• both sexes affected

Question 15

Give an example of an autosomal dominant condition

Answer 15

Marfan syndrome
- issue with all fibrous connective tissue
- Caused by defects in fibrin gene in chromosome 15

Question 16

are mendelian ratios observed in families?

Answer 16

No

Question 17

Give an example of an autosomal recessive condition

Answer 17

Phenylketonuria (PKU)
- can’t metabolise phenylalanine
- caused by a defect in the phenylalanine hydroxylate gene on chromosome 12

Question 18

What are signs of an autosomal recessive condition?

Answer 18

• most generations unaffected
• affects siblings of both sexes
• parents must be heterozygous and unaffected

Question 19

What are signs of an X-linked dominant condition?

Answer 19

• disease in all generations
• affected fathers would pass it on to daughters only
• affected mothers would pass it onto both daughters and sons

Question 20

What is an example of an X-linked recessive condition?

Answer 20

Heamophilia A
- difficulty forming blood clots
- defect in factor VIII gene on X chromosome

Question 21

What are signs of an X-linked recessive condition?

Answer 21

• jumps a generation
• mostly males affected
• females can be heterozygous carriers

Question 22

How do you determine the probabilities of an offspring genotype?

Answer 22

• find probability of gamete
• if single gene that will be 1/2
• multiply the probabilities of gametes to get probabilities of offspring

Question 23

How would you write that two genes are linked?

Answer 23

by using a slash:
ex AB/ab

Question 24

How would you write that two genes are unlinked?

Answer 24

using a semi-colon:
ex A/a ; B/b

Question 25

How would you write that two genes have unknown linkage?

Answer 25

with a dot
ex A/a . B/b